Optical device with tunable coherent receiver

The present invention generally relates to the field of optical telecommunications, and more specifically to optical devices such as optical insert / branch multiplexers (OADMs).

In state-of-the-art Optical Wavelength Division Multiplexing (WDM) communication systems, the wavelengths of multiple, individually data-modulated light are multiplexed into fiber optics and separated via an annular or network optical network. Will be sent to. Optical devices such as OADMs are commonly employed along the path from source to destination to modify the content of the multiplex and, in some cases, the quality of the multiplex. Such modifications include the step of preparing the multiplexing by adding, branching, substituting, and / or frequency converting the wavelengths of the light carrying the data within the multiplexing. On the input or "branch" side of the OADM, the input WDM signal is typically split into a passing leg and a branch leg (eg, using a power divider). The branch leg is typically a data-modulated wavelength λ for input multiplexing._dIs sent to a receiver configured to receive, detect, demodulate, and send the rest of the wavelengths in the multiplexing to the insert side of the OADM. The passing leg is usually the branch wavelength λ_dIs fed to a wavelength blocker configured to block and send the remaining wavelengths of the multiplexing to the "addition" side of the OADM. Alternatively, power splitting and wavelength blocking functionality can be incorporated into the WDM demultiplexing filter.

On the insert side of the OADM, the optical transmitter branches the locally supplied data stream from the branch side of the OADM to the same wavelength λ._dIt is configured to modulate towards the optical carrier of. This modulated wavelength from the transmitter is then combined with the wavelength of the multiplexing sent from the branch side to the insertion side to form a new multiplexing output from the OADM.

The transmitter in the OADM is generally a type of externally modulated laser. Such transmitters are fixed wavelength or tunable coupled to a modulator (eg, a Mach-Zehnder modulator) whose modulation is controlled by a properly encoded type of locally supplied data stream. Includes laser.

The receiver is typically of the direct detection type. Such receivers typically include pin-type diodes or avalanche diodes coupled to amplifiers, filtering electronics, and sampling / decision circuits.

<p> According to one aspect of the invention, the optical apparatus of the present invention comprises an optical receiver configured to process at least a portion of an input optical signal received by the optical apparatus and an output optical signal transmitted by the optical apparatus. With an optical transmitter configured to produce at least a portion of the light, the optical transmitter is configured to generate light for a portion of said output optical signal produced by the optical transmitter. An optical device comprising a generator, the optical receiver receiving and using a portion of light produced by the optical generator, optically coupled to the optical generator to process a portion of the input optical signal. Is.</p><p> According to a further aspect of the present invention, the method of processing a WDM optical signal according to the present invention includes a step of dividing the input WDM optical signal received by the optical device into first and second parts, and a step of dividing the input WDM optical signal. The step of branching the first optical signal from the first part at the receiver, the step of blocking the first optical signal from the second part of the input WDM optical signal, and the output WDM transmitted by the optical device. The first and second optical signals include a step of adding a second optical signal to the rest of the optical signal of the second portion of the input WDM optical signal to generate an optical signal. The WDM optical signal is processed in an optical device that has substantially the same optical carrier wavelength, and some of the light used to add the second optical signal branches the first optical signal. Is the method used for.</p><p> According to yet another aspect of the invention, the method according to the invention is a step of wavelength demultiplexing the input WDM optical signal received by the optical device into N signals and a single first wavelength. The process of receiving one of the wavelength signals at the receiver, the process of transmitting the remaining N-1 single wavelength signals to the output multiplexer, and the process of producing substantially first wavelength light to the receiver. In the multiplexer, the inserted optical signal and N-1 remaining single wavelength signals are combined with the step of feeding the transmitter to generate an additional optical signal of substantially the first wavelength. A method of processing a WDM optical signal within an optical device that includes the process of forming one new N-signal WDM optical output.</p>

<p> Optical insertion / branching with an insertion side laser that provides a reference for the receiving side local oscillator in the coherent receiver included in the optics as well as the source for the insertion side wavelength to be inserted into the output of the device. The problems of the prior art are addressed according to the principles of the present invention with optical devices such as multiplex devices (OADMs). Thus, instead of providing another local oscillator (LO) within the front end of the coherent receiver within the receiving side of the optics, the optics of the present invention are either heterodyne or homodyne configurations. The optical signal generated by the insertion side laser is used to supply the mixing frequency to the coherent receiver.</p><p> In one embodiment, the present invention comprises an optical receiver configured to process at least a portion of an input optical signal received by an optical device and at least a portion of an output optical signal transmitted by the optical device. It is an optical device provided with an optical transmitter configured in. This optical transmitter comprises an optical generator configured to produce light for a portion of the output optical signal produced by the optical transmitter, and the optical receiver is the light produced by the optical generator. Receives and uses the portion of to process the portion of the input optical signal.</p><p> In another embodiment, the invention is a method for processing WDM optical signals within an optical device. The present invention comprises (a) dividing the input WDM optical signal received by the optical device into first and second parts, and (b) dividing the first to first optical signals of the input WDM optical signal. The step of branching, (c) the step of blocking the first optical signal from the second part of the input WDM optical signal, and (d) the input WDM to generate the output WDM optical signal transmitted by the optics. The rest of the optical signal in the second portion of the optical signal includes the step of inserting the second optical signal. In this method, the first and second optical signals have substantially the same basic carrier wavelength, and the light used to insert the second optical signal to branch the first optical signal. A part of is used.</p>

In the specification of the present application, reference to "one embodiment" or "a certain embodiment" includes, at least one embodiment of the present invention, a specific feature, structure, or property described in relation to the embodiment. It means that it can be done. In various cases of the present specification, the phrase "in one embodiment" does not necessarily mean the same embodiment and is alternative or alternative to each other. It does not mean an embodiment.

Conventional Optical Insertion / Branching Multiplexer (OADM) FIG. 1 shows a typical OADM100 of the present invention. As shown, the OADM100 includes a branch side 102 and an insertion side 104. The branch side includes a splitter 106, a wavelength blocker 108, and a receiver 110. The insertion side is equipped with a transmitter 112 and a coupler 114.

At the branch side 102 of the OADM, the data-coded optical signal S_a(λ_i)|_{i = 1 ... N}The input multiplexing of is received from the network and is split by the power divider 106 into a branch leg sent to the receiver 110 and a passing leg sent to the wavelength blocker 108. On the receiver 110, a component (eg, S_a(λ_d)) One of the "branch wavelength" components of the branched leg multiplexing signal is selected from multiplexing by the demultiplexing selector 116, which is carried to the photodiode 118, where it is from the optical signal. It is converted into an electric signal. The electrical output of the light diode is then amplified by the backup amplifier 120 and filtered by the lowpass filter 122. The output of the lowpass filter is s by the OADM entity upstream._d(λ_d) Is carried to the sampling / determination circuit 124 to detect and recover the modulated data. The recovered data is then "branched" to the local client. The wavelength blocker 108, which receives a copy of the wavelength multiplexing on the "passing leg" from the splitter 106, is a branched signal component S._a(λ_d) Related to the branched wavelength λ_dAnd the component S in the multiplexing_d(λ_i)|_{i = 1 ... N, i d}It is configured to send the rest of the to the OADM insertion side. Alternatively, instead of the colorless splitter 106 on the insertion side, the Demax Select 116, and the wavelength blocker 108, and the combiner 114 on the branch side, the OADM's state-of-the-art implementation will function. A wavelength selective branch filter on the insertion side and a wavelength selective insertion filter on the branch side may be used without changing the property. This alternative configuration has the advantage of reducing insertion loss.

On the insertion side 104 of the OADM, the optical transmitter 112 branches the locally supplied data stream from the branch side of the OADM to the same wavelength λ._dIt is configured to modulate the optical carrier wave of. Then this modulated optical carrier from the transmitter is S_a(λ_d) Is the new multiplexed signal S output from the OADM._a(λ_i)|_{i = 1 ... N}Is combined with the wavelength of the multiplexing carried from the branch side to the insertion side of the OADM in the coupler 114 to form.

Specifically, in the exemplary externally modulated transmitter configuration 112 shown in FIG. 1, the laser 128 has a wavelength of λ._dAnd its output is sent to an external modulator 130 (eg Mach-Zehndrator) where the wavelength λ_dThe laser output of is modulated with data from a local client that may have been pre-encoded (eg, return-to-zero (RZ) encoded) by the encoder 126. Subsequently, this modulated insert-side component signal S_a(λ_d) Was sent to the coupler 114, where the insert multiplexing S was sent to the coupler by the branch side 102._a(λ_i)|_{i = 1 ... N, i d}Combined with the components of, the resulting complete multiplexing is then output from the OADM.

Note that the receiver 110 is of the direct detection type, as is commonly seen in the prior art. However, recently, there has been a growing interest in using coherent receivers, especially in free-space optical communication applications. Typically, such receivers use a local oscillator (LO) at their front end to supply mixing frequencies in either heterodyne or homodyne configurations.

Coherent OADM FIG. 2 shows an exemplary coherent receiver-based OADM200 according to a preferred embodiment of the present invention.

As shown, the OADM200 includes a branch side 202 and an insertion side 204. The branch side comprises a splitter 206, a wavelength blocker 208, and a coherent receiver 210 and can be implemented in either a balanced configuration (not shown) or a single-ended configuration (not shown). The insertion side includes a transmitter 212 and a coupler 214.

At the branch side 202 of the OADM, the data-coded optical signal S_d(λ_i)|_{i = 1 ... N}The input multiplexing of is divided into a branch leg sent to the receiver 210 and a passing leg sent to the wavelength blocker 208 using the power divider 206.

At receiver 210, branch leg multiplexing is sent to input 234 of combiner 236. The other input (238) of the coupler 236 is supplied from the insertion side of the OADM by one output of the splitter 232 of the transmitter 212. Splitter 232 has wavelength λ_dNote that it is supplied by a laser 228 that is designed to transmit an optical signal that is collected in. Therefore, in the coupler 236, the received signal S_d(λ_i)|_{i = 1 ... N}And wavelength λ_dSome of the output from the laser signal of is hitting each other against each of the light diodes 216 and 218, resulting in the signal S of interest._d(λ_d) Hetero dining (if the beat frequency is not in baseband) or homo dining (if the beat frequency is in baseband). Alternatively, a phase diversity coherent receiver can be used to coherently detect the branched signal. This electrical signal is then further processed by the appropriate signal processing electronics 222 (eg, in the case of a balanced setup, the difference is calculated (220), and in the case of a phase diversity setting, this electrical signal is further processed. Squared and added, demodulated to baseband in the case of heterodyne settings, or simply filtered and amplified by a lowpass filter in the case of homodyne settings). Subsequently, the processed signal is s_a(λ_d) Is sent to the sampling / decision circuit 224 to detect and recover the modulated data. The recovered data is then "branched" to the local client.

The wavelength blocker 208, which receives a copy of the wavelength multiplexing on the "passing leg" from the splitter 206, is a branched signal component S._d(λ_d) Related to the branched wavelength λ_dAnd the component S in the multiplexing_d(λ_i)|_{i = 1 ... N, i d}It is configured to send the rest of the to the OADM insertion side.

On the insertion side 204 of the OADM, the optical transmitter 212 branches the locally supplied data stream from the branch side of the OADM to the same wavelength λ._dIt is configured to modulate the optical carrier wave of. Then this modulated optical carrier from the transmitter is s_a(λ_d) Is the new multiplexed signal S output from the OADM._a(λ_i)|_{i = 1 ... N}Is combined with the wavelength of the multiplexing carried from the branch side to the insertion side of the OADM to form. This transmitter has a wavelength of λ_dIt is configured to supply the light of the branch side 202 to the receiver of the branch side 202.

More specifically, in the exemplary externally modulated transmitter configuration 212 shown in FIG. 2, the laser 228 has a wavelength of λ._dAnd its output is sent to the splitter 232. One of the outputs of the splitter 232 is sent to the input 238 of the coupler 236 of the receiver 210. The other output is sent to an external modulator 230 (eg, a Mach-Zehndrator) where the wavelength λ_dThe laser output of is modulated with data from a local client that may have been pre-encoded (eg, return-to-zero (RZ) encoded) by encoder 226. Subsequently, this modulated inserter component signal s_a(λ_d) Is sent to the coupler 214, where the input multiplexing component S sent to the coupler by the branch side 202._d(λ_i)|_{i = 1 ... N, i d}Combined with, then the resulting combined multiplexing is output from the OADM.

FIG. 3 shows an alternative embodiment 300 of the optical device of the present invention. The components of this embodiment behave similarly to the corresponding components of the embodiment of FIG. However, in the embodiment of FIG. 3, the splitter and wavelength blocker of FIG. 2 is replaced by the demultiplexing filter 302, and the coupler 214 of FIG. 2 is replaced by the multiplexing filter 304. The multiplex filter produces N output channels, each of which has a single wavelength. One of these wavelengths is sent to receiver 210, where it is processed as described above for the embodiment of FIG. The remaining outputs as well as the optical signals output from the transmitter 212 are sent to the multiplexing circuit filter 304, which combines the signals to form the overall output of the device.

Note that the receivers described in FIGS. 2 and 3 can be heterodyne, homodyne, or "phase diversity coherent" homodyne receivers. In the latter case, the local laser does not necessarily match the phase of the input signal or is out of phase, but the signal is basically demodulated in the baseband by optical beat processing. In a strict homodyne receiver, a special circuit is added to the receiver to match the phase of the received carrier with the LO. This match can be used as a reference when the phase variation of the received signal (eg, for phase modulation) can be measured by the local oscillator, so some modulation scheme (eg, phase shift). It is useful in systems that employ key modulation). In an alternative embodiment of the invention, the output of the splitter 232 passes through the phase adjuster before being sent to the coupler 236. In the phase adjuster, the phase of the laser is the input signal s to assist in the actual homodyne reception._d(λ_d) May be adjusted to match the phase. Alternatively, the phase of the laser 228 may be adjusted directly, as will be appreciated by those skilled in the art.

Although not explicitly shown in FIG. 2, in one or more embodiments of the invention, the wavelength blocked by the wavelength blocker 208 and the fundamental wavelength emitted by the laser 228 are variable and dynamically variable (eg,). It may be (via a controller with simple network management protocol support).

The present invention, as described with respect to the exemplary OADM embodiment 200 of FIG. 2, includes amplitude-shifted (eg, on-off keyed (OOF)) optical signals and, as will be appreciated by those skilled in the art. Demodulate other modulation formats (eg, Carrier Suppression On-Off Keying, Duo Binary Method, Alternate Mark Inversion Code, Chirp Zero Reset, Differential Phase Shift Keying (DPSK), and Acting 4-Phase Phase Shift Keying (DPQSK)) May be used for.

The coherent receiver 210, as shown in the exemplary embodiment of FIG. 2, comprises a circuit for converting the homodyne optical signal into an electrical format, but the combined local oscillator signal and the received signal. A device comprising a mechanism for transmitting a combined signal and branching the combined signal to a local client or distant location without first converting the combined signal into an electrical region or homodining is the spirit and scope of the invention. It is in. Similarly, homodine the optical signal received by some of the light used by the transmitter, and then perform an OE conversion as in the discussion corresponding to receiver 210 in FIG. Devices with receivers that perform EO conversion before branching the signal to a local client or further processing in the optical domain are also in the spirit and scope of the invention.

Although the present invention has been described for preferred embodiments with balanced receivers, as discussed, the configuration of single-ended, homodyne, heterodyne or phase diversity homodyne receivers is the spirit of the invention. And in range.

Although the invention has been described with respect to devices known in the art as OADMs and with respect to one branch and one insertion wavelength, the concepts and advantages of the invention also apply to a variety of optics and subsystems. There may be both a receiver and a transmitter, and one or more lasers or laser sources in the device may be shared with the receiver's optics. As will be appreciated by those skilled in the art, this device also applies to devices that receive, block, and / or transmit two or more simultaneous wavelengths. The present invention is also one of an optical communication system in which two or more input data signals corresponding to wavelengths in an input WDM signal are dumped (ie, do not pass together along locally inserted light). It also applies to end nodes.

It should be noted that the components of the invention may be practiced by different techniques and in different techniques, while still in the principles and scope of the invention. These techniques and techniques include optical integrated receiver technology, optical integrated (silicon on silicon substrate or Si: SiO).₂Etc.), optical fiber, free-space optical communication, thin films, InGaAs, micromirror microelectromechanical arrays, and optical gate subsystems, but are not limited to these.

Although the present invention has been described with respect to embodiments for explanation, this description should not be construed in a limited sense. In addition to the various modifications of the embodiments described, other embodiments of the invention that are apparent to those skilled in the art to which the invention relates are described in the invention, as specified in the claims of the invention. It is considered to exist in principle and scope.

The process of the method claims of the invention may be detailed in certain circumstances with the corresponding labeling, but the enumeration of claims of the invention specifies in order to carry out some or all of those processes. By the absence of implied sequences of, the steps are not necessarily intended to be limited to being performed in that particular context.

Other aspects, features, and advantages of the present invention will be more complete from the detailed description and accompanying drawings herein.

<figref num="1">It is a figure which shows the exemplary optical insertion / branching multiplexer (OADM) 100 by the prior art.</figref><figref num="2">FIG. 5 illustrates an exemplary coherent receiver-based OADM200 according to a preferred embodiment of the present invention.</figref><figref num="3">FIG. 5 illustrates another exemplary coherent receiver-based optical device 300 according to the present invention.</figref>