Optical wavelength multiplexing/demultiplexing circuit

The present invention relates to an array waveguide diffraction grating type optical wavelength junction / demultiplexing circuit. More specifically, the present invention relates to an array waveguide diffraction grating type optical wavelength junction / demultiplexing circuit that uses transmission wavelengths of a plurality of diffraction orders.

A planar lightwave circuit (PLC) is composed of a quartz glass waveguide formed on a silicon substrate, and is widely used as a component for optical communication. Arrayed Waveguide Grating (AWG) using PLC technology is a circuit that realizes an optical wavelength division multiplexing function, and has an optical wavelength that transmits multiple optical signals with different wavelengths through a single optical fiber. It plays an important role in multiplexing (WDM) communication.

The AWG includes several tens to several hundreds of waveguides, and optical signals distributed in the same phase are given a phase difference according to a certain path length difference between adjacent waveguides. Since the phase difference given by the array waveguide depends on the wavelength, it causes dispersion in the focusing angle in the slab waveguide further connected to the AWG. Optical signals are obtained from different output waveguides depending on the wavelength according to the angular dispersion to be focused. The diffraction angle satisfies the grating equation including the diffraction order. Optical wavelength combined and demultiplexed circuits that use multiple transmission wavelengths of different diffraction orders are also called cyclic AWGs or colorless AWGs.

FIG. 26 is a plan view showing the configuration of the prior art cyclic AWG. The cyclic AWG9100 is configured by sequentially connecting a first input / output waveguide 9101, a first slab waveguide 9102, an array waveguide 9103, a second slab waveguide 9104, and a second input / output waveguide 9105. Has been done. The cyclic AWG9100 operates as an optical wavelength combined / demultiplexing circuit. That is, it has a function of combining a plurality of signal lights input for each wavelength channel into each of the first input / output waveguides 9101 and outputting them as wavelength multiplex signal light by joining the second input / output waveguide 9105. , The wavelength multiplex signal light input to the second input / output waveguide 9105 is demultiplexed into each waveguide of the first input / output waveguide 9101, and has a function of outputting as signal light for each wavelength channel.

In FIG. 26, the length of the individual waveguides of the array waveguide 9103 is designed to be sequentially lengthened by a fixed amount of ΔL. At this time, the transmission center wavelength λ from the central waveguide of each of the first input / output waveguides 9101 to the second input / output waveguide 9102._CIs expressed by the following equation. λ_C= n_aΔL / M equation (1)

Where n_aIs the effective index of refraction of the array waveguide 9101 and M is the diffraction order of the AWG. Since M can be any integer, there are multiple transmission center wavelengths for the AWG. The difference between the transmission center wavelength (transmission center frequency) corresponding to a certain diffraction order and the transmission center wavelength (transmission center frequency) corresponding to a different diffraction order is the AWG's Free Spectral Range (FSR). )is called. FSR is usually represented by the frequency interval (GHz). The cyclic AWG is an AWG that selects the value of this FSR so as to match the desired demultiplexing characteristics and uses transmission wavelengths corresponding to a plurality of different diffraction orders.

FIG. 27 is a conceptual diagram of a wavelength combiner / demultiplexer showing a design example of the wavelength combiner / demultiplexer function of the cyclic AWG. The wavelength merging / demultiplexing circuit 9200 using the cyclic AWG has a plurality of ports 9201 corresponding to the first input / output waveguide and a port 9202 corresponding to the second input / output waveguide. In this example, a plurality of ports 9201 are composed of 8 ports (wavelengths), and the interval between the transmission center wavelengths of each port is 100 GHz. The FSR is designed to be 800GHz. Here, each wavelength of the optical signal included in the wavelength division multiplexing signal at 100 GHz intervals is λ.₁, Λ₂, ..., λ₄₈And. The wavelength merging and demultiplexing circuit 9200 using the cyclic AWG combines the signal light of 800 GHz cycle input from each port of multiple ports 9201 (first input / output waveguide) into the second input / output waveguide. It has a function of dividing the wavelength multiplex signal light into signal light having a period of 800 GHz and outputting it in the opposite direction. More specific frequencies will be described later.

The cyclic AWG9100 that realizes the optical duplexer 9200 shown in FIG. 27 can be realized by the following configuration as an example. The difference in refractive index between the core and clad of the waveguide is 1.5%, and the core thickness is 4.5 μm. The core widths of the first input / output waveguide 9101, the array waveguide 9103, and the second input / output waveguide 9105 are 4.5 μm, respectively. The number of array waveguide 9103s is 50, and the waveguide length difference ΔL is 254.2475 μm. The lengths of the first slab waveguide 9102 and the second slab waveguide 9104 are both 1128 μm. Further, the waveguide spacing of the first input / output waveguide 9101 in the portion connected to the first slab waveguide 9102 is 15 μm, and the first slab waveguide 9102 and the second slab waveguide 9104 are connected, respectively. The waveguide spacing of the array waveguide 9103 in the part is 10 μm.

FIG. 28 is a table showing the transmission center wavelengths of each signal light to be combined and demultiplexed by the corresponding optical frequencies in the optical combined demultiplexer of FIG. 27 configured by the cyclic AWG. Each port of the first input / output waveguide 9101 uses a plurality of different transmission wavelengths corresponding to the diffraction order. For example, referring to the column of port 1 in the table, the frequency 196400 GHz corresponds to the diffraction order 242, the frequency 195600 GHz corresponds to the diffraction order 241 and the frequency 194800 GHz corresponds to the diffraction order 240. Here, looking at each optical signal of wavelength division multiplexing light input to one port, when the diffraction order is different by one, the frequency interval between two adjacent optical frequencies is 800 GHz. That is, the frequency interval between two adjacent optical frequencies corresponds to FSR. Also, looking at the frequencies between adjacent ports, different frequencies are arranged by 100 GHz. From port 1 to port 8, frequencies are sequentially arranged at intervals of 100 GHz, and following the frequency of port 8, the next frequency is assigned to port 1 again, and the frequencies are arranged cyclically (cyclically). You can see that it is configured.

The frequency of each signal light shown in Fig. 28 has a group of optical frequencies at 100 GHz intervals that match the frequency grid defined in the International Standard ITU-T G.694.1 Recommendation (hereinafter referred to as the "ITU-T grid"). doing. Wavelength λ of the first port in FIG. 27₁Corresponds to 196400GHz (wavelength 1526.438nm) at the top left of the table, and the wavelength λ of the 8th port.₄₈Corresponds to 191700 GHz (wavelength 1563.862 nm) at the bottom right of the table. The frequency range shown in FIG. 28 corresponds to the C band (wavelength: 1530 to 1565 nm), which is a commonly used region for optical wavelength division multiplexing communication.

29 and 30 are diagrams showing a configuration example when the cyclic AWG is used in an actual WDM system. 29 and 30 show the system configurations at different expansion stages, with FIG. 29 corresponding to the initial stage and FIG. 30 corresponding to the post-expansion stage. Referring to FIG. 29, the WDM system has a 6-branch coupler 9400, which could be replaced by a 6-port wavelength division multiplexing filter 9400. The cyclic AWG9401 shown in Figure 27 is connected to one port on the coupler 9400. Figure 30 shows the state of a WDM system that has undergone expansion, with six cyclic AWG9401-9406 connected to the six ports of the coupler or filter 9400. As a whole, it functions as a wavelength division multiplexing filter with 48 ports for input and output of wavelength division multiplexing light.

When introducing a WDM system, it is not necessary to operate signals of all wavelengths in the C band at the initial stage. It is usual to install an optical transmitter / receiver with a required number of wavelengths, start operation, and then increase the number of wavelengths according to the demand for transmission capacity. Therefore, instead of installing a wavelength combined / demultiplexing filter for 48 ports as shown in Fig. 30, at the initial stage, only cyclic AWG corresponding to a part of the wave number (8 in this case) is introduced as shown in Fig. 29. It is preferable to do so. It is economical from the viewpoint of operation cost to start operation with low initial cost and finally increase the number of cyclic AWGs to 6 as shown in Fig. 30 to realize a 48-port combined demultiplexing filter. is there.

In addition, when adding a system, by using the same type of cyclic AWG, it is possible to unify the parts required for maintenance, reduce the types of maintenance parts, and reduce operating costs. From this point of view, the cyclic AWG, which can cover the entire C band, is easier to manage and maintain the system than using multiple types of non-cyclic AWGs that are separately designed for exclusive use and have different transmission center wavelengths. Desirable in terms of cost.

<p num="0014"><patcit num="1"><text>International Publication Patent WO98 / 36299 Specification</text></patcit></p>

<p num="0015"><nplcit num="1"><text>H. Takahashi, K. Oda, H. Toba, and Y. Inoue, Transmission characteristics of arrayed-waveguide N x N wavelength multiplexer, IEEE Journal of Lightwave Technology, vol. 13, pp. 447-455, 1995</text></nplcit></p>

<p num="0016"> However, in the cyclic AWG, the transmitted center wavelength actually realized has a deviation from the specified grid such as ITU-T, and there is a problem in narrowing the band of the communication channel in terms of its accuracy. .. In the cyclic AWG, for all transmission center wavelengths corresponding to the combination of input / output waveguides (ports) and diffraction order used, the actually realized transmission center wavelength is the desired signal light wavelength, or ITU-T clip. It does not exactly match the wavelength specified in. This is due to the following two reasons. One is that the transmission center wavelength of the AWG and the FSR are not parameters that are determined independently, so if the design is designed to prioritize the transmission center wavelength, the FSR will usually deviate from the target value. according to. The other is that the FSR value changes slightly depending on the input / output waveguide. Even if the FSR for a specific port is as the target value, it deviates from the FSR target value for other ports. The principle grid wavelength shift in the cyclic AWG is described in detail in Non-Patent Document 1.</p><p num="0017"> FIG. 31 is a diagram illustrating the deviation of the transmission center wavelength from the ITU-T crid in the actual cyclic AWG. In FIG. 31, the horizontal axis is the wavelength λ of the signal light._NThe wavelength (channel) number N corresponding to is shown, and the vertical axis shows the amount of deviation from the ITU-T grid in terms of optical frequency. For all 48 channels of signal light with transmission center wavelengths shown in FIGS. 27 and 28, the maximum transmission center wavelength of the cyclic AWG actually produced is ± 12 GHz (± 0.096) from the specified value of the ITU-T grid. There is a deviation of nm).</p><p num="0018"> The above-mentioned problem of wavelength shift in the cyclic AWG can be solved to some extent by the prior art. In the cyclic AWG, in order to suppress fluctuations in the transmission center wavelength due to the environmental temperature, a temperature control type configured to keep the temperature of the AWG circuit constant by a heater or the like is used. When cyclic AWGs are used in WDM systems such as those shown in FIGS. 29 and 30, the transmission center is fine-tuned to keep the set temperature constant according to the diffraction order corresponding to the wavelength used in each AWG. The wavelength grit shift can be reduced.</p><p num="0019"> For example, the AWG9401 using an optical signal having a wavelength number N of 1 to 8 shown in FIG. 30 corresponds to a diffraction order of 242 as shown in FIG. 28. For this AWG9401, the set temperature of the AWG may be adjusted relatively in a direction that compensates (cancels) the negative frequency shift amount (-5 to -13 GHz: Fig. 31). Similarly, the AWG9402, which uses an optical signal with a wavelength number N of 9 to 16, has a diffraction order of 241 and compensates (cancels) the negative frequency shift (-4 to -8 GHz) for this AWG. Adjust the set temperature of the AWG relatively in the same direction. In addition, the AWG9406, which uses an optical signal with a wavelength number N of 41 to 48, corresponds to a diffraction order of 237, and this AWG compensates for a positive frequency shift (+4 to + 12.5 GHz) (offset). Adjust the set temperature of the AWG relatively in the same direction. Therefore, in the WDM system with the post-expansion configuration shown in FIG. 30, each of the six cyclic AWG9401 to 9406 is adjusted to a set temperature finely adjusted according to the diffraction order used. It will be.</p><p num="0020"> FIG. 32 is a diagram illustrating the deviation of the transmission center wavelength from the ITU-T crid when the temperature of the AWG is optimally adjusted according to the diffraction order used. Compared with the frequency deviation amount in FIG. 31 without temperature compensation, the absolute value of the deviation amount is considerably suppressed, but the maximum value of the deviation amount still reaches ± 5 GHz (± 0.04 nm). As described above, in the cyclic AWG according to the prior art, the transmission center wavelength of the AWG that can be actually manufactured has a deviation from the ITU-T clip.</p><p num="0021"> As already mentioned, WDM technology is used, for example, in the C band (wavelength: 1530 to 1565 nm), which has high light transmittance and can be applied to an erbium-added optical fiber amplifier. In response to the increase in communication traffic, the channel bandwidth corresponding to one optical signal is becoming narrower in order to multiplex more optical signals. In recent years, the transition from the conventional channel arrangement configuration at 50 GHz intervals to the channel arrangement configuration at 25 GHz intervals (channel bandwidth is also 25 GHz) is progressing. For example, there is a demand for a system that uses WDM signals in which 192 channels of optical signals are arranged at 25 GHz intervals and multiplexed.</p><p num="0022"> Under these circumstances, the problem of frequency shift of the cyclic AWG cannot be completely suppressed even if the operating temperature of the AWG circuit is finely adjusted according to the diffraction order. In a WDM system with a narrow wavelength channel interval that requires accuracy of the transmission center wavelength, there is a problem that the required performance cannot be satisfied in some cases.</p><p num="0023"> The present invention has been made in view of such a problem, and an object of the present invention is to compensate for the deviation of the transmission center wavelength (transmission center frequency) occurring in the cyclic AWG from the ITU-T grid, and to compensate for the deviation of the transmission center wavelength (transmission center frequency) from the ITU-T grid, and to compensate for the deviation of the transmission center wavelength from the ITU-T grid. An object of the present invention is to provide an optical wavelength combined / demultiplexing circuit having excellent accuracy of transmission center wavelength in the region.</p>

<p num="0024"> In order to achieve such a problem, the invention of claim 1 is an array waveguide composed of a waveguide that is sequentially lengthened by a predetermined optical path length difference, and a first connected to one end of the array waveguide. In a wavelength-coupling / demultiplexing circuit that includes a slab waveguide and a second slab waveguide connected to the other end of the array waveguide and uses transmitted wavelengths corresponding to multiple diffraction orders, each via an interference circuit. Further, a plurality of first input / output waveguides optically connected to the first slab waveguide and a second input / output waveguide connected to the second slab waveguide are further provided. The interference circuit includes a primary mode excitation mechanism that converts a part of the ground mode light input from each of the plurality of first input / output waveguides into primary mode light, and the primary mode excitation mechanism. Optically connected to, at least basal mode light and primary mode light can propagate, and give a predetermined phase difference to a predetermined transmitted wavelength between the basal mode light and the primary mode light. It has a mode waveguide, and the peak position of the optical field distribution formed on the connection surface between the interference circuit and the first slab waveguide changes in the waveguide width direction of the multimode waveguide depending on the wavelength. The optical wavelength combined and demultiplexed circuit is configured to compensate for the deviation of the transmitted wavelength corresponding to the plurality of diffraction orders from the standardized grid due to the change.</p><p num="0025"> Here, the standardized grid corresponds to, for example, the frequency grid ITU-T grid defined in the International Standard ITU-T G.694.1 Recommendation. Further, the waveguide width direction of the multimode waveguide in which the peak position of the optical field distribution changes corresponds to, for example, the p-axis direction in FIGS. 4, 10, 15, and 22.</p><p num="0026"> The invention of claim 2 is the optical wavelength combined / demultiplexing circuit of claim 1, wherein the ratio of the power converted into the primary mode light by the primary mode excitation mechanism with respect to the total power of the input light. However, each of the plurality of first input / output waveguides is different from each other.</p><p num="0027"> The invention of claim 3 is the optical wavelength combined / demultiplexing circuit of claim 1 or 2, wherein the phase difference between the base mode light and the primary mode light has a predetermined length. It is characterized in that it changes depending on the wavelength in the waveguide.</p><p num="0028"> The invention of claim 4 is an optical wavelength combined / demultiplexing circuit according to any one of claims 1 to 3, wherein the primary mode excitation mechanism includes an optical splitter, a first arm waveguide connected to the optical splitter, and an optical splitter. The first arm waveguide is connected to the second arm waveguide, and the ground mode light input from the second arm waveguide is converted into the primary mode. It is composed of an optical mode synthesis coupler that merges with the ground mode input from the arm waveguide and outputs, and the phase difference between the ground mode light and the primary mode light is the first arm waveguide and the second arm waveguide. It is characterized in that it changes depending on the wavelength in the set optical path length difference of the arm waveguide.</p><p num="0029"> The invention of claim 5 is the optical wavelength combined / demultiplexing circuit of claim 4, wherein the optical mode synthesis coupler is a directional coupler composed of two waveguides having different widths. To do.</p><p num="0030"> The invention of claim 6 is the optical wavelength combined / demultiplexing circuit according to any one of claims 1 to 3, wherein the primary mode excitation mechanism is a waveguide offset connected by shifting the central axis of the width of the waveguide core. It is characterized by being.</p><p num="0031"> The invention of claim 7 is the optical wavelength combined / demultiplexing circuit according to any one of claims 1 to 6, wherein the multimode waveguide is connected to the first slab waveguide via a tapered waveguide. It is characterized by that.</p>

<p num="0032"> As described above, according to the present invention, it is possible to suppress the deviation of the transmission center wavelength from the ITU-T clip in the cyclic AWG type optical wavelength combined / demultiplexing circuit. It is possible to realize a cyclic AWG type optical wavelength division multiplexing circuit applicable to WDM systems with narrow wavelength channel spacing.</p>

<figref num="1">FIG. 1 is a conceptual diagram illustrating an electric field distribution (optical field) of basal mode light and primary mode light waveguideing through an optical waveguide.</figref><figref num="2">FIG. 2 is a plan view showing the configuration of the cyclic AWG according to the first embodiment of the present invention.</figref><figref num="3">FIG. 3 is a table showing the transmitted central light frequencies of each signal light to be demultiplexed in the optical demultiplexer of FIG. 2 configured by the cyclic AWG of the present invention.</figref><figref num="4">FIG. 4 is an enlarged view from the waveguide offset in the cyclic AWG of the first embodiment to the vicinity of the linear tapered waveguide.</figref><figref num="5">FIG. 5 is a diagram showing parameter values related to compensation of the transmission center wavelength at each port of the cyclic AWG according to the first embodiment of the present invention.</figref><figref num="6">FIG. 6 is a diagram showing the change of the peak position of the optical field distribution at the end of the linear tapered waveguide in Example 1 depending on the frequency of the propagating light wave for each port.</figref><figref num="7">FIG. 7 is a diagram showing the amount of deviation of the transmission center wavelength from the ITU-T clip for the cyclic AWG of Example 1.</figref><figref num="8">FIG. 8 is a plan view showing the configuration of the cyclic AWG according to the second embodiment of the present invention.</figref><figref num="9">FIG. 9 is a diagram showing a configuration of a cross section across the groove in the athermal cyclic AWG of the second embodiment.</figref><figref num="10">FIG. 10 is an enlarged view from the waveguide offset in the cyclic AWG of the second embodiment to the vicinity of the linear tapered waveguide.</figref><figref num="11">FIG. 11 is a diagram showing parameter values related to compensation of the transmission center wavelength at each port of the cyclic AWG according to the second embodiment of the present invention.</figref><figref num="12">FIG. 12 is a diagram showing the change of the optical field distribution peak position at the end of the linear tapered waveguide in Example 2 depending on the frequency of the propagating light wave for each port.</figref><figref num="13">FIG. 13 is a diagram showing the amount of deviation of the transmission center wavelength from the ITU-T clip for the cyclic AWG of Example 2.</figref><figref num="14">FIG. 14 is a plan view showing the configuration of the cyclic AWG according to the third embodiment of the present invention.</figref><figref num="15">FIG. 15 is an enlarged view from the optical splitter in the cyclic AWG of the third embodiment to the vicinity of the linear tapered waveguide.</figref><figref num="16">FIG. 16 is a diagram showing parameter values related to compensation of the transmission center wavelength at each port of the cyclic AWG of Example 3.</figref><figref num="17">FIG. 17 is a diagram showing the change of the optical field distribution peak position at the end of the linear tapered waveguide in Example 3 depending on the frequency of the propagating light wave for each port.</figref><figref num="18">FIG. 18 is a diagram showing the amount of deviation of the transmission center wavelength from the ITU-T clip for the cyclic AWG of Example 3.</figref><figref num="19">FIG. 19 is an enlarged view showing another configuration example of the optical mode synthesis coupler.</figref><figref num="20">FIG. 20 is an enlarged view showing still another configuration example of the optical mode synthesis coupler.</figref><figref num="21">FIG. 21 is a plan view showing the configuration of the cyclic AWG according to the fourth embodiment of the present invention.</figref><figref num="22">FIG. 22 is an enlarged view of the cyclic AWG of the fourth embodiment from the optical splitter to the vicinity of the linear tapered waveguide.</figref><figref num="23">FIG. 23 is a diagram showing parameter values related to compensation of the transmission center wavelength at each port of the cyclic AWG of Example 4.</figref><figref num="24">FIG. 24 is a diagram showing the change of the optical field distribution peak position at the end of the linear tapered waveguide in Example 4 depending on the frequency of the propagating light wave for each port.</figref><figref num="25">FIG. 25 is a diagram showing the amount of deviation of the transmission center wavelength from the ITU-T crid for the cyclic AWG of Example 4.</figref><figref num="26">FIG. 26 is a plan view showing the configuration of the prior art cyclic AWG.</figref><figref num="27">FIG. 27 is a conceptual diagram of a wavelength combiner / demultiplexer showing a design example of the wavelength combiner / demultiplexer function of the cyclic AWG.</figref><figref num="28">FIG. 28 is a table showing each wavelength of the signal light combined and demultiplexed by the optical duplexer of FIG. 27 in terms of optical frequency.</figref><figref num="29">FIG. 29 is a diagram showing a configuration example in the initial stage when the cyclic AWG is used in an actual WDM system.</figref><figref num="30">FIG. 30 is a diagram showing a configuration example of the stage after expansion when the cyclic AWG is used in an actual WDM system.</figref><figref num="31">FIG. 31 is a diagram illustrating the deviation of the transmission center wavelength from the ITU-T crid in the actual cyclic AWG.</figref><figref num="32">FIG. 32 is a diagram illustrating the deviation of the transmission center wavelength from the ITU-T crid when the temperature of the AWG is optimally adjusted according to the diffraction order used.</figref><figref num="33">FIG. 33 is a diagram illustrating the amount of frequency deviation for each port of the temperature control type cyclic AWG.</figref><figref num="34">FIG. 34 is a diagram illustrating the amount of frequency shift for each port of the cyclic AWG with athermalization.</figref>

In the prior art cyclic AWG, the temperature of each of the plurality of AWGs used in the WDM system is adjusted to compensate for the frequency shift. However, the amount of deviation is only corrected for each diffraction order corresponding to the wavelength used in the AWG, which is insufficient. In the present invention, the position of the optical field is adjusted for each port, focusing on a plurality of ports (input / output waveguides) connected to at least one slab waveguide of the cyclic AWG from a completely different viewpoint. By having a mechanism for changing the position of the optical field in the width direction of the waveguide on the connection surface of the slab waveguide according to the wavelength, the frequency deviation of the transmission center wavelength is significantly reduced. The position of the optical field is adjusted by adjusting the amount of light generated in two different modes and the phase difference for each port, and the transmission center wavelengths of multiple optical signals with different optical frequencies appearing in one port. It can be corrected at the same time. Hereinafter, the operating principle of the cyclic AWG according to the present invention will be described.

FIG. 1 is a conceptual diagram illustrating an electric field distribution (optical field) of basal mode light and primary mode light waveguideing through an optical waveguide. The light propagating through the core on the waveguide may include light in different propagation modes. FIG. 1 illustrates the mode of propagating light when looking at the cross section at the connection between one slab waveguide of the cyclic AWG and the input / output waveguide connected to this slab waveguide. .. The horizontal axis in FIG. 1 indicates the position of the input / output waveguide in the width direction. The portion indicated as the waveguide end on the horizontal axis corresponds to the position at both ends of the waveguide core portion. The vertical axis shows the intensity distribution of the optical field.

Again, referring to the prior art cyclic AWG9100 with the configuration shown in FIG. 26, usually only ground mode light propagates through each waveguide of the first I / O waveguide 9101 consisting of multiple waveguides. Therefore, the peak position of the optical field 1 excited at the connection between the first slab waveguide 9102 and one of the first input / output waveguides 9101 does not change depending on the wavelength, and is generally the waveguide. It is the center position of the cross section (indicated by a dashed line). Here, consider a case where the primary mode light 3 is mixed in the above-mentioned light field 1 at a specific intensity ratio. At this time, due to the interference between the base mode light 1 and the primary mode light 3, the peak position of the optical field of the interference light 2 shifts the cross section of the waveguide in the lateral direction (waveway width direction).

The amount of shift of the peak position of the optical field of the interference light 2 in the waveguide width direction changes depending on the intensity ratio and the phase difference of both mode lights. When the phase difference between the basal mode light and the primary mode light is 0, the shift amount is simply determined by the intensity ratio of both mode lights. On the other hand, when a phase difference is given between the basal mode light and the primary mode light, the influence of the interference between the two mode lights is alleviated by the phase difference. Specifically, the shift amount of the peak position of the optical field of the interference light 2 in the p-axis direction decreases as the phase difference between the two mode lights increases. Therefore, when the phase difference between the two mode lights is π / 2, the shift amount becomes 0 regardless of the intensity ratio of the two mode lights.

Here, paying attention to the port connected to one slab waveguide of the cyclic AWG, for example, the port is the first composed of a plurality of waveguides connected to one slab waveguide 9101 in FIG. Corresponds to each of the input / output waveguides 9101. At each port, light that is demultiplexed or demultiplexed by the optical demultiplexing circuit is input or output. In the following description, one port can be considered in association with one input / output waveguide. Note that the first I / O waveguide 9101 in FIG. 26 contains eight I / O waveguides, but may contain different numbers of I / O waveguides depending on the specifications of the demultiplexing characteristics. I want to be.

In the present invention, for a plurality of optical signals having different wavelengths (frequency) transmitted through each port of the cyclic AWG, the phase difference between the base mode light and the primary mode light according to the wavelength (frequency). Configure the input / output waveguide so that The phase difference between the basal mode light and the primary mode light is set for each of a plurality of optical signals having different wavelengths transmitted through one port of the AWG. As a result, the position of the light incident on the first slab waveguide 9102 can be changed according to the wavelength (frequency) of the transmitted light signal.

The transmission center wavelength of the AWG at that port, depending on the peak position of the optical field at the connection between the waveguide corresponding to one port of the first I / O waveguide 9101 and the first slab waveguide 9102. Fluctuates. Therefore, in the first input / output waveguide 9101, by providing an appropriate mechanism, the primary mode light having a predetermined intensity ratio is excited, and the phase difference between the primary mode light and the base mode light is the wavelength. It suffices if it changes depending on. If the intensity ratio of primary mode light and ground mode light and the phase difference between them can be controlled according to the wavelength, different wavelengths (transmission center) appearing at each port, which has been a problem in cyclic AWG according to the prior art. It is possible to simultaneously correct the transmission center wavelengths of a plurality of optical signals having wavelengths).

Therefore, the wavelength junction grating circuit (cyclic AWG) of the present invention is an array waveguide composed of a waveguide that is sequentially lengthened by a predetermined optical path length difference, and a first slab waveguide connected to one end of the array waveguide. In a wavelength junction / demultiplexing circuit that includes a second slab waveguide connected to the other end of the array waveguide and uses transmission wavelengths corresponding to a plurality of diffraction orders, each of the first is passed through an interference circuit. A plurality of first input / output waveguides optically connected to the slab waveguide of the above, and a second input / output waveguide connected to the second slab waveguide are further provided.

The interference circuit of the wavelength merging / demultiplexing circuit of the present invention includes a primary mode excitation mechanism that converts a part of the ground mode light input from each of the plurality of first input / output waveguides into primary mode light. , Optically connected to the primary mode excitation mechanism, at least capable of propagating ground mode light and primary mode light, with respect to a predetermined transmission wavelength between the ground mode light and the primary mode light. It has a multi-mode waveguide that gives a predetermined phase difference, and the peak position of the optical field distribution formed on the connection surface between the interference circuit and the first slab waveguide is determined by the wavelength of the multi-mode waveguide. It changes in the width direction of the waveguide, and the change is configured to compensate for the deviation of the transmission wavelength corresponding to the plurality of diffraction orders from the standardized grid.

Hereinafter, the configuration and operation of the present invention will be described in more detail together with specific examples. In the following examples, a specific configuration including various combinations of a cyclic AWG and an athermal AWG configuration having a configuration peculiar to the present invention and an effect of improving wavelength deviation are shown.

<p num="0044"> FIG. 2 is a plan view showing the configuration of the cyclic AWG according to the first embodiment of the present invention. The cyclic AWG100, like the prior art AWG, has a first I / O waveguide 101, a first slab waveguide 102, an array waveguide 103, a second slab waveguide 104, and a second I / O guide. It is equipped with a waveguide 105. In the cyclic AWG100 of the present invention, between the first input / output waveguide 101 and the first slab waveguide 102, a primary mode photoexcitation mechanism, a waveguide offset 106, a multimode waveguide 107, and a tapered waveguide 108 Is further equipped.</p><p num="0045"> Therefore, the cyclic AWG100 includes an array waveguide 103 composed of a waveguide that is sequentially lengthened by a predetermined optical path length difference, a first slab waveguide 102 connected to one end of the array waveguide, and the other end of the array waveguide. It is a wavelength combining and demultiplexing circuit that includes a second slab waveguide 104 connected to and uses transmission wavelengths corresponding to a plurality of diffraction orders. Further, a plurality of first input / output waveguides 101, each optically connected to the first slab waveguide via an interference circuit, and a second input connected to the second slab waveguide. It will further include an output waveguide 105.</p><p num="0046"> A waveguide offset 106, a multimode waveguide 107, and a tapered waveguide 108, which are primary mode photoexcitation mechanisms, constitute an interference circuit. That is, the interference circuit includes a primary mode excitation mechanism that converts a part of the ground mode light input from each of the plurality of first input / output waveguides into primary mode light, and the primary mode excitation mechanism. Optically connected to, at least basal mode light and primary mode light can propagate, and give a predetermined phase difference to a predetermined transmitted wavelength between the basal mode light and the primary mode light. It will have a mode waveguide.</p><p num="0047"> Each part of the cyclic AWG100 has the following configuration. For all waveguides, the difference in index of refraction between core and clad is 1.5% and the core thickness is 4.5 μm. The core width of the first input / output waveguide 101, the array waveguide 103, and the second input / output waveguide 105 is 4.5 μm. The array waveguide 103 has 50 waveguides and is designed to be sequentially longer by a fixed amount ΔL than the inner waveguide, and the ΔL is 254.2475 μm. The length of the first slab waveguide 102 and the length of the second slab waveguide 104 are 1128 μm, respectively. The array spacing of the linear taper waveguide 108 at the portion connected to the first slab waveguide 102 is 15 μm, and the waveguide spacing of the array waveguide 103 at the portion connected to the first slab waveguide 102 and the second slab. The waveguide spacing of the array waveguide 103 of the portion connected to the waveguide 104 is 10 μm, respectively. The first input / output waveguide 101 is composed of eight waveguides, and has eight ports as an optical duplexer. The combined demultiplexing optical frequency interval between two adjacent ports is 100GHz, and the FSR is designed with a target value of 800GHz.</p><p num="0048"> FIG. 3 is a table showing the transmission center wavelengths of each signal light to be demultiplexed by the corresponding optical frequencies in the optical demultiplexer of FIG. 2 configured by the cyclic AWG of the present invention. That is, each optical frequency in FIG. 3 is an optical frequency defined by the ITU-T grid, and the optical frequency targeted by the cyclic AWG of the present invention is shown. In the cyclic AWG of the present invention, the amount of deviation between the realized transmission center frequency and the target optical frequency is significantly suppressed as compared with the prior art. As shown in FIG. 3, a plurality of transmission wavelengths corresponding to different diffraction orders in each port from the first port (hereinafter, abbreviated as port 1) to the port 8 of the first input / output waveguide 101. Is used. Cyclic AWG100 from 196400 GHz (wavelength 1526.438 nm) corresponding to diffraction order 242 at the top port 1 in the table to 191700 GHz (wavelength 1563.862 nm) corresponding to diffraction order 237 at the bottom 8 port in the table. The signal light of 48 channels of is demultiplexed.</p><p num="0049"> Focusing on one port here, it should be noted that a plurality of optical signals having different optical frequencies corresponding to different diffraction orders are combined and demultiplexed. For example, at port 1, optical signals with six different optical frequencies are demultiplexed from an optical frequency of 196400 GHz corresponding to a diffraction order 242 to an optical frequency of 192400 GHz corresponding to a diffraction order 237 of a different value. Two adjacent two of these six different optical frequencies have an FSR spacing. For example, there is a difference of 800 GHz corresponding to FSR between the optical frequency 196400 GHz corresponding to the diffraction order 242 and the optical frequency 195600 GHz corresponding to the diffraction order 241 of one different value. The same applies to each port from port 2 to port 8.</p><p num="0050"> FIG. 4 is an enlarged view showing the configuration from the waveguide offset to the vicinity of the linear taper waveguide in the cyclic AWG of the first embodiment of the present invention. One port (input / output waveguide) in the first input / output waveguide 101 is shown, and each code of the component is the same as that shown in FIG. In this embodiment, the multimode waveguide 107 is connected to the first slab waveguide 102 via the tapered waveguide 108. The waveguide width of the multimode waveguide 107 is 7 μm, and the waveguide width of the linear taper waveguide 108 is 11.5 μm at the portion connected to the first slab waveguide 102. Here, in the waveguide offset 106, the core width is expanded to the same level as that of the multimode waveguide 107 by the linear taper, and the central axis of the waveguide core is shifted to connect to the multimode waveguide 107. At this discontinuous core connection at the waveguide offset 106, some power of the ground mode light is converted and the primary mode light is excited.</p><p num="0051"> FIG. 5 is a diagram showing parameters related to compensation of the transmission center wavelength at each port of the cyclic AWG according to the first embodiment of the present invention. For each of the eight ports, the amount of central axis misalignment (μm) of the waveguide offset 106, the ratio of optical power converted from ground mode to primary mode at the waveguide offset (%), and the length of the multimode waveguide 107. The design values of the offset (μm) and the length (μm) of the linear taper waveguide 108 are shown.</p><p num="0052"> In the cyclic AWG of the present invention, the waveguide at the connection portion of the slab waveguide so as to cancel the frequency deviation (wavelength deviation amount) of the transmission center frequency (transmission center wavelength) when the AWG is manufactured by the configuration of the prior art. Adjust the peak position of the optical field in the width direction. The peak position of the optical field can be realized by setting the amount of primary mode light generated and the phase according to the "frequency shift amount" to be offset.</p><p num="0053"> Therefore, in the cyclic AWG of the present invention, as a means for adjusting the peak position of the optical field, a means for controlling the amount of primary mode light generated and a means for controlling the phase difference between the primary mode light and the base mode light are controlled. Provide means to do so. By combining these means, the amount and phase of the primary mode light generated are adjusted, and the peak position of the optical field in the width direction of the waveguide at the connection portion of the slab waveguide is adjusted.</p><p num="0054"> Increasing the amount of central axis deviation of the waveguide offset 106 increases the ratio of optical power converted from the base mode to the primary mode. Therefore, when the AWG is manufactured by the configuration of the prior art, the central axis deviation amount of the waveguide offset 106 may be increased for a port having a large frequency deviation amount (wavelength deviation amount) of the transmission center frequency (transmission center wavelength). .. That is, for a port having a large frequency deviation, the central axis deviation amount of the waveguide offset 106 may be set large. Since the ITU-T grid customarily identifies and defines channels by frequency, the amount of deviation can also be expressed by the transmission center wavelength of the channel, but in the following description, the amount of frequency deviation will be described. It should be noted that both the wavelength shift and the frequency shift mean the same event in terms of deviation from the target value specified in the ITU-T grid.</p><p num="0055"> The cyclic AWG of this embodiment is premised on a temperature adjustment type in which the operating temperature of the AWG is finely adjusted according to the diffraction order. That is, it is assumed that the AWG of this embodiment operates so as to suppress the deviation amount of the transmission center frequency by adjusting the temperature for each AWG. Therefore, the frequency shift to be compensated by the present invention is as shown in FIG. Here, in order to clarify the amount of frequency deviation to be compensated for each port more specifically, the amount of frequency deviation for each port is determined.</p><p num="0056"> FIG. 33 is a diagram illustrating the amount of frequency deviation for each port of the temperature control type cyclic AWG. Each plot point is the same as the one showing the wavelength dependence of the frequency shift shown in FIG. The horizontal axis of FIG. 33 is the wavelength number, and the wavelength numbers 1 to 48 correspond from the left side to the right side, and the vertical axis indicates the amount of frequency deviation for each wavelength number. Therefore, note that when the horizontal axis is read as frequency, the frequency is lower on the right side and higher on the left side. Simply, the frequency-dependent characteristics and the wavelength-dependent characteristics can be considered to have opposite polarities in slope.</p><p num="0057"> Here, the eight plot point groups 1001 in which the wavelength numbers 1 to 8 at the left end are connected correspond to the wavelength group having the diffraction order 242. Similarly, the eight connected plot point groups 1006 with wavelength numbers 41 to 48 at the right end correspond to wavelength groups with a diffraction order of 237. In the cyclic AWG of the present invention, the frequency deviation is compensated for each port by adjusting the peak position of the optical field in the width direction of the waveguide at the connection portion of the slab waveguide. Therefore, it is necessary to first grasp the amount of frequency deviation for each port and perform frequency compensation according to the amount of deviation.</p><p num="0058"> In FIG. 33, the curve connecting a plurality of plot points of the wavelength corresponding to port 1 is referred to as P1. Here, the wavelengths corresponding to port 1 correspond to the six frequencies (196400, 195600, 194800, 194000, 193200, 192400 GHz) in the column indicated by 1 in the table of FIG. The curve P1 shows the frequency characteristics of the frequency shift to be compensated for the wavelength corresponding to the port 1. Similarly, the curve connecting multiple plot points of the wavelength corresponding to port 8 is indicated by P8. Here, the wavelengths corresponding to port 8 correspond to the six frequencies (195700, 194900, 194100, 193300, 192500, 191700G) in the column indicated by 8 in Table 3 of FIG. The curve P8 shows the frequency characteristics of the frequency shift to be compensated for the wavelength corresponding to the port 8. Although not shown in FIG. 33 because the drawing becomes complicated, curves P2 to P7 corresponding to ports 2 to 7 can be assumed in the same manner.</p><p num="0059"> In this way, from FIG. 33, the magnitude of the frequency shift and the frequency (wavelength) characteristics can be grasped for each of the ports 1 to 8. Focusing on port 4 and port 5 (P4, P5) in FIG. 33, it can be seen that the frequency deviation is about 1 GHz at the maximum, which is a level that does not require compensation. On the other hand, as is clear from the curves (straight lines) of P1 and P8, the maximum value of the deviation amount to be compensated for both port 1 and port 8 is relatively large at 4 GHz, and the frequency characteristics of the frequency deviation amount are It can be seen that the slopes are opposite to each other. Therefore, if compensation can be made according to the maximum amount of frequency deviation and frequency characteristics (tilt / shape) that differ for each port, each port can be adapted to the frequency characteristics of the amount of frequency deviation for each port. , It can be expected to effectively suppress the frequency shift. In addition, the frequency characteristics of the "correction amount" for a plurality of different frequencies appearing in one port can be grasped from each plot point in FIG. 33, and can be easily determined based on each curve of P1 to P8. .. As described above, in the present embodiment, since the amount of frequency deviation is large in the ports 1 and 8 located at both ends in the first input / output waveguide 101, the frequency deviation to be corrected by the present invention. The "correction amount" of is also increased.</p><p num="0060"> With reference to FIG. 5 again, in this embodiment, the central axis deviation amount of the waveguide offset 106 is made larger and the power ratio converted to the primary mode is relative to each other at the ports 1 and 8 located at both ends. Increase the target (1.5%). Further, in the ports 4 and 5 located near the center of the first input / output waveguide 101, the central axis deviation amount of the waveguide offset 106 is set to zero so that there is no power to be converted to the primary mode. Designed to (0%). In this way, the amount of primary mode light generated is controlled by the amount of central axis deviation of the waveguide offset 106 according to the maximum value of the amount of frequency deviation to be compensated.</p><p num="0061"> Therefore, in the cyclic AWG of the present invention, the ratio of the power converted into the primary mode light by the primary mode excitation mechanism (that is, the waveguide offset 106) to the total power of the input light is a plurality of the above. It will be different for each waveguide of the first input / output waveguide 101.</p><p num="0062"> The cyclic AWG of the present invention is further configured as follows. At each port of the first input / output waveguide 101, some optical power is converted to the primary mode at the waveguide offset 106. Both the ground mode light and the primary mode light reach the connection point of the linear taper waveguide 108 and the first slab waveguide 102. At this time, the difference between the effective refractive index for the light in the base mode and the effective refractive index for the light in the primary mode, which is generated by propagating through the multimode waveguide 107 and the linear tapered waveguide 108, differs depending on the wavelength (frequency). Therefore, the phase difference between the basal mode light and the primary mode light after passing through the multimode waveguide 107 and the linear taper waveguide 108 also changes depending on the wavelength (frequency). Therefore, the peak position of the distribution of the optical field at the end (connection portion) of the linear tapered waveguide 108 also changes depending on the wavelength (frequency). Therefore, the phase difference between the basal mode light and the primary mode light will change with wavelength in the multimode waveguide 107 having a predetermined length.</p><p num="0063"> In other words, the peak position of the distribution of the optical field has a wavelength (frequency) -dependent characteristic. On the contrary, if this is used, the wavelength (frequency) -dependent characteristic of the peak position of the distribution of the optical field can be controlled by changing the length of the multimode waveguide 107 and the linear taper waveguide 108.</p><p num="0064"> Therefore, for each port, so as to match the frequency deviation amount of the plurality of light waves (signals) transmitted through the port at each frequency, that is, to match the frequency-dependent characteristic (wavelength-dependent characteristic) of the frequency deviation amount. In addition, the lengths of the multimode waveguide 107 and the tapered waveguide 108 may be determined. The determined length described above gives a "predetermined phase difference" between the basal mode light and the primary mode light for a predetermined wavelength (frequency). At this time, the frequency (wavelength) characteristic (slope / shape) of the correction amount for correcting the deviation amount of the transmitted peripheral center wave number is determined by the predetermined phase difference. As described with FIG. 33, the magnitude of the frequency deviation and the frequency (wavelength) characteristics (slope / shape) are grasped for each of the ports 1 to 8. Therefore, by giving a "predetermined phase difference" and determining the frequency (wavelength) characteristic (slope / shape) of the compensation amount of the frequency shift, the frequency (wavelength) of the frequency shift of P1 to P8 grasped from FIG. 33 It can be adapted to the characteristics.</p><p num="0065"> Therefore, the lengths of the multimode waveguide 107 and the tapered waveguide 108 serve as a means of controlling the phase difference between the primary mode light and the basal mode light and are compatible with the frequency (wavelength) characteristics of the frequency shift. As such, it functions to determine the frequency characteristics (tilt / shape) of the correction amount. By this function of the present invention, the frequency shift is corrected according to the shift amount of the peak position of the optical field at the end of the linear tapered waveguide 108 (wavelength direction: p-axis), and the frequency shift is corrected and transmitted through a certain port. For a plurality of light waves (signals) having different frequencies, a plurality of transmitted center wavelengths can be collectively corrected at the same time so as to match the frequency characteristics of the amount of frequency deviation.</p><p num="0066"> FIG. 6 is a diagram showing how the peak position of the optical field distribution at the end of the linear tapered waveguide in this embodiment changes depending on the frequency of the propagating light wave for each port. Here, the peak position p (μm) on the vertical axis corresponds to the position of the p coordinate axis in FIG. 4, and p = 0 is the center position of the linear tapered waveguide. The horizontal axis is the frequency of the light wave, which corresponds to the frequency in the wavelength range of 1 to 48. As already described, the transmission center frequency can be changed and corrected by shifting the peak position of the optical field distribution on the vertical axis. Therefore, the vertical axis in FIG. 6 means the correction amount of the frequency shift. Here, the magnitude and frequency (wavelength) characteristics of the frequency deviation for each port of ports 1 to 8 described with reference to FIG. 33 correspond to the magnitude and frequency characteristics of the correction amount shown in FIG. Please note that.</p><p num="0067"> For example, in port 1 and port 8, the magnitude and frequency characteristics of the correction amount of port 1 and port 8 of FIG. 6 are set so as to cancel the frequency deviation amounts of P1 and P8 described in FIG. 33. That is, the peak position is 0 (correction amount is 0) near the center of the horizontal axis (194000 GHz), and the correction amount of port 1 and port 8 is set so that the correction amount is maximized at both ends of the horizontal axis. .. This corresponds to the fact that the amount of frequency shift shown by P1 and P8 in FIG. 33 is 0 near the wavelength number 24 near the center of the horizontal axis and is maximum at both ends. Further, the correction amounts of port 1 and port 8 in FIG. 6 have opposite slopes in their frequency characteristics. This also corresponds to the fact that the slopes of the frequency shift amounts of P1 and P8 in FIG. 33 are reversed.</p><p num="0068"> Also, pay attention to port 4 and port 5. Since the central axis deviation amount of the waveguide offset is set to 0 μm as shown in FIG. 5, the correction amount shown in FIG. 6 is 0. This corresponds to the fact that the curves P4 and P5 shown in FIG. 33 have almost no frequency deviation and no correction is required. The maximum value of the correction amount and the magnitude of the slope of the correction amount at each port in FIG. 6 correspond to the amount of central axis deviation of the waveguide offset shown in FIG. This is clear, for example, by comparing the central axis deviation amount of the waveguide offset in ports 1 to 4 shown in FIG. 5 with the correction amount characteristic shown in FIG.</p><p num="0069"> Furthermore, note that the length of the multimode waveguide shown in FIG. 5 is 173 μm discontinuous between the first group of ports 1 to 4 and the second group of ports 5 to 8. I want to be. It should be noted that each of the curves of the frequency shift "correction amount" shown in FIG. 6 has a sine function-like shape, and the phase is inverted between the two groups. The discontinuity in the length of the multimode waveguide between the above two groups means the inversion of the phase of the "correction amount" curve, and the inclination of the correction amount in FIG. 6 is positive or negative. Correspond.</p><p num="0070"> As described above, the change in the peak position of the optical field at the end of the linear tapered waveguide in the cyclic AWG of the present invention corrects the deviation of the transmission center frequency possessed by the conventional cyclic AWG. This correction is performed by setting the amount of central axis deviation of the waveguide offset 106 for each port and controlling the amount of primary mode light generated. In addition, the correction amount changes depending on the frequency, and for light waves of different frequencies appearing in one port, multiple transmission center wavelengths are simultaneously corrected at the same time so as to match the frequency characteristics of the frequency shift amount. can do.</p><p num="0071"> FIG. 7 is a diagram showing the amount of deviation of the transmission center wavelength from the ITU-T clip for the cyclic AWG of this embodiment. The cyclic AWG of this embodiment is a temperature control type, and the temperature to be kept constant is finely adjusted according to the diffraction order used. The maximum frequency deviation of the cyclic AWG of this example from the ITU-T crid is ± 1.2 GHz (± 0.010 nm), and the amount of frequency deviation is larger than that of the conventional cyclic AWG (Fig. 32). It has been reduced to about 1/5. A cyclic AWG with a transmission center frequency (wavelength) that is more consistent with the ITU-T crid has been realized.</p><p num="0072"> In the design values (FIG. 5) of the cyclic AWG ports described in the present embodiment, the ports 4 and 5 do not have the axial offset of the waveguide offset, and the primary mode is not excited. .. For ports that do not need to excite the primary mode, that is, ports that do not need to compensate for frequency deviations from the ITU-T grid, of course, the waveguide offset 106, the multimode waveguide 107, the straight line. It is not necessary to provide the tapered waveguide 108. These ports may directly connect the first input / output waveguide 101 and the first slab waveguide 102. The same applies to other examples described later.</p><p num="0073"> The cyclic AWG of this example was a temperature adjustment type in which the operating temperature of the AWG was finely adjusted according to the diffraction order. The present invention is also applicable to athermalized, non-temperature controlled cyclic AWGs, as described in the following examples.</p>

<p num="0074"> The optical wavelength combined / demultiplexing circuit according to the second embodiment of the present invention is obtained by applying the configuration peculiar to the present invention described in the first embodiment to the athermalized cyclic AWG. In the cyclic AWG of this embodiment, it is not necessary to adjust the temperature for each AWG. The amount of compensation for frequency deviation is larger than that in Example 1. Hereinafter, the configuration and operation of the cyclic AWG of this embodiment will be described in detail.</p><p num="0075"> FIG. 8 is a plan view showing the configuration of the cyclic AWG according to the second embodiment of the present invention. The cyclic AWG200, like the prior art AWG, has a first I / O waveguide 201, a first slab waveguide 202, an array waveguide 203, a second slab waveguide 204, and a second I / O guide. It is equipped with a waveguide 205. The cyclic AWG200 of the present invention has a primary mode photoexcitation mechanism, a waveguide offset 206, a multimode waveguide 207, and a linear taper waveguide, between the first input / output waveguide 101 and the first slab waveguide 202. It also has a 208. In the cyclic AWG200 of this embodiment, in order to eliminate the need for temperature adjustment, a groove 209 for dividing the waveguide is formed in the middle of the first slab waveguide 202, and the groove 209 is filled with a silicone resin. Has been done. This groove 209 realizes an athermal cyclic AWG.</p><p num="0076"> FIG. 9 is a diagram showing a configuration of a cross section crossing a groove in the athermal cyclic AWG of this embodiment. FIG. 9 shows an enlarged cross-sectional structure of the line segment AA ́ portion in the first slab waveguide 202 of FIG. In FIG. 9, the slab waveguide 202 is configured on a silicon substrate 210 and includes a waveguide core 211 and a clad 212. The plurality of grooves 209 are formed by removing a part of the waveguide core 211 and the cladding 211, and divide the waveguide core 211.</p><p num="0077"> The configuration parameters of each part of the athermal cyclic AWG200 have the following configurations. For all waveguides, the difference in index of refraction between core and clad is 1.5% and the core thickness is 4.5 μm. The core width of the first input / output waveguide 201, the array waveguide 203, and the second input / output waveguide 205 is 4.5 μm. The array waveguide 203 has 50 waveguides and is designed to be sequentially longer by a fixed amount ΔL than the inner waveguide, and the ΔL is 254.5987 μm.</p><p num="0078"> As shown in FIG. 9, the groove 209 is divided into a plurality of grooves. This is because the radiation loss can be further reduced when a plurality of grooves are formed as compared with the case where a single groove is formed. The array waveguide 203 is designed so that each waveguide is sequentially lengthened by a certain amount ΔL. That is, the difference in waveguide length between two adjacent waveguides is ΔL. The sum of the lengths divided by the plurality of grooves 209 in the first slab waveguide 202 is the amount of light waves input to each waveguide in proportion to ΔL according to the length of each waveguide of the array waveguide 203. ΔL ́ The shape is such that it becomes longer in sequence.</p><p num="0079"> Here, α is the temperature coefficient of the effective refractive index n of the array waveguide and the slab waveguide (α = dn / dT, T is the temperature), and α ́ is the temperature coefficient of the refractive index n ́ of the temperature compensating material inserted in the groove. Let (α ́ = dn ́ / dT). At this time, the cyclic AWG of this embodiment is designed to satisfy the relationship of ΔL ́ = ΔL / (1-α ́ / α). As a result, the temperature change of the optical path length difference between the array waveguide and the slab waveguide is canceled by the temperature change of the optical path length difference of the temperature compensating material, and the temperature dependence of the transmission center wavelength is compensated. As the temperature compensating material, a material in which α ́ has a different sign from α and | α ́ | is sufficiently larger than | α | is particularly preferable. As a material under such conditions, there is a silicone resin which is an optical resin applied in this embodiment, and α ́ is about -35 × α.</p><p num="0080"> The length of the first slab waveguide 202 and the second slab waveguide 204 is 1128 μm, respectively. The array spacing of the linearly tapered waveguide 208 connecting to the first slab waveguide 202 is 15 μm, the waveguide spacing of the array waveguide 203 connecting to the first slab waveguide 202 and the second slab. The waveguide spacing of the array waveguide 203 of the portion connected to the waveguide 204 is 10 μm, respectively. The first input / output waveguide 201 is composed of eight waveguides, and has eight ports as an optical duplexer. The combined demultiplexing optical frequency interval between two adjacent ports is 100GHz, and the FSR is designed with a target value of 800GHz.</p><p num="0081"> Each optical frequency of the signal light combined and demultiplexed by the athermal cyclic AWG of this embodiment is the same as that of Example 1, and is shown in FIG. Multiple transmission wavelengths corresponding to the diffraction order are used in ports 1 to 8 of the first input / output waveguide 201, and 48 channels of signal light from 196400 GHz (wavelength 1526.438 nm) to 191700 GHz (wavelength 1563.862 nm) are transmitted. It is split into waves.</p><p num="0082"> FIG. 10 is an enlarged view from the waveguide offset in the cyclic AWG of the second embodiment to the vicinity of the linear tapered waveguide. The configuration is the same as that shown in FIG. 8 in Example 1. One port (input / output waveguide) in the first input / output waveguide 101 is shown, and each reference numeral of the component is the same as that shown in FIG. In this embodiment, the multimode waveguide 207 is connected to the first slab waveguide 202 via the tapered waveguide 208. The waveguide width of the multimode waveguide 207 is 7 μm, and the waveguide width of the linear taper waveguide 208 is 11.5 μm at the portion connected to the first slab waveguide 202. Here, in the waveguide offset 206, the core width is expanded to the same level as the multimode waveguide 207 by a linear taper, and the central axis of the waveguide core is shifted to connect to the multimode waveguide 207. At this discontinuous core connection at the waveguide offset 206, some power of the ground mode light is converted and the primary mode light is excited.</p><p num="0083"> FIG. 11 is a diagram showing parameter values related to compensation of the transmission center wavelength at each port of the cyclic AWG according to the second embodiment of the present invention. For each of the eight ports, the amount of central axis misalignment (μm) of the waveguide offset 206, the ratio of optical power converted from ground mode to primary mode at the waveguide offset (%), and the length of the multimode waveguide 207. The design values of the offset (μm) and the length (μm) of the linear taper waveguide 208 are shown.</p><p num="0084"> Even in the athermal cyclic AWG of the present invention, the connection with the slab waveguide is made so as to cancel the frequency deviation (wavelength deviation amount) of the transmission center frequency (transmission center wavelength) when the AWG is manufactured by the configuration of the prior art. Adjust the peak position of the optical field in the width direction of the waveguide (p-axis) in the section. The peak position of the optical field can be realized by setting the amount of primary mode light generated and the phase according to the "shift amount" to be offset.</p><p num="0085"> Even in the athermalized cyclic AWG of the present invention, as a means for adjusting the peak position of the optical field, a means for controlling the amount of primary mode light generated and a phase difference between the primary mode light and the basal mode light. Provide means to control. By combining these means, the amount and phase of the primary mode light generated are adjusted, and the peak position of the optical field in the width direction of the waveguide at the connection with the slab waveguide is adjusted.</p><p num="0086"> Unlike the first embodiment, the cyclic AWG of the present embodiment is athermalized, so it is premised on a non-temperature adjustment type in which the operating temperature of the AWG is not finely adjusted. Therefore, the amount of frequency deviation to be compensated by the cyclic AWG of this embodiment is as shown in FIG. Compared with the frequency deviation amount to be compensated in Example 1 shown in FIG. 32, the magnitude of the deviation amount and the frequency-dependent characteristic (wavelength-dependent characteristic) are significantly different. Therefore, the peak position of the optical field is adjusted by a setting different from that of the first embodiment. Here, as in the first embodiment, the frequency deviation amount for each port is determined in order to clarify the frequency deviation amount to be compensated for each port more concretely.</p><p num="0087"> FIG. 34 is a diagram illustrating the amount of frequency shift for each port of the athermalized cyclic AWG. Each plot point is the same as the one showing the wavelength dependence of the frequency shift shown in FIG. The horizontal axis of FIG. 34 is the wavelength number, and the wavelength numbers 1 to 48 correspond from the left side to the right side, and the vertical axis indicates the amount of frequency deviation of the transmission center frequency for each wavelength number (wavelength). Has been done. Therefore, it should be noted that when the horizontal axis is read as frequency, the frequency is lower on the right side of the horizontal axis and higher on the left side. Simply, the frequency-dependent characteristics and the wavelength-dependent characteristics can be considered to have opposite polarities in slope.</p><p num="0088"> The eight connected plot point groups 1101 corresponding to the leftmost wavelength numbers 1 to 8 correspond to the wavelength group having a diffraction order of 242. Similarly, the eight connected plot point groups 1106 corresponding to the rightmost wavelength numbers 41 to 48 correspond to the wavelength group of diffraction order 237. Even in the athermalized cyclic AWG of the present invention, the frequency deviation is compensated for each port by adjusting the peak position of the optical field in the width direction of the waveguide at the connection portion of the slab waveguide. Therefore, it is necessary to first grasp the amount of frequency deviation for each port and perform frequency compensation according to the amount of deviation.</p><p num="0089"> In FIG. 34, the curve connecting a plurality of plot points of the wavelength corresponding to port 1 is referred to as P1. Here, the wavelengths corresponding to port 1 correspond to the six frequencies (196400, 195600, 194800, 194000, 193200, 192400 GHz) in the column indicated by 1 in the table of FIG. The curve P1 shows the frequency characteristics of the frequency shift to be compensated for the wavelength corresponding to the port 1. Similarly, the curve connecting multiple plot points of the wavelength corresponding to port 8 is indicated by P8. Here, the wavelengths corresponding to port 8 correspond to the six frequencies (195700, 194900, 194100, 193300, 192500, 191700G) in the column indicated by 8 in Table 3 of FIG. The curve P8 shows the frequency characteristics of the frequency shift to be compensated for the wavelength corresponding to the port 8. Although not shown in FIG. 34, curves P2 to P7 can be assumed for ports 2 to 7 in the same manner.</p><p num="0090"> In this way, from FIG. 34, the magnitude of the frequency shift and the frequency (wavelength) characteristics can be grasped for each of the ports 1 to 8. From FIG. 34, it can be seen that the maximum value of the amount of frequency deviation is larger in port 8 than in port 1. It can also be seen that the wavelength (optical frequency) at which the frequency shift amount becomes 0 shifts to the long wavelength side from port 1 to port 8. Therefore, by compensating according to the maximum amount of frequency deviation and frequency characteristics (inclination / shape) that differ for each port, for each port, for each port, as in the case of the first embodiment. The frequency shift can be effectively suppressed so as to match the frequency characteristic of the frequency shift amount. The frequency characteristics of the "correction amount" for a plurality of different frequencies appearing in one port can also be easily determined based on the curves P1 to P8 that can be grasped from the plot points in FIG. 34.</p><p num="0091"> With reference to FIG. 11 again, in this embodiment, as the port number increases from port 1 to port 8, the amount of central axis deviation of the waveguide offset 206 is gradually increased, and the power ratio converted to the primary mode is relative. Increased to (from 2.5% to 6.0%). In this way, the amount of primary mode light generated is controlled by the amount of central axis deviation of the waveguide offset 206 according to the maximum value of the amount of frequency deviation to be compensated.</p><p num="0092"> The athermalized cyclic AWG of the present invention further peaks the distribution of the optical field by varying the lengths of the multimode waveguide 207 and the linear taper waveguide 208, as in Example 1 as follows. It controls the wavelength (frequency) -dependent characteristics of the position. Therefore, for each port, so as to match the frequency deviation amount of the plurality of light waves (signals) transmitted through the port at each frequency, that is, to match the frequency-dependent characteristic (wavelength-dependent characteristic) of the frequency deviation amount. In addition, the lengths of the multimode waveguide 207 and the tapered waveguide 208 may be determined.</p><p num="0093"> The determined length described above gives a "predetermined phase difference" between the basal mode light and the primary mode light for a given frequency (wavelength). At this time, the frequency (wavelength) characteristic (slope / shape) of the correction amount for correcting the deviation amount of the transmitted peripheral center wave number is determined by the predetermined phase difference. As described with FIG. 34, the magnitude of the frequency deviation and the frequency (wavelength) characteristics (slope / shape) are grasped for each of the ports 1 to 8. Therefore, by giving a "predetermined phase difference" and determining the frequency (wavelength) characteristic (slope / shape) of the compensation amount of the frequency shift, the frequency (wavelength) of the frequency shift of P1 to P8 grasped from FIG. 34 It can be adapted to the characteristics.</p><p num="0094"> From FIG. 34, it can be seen that the wavelength (frequency) at which the amount of frequency deviation becomes 0 gradually fluctuates in the direction of increasing the wavelength number depending on the port. Therefore, the lengths of the multimode waveguide 207 and the tapered waveguide 208 may be determined for each port so as to match the wavelength (frequency) at which the frequency deviation amount becomes 0. In this embodiment, as shown in FIG. 11, by sequentially shortening the length of the multimode waveguide 206 from port 1 to port 8, the curve of the amount of correction for the frequency shift (as will be described later) The phase of the sine function) is adjusted.</p><p num="0095"> FIG. 12 is a diagram showing the change of the optical field distribution peak position at the end of the linear tapered waveguide in this embodiment depending on the frequency of the propagating light wave for each port. Here, the peak position p (μm) on the vertical axis corresponds to the position of the p coordinate axis in FIG. 10, and p = 0 is the center position of the linear tapered waveguide. The horizontal axis is the frequency of the light wave, which corresponds to the frequency in the wavelength range of 1 to 48. As already described, the transmission center frequency can be changed and corrected by shifting the peak position of the optical field distribution on the vertical axis. Therefore, the vertical axis of FIG. 12 means the correction amount of the frequency deviation.</p><p num="0096"> Similar to the case of the first embodiment, the magnitude and frequency (wavelength) characteristics of the frequency deviation for each port of ports 1 to 8 described with reference to FIG. 34, and the magnitude of the correction amount shown in FIG. Note that the frequency characteristics correspond. That is, the characteristics of the frequency deviation amount of P1 to P8 shown in FIG. 34 and the characteristics of the "correction amount" of the frequency deviation of each port shown in FIG. 12 are opposite to each other. For example, the amplitude (maximum value) of the frequency deviation correction amount in FIG. 12 corresponds to the maximum value of the frequency deviation amount in FIG. 34. The amplitude of the frequency deviation correction amount of each port corresponds to the central axis deviation amount of the waveguide offset 206 in FIG. Further, the position where the frequency deviation correction amount in FIG. 12 is 0 corresponds to the position where the frequency deviation amount in FIG. 34 is 0. The position where the frequency shift correction amount of each port is 0 is controlled (set) by the length of the multimode waveguide 207 in FIG.</p><p num="0097"> The curve of the correction amount of the frequency deviation in FIG. 6 of Example 1 and FIG. 12 of Example has a sine-function-like characteristic when shown in a wider frequency range. Then, it can be considered that the amount of the central axis deviation of the waveguide offset 206 determines the maximum amplitude of this sine function-like characteristic. Further, it can be considered that the lengths of the multimode waveguide 207 and the tapered waveguide 208 determine the phase of the sine function-like characteristic.</p><p num="0098"> In the cyclic AWGs of Examples 1 and 2, the means of controlling the amount of primary mode light generated corresponds to the waveguide offset as a means of adjusting the peak position of the optical field. Further, the means for controlling (setting) the phase difference between the primary mode light and the base mode light corresponds to the lengths of the multimode waveguide 207 and the tapered waveguide 208. By combining these means, the amount and phase of the primary mode light generated are adjusted, and the peak position of the optical field in the width direction of the waveguide at the connection portion of the slab waveguide is adjusted. In this way, the shift in the transmission center frequency of the conventional cyclic AWG is corrected by the change in the peak position of the optical field at the end of the linear taper waveguide in the athermalized cyclic AWG of this embodiment. become.</p><p num="0099"> The correction of the deviation of the transmission center frequency is performed by setting the amount of deviation of the center axis of the waveguide offset 106 for each port and controlling the amount of primary mode light generated. In addition, the correction amount changes depending on the frequency, and for light waves of different frequencies appearing in one port, multiple transmission center wavelengths are simultaneously corrected at the same time so as to match the frequency characteristics of the frequency shift amount. can do. That is, the frequency shift correction amount changes depending on the frequency for light waves of different frequencies appearing in one port.</p><p num="0100"> FIG. 13 is a diagram showing the amount of deviation of the transmission center wavelength from the ITU-T clip for the cyclic AWG of Example 2. The cyclic AWG of this embodiment is athermalized, is a non-temperature control type, and the temperature of the AWG is not controlled. The maximum frequency deviation from the ITU-T crid in the cyclic AWG of this example is ± 1.7 GHz (± 0.014 nm), assuming that the conventional cyclic AWG is athermal (Fig. 31). In comparison, the amount of frequency shift is reduced to about 1/5. A cyclic AWG with a transmission center frequency (wavelength) that is more consistent with the ITU-T crid has been realized.</p><p num="0101"> In this embodiment, not the temperature adjustment has been to provide a groove 209 for a principal in the first slab waveguide 202, for example, on the second slab waveguide 204 and the arrayed waveguide 203 Needless to say, a plurality of grooves 209 may be provided and filled with a silicone resin.</p><p num="0102"> In the first and second embodiments described above, examples of controlling the amount of primary mode light generated by using the waveguide offsets 106 and 206 have been shown, but the present invention is not limited to this. Other means can be used to control the amount of primary mode light generated and correct for deviations in the transmitted center frequency, and in the next embodiment, a die according to another configuration of the present invention. Indicates click AWG.</p>

<p num="0103"> FIG. 14 is a plan view showing the configuration of the cyclic AWG according to the third embodiment of the present invention. The cyclic AWG300 of this embodiment has a first input / output waveguide 301, a first slab waveguide 302, an array waveguide 303, a second slab waveguide 304, and a second slab waveguide 304, similarly to the prior art AWG. The input / output waveguide 305 is provided. The cyclic AWG300 of the present invention has an optical splitter 306, a delay circuit 307 consisting of two arm waveguides, an optical mode synthesis coupler 308, between the first input / output waveguide 301 and the first slab waveguide 302. It further includes a multimode waveguide 309 and a linear taper waveguide 310.</p><p num="0104"> In this embodiment, an optical splitter 306, a delay circuit 307 composed of two arm waveguides, an optical mode synthesis coupler 308, a multimode waveguide 309, and a linear tapered waveguide 310 constitute an interference circuit. That is, the primary mode excitation mechanism that converts a part of the basal mode light input from each of the plurality of first input / output waveguides into the primary mode light is from the optical splitter 306 and the two arm waveguides. It corresponds to the delay circuit 307 and the optical mode synthesis coupler 308.</p><p num="0105"> The configuration parameters of each part of the cyclic AWG300 are almost the same as the configuration of the first embodiment, and have the following configurations. For all waveguides, the difference in index of refraction between core and clad is 1.5% and the core thickness is 4.5 μm. The core width of the arm waveguide of the first input / output waveguide 301, the array waveguide 303, the second input / output waveguide 305, and the delay circuit 307 is 4.5 μm. The array waveguide 303 has 50 waveguides and is designed to be sequentially longer by a fixed amount ΔL than the inner waveguide, and the ΔL is 254.2475 μm.</p><p num="0106"> The length of the first slab waveguide 302 and the length of the second slab waveguide 304 are 1128 μm, respectively. The array spacing of the linear taper waveguide 308 connecting to the first slab waveguide 302 is 15 μm, and the waveguide spacing of the array waveguide 303 connecting to the first slab waveguide 302 and the second slab. The waveguide spacing of the array waveguide 303 of the portion connected to the waveguide 304 is 10 μm, respectively. The first input / output waveguide 301 is composed of eight waveguides, and has eight ports as an optical duplexer. The combined demultiplexing optical frequency interval between two adjacent ports is 100GHz, and the FSR is designed with a target value of 800GHz.</p><p num="0107"> Each optical frequency of the signal light combined and demultiplexed by the cyclic AWG of this example is the same as that of Example 1, and is shown in FIG. Multiple transmission wavelengths corresponding to the diffraction order are used in ports 1 to 8 of the first input / output waveguide 301, and 48 channels of signal light from 196400 GHz (wavelength 1526.438 nm) to 191700 GHz (wavelength 1563.862 nm) are transmitted. It is split into waves.</p><p num="0108"> FIG. 15 is an enlarged view from the optical splitter in the cyclic AWG of the third embodiment to the vicinity of the linear tapered waveguide. One port (input / output waveguide) in the first input / output waveguide 301 is shown, and each reference numeral of the component is the same as that shown in FIG. In this embodiment, the waveguide width of the multimode waveguide 309 is 7 μm, and the waveguide width of the linear taper waveguide 310 is 11.5 μm at the portion connected to the first slab waveguide 302. A directional coupler is used as the optical splitter 306.</p><p num="0109"> The delay circuit 307 is composed of a first arm waveguide 307a and a second arm waveguide 307b. As the optical mode synthesis coupler 308, a directional coupler having an asymmetric waveguide width is used, and the width of the waveguide 308a connected to the first arm waveguide 307a is 2 μm, and the width of the waveguide 308a is connected to the second arm waveguide 307b. The width of the waveguide 308b was set to 7 μm. Further, the width of the waveguide is smoothly converted from the first arm waveguide 307a to the waveguide 308a and from the second arm waveguide 307b to the waveguide 308b by the tapered waveguide. The length of the waveguides 308a and 308b was set to 500 μm including the tapered waveguide.</p><p num="0110"> At this time, the effective refractive index of the ground mode of the waveguide 308a and the effective refractive index of the primary mode of the waveguide 308b are almost equal to each other, and the ground mode light input from the first arm waveguide 307a to the waveguide 308a is conducted. Coupling to the primary mode of the waveguide 308b. Further, the ground mode light input from the second arm waveguide 307b propagates through the waveguide 308b as it is in the ground mode. Therefore, the base mode and the primary mode are combined and output to the multimode waveguide 309. In the design of this embodiment, the coupling rate of the optical mode synthesis coupler 308 from the waveguide 308a to the waveguide 308b is 70%. The cyclic AWG of this embodiment is premised on a temperature adjustment type in which the operating temperature of the AWG is finely adjusted according to the diffraction order as in the first embodiment. In the cyclic AWG of this embodiment, the temperature is adjusted for each AWG to further suppress the deviation amount of the transmission center frequency. Therefore, the amount of frequency deviation to be compensated for in the cyclic AWG of this embodiment is as shown in FIG. 32 described as the characteristics of the frequency deviation in Example 1. The amount of frequency deviation to be compensated for at each port is the same as in the case of the first embodiment.</p><p num="0111"> FIG. 16 is a diagram showing parameter values related to compensation of the transmission center wavelength at each port of the cyclic AWG according to the third embodiment of the present invention. For each of the eight ports, the branch ratio of the optical splitter 306, the difference in length of the first arm waveguide 307a relative to the second arm waveguide 307b, 1 for the total power of light output from the optical mode synthesis coupler 308. The design values of the power ratio of the next mode light, the length of the multimode waveguide 309 (μm), and the length of the linear taper waveguide 310 (μm) are shown.</p><p num="0112"> In this embodiment, instead of the waveguide offset 106 and the waveguide offset 206 in the first and second embodiments, the portion from the optical splitter 306 to the multimode waveguide 309 determines the amount and phase of the primary mode light generated. Acts to control. In this embodiment, the power ratio converted to the primary mode is increased by increasing the branch ratio of the optical splitter 306 at ports 1 and 8 located at the inner ends of the first input / output waveguide 301. ing. In addition, the branch ratio of the optical splitter 306 is set to zero at ports 4 and 5 located near the center of the first input / output waveguide 301, and it is designed so that there is no power to be converted to the primary mode. There is.</p><p num="0113"> A part of the optical power branched to the first arm waveguide 307a by the optical splitter 306 of each port is converted to the primary mode by the optical mode synthesis coupler 308. Both the ground mode light and the primary mode light reach the connection point of the linear taper waveguide 310 and the first slab waveguide 302 (the end of the linear taper waveguide 310). The phase difference between the base mode light and the primary mode light of the light reaching this connection point is the difference in length between the first arm waveguide 307a and the second arm waveguide 307b, and a predetermined length. It is caused by the multimode waveguide 309 and the linear taper waveguide 310 having. Since the phase difference changes depending on the wavelength (frequency), in the optical field distribution at the end of the linear tapered waveguide 310, the peak position is (depending on) the wavelength in the width direction of the waveguide (on the p-axis). ).</p><p num="0114"> Here, the phase difference between the basal mode light and the primary mode light of the light reaching the end of the linear tapered waveguide 310 in this embodiment will be considered. The phase difference between the two-mode lights is the phase difference (first phase difference) given by the difference in length between the first arm waveguide 307a and the second arm waveguide 307b, and a predetermined length. Is the sum of the phase differences (second phase differences) given by the multimode waveguide 309 and the linear taper waveguide 310. In this embodiment, if the sum of the two phase differences is an amount that should be set according to the frequency shift to be compensated, the ratio for distributing the two types of phase differences can be set in any way. it can. In this embodiment, the lengths of the first arm waveguide 307a and the second arm waveguide 307b in ports 1 to 8 are the same, and a constant phase difference (first phase difference) is provided for all ports. ) Is given, and by adjusting the length of the multimode waveguide 309 of each port, a different phase difference (second phase difference) is adjusted for each port.</p><p num="0115"> Therefore, in this embodiment, the primary mode excitation mechanism includes an optical splitter, a first arm waveguide and a second arm waveguide connected to the optical splitter, and the first arm waveguide and the second arm waveguide. An optical mode synthesis coupler that connects to the arm waveguide, converts the ground mode light input from the second arm waveguide into the primary mode, merges with the ground mode input from the first arm waveguide, and outputs the light. Consists of. The phase difference between the ground mode light and the primary mode light is the set optical path length difference between the first arm waveguide and the second arm waveguide, and the taper guide with the multimode waveguide 309 having a predetermined length. The waveguide 310 will change depending on the wavelength.</p><p num="0116"> Also in this embodiment, the amount and phase of the primary mode light generated can be adjusted, and the peak position of the optical field in the width direction of the waveguide at the connection portion of the slab waveguide can be adjusted. Example 1 and Example 2 in that the change in the peak position of the optical field at the end of the linear taper waveguide in the cyclic AWG compensates for the deviation of the transmission center frequency of the conventional cyclic AWG. Works exactly like.</p><p num="0117"> FIG. 17 is a diagram showing the change of the optical field distribution peak position at the end of the linear tapered waveguide in this embodiment depending on the frequency of the propagating light wave for each port. Here, the peak position p (μm) on the vertical axis corresponds to the position of the p coordinate axis in FIG. 15, and p = 0 is the center position of the linear tapered waveguide. The horizontal axis is the frequency of the light wave, which corresponds to the frequency in the wavelength range of 1 to 48. As already described, the transmission center frequency can be changed and corrected by shifting the peak position of the optical field distribution on the vertical axis. Therefore, the vertical axis of FIG. 17 means the correction amount of the frequency deviation. As a matter of course, since the characteristics of the correction amount for correcting the same frequency deviation as in the first embodiment, FIGS. 6 and 17 have almost the same characteristics.</p><p num="0118"> In this embodiment, the correction of the deviation of the transmission center frequency is performed by setting the branch ratio of the optical splitter 306 for each port and controlling the amount of primary mode light generated. In addition, the correction amount changes depending on the frequency, and for light waves of different frequencies appearing in one port, multiple transmission center wavelengths are simultaneously corrected at the same time so as to match the frequency characteristics of the frequency shift amount. can do. That is, the frequency shift correction amount changes depending on the frequency for light waves of different frequencies appearing in one port.</p><p num="0119"> FIG. 18 is a diagram showing the amount of deviation of the transmission center wavelength from the ITU-T clip for the cyclic AWG of Example 2. The cyclic AWG of this embodiment is a temperature control type, and the temperature to be kept constant is finely adjusted according to the diffraction order used. The maximum frequency deviation of the cyclic AWG of this example from the ITU-T crid is ± 1.2 GHz (± 0.010 nm), and the amount of frequency deviation is larger than that of the conventional cyclic AWG (Fig. 32). It has been reduced to about 1/5. A cyclic AWG with a transmission center frequency (wavelength) that is more consistent with the ITU-T crid has been realized.</p><p num="0120"> In this embodiment, as shown in FIG. 15, an asymmetric directional coupler is applied as the optical mode synthetic coupler 308, but the specific configuration of the optical mode synthetic coupler 308 is limited to the directional coupler 308. Not done.</p><p num="0121"> FIG. 19 is an enlarged view showing another configuration example of the optical mode synthesis coupler. The optical mode synthesis coupler 308 configured in FIG. 19 is an asymmetric directional coupler as shown in FIG. 15, but the output waveguide connected to the waveguide 308a is terminated by a groove 311. Here, a light-shielding material that absorbs light waves is inserted in the groove 311. Also, the interface between the light-shielding material and the output waveguide is not perpendicular to the waveguide, but is tilted 8 degrees from the vertical plane. By adopting the configuration of the optical mode synthesis coupler of FIG. 19, the light remaining slightly from the waveguide 308a without being coupled to the waveguide 308b is blocked as compared with the configuration of FIG. Prevents stray light from entering the waveguide 302 and the like. In addition, since the reflection of stray light can be suppressed, it is possible to realize an excellent cyclic AWG due to crosstalk and reflection characteristics.</p><p num="0122"> FIG. 20 is an enlarged view showing still another configuration example of the optical mode synthesis coupler. The optical mode synthesis coupler 308 having the configuration shown in FIG. 20 is an asymmetric directional coupler as shown in FIG. 15, but the waveguide 308a has a structure in which the width gradually narrows and the width disappears and ends. It has become. At this time, the lengths of the waveguides 308a and 308b are designed to be 1500 μm. By adopting the configuration of the optical mode synthesis coupler of FIG. 20, the coupling rate of the light wave from the waveguide 308a to the waveguide 308b can be made almost 100% as compared with the configuration of FIG. Therefore, it is possible to realize a cyclic AWG with excellent loss characteristics.</p><p num="0123"> Further, in this embodiment, as shown in FIG. 15, a single directional coupler is applied as the optical splitter 306, but the optical splitter 306 is not limited to this configuration. For example, it can be realized by an asymmetric Y-branch circuit, MMI, and a wavelength-independent coupler (WINC).</p><p num="0124"> In this embodiment as well, as in the first embodiment, the deviation of the transmission center frequency of the conventional cyclic AWG is corrected by the change of the peak position of the optical field at the end of the linear taper waveguide in the cyclic AWG. It will be. This correction is performed by setting the branch ratio of the optical splitter 306 for each port and controlling the amount of primary mode light generated. In addition, the correction amount changes depending on the frequency, and for light waves of different frequencies appearing in one port, multiple transmission center wavelengths are simultaneously corrected at the same time so as to match the frequency characteristics of the frequency shift amount. can do. The configuration of Example 3 can also be athermal. The following example is a combination of the cyclic AWG configuration of Example 3 and the athermal AWG configuration of Example 2.</p>

<p num="0125"> FIG. 21 is a plan view showing the configuration of the cyclic AWG according to the fourth embodiment of the present invention. The cyclic AWG400 of the present embodiment has a first input / output waveguide 401, a first slab waveguide 402, an array waveguide 403, a second slab waveguide 404, and a second slab waveguide, similar to the prior art AWG. It is equipped with an input / output waveguide 405. Similar to Example 3, the cyclic AWG400 of the present invention is a delay circuit 407 composed of an optical splitter 406 and two arm waveguides between a first input / output waveguide 401 and a first slab waveguide 402. , Optical mode composite coupler 408, multimode waveguide 409, linear taper waveguide 410. In this embodiment, in order to further eliminate the need for temperature adjustment, a groove 409 that divides the waveguide is formed in the middle of the first slab waveguide 402, and the groove 409 is filled with a silicone resin. .. This groove 409 realizes an athermal cyclic AWG.</p><p num="0126"> The configuration parameters of each part of the athermal cyclic AWG400 have the following configurations. For all waveguides, the difference in index of refraction between core and clad is 1.5% and the core thickness is 4.5 μm. The core width of the arm waveguide of the first input / output waveguide 401, the array waveguide 403, the second input / output waveguide 405, and the delay circuit 407 is 4.5 μm. Arrayed waveguide 403 has 50 waveguides and is designed to be sequentially longer by a certain amount ΔL than the inner waveguide, and ΔL is 254.60 μm.</p><p num="0127"> As shown in FIG. 21, the groove 409 is divided into a plurality of grooves. This is because the radiation loss can be further reduced when a plurality of grooves are formed as compared with the case where a single groove is formed. The array waveguide 403 is designed so that each waveguide is sequentially lengthened by a certain amount ΔL. That is, the difference in waveguide length between two adjacent waveguides is ΔL. The sum of the lengths divided by the plurality of grooves 409 in the first slab waveguide 402 is the amount of light waves input to each waveguide in proportion to ΔL according to each waveguide length of the array waveguide 403. ΔL ́ = 1/34 × ΔL The shape is such that the length increases in sequence.</p><p num="0128"> The length of the first slab waveguide 402 and the length of the second slab waveguide 404 are 1128 μm, respectively. The array spacing of the linearly tapered waveguide 408 connecting to the first slab waveguide 402 is 15 μm, the waveguide spacing of the array waveguide 403 connecting to the first slab waveguide 402 and the second slab. The waveguide spacing of the array waveguide 403 connected to the waveguide 404 is 10 μm, respectively. The first input / output waveguide 401 is composed of eight waveguides, and has eight ports as an optical duplexer. The combined demultiplexing optical frequency interval between two adjacent ports is 100GHz, and the FSR is designed with a target value of 800GHz.</p><p num="0129"> Each optical frequency of the signal light combined and demultiplexed by the cyclic AWG of this example is the same as that of Examples 1 to 3, and is shown in FIG. Multiple transmission wavelengths corresponding to the diffraction order are used in ports 1 to 8 of the first input / output waveguide 401, and 48 channels of signal light from 196400 GHz (wavelength 1526.438 nm) to 191700 GHz (wavelength 1563.862 nm) are transmitted. It is split into waves.</p><p num="0130"> FIG. 22 is an enlarged view of the cyclic AWG of the fourth embodiment from the optical splitter to the vicinity of the linear tapered waveguide. One port (input / output waveguide) in the first input / output waveguide 401 is shown, and each reference numeral of the component is the same as that shown in FIG. In this embodiment, the waveguide width of the multimode waveguide 409 is 7 μm, and the waveguide width of the linear taper waveguide 410 is 11.5 μm at the portion connected to the first slab waveguide 402. A directional coupler is used as the optical splitter 406.</p><p num="0131"> The delay circuit 407 is composed of a first arm waveguide 407a and a second arm waveguide 407b. As the optical mode synthesis coupler 408, a directional coupler having an asymmetric waveguide width is used, and the width of the waveguide 408a connected to the first arm waveguide 407a is 2 μm, and the width of the waveguide 408a is connected to the second arm waveguide 407b. The width of the waveguide 408b was set to 7 μm. Further, the width of the waveguide is smoothly converted from the first arm waveguide 407a to the waveguide 408a and from the second arm waveguide 407b to the waveguide 408b by the tapered waveguide. The length of the waveguides 408a and 408b was set to 500 μm including the tapered waveguide.</p><p num="0132"> At this time, the effective refractive index of the ground mode of the waveguide 408a and the effective refractive index of the primary mode of the waveguide 408b are almost equal to each other, and the ground mode light input from the first arm waveguide 407a to the waveguide 408a is conducted. Coupling to the primary mode of the waveguide 408b. Further, the ground mode light input from the second arm waveguide 407b propagates through the waveguide 408b as it is in the ground mode. Therefore, the base mode and the primary mode are combined and output to the multimode waveguide 409. In the design of this embodiment, the coupling rate of the optical mode synthesis coupler 408 from the waveguide 408a to the waveguide 408b is 70%.</p><p num="0133"> FIG. 23 is a diagram showing parameter values related to compensation of the transmission center wavelength at each port of the cyclic AWG according to the fourth embodiment of the present invention. For each of the eight ports, the branch ratio of the optical splitter 406, the difference in length of the first arm waveguide 407a with respect to the second arm waveguide 407b, 1 for the total power of light output from the optical mode synthesis coupler 408. The design values of the power ratio of the next mode light, the length of the multimode waveguide 409 (μm), and the length of the linear taper waveguide 410 (μm) are shown.</p><p num="0134"> In this embodiment as well, similarly to the third embodiment, the portion from the optical splitter 406 to the multimode waveguide 409 operates so as to control the amount of primary mode light generated and the phase. Unlike Example 3, the cyclic AWG of this example is athermalized, so it is premised on a non-temperature adjustment type in which the operating temperature of the AWG is not finely adjusted. Therefore, the frequency shift to be compensated by the cyclic AWG of this embodiment is as shown in FIG. 31 as in Example 2. That is, as in Example 2, FIG. 34 shows the amount of frequency shift for each port of the athermalized cyclic AWG.</p><p num="0135"> Therefore, by compensating according to the maximum amount of frequency deviation and the frequency characteristic (inclination / shape) that are different for each port shown in FIG. 34, as in the case of the third embodiment, the ports are assigned to the ports. The frequency deviation can be effectively suppressed so as to match the frequency characteristics of each frequency deviation amount. In addition, the frequency characteristics of the correction amount for a plurality of different frequencies appearing in one port can be easily determined based on the curves P1 to P8 that can be grasped from the plot points in FIG. 34.</p><p num="0136"> In this embodiment, a part of the optical power branched to the first arm waveguide 407a by the optical splitter 406 of each port is converted into the primary mode by the optical mode synthesis coupler 408. Both the ground mode light and the primary mode light reach the connection point of the linear taper waveguide 410 and the first slab waveguide 402 (the end of the linear taper waveguide 410). The phase difference between the base mode light and the primary mode light of the light reaching this connection point is the difference in length between the first arm waveguide 407a and the second arm waveguide 407b and a predetermined length. It is caused by the multi-mode waveguide 409 and the linear taper waveguide 410. Since the phase difference changes depending on the wavelength (frequency), in the optical field distribution at the end of the linear tapered waveguide 410, the peak position is (depending on) the wavelength in the width direction of the waveguide (on the p-axis). ).</p><p num="0137"> Similar to the third embodiment, in this embodiment as well, the phase difference (first phase difference) given by the difference in length between the first arm waveguide 407a and the second arm waveguide 407b, It is the sum of the phase differences (second phase differences) given by the multimode waveguide 409 and the linear taper waveguide 410 having a predetermined length. In this embodiment, the lengths of the first arm waveguide 407a and the second arm waveguide 407b in ports 1 to 8 are the same, and a constant phase difference (first phase difference) is provided for all ports. ) Is given, and by adjusting the length of the multimode waveguide 409 of each port, a different phase difference (second phase difference) is adjusted for each port.</p><p num="0138"> Therefore, also in this embodiment, the amount and phase of the primary mode light generated are adjusted, and the peak position of the optical field in the waveguide width direction at the connection portion of the slab waveguide is adjusted. Example 1 to Example 3 in that the deviation of the transmission center frequency possessed by the conventional cyclic AWG is corrected by the change in the peak position of the optical field at the end of the linear taper waveguide in the cyclic AWG. Works exactly like.</p><p num="0139"> Referring to FIG. 23 again, in this embodiment, as the port number increases from port 1 to port 8, the branch ratio of the optical splitter 406 is sequentially increased, and the power ratio converted to the primary mode is relatively increased. (From 2.5% to 6.0%). In this way, the amount of primary mode light generated is controlled by the branch ratio of the optical splitter 406 according to the maximum value of the amount of frequency shift to be compensated.</p><p num="0140"> FIG. 24 is a diagram showing the change of the optical field distribution peak position at the end of the linear tapered waveguide in this embodiment depending on the frequency of the propagating light wave for each port. Here, the peak position p (μm) on the vertical axis corresponds to the position of the p coordinate axis in FIG. 22, and p = 0 is the center position of the linear tapered waveguide. The horizontal axis is the frequency of the light wave, which corresponds to the frequency in the wavelength range of 1 to 48. As already described, the transmission center frequency can be changed and corrected by shifting the peak position of the optical field distribution on the vertical axis. Therefore, the vertical axis of FIG. 24 means the correction amount of the frequency deviation. As a matter of course, since it is the characteristic of the correction amount for correcting the same frequency deviation as in the second embodiment, FIGS. 12 and 24 have almost the same characteristics.</p><p num="0141"> In this embodiment, the correction of the deviation of the transmission center frequency is performed by setting the branch ratio of the optical splitter 406 for each port and controlling the amount of primary mode light generated. In addition, the correction amount changes depending on the frequency, and for light waves of different frequencies appearing in one port, multiple transmission center wavelengths are simultaneously corrected at the same time so as to match the frequency characteristics of the frequency shift amount. can do. That is, the frequency shift correction amount changes depending on the frequency for light waves of different frequencies appearing in one port.</p><p num="0142"> FIG. 25 is a diagram showing the amount of deviation of the transmission center wavelength from the ITU-T crid for the cyclic AWG of Example 4. The cyclic AWG of this embodiment is athermalized, is a non-temperature control type, and the temperature of the AWG is not controlled. The maximum frequency deviation from the ITU-T crid in the cyclic AWG of this example is ± 1.7 GHz (± 0.014 nm), assuming that the conventional cyclic AWG is athermal (Fig. 31). In comparison, the amount of frequency shift is reduced to about 1/5. A cyclic AWG with a transmission center frequency (wavelength) that is more consistent with the ITU-T crid has been realized.</p><p num="0143"> In this embodiment, as shown in FIG. 22, an asymmetric directional coupler is applied as the optical mode synthetic coupler 408, but the specific configuration of the optical mode synthetic coupler 408 is limited to the directional coupler 408. Not done. As shown in FIG. 19 described in the third embodiment, it is possible to adopt a configuration in which the output waveguide connected to the waveguide 408a is terminated by a groove in which a light-shielding material is inserted to suppress stray light and reflection. Further, as shown in FIG. 20, a configuration in which the width of the waveguide 408a is gradually narrowed and terminated so that the light coupling rate to the waveguide 408b is almost 100% is also applicable.</p><p num="0144"> Further, in this embodiment, as shown in FIG. 22, a single directional coupler is applied as the optical splitter 406, but the specific configuration of the optical splitter 406 is not limited to the directional coupler. For example, it is also realized by an asymmetric Y-branch circuit, MMI, and a wavelength-independent coupler (WINC).</p><p num="0145"> In this embodiment, a groove 411 is provided in the first slab waveguide 402 to eliminate the need for temperature adjustment. However, the present invention is not limited to this configuration, and it goes without saying that, for example, a plurality of grooves 411 may be provided in the second slab waveguide 404 or the array waveguide 403 and filled with the silicone resin.</p><p num="0146"> As described above, in the third and fourth embodiments, the first arm waveguide and the first arm waveguide have different phase differences between the basal mode light and the first mode light that reach the end of the linear tapered waveguide. The phase difference given by the difference in length between the two arm waveguides (first phase difference) and the phase difference given by the multimode waveguide and the linear taper waveguide having a predetermined length (second phase difference). Is the sum of the phase differences). Therefore, the sum of the two phase differences can be appropriately distributed as the amount to be set according to the frequency shift to be compensated. Therefore, unlike those shown in FIGS. 16 and 23, the length between the first arm waveguide and the second arm waveguide can be varied for each port.</p><p num="0147"> Here, the above two types of phase differences can be explained as follows from the relationship between the frequency-dependent changes in the propagating light waves at the optical field distribution peak positions at the ends of the linear tapered waveguides shown in FIGS. 17 and 24. .. As already mentioned, FIGS. 17 and 24 correspond to the "correction curve" of the frequency shift. This correction curve has a sine function-like shape.</p><p num="0148"> Specifically, it can be seen that the phase difference between the basal mode light and the primary mode light is adjusted by using the following parameters of the sine function-shaped curve.</p><p num="0149"> The sine-function-like correction curve y can be expressed by, for example, the following equation, where x is a normalized frequency. y = A × sin (B × x + C) Equation (2)</p><p num="0150"> Here, one of the parameters that can be adjusted is C of the sine function, and by setting C, the peak wavelength (frequency) of the correction curve can be set. Further, by setting B, the period of the correction curve, that is, the wavelength dependence can be set. In the third and fourth embodiments, the period (B) of the sine function curve is adjusted by the first phase difference due to the difference in length between the first arm waveguide and the second arm waveguide. It can be seen that the peak wavelength (C) of the sine curve is adjusted by the second phase difference due to the length of the multimode waveguide. This is an example of distributing two types of phase differences. In the present invention, the sum of the two types of phase differences is appropriately set as an amount to be set according to the frequency shift to be compensated. Can be distributed. In addition, in Example 1 and Example 2, both B and C are adjusted only by the length of the multimode waveguide.</p><p num="0151"> As can be seen from the above four examples, the temperature control type cyclic AWG optical wavelength duplexing circuit or the athermal type cyclic AWG optical wavelength duplexing circuit of the present invention has been a problem in the prior art. The deviation of the transmission center wavelength from the ITU-T grid is suppressed, and an optical wavelength combined / demultiplexing circuit with excellent transmission center wavelength accuracy can be obtained.</p><p num="0152"> In all the examples, the difference in the specific refractive index of the waveguide, the core width and the core thickness are limited to specific values, but the scope of application of the present invention is not limited to these values.</p><p num="0153"> In all embodiments, the design parameters of the AWG have been described using specific values as an example, but the scope of the present invention will depend on the required demultiplexing characteristics and the channel configuration of the system, and will also be derived. It can be realized by various modifications according to the configuration of the waveguide, and is not limited to the parameters of the embodiment.</p><p num="0154"> In all the embodiments, the number of wavelengths and the wavelength (frequency) interval of the signal to be demultiplexed have been described for a specific example, but the present invention can be applied to other configurations with various modifications. Therefore, it is not limited to the parameters of the embodiment.</p><p num="0155"> In Examples 2 and 4, a silicone resin was used as the temperature compensation material, but the present invention is not limited to this material and has a refractive index temperature coefficient different from the effective refractive index temperature coefficient of the waveguide. Any other material can be applied.</p><p num="0156"> In all the embodiments, the configuration in which the second input / output waveguide and the second slab waveguide are directly connected has been described as an example, but a linear taper waveguide may be applied to this connection portion. In this case, the transmittance shape of the cyclic AWG is Gaussian. Further, a tapered waveguide that excites a secondary mode, for example, a parabola-shaped tapered waveguide, may be applied to the connection portion of the second input / output waveguide and the slab waveguide. In this case, the cyclic AWG can achieve a flat transmittance shape.</p>

The present invention can generally be used in communication systems. In particular, it can be used for optical communication systems.

100, 200, 300, 400, 9100 Cyclic AWG 101, 201, 301, 401, 9101 1 I / O waveguides 102, 202, 302, 402, 9102 First slab waveguide 103, 203, 303, 403, 9103 Array waveguide 104, 204, 304, 404, 9104 Second slab waveguide 105, 205, 305, 405, 9105 Second I / O waveguide 106, 206 waveguide offset 107, 207, 309, 409 Multimode waveguide 108, 208, 310, 410 Linear taper waveguide 210 Silicon substrate 211 waveguide core 212 clad 306, 406 Optical splitter 307, 407 Delay circuit 307a, 307b, 407a, 407b arm waveguide 308, 408 Optical mode synthetic coupler 308a, 408a, 308b, 408b waveguide 209, 311 and 411 grooves 9200 Cyclic AWG circuit 9201 Port connected to the first I / O waveguide 9202 Port to second I / O waveguide 9400 6-branch coupler or 6-port wavelength grouping demultiplexer filter 9401, 9402, 9403, 9404, 9405, 9406 Cyclic AWG