Method and apparatus for wavelength selective switch

The present invention relates to an optical switch, and more particularly to a device and method for selectively switching wavelengths.

In the case of optical transmission network equipment, reconstructable optical insertion / branch multiplexers (ROADMs) can be used to flexibly expand network capabilities and reduce operating costs. Wavelength selection switches (WSS) are an option when using current ROADM technology. In the case of 1 × N type WSS (wavelength selection switch), 1 is a common (COM) port, and N represents the number of branch ports. When WSS (Wavelength Selection Switch) is activated, when WDM signals are input from COM ports, these signals are separated by optical wavelength, and then each wavelength is out of N branch ports according to system requirements. Routed to one branch port. On the contrary, these optical signals can be received as inputs from N branch ports and can be transmitted as outputs from COM ports.

<p num="0003"> ROADM provides an automated mechanism that flexibly increases capacity as needed without resorting to costly and disruptive "forklift" upgrades. The advantage of ROADM networks is that they dynamically increase capacity when and wherever they are needed, ensuring that the underlying network automatically compensates for increased traffic. Is what you can do. This eliminates the need for manual adjustments or major upgrades. Since ROADM can provide the insertion / branching function in a plurality of directions for a plurality of wavelength channels, it is suitable for realizing multi-directional interconnection between network ring groups and constructing a mesh type network.</p>

<p num="0004"> According to one embodiment, the optical switch includes a liquid crystal cell and a switchable polarizing diffraction grating (SPG) cell adjacent to the liquid crystal cell. The SPG includes a first glass substrate, a first electrode layer covering the first glass substrate, a photoalignment layer covering the first electrode layer, a liquid crystal material covering the photoalignment layer, and the like. Includes a second photoalignment layer that covers the liquid crystal material. The first photoalignment layer and the second photoalignment layer are photosensitive polymers that are physically altered by being exposed using two interference light beams in which the directions of rotation of circularly polarized light are opposite to each other. Including. The SPG further includes a second electrode layer covering the second photoalignment layer and a second glass substrate covering the second electrode layer.</p><p num="0005"> According to another embodiment, the optical switch includes a liquid crystal cell and a polymer liquid crystal polarizing diffraction grating (PPG) cell adjacent to the liquid crystal cell. The PPG is a photosensitive polymer that is physically altered by being exposed to a glass substrate and two interference light beams that cover the glass substrate and whose circularly polarized light rotates in opposite directions. It includes a photoaligned layer including the photoaligned layer and a polymerized liquid crystal layer that covers the photoaligned layer on the opposite side of the glass substrate and is physically changed by irradiation using a uniform light beam.</p><p num="0006"> According to still another embodiment, the method of operating the optical switch including the polarizing diffraction grating includes a step of polarizing the incident light beam to circularly polarized light, a step of guiding the polarized light beam to the polarizing diffraction grating, and the above-mentioned step. In a polarizing diffraction grating, a hologram pattern formed inside the polarizing diffraction grating is formed by using the polarized incident light beam with a diffraction order corresponding to the circular polarization of the incident light beam and two interference light beams. It includes a step of diffracting at a predetermined angle corresponding to a direction.</p><p num="0007"> For a more complete understanding of the present invention and its advantages, the following description will then be referred to in conjunction with the accompanying drawings.</p>

<figref num="1a">The process of forming a switchable polarizing diffraction grating (SPG) cell is shown.</figref><figref num="1b">The process of forming a switchable polarizing diffraction grating (SPG) cell is shown.</figref><figref num="2a">It shows an SPG cell in a state where no voltage is applied.</figref><figref num="2b">The SPG cell in the state where the voltage is applied is shown.</figref><figref num="3a">Shows different operating modes of the SPG cell.</figref><figref num="3b">Shows different operating modes of the SPG cell.</figref><figref num="3c">Shows different operating modes of the SPG cell.</figref><figref num="4a">The process of forming a polymer liquid crystal polarized diffraction grating (PPG) cell is shown.</figref><figref num="4b">The process of forming a polymer liquid crystal polarized diffraction grating (PPG) cell is shown.</figref><figref num="4c">The process of forming a polymer liquid crystal polarized diffraction grating (PPG) cell is shown.</figref><figref num="4d">The process of forming a polymer liquid crystal polarized diffraction grating (PPG) cell is shown.</figref><figref num="5a">It shows different operation modes of PPG cells.</figref><figref num="5b">It shows different operation modes of PPG cells.</figref><figref num="6">The specific optical system of the wavelength selection switch (WSS) is shown.</figref><figref num="7a">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7b">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7c">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7d">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7e">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7f">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7g">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7h">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="8">A specific optical switch engine using a composite element of an LC cell and an SPG cell is shown.</figref><figref num="9">Another specific optical switch engine using a composite element of an LC cell and an SPG cell is shown.</figref><figref num="10">Yet another specific optical switch engine using a composite element of an LC cell and an SPG cell is shown.</figref><figref num="11a">The different operation modes of the composite element of the LC cell and the PPG cell are shown.</figref><figref num="11b">The different operation modes of the composite element of the LC cell and the PPG cell are shown.</figref><figref num="11c">The different operation modes of the composite element of the LC cell and the PPG cell are shown.</figref><figref num="11d">The different operation modes of the composite element of the LC cell and the PPG cell are shown.</figref><figref num="12">A specific optical switch engine using a composite element of an LC cell and a PPG cell is shown.</figref><figref num="13">A specific method for operating an optical switch engine using an LC cell and an SPG cell is shown.</figref><figref num="14">A specific method for operating an optical switch engine using an LC cell and a PPG cell is shown.</figref>

Techniques for constructing and using the currently preferred embodiments will be described in detail below. However, it should be understood that the present invention provides many applicable and innovative concepts that can be embodied in a wide variety of specific situations. The particular embodiments described merely illustrate specific ways in which the invention is constructed and used, and do not limit the scope of the invention.

Technologies currently used in wavelength selection switch (WSS) products include microelectromechanical systems (MEMS), liquid crystal on silicon (LCOS), liquid crystals with wedge-shaped crystals (LC), and digital micromirror devices (DMD). Can be mentioned. For these techniques, these optics can be similar to each other, except that the optical switch engines are different.

In MEMS (Micro Electromechanical Systems), these wavelengths are diffracted by a diffraction grating towards different channels, and then each wavelength is incident on a corresponding MEMS reflection mirror. By controlling the voltage applied to each MEMS reflection mirror, the rotation angle of the mirror can be controlled to control the light reflection angle. Each wavelength can be reflected at a predetermined angle according to the requirements of the network. Wavelength beams reflected from multiple channels at the same angle can be diffracted into a single beam after passing through the grating a second time, then incident on the output port and coupled. In order to control the amount of light attenuation at the time of switching and realize the hitless function, each MEMS mirror has two rotation directions, port switching is performed in one rotation, and the attenuation and hitless in the other rotation. Control functions. The MEMS-based WSS has the advantages that the optical system is simple and the performance is good. However, the MEMS-based WSS has a high cost required for forming a MEMS chip due to a relatively low yield, a high cost required for an electronic element due to a high voltage drive requirement for a MEMS mirror, and a difficulty in realizing a large number of ports. And it has some drawbacks such as the difficulty of designing flexible grid functions.

LCOS is another technology used in WSS (wavelength selection switch) systems. The LCOS consists of an LC layer arranged between the glass substrate and the back surface of silicon. In the LCOS-based WSS, each wavelength light separated by the diffraction grating is incident on the LCOS panel and irradiated to the M × N pixels. By controlling the voltage applied to these pixels, it is possible to form an LC (liquid crystal) phase diffraction grating in which the incident light beam is diffracted at a predetermined angle. Different diffraction angles can be obtained by changing the LC (liquid crystal) diffraction grating pitch. Therefore, the light beam can be routed to a predetermined output port by controlling the LC (liquid crystal) phase diffraction grating pitch for a certain wavelength light. The LCOS-based WSS has several advantages such as a simple optical system, a large number of ports can be easily realized, and a flexible grid function can be easily realized. The defects include the complexity of the electronic drive system, the extremely complex control software, the difficulty of achieving low crosstalk, and the extremely high sensitivity to temperature.

Another technique used for WSS (Wavelength Selector Switch) is LC with crystal wedges. The WSS design using LC with crystal wedges was published on March 3, 2009, and published "Apparatus And Method for Optical Switching with Liquid Crystals And Birefringent Crystal Wedges (Liquid Crystal and Birefringence Crystal Wedges). ) , U.S. Pat. No. 7,499,608. Such a WSS switch engine consists of several stages of LC cells and wedge plate composite elements, depending on the required number of output ports. In each stage, the LC cell is used to switch the polarization and the wedge plate is used to refract the light in two directions depending on the polarization of the incident light. As a result, a 1 × 2 type optical switch is obtained. Therefore, when N stages are stacked, 1 × 2^NA type optical switch is obtained. The LC cell used is separated into M pixels defined by the number of optical channels required. By controlling the voltage applied to the LC pixel, the corresponding wavelength light can be routed to a predetermined output port group. Such a WSS has the advantages that the driving electronic element is simple, exhibits high vibration resistance, and exhibits high reliability. Defects include high costs due to high material costs, relatively low yields due to complex device assembly processes, and the difficulty of achieving a very large number of ports.

DMD (Digital Micromirror Device) technology is also used in WSS systems. In such a system, each wavelength light is incident on several DMD / MEMS mirrors. By controlling the rotation angles of these mirrors, the light beam can be guided to a predetermined angle. Since these mirrors have only two deflection positions, one DMD chip WSS can only realize a 1x2 type switch. In order to increase the number of switch ports of WSS, more DMD chips are required, and the optical system design becomes expensive and very difficult.

As explained above, WSS systems using existing technology have complex software for driving electronic components, high material cost, low vibration immunity, and expansion to a large number of ports. It has defects including being difficult to do. Described herein are specific systems and methods for implementing WSS (Wavelength Selector Switch). In different embodiments, switchable polarizing diffraction grating (SPG) cell and LC cell composite elements, as well as polymer liquid crystal polarizing diffraction grating (PPG) cell and LC cell composite elements, are used to malfunction the systems listed above. Realize a 1xN type WSS system that solves at least some of our problems.

1a and 1b show the SPG cell formation process 100. When forming a conventional LC cell, the LC alignment layer is formed by rubbing or exposing two polymer layers covering two substrates used to sandwich the LC. The SPG cell forming process 100 is different with respect to the process of forming the LC alignment layer. In the first step (FIG. 1a) of the SPG cell forming process 100, the two photosensitive polymer layers 102 coat the two glass substrates 106, respectively, and then the two glass substrates are combined to fill the LC. Leave a gap to do. An electrode (conductor) layer 104 is further added between each photosensitive polymer layer 102 and a glass substrate 106 corresponding to each photosensitive polymer layer 102. Next (Fig. 1b), two interferometric ultraviolet (UV) light beams 192 (with right and left circularly polarized light) that rotate in opposite directions of circularly polarized light (at an appropriate angle of incidence) 2 Used to expose one polymer layer 102 (eg, via these glass substrates 106), a holographic pattern is formed on these polymer layers 102. By performing this interference beam exposure on each surface of the SPG cell, the alignment layer is formed from the photosensitive polymer layer 102. When LC108 is filled in the gap and sandwiched between two glass substrates, the molecules of LC108 are holographic patterns and positions formed on these photosensitive polymer layers 102 that act as LC alignment layers at this stage. Oriented to match.

2a and 2b show the SPG cell 200 in the state where the voltage is applied and in the state where the voltage is not applied, respectively. The SPG cell 200 can be formed using the forming process 100. In a state where no voltage is applied to the electrode layer 204 (FIG. 2a), the LC208 of the SPG cell 200 forms a diffraction grating, which allows the incident light to any part of the glass substrate 206 to be oriented in these diffraction gratings. It is diffracted in a direction determined by the angles of the two exposure beams for forming the layer 202 (direction determined during the forming process 100). When a non-zero voltage is applied to these electrode layers 204 (FIG. 2b), the LC208 molecules are oriented so that they are aligned with the electric field generated by the applied voltage, and thus the effect of the LC diffraction grating. (Produced by the alignment layer 202) is canceled out, and incident light on any portion of the glass substrate 206 is not diffracted. To counteract the effects of the LC diffraction grating, a voltage large enough, for example, the threshold voltage (V)_th) Is required.

The SPG cell described above has three diffraction orders of 0th order and ± 1st order, which are different from ordinary diffraction gratings. 3a to 3c show different operation modes 300 of the SPG cell. Each operation mode corresponds to one diffraction order, and the light of each order is diffracted at different angles. In a state where a sufficiently large voltage is applied to the SPG cell (FIG. 3a), the light is diffracted into 0th-order light regardless of the polarization of the incident light. In the state where no voltage is applied or when a low voltage is applied (FIGS. 3b and 3c), the diffracted light direction differs depending on the polarization of the incident light. The right-circularly polarized incident light beam is diffracted into +1 degree light (FIG. 3a), whereas the left-circularly polarized incident light beam is diffracted into -1st order light (FIG. 3c). After being diffracted by the SPG cell, the circularly polarized light is inverted as shown in FIGS. 3b and 3c (switching between right and left circularly polarized light).

4a-4d show the PPG cell formation process 400. In the first step (FIG. 4a) of the PPG cell forming process 400, the glass substrate 406 is coated with the photoalignment layer 402. In the second step (FIG. 4b), the polymer layer 402 is exposed with two interfering UV beams (492) in which the directions of rotation of the circularly polarized light are opposite to each other. In the third step (FIG. 4c), the upper surface of the photoalignment layer 402 is coated with the polymerizable LC layer 403. In the fourth step (FIG. 4d), the uniform UV beam 494 is used to irradiate the polymerizable LC layer 403 to polymerize the LC composition (molecule) of the layer. In this way, the polymer diffraction grating is formed on the glass substrate 406.

The resulting PPG cell is a diffraction grating with constant characteristics in that the diffraction characteristics of the PPG cell cannot be changed by applying a voltage (as in the case of the SPG cell described above). Is. 5a and 5b show different operating modes 500 of the PPG cell. Each operation mode corresponds to one diffraction order, and each order light is diffracted at different angles. The incident light beam is diffracted in one of the two directions. Specifically, the incident light beam with right-handed circularly polarized light is diffracted into +1st-order light (FIG. 5a), whereas the incident light beam with left-handed circularly polarized light is diffracted into -1st-order light (FIG. 5b). ). In either case, after diffraction, the direction of rotation of the polarized light of the beam changes, that is, switches in the opposite direction of rotation.

FIG. 6 shows a specific optical system 600 of WSS (wavelength selection switch). The WSS optical system 600 includes a fiber array 601, a microlens array 602, a beam deflection array 603, a 1/2 wave plate array 604, a cylindrical lens 605, a cylindrical reflection mirror 606, a diffraction grating 607, and an optical switch. Includes engine 608. These components of WSS optical system 600 can be arranged as shown in FIG. 6, or can be arranged in any other suitable arrangement that achieves the same or similar function. In other embodiments, the same constituent elements as those described above may be used, or yet another constituent element different from the constituent elements described above may be used. Instead of some of these constituent elements, the same constituent elements that realize the same function, or a combination of other constituent elements may be used.

Fiber array 601 is used for input and output ports. When an input or incident light beam from one fiber 601 passes through a microlens array 602, a beam deflection array 603, and a 1/2 wave plate array 604, the beam is two parallels with the same linearly polarized light. Separated into beams. The two light beams then become collimated beams after passing through the cylindrical lens 605 and the cylindrical reflection mirror 606. Next, these light beams are diffracted by the diffraction grating 607 and separated into a plurality of wavelengths. The light of each wavelength is then focused on the optical switch engine 608. The optical switch engine 608 routes light of each wavelength to a predetermined port. The corresponding light beam passes through the optical system 600 again (in reverse order of the plurality of components), is incident on a predetermined output fiber, and is coupled.

The optical switch engine 608 of WSS optical system 600 is realized by using an appropriate WSS (wavelength selection switch) system including a composite element of SPG cell and LC cell described below, or a composite element of PPG cell and LC cell. Can be done. Compared to other WSS (wavelength selection switch) technologies used (eg MEMS, LCOS, LC, wedge plates, DMDs), WSS systems using SPG or PPG have a simple optical system, electronic drive circuits. It has the advantages of being simple, reliable, high performance, easily realizing a large number of ports, and keeping the product cost low.

7a to 7h show different operation modes 700 of the composite elements of the LC cell and the SPG cell. The LC cell 710 is arranged in front of the SPG cell 720 (when viewed from the incident light). The LC cell 710 is used to control or switch the polarization of light. The SPG cell 720 is also used to diffract the light beam in a predetermined direction.

As shown in FIGS. 7a, 7c, 7e, and 7h, when a relatively large voltage (VH) (eg, a voltage above the threshold) is applied to the LC cell 710, the polarized light beam passes through the LC cell. But it doesn't change. As shown in FIGS. 7b, 7d, 7f, and 7g, when no voltage is applied to the LC cell 710, or when a relatively small voltage (VL) (for example, a voltage below the threshold value) is applied to the LC cell 710. , The rotation direction of the polarized light of the incident light beam is switched. As shown in FIGS. 7a, 7b, 7e, and 7f, when a relatively large voltage (VH) (for example, a voltage exceeding the threshold value) is applied to the SPG cell 720, the input light is polarized in any state. The light beam is diffracted into 0th order light. As shown in FIGS. 7c, 7d, 7g, and 7h, when no voltage is applied to the SPG cell 720, or when a relatively small voltage (VL) (for example, a voltage below the threshold value) is applied to the SPG cell 720. , Depending on the polarization of the incident light controlled by the LC cell 710, the light beam can be diffracted to be either +1 or -1st order light. Regardless of whether the input light is right-handed or left-handed, the composite elements of LC cell 710 and SPG cell 720 route the light beam in three directions to form a 1x3 optical switch. To do. N groups of LC cells and SPG cells are 1x3^NA type optical switch can be realized.

FIG. 8 shows a specific cross section of an optical switch engine 800 using a composite element of an LC cell and an SPG cell. The optical switch engine 800 can be used as the optical switch engine 608 of the WSS optical system 600. The optical switch engine 800 includes a variable optical attenuator (VOA) 805 including an LC cell 810 connected to a polarizing plate 815, a 1/4 wave plate (QWP) 840, and two consecutive LC cells 810 and an SPG cell 820. It comprises a 1 × 9 type optical switch 830 including a pair consisting of a prism or a mirror 890. These components can be arranged as shown in FIG. 8 or in another suitable order. The LC cell 810 and the SPG cell 820 can have M pixels in a direction orthogonal to the N = 9 beams (direction perpendicular to the paper surface of FIG. 8). In FIG. 8, N is the number of beams corresponding to the number of ports, and M is the number of pixels corresponding to the number of wavelength channels. The LC cell used in the optical engine 800 may be an electrically controlled birefringence (ECB) cell, a twisted nematic (TN) cell, and a vertically oriented (VA) cell.

For brevity, the operating principle of a switch engine is described for one wavelength as illustrated in the cross section of engine 800 in FIG. However, the same operating principle applies to all M pixels.

The input light first passes through the VOA805, which is used to control the attenuation of the light output. By controlling the voltage applied to the LC cell 810, the amount of light output of the VOA 805 can be controlled. QWP840 is used to change the linearly polarized light into circularly polarized light. Next, the light beam passes through two groups of LC cells 810 and SPG cells 820 (1 × 9 type optical switch 830). Therefore, the output beam can have nine different angles with respect to the optical axis. The beam is then reflected by a prism or mirror 890 and, after passing through switch 830, becomes parallel to the optical axis. The optical switch engine 800 is properly designed to allow approximately equal distances between any two adjacent optical paths (nine switching angles). Therefore, the reference fiber array can be used as an optical output port (eg, with nine output ports).

FIG. 9 shows a cross section of another specific optical switch engine 900 using a composite element of an LC cell and an SPG cell. The optical switch engine 900 can be used as the optical switch engine 608 of the WSS optical system 600. The optical switch engine 900 includes a VOA 905 including an LC cell 910 connected to a polarizing plate 915, a pair of LC cells 910 and an SPG cell 920, and a 1 × 7 type optical switch 930 including a second SPG cell 920 in the subsequent stage. And a prism or mirror 890. These components can be arranged as shown in FIG. 9 or in another suitable order. The LC cell 910 and the SPG cell 920 can further have M pixels in a direction orthogonal to N = 7 beams (direction perpendicular to the paper surface of FIG. 9). One difference between the optical switch engine 900 and the optical switch engine 800 is that the optical switch engine 900 realizes a 1 × 7 type optical switch by using one LC cell 910 and two SPG cells 920. Is. In the 1 × 7 type optical switch, the LC cell 910 is used to control the polarization of the light, and the two SPG cells 920 are used to diffract the light at a predetermined angle. Furthermore, the optical switch engine 900 does not include QWP. Instead, the VOA905 LC cell 910 is designed as a switchable quarter wave plate (switching between λ / 4 and 3λ / 4), transforming the linearly polarized light of the incident light into circularly polarized light. To increase the number of optical output ports, more SPG cells 920 can be added to the optical switch engine 900, for example in front of the mirror or prism 990. For example, when there are N SPG cells 920, 1 × (2)^{N + 1}-1) A type optical switch engine may be mounted.

FIG. 10 shows a specific cross section of yet another optical switch engine 1000 using a composite element of an LC cell and an SPG cell. The optical switch engine 1000 can be used as the optical switch engine 608 of the WSS optical system 600. The optical switch engine 1000 includes a VOA 1005 including an LC cell 1010 connected to a polarizing plate 1015, a QWP 1040, a 1 × 8 optical switch 1030 including three SPG cells 1020, and a prism or a mirror 1090. These components can be arranged as shown in FIG. 10 or in another suitable order. These SPG cells 1020 can further have M pixels in a direction orthogonal to N = 8 beams (direction perpendicular to the paper surface of FIG. 10). Unlike the optical switch engines 800 and 900 described above, the optical switch engine 1000 controls the optical diffraction angle using only the SPG cell group 1020 without using the LC cell. After the light beam has passed through VOA1005 and QWP1040, the linearly polarized light of the input beam changes to circularly polarized light. Each SPG cell 1020 can diffract the light beam into two angles. Therefore, if there are N SPG cells, 1 × 2^NA type optical switch engine can be formed.

11a to 11d show different operation modes 1100 of the composite elements of the LC cell and the SPG cell. The LC cell 1110 is arranged in front of the SPG cell 1150 (when viewed from the incident light). LC cells 1110 are used to control or switch the polarization of light, and PPG cells 1150 are used to diffract the light beam in one of two directions, depending on the polarization of the input light. Therefore, the N group consisting of LC cells and PPG cells is 1 × 2.^NA type optical switch can be configured.

As shown in FIGS. 11a and 11d, when VH (eg, a voltage above the threshold) is applied to the LC cell 1110, the polarization of the incident light beam does not change as it passes through the LC cell. As shown in FIGS. 11b and 11c, when no voltage is applied to the LC cell 1110 or when VL (for example, a voltage below the threshold value) is applied to the LC cell 1110, the polarization of the incident light beam is switched between left and right. As shown in FIGS. 11a and 11c, when the incident light on the PPG cell 1150 has right circularly polarized light, the light beam is diffracted into +1 degree light. As shown in FIGS. 11b and 11d, when the incident light on the PPG cell 1150 is left circularly polarized, the light beam is diffracted into -1st order light.

FIG. 12 shows a specific cross section of an optical switch engine 1200 using a composite element of an LC cell and an SPG cell. The optical switch engine 1200 can be used as the optical switch engine 608 of the WSS optical system 600. The optical switch engine 1200 includes a VOA 1205 including an LC cell 1210 connected to a polarizing plate 1215, a 1 × 4 optical switch 1230 including a pair consisting of two consecutive LC cells 1210 and a PPG cell 1250, and a prism or mirror 1290. And. These components can be arranged as shown in FIG. 12 or in another suitable order. These LC cells 1210 and PPG cells 1250 can have M pixels in a direction orthogonal to N = 4 beams (direction perpendicular to the paper surface of FIG. 12). Similar optical switches can be designed to have any number of output ports by stacking and coalescing the required number of LC and PPG pairs.

FIG. 13 shows a specific method 1300 for operating an optical switch engine using an LC cell and an SPG cell. For example, method 1300 is performed using any of the optical switch engines 800, 900, and 1000. In step 1310, the incident light beam is polarized to left or right circularly polarized light. For example, QWP840 or 1040, or electrically switchable (by applying a voltage) LC, is used to convert a linearly polarized incident light beam into circularly polarized light. In step 1320, the circularly polarized light beam is diffracted using at least one SPG cell. The direction of rotation of the polarized light of the diffracted light beam is further switched. For example, the circularly polarized light can be electrically switched between the counterclockwise direction and the clockwise direction of the 1 × 9 type optical switch 830, and the first LC810 (or the LC910 of the 1 × 7 type optical switch 930) can be electrically switched. ) Is switched, and then it is diffracted to the corresponding angle by the next stage SPG820 (or 920) which is electrically switchable. In another example, the circularly polarized light is diffracted directly at the corresponding angle by the electrically switchable first SPG 1020 of the 1x8 optical switch 1030.

FIG. 14 shows a specific method 1400 for operating an optical switch engine using an LC cell and a PPG cell. For example, method 1400 is carried out using an optical switch engine 1200. In step 1410, the incident light beam is polarized to left or right circularly polarized light. For example, an electrically switchable LC is used to convert a linearly polarized incident light beam into circularly polarized light. In step 1420, the circularly polarized light beam is diffracted using at least a pair of LC and PPG cells. The direction of rotation of the polarized light of the diffracted light beam is further switched. For example, circularly polarized light is switched between counterclockwise and clockwise using an electrically switchable first LC1210 of a 1x4 optical switch 1230, followed by electrical switching. It is diffracted to the corresponding angle by the possible next stage SPG1250.

Although the present invention has been described with reference to exemplary embodiments, this description should not be construed in a limited sense. Various variations and combinations of the exemplary embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art by reference to the description. Accordingly, the appended claims include all such modifications or embodiments.

The present invention relates to an optical switch, and more particularly to a device and method for selectively switching wavelengths.

In the case of optical transmission network equipment, reconstructable optical insertion / branch multiplexers (ROADMs) can be used to flexibly expand network capabilities and reduce operating costs. Wavelength selection switches (WSS) are an option when using current ROADM technology. In the case of 1 × N type WSS (wavelength selection switch), 1 is a common (COM) port, and N represents the number of branch ports. When WSS (Wavelength Selection Switch) is activated, when WDM signals are input from COM ports, these signals are separated by optical wavelength, and then each wavelength is out of N branch ports according to system requirements. Routed to one branch port. On the contrary, these optical signals can be received as inputs from N branch ports and can be transmitted as outputs from COM ports.

<p num="0003"> ROADM provides an automated mechanism that flexibly increases capacity as needed without resorting to costly and disruptive "forklift" upgrades. The advantage of ROADM networks is that they dynamically increase capacity when and wherever they are needed, ensuring that the underlying network automatically compensates for increased traffic. Is what you can do. This eliminates the need for manual adjustments or major upgrades. Since ROADM can provide the insertion / branching function in a plurality of directions for a plurality of wavelength channels, it is suitable for realizing multi-directional interconnection between network ring groups and constructing a mesh type network.</p>

<p num="0004"> According to one embodiment, the optical switch includes a liquid crystal cell and a switchable polarizing diffraction grating (SPG) cell adjacent to the liquid crystal cell. The SPG includes a first glass substrate, a first electrode layer covering the first glass substrate, a photoalignment layer covering the first electrode layer, a liquid crystal material covering the photoalignment layer, and the like. Includes a second photoalignment layer that covers the liquid crystal material. The first photoalignment layer and the second photoalignment layer are photosensitive polymers that are physically altered by being exposed using two interference light beams in which the directions of rotation of circularly polarized light are opposite to each other. Including. The SPG further includes a second electrode layer covering the second photoalignment layer and a second glass substrate covering the second electrode layer.</p><p num="0005"> According to another embodiment, the optical switch includes a liquid crystal cell and a polymer liquid crystal polarizing diffraction grating (PPG) cell adjacent to the liquid crystal cell. The PPG is a photosensitive polymer that is physically altered by being exposed to a glass substrate and two interference light beams that cover the glass substrate and whose circularly polarized light rotates in opposite directions. It includes a photoaligned layer including the photoaligned layer and a polymerized liquid crystal layer that covers the photoaligned layer on the opposite side of the glass substrate and is physically changed by irradiation using a uniform light beam.</p><p num="0006"> According to still another embodiment, the method of operating the optical switch including the polarizing diffraction grating includes a step of polarizing the incident light beam to circularly polarized light, a step of guiding the polarized light beam to the polarizing diffraction grating, and the above-mentioned step. In a polarizing diffraction grating, a hologram pattern formed inside the polarizing diffraction grating is formed by using the polarized incident light beam with a diffraction order corresponding to the circular polarization of the incident light beam and two interference light beams. It includes a step of diffracting at a predetermined angle corresponding to a direction.</p><p num="0007"> For a more complete understanding of the present invention and its advantages, the following description will then be referred to in conjunction with the accompanying drawings.</p>

<figref num="1a">The process of forming a switchable polarizing diffraction grating (SPG) cell is shown.</figref><figref num="1b">The process of forming a switchable polarizing diffraction grating (SPG) cell is shown.</figref><figref num="2a">It shows an SPG cell in a state where no voltage is applied.</figref><figref num="2b">The SPG cell in the state where the voltage is applied is shown.</figref><figref num="3a">Shows different operating modes of the SPG cell.</figref><figref num="3b">Shows different operating modes of the SPG cell.</figref><figref num="3c">Shows different operating modes of the SPG cell.</figref><figref num="4a">The process of forming a polymer liquid crystal polarized diffraction grating (PPG) cell is shown.</figref><figref num="4b">The process of forming a polymer liquid crystal polarized diffraction grating (PPG) cell is shown.</figref><figref num="4c">The process of forming a polymer liquid crystal polarized diffraction grating (PPG) cell is shown.</figref><figref num="4d">The process of forming a polymer liquid crystal polarized diffraction grating (PPG) cell is shown.</figref><figref num="5a">It shows different operation modes of PPG cells.</figref><figref num="5b">It shows different operation modes of PPG cells.</figref><figref num="6">The specific optical system of the wavelength selection switch (WSS) is shown.</figref><figref num="7a">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7b">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7c">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7d">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7e">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7f">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7g">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="7h">It shows different operation modes of the composite element of the liquid crystal (LC) cell and the SPG cell.</figref><figref num="8">A specific optical switch engine using a composite element of an LC cell and an SPG cell is shown.</figref><figref num="9">Another specific optical switch engine using a composite element of an LC cell and an SPG cell is shown.</figref><figref num="10">Yet another specific optical switch engine using a composite element of an LC cell and an SPG cell is shown.</figref><figref num="11a">The different operation modes of the composite element of the LC cell and the PPG cell are shown.</figref><figref num="11b">The different operation modes of the composite element of the LC cell and the PPG cell are shown.</figref><figref num="11c">The different operation modes of the composite element of the LC cell and the PPG cell are shown.</figref><figref num="11d">The different operation modes of the composite element of the LC cell and the PPG cell are shown.</figref><figref num="12">A specific optical switch engine using a composite element of an LC cell and a PPG cell is shown.</figref><figref num="13">A specific method for operating an optical switch engine using an LC cell and an SPG cell is shown.</figref><figref num="14">A specific method for operating an optical switch engine using an LC cell and a PPG cell is shown.</figref>

Techniques for constructing and using the currently preferred embodiments will be described in detail below. However, it should be understood that the present invention provides many applicable and innovative concepts that can be embodied in a wide variety of specific situations. The particular embodiments described merely illustrate specific ways in which the invention is constructed and used, and do not limit the scope of the invention.

Technologies currently used in wavelength selection switch (WSS) products include microelectromechanical systems (MEMS), liquid crystal on silicon (LCOS), liquid crystals with wedge-shaped crystals (LC), and digital micromirror devices (DMD). Can be mentioned. For these techniques, these optics can be similar to each other, except that the optical switch engines are different.

In MEMS (Micro Electromechanical Systems), these wavelengths are diffracted by a diffraction grating towards different channels, and then each wavelength is incident on a corresponding MEMS reflection mirror. By controlling the voltage applied to each MEMS reflection mirror, the rotation angle of the mirror can be controlled to control the light reflection angle. Each wavelength can be reflected at a predetermined angle according to the requirements of the network. Wavelength beams reflected from multiple channels at the same angle can be diffracted into a single beam after passing through the grating a second time, then incident on the output port and coupled. In order to control the amount of light attenuation at the time of switching and realize the hitless function, each MEMS mirror has two rotation directions, port switching is performed in one rotation, and the attenuation and hitless in the other rotation. Control functions. The MEMS-based WSS has the advantages that the optical system is simple and the performance is good. However, the MEMS-based WSS has a high cost required for forming a MEMS chip due to a relatively low yield, a high cost required for an electronic element due to a high voltage drive requirement for a MEMS mirror, and a difficulty in realizing a large number of ports. And it has some drawbacks such as the difficulty of designing flexible grid functions.

LCOS is another technology used in WSS (wavelength selection switch) systems. The LCOS consists of an LC layer arranged between the glass substrate and the back surface of silicon. In the LCOS-based WSS, each wavelength light separated by the diffraction grating is incident on the LCOS panel covering the M × N pixels. By controlling the voltage applied to these pixels, it is possible to form an LC (liquid crystal) phase diffraction grating in which the incident light beam is diffracted at a predetermined angle. Different diffraction angles can be obtained by changing the LC (liquid crystal) diffraction grating pitch. Therefore, the light beam can be routed to a predetermined output port by controlling the LC (liquid crystal) phase diffraction grating pitch for a certain wavelength light. The LCOS-based WSS has several advantages such as a simple optical system, a large number of ports can be easily realized, and a flexible grid function can be easily realized. The defects include the complexity of the electronic drive system, the extremely complex control software, the difficulty of achieving low crosstalk, and the extremely high sensitivity to temperature.

Another technique used for WSS (Wavelength Selector Switch) is LC with crystal wedges. The WSS design using LC with crystal wedges was published on March 3, 2009, and published "Apparatus And Method for Optical Switching with Liquid Crystals And Birefringent Crystal Wedges (Liquid Crystal and Birefringence Crystal Wedges). ) , U.S. Pat. No. 7,499,608. Such a WSS switch engine consists of several stages of LC cells and wedge plate composite elements, depending on the required number of output ports. In each stage, the LC cell is used to switch the polarization and the wedge plate is used to refract the light in two directions depending on the polarization of the incident light. As a result, a 1 × 2 type optical switch is obtained. Therefore, when N stages are stacked, 1 × 2^NA type optical switch is obtained. The LC cell used is separated into M pixels defined by the number of optical channels required. By controlling the voltage applied to the LC pixel, the corresponding wavelength light can be routed to a predetermined output port group. Such a WSS has the advantages that the driving electronic element is simple, exhibits high vibration resistance, and exhibits high reliability. Defects include high costs due to high material costs, relatively low yields due to complex device assembly processes, and the difficulty of achieving a very large number of ports.

DMD (Digital Micromirror Device) technology is also used in WSS systems. In such a system, each wavelength light is incident on several DMD / MEMS mirrors. By controlling the rotation angles of these mirrors, the light beam can be guided to a predetermined angle. Since these mirrors have only two deflection positions, one DMD chip WSS can only realize a 1x2 type switch. In order to increase the number of switch ports of WSS, more DMD chips are required, and the optical system design becomes expensive and very difficult.

As explained above, WSS systems using existing technology have complex software for driving electronic components, high material cost, low vibration immunity, and expansion to a large number of ports. It has defects including being difficult to do. Described herein are specific systems and methods for implementing WSS (Wavelength Selector Switch). In different embodiments, switchable polarizing diffraction grating (SPG) cell and LC cell composite elements, as well as polymer liquid crystal polarizing diffraction grating (PPG) cell and LC cell composite elements, are used to malfunction the systems listed above. Realize a 1xN type WSS system that solves at least some of our problems.

1a and 1b show the SPG cell formation process 100. When forming a conventional LC cell, the LC alignment layer is formed by rubbing or exposing two polymer layers deposited on two substrates used to sandwich the LC. The SPG cell forming process 100 is different with respect to the process of forming the LC alignment layer. In the first step (FIG. 1a) of the SPG cell forming process 100, the two photosensitive polymer layers 102 are respectively deposited on the two glass substrates 106, and then the two glass substrates are combined to form an LC. Leave a gap for filling. An electrode (conductor) layer 104 is further added between each photosensitive polymer layer 102 and a glass substrate 106 corresponding to each photosensitive polymer layer 102. Next (Fig. 1b), two interferometric ultraviolet (UV) light beams 192 (with right and left circularly polarized light) that rotate in opposite directions of circularly polarized light (at an appropriate angle of incidence) 2 Used to expose one polymer layer 102 (eg, via these glass substrates 106), a holographic pattern is formed on these polymer layers 102. By performing this interference beam exposure on each surface of the SPG cell, the alignment layer is formed from the photosensitive polymer layer 102. When LC108 is filled in the gap and sandwiched between two glass substrates, the molecules of LC108 are holographic patterns and positions formed on these photosensitive polymer layers 102 that act as LC alignment layers at this stage. Oriented to match.

2a and 2b show the SPG cell 200 in the state where the voltage is applied and in the state where the voltage is not applied, respectively. The SPG cell 200 can be formed using the forming process 100. In a state where no voltage is applied to the electrode layer 204 (FIG. 2a), the LC208 of the SPG cell 200 forms a diffraction grating, which allows the incident light to any part of the glass substrate 206 to be oriented in these diffraction gratings. It is diffracted in a direction determined by the angles of the two exposure beams for forming the layer 202 (direction determined during the forming process 100). When a non-zero voltage is applied to these electrode layers 204 (FIG. 2b), the LC208 molecules are oriented so that they are aligned with the electric field generated by the applied voltage, and thus the effect of the LC diffraction grating. (Produced by the alignment layer 202) is canceled out, and incident light on any portion of the glass substrate 206 is not diffracted. To counteract the effects of the LC diffraction grating, a voltage large enough, for example, the threshold voltage (V)_th) Is required.

The SPG cell described above has three diffraction orders of 0th order and ± 1st order, which are different from ordinary diffraction gratings. 3a to 3c show different operation modes 300 of the SPG cell. Each operation mode corresponds to one diffraction order, and the light of each order is diffracted at different angles. In a state where a sufficiently large voltage is applied to the SPG cell (FIG. 3a), the light is diffracted into 0th-order light regardless of the polarization of the incident light. In the state where no voltage is applied or when a low voltage is applied (FIGS. 3b and 3c), the diffracted light direction differs depending on the polarization of the incident light. The right-circularly polarized incident light beam is diffracted into +1 degree light (FIG. 3a), whereas the left-circularly polarized incident light beam is diffracted into -1st order light (FIG. 3c). After being diffracted by the SPG cell, the circularly polarized light is inverted as shown in FIGS. 3b and 3c (switching between right and left circularly polarized light).

4a-4d show the PPG cell formation process 400. In the first step (FIG. 4a) of the PPG cell forming process 400, the photoalignment layer 402 is deposited on the glass substrate 406. In the second step (FIG. 4b), the polymer layer 402 is exposed with two interfering UV beams (492) in which the directions of rotation of the circularly polarized light are opposite to each other. In the third step (FIG. 4c), the polymerizable LC layer 403 is deposited on the upper surface of the photoalignment layer 402. In the fourth step (FIG. 4d), the uniform UV beam 494 is used to irradiate the polymerizable LC layer 403 to polymerize the LC composition (molecule) of the layer. In this way, the polymer diffraction grating is formed on the glass substrate 406.

The resulting PPG cell is a diffraction grating with constant characteristics in that the diffraction characteristics of the PPG cell cannot be changed by applying a voltage (as in the case of the SPG cell described above). Is. 5a and 5b show different operating modes 500 of the PPG cell. Each operation mode corresponds to one diffraction order, and each order light is diffracted at different angles. The incident light beam is diffracted in one of the two directions. Specifically, the incident light beam with right-handed circularly polarized light is diffracted into +1st-order light (FIG. 5a), whereas the incident light beam with left-handed circularly polarized light is diffracted into -1st-order light (FIG. 5b). ). In either case, after diffraction, the direction of rotation of the polarized light of the beam changes, that is, switches in the opposite direction of rotation.

FIG. 6 shows a specific optical system 600 of WSS (wavelength selection switch). The WSS optical system 600 includes a fiber array 601, a microlens array 602, a beam deflection array 603, a 1/2 wave plate array 604, a cylindrical lens 605, a cylindrical reflection mirror 606, a diffraction grating 607, and an optical switch. Includes engine 608. These components of WSS optical system 600 can be arranged as shown in FIG. 6, or can be arranged in any other suitable arrangement that achieves the same or similar function. In other embodiments, the same constituent elements as those described above may be used, or yet another constituent element different from the constituent elements described above may be used. Instead of some of these constituent elements, the same constituent elements that realize the same function, or a combination of other constituent elements may be used.

Fiber array 601 is used for input and output ports. When an input or incident light beam from one fiber 601 passes through a microlens array 602, a beam deflection array 603, and a 1/2 wave plate array 604, the beam is two parallels with the same linearly polarized light. Separated into beams. The two light beams then become collimated beams after passing through the cylindrical lens 605 and the cylindrical reflection mirror 606. Next, these light beams are diffracted by the diffraction grating 607 and separated into a plurality of wavelengths. The light of each wavelength is then focused on the optical switch engine 608. The optical switch engine 608 routes light of each wavelength to a predetermined port. The corresponding light beam passes through the optical system 600 again (in reverse order of the plurality of components), is incident on a predetermined output fiber, and is coupled.

The optical switch engine 608 of WSS optical system 600 is realized by using an appropriate WSS (wavelength selection switch) system including a composite element of SPG cell and LC cell described below, or a composite element of PPG cell and LC cell. Can be done. Compared to other WSS (wavelength selection switch) technologies used (eg MEMS, LCOS, LC, wedge plates, DMDs), WSS systems using SPG or PPG have a simple optical system, electronic drive circuits. It has the advantages of being simple, reliable, high performance, easily realizing a large number of ports, and keeping the product cost low.

7a to 7h show different operation modes 700 of the composite elements of the LC cell and the SPG cell. The LC cell 710 is arranged in front of the SPG cell 720 (when viewed from the incident light). The LC cell 710 is used to control or switch the polarization of light. The SPG cell 720 is also used to diffract the light beam in a predetermined direction.

As shown in FIGS. 7a, 7c, 7e, and 7h, when a relatively large voltage (VH) (eg, a voltage above the threshold) is applied to the LC cell 710, the polarized light beam passes through the LC cell. But it doesn't change. As shown in FIGS. 7b, 7d, 7f, and 7g, when no voltage is applied to the LC cell 710, or when a relatively small voltage (VL) (for example, a voltage below the threshold value) is applied to the LC cell 710. , The rotation direction of the polarized light of the incident light beam is switched. As shown in FIGS. 7a, 7b, 7e, and 7f, when a relatively large voltage (VH) (for example, a voltage exceeding the threshold value) is applied to the SPG cell 720, the input light is polarized in any state. The light beam is diffracted into 0th order light. As shown in FIGS. 7c, 7d, 7g, and 7h, when no voltage is applied to the SPG cell 720, or when a relatively small voltage (VL) (for example, a voltage below the threshold value) is applied to the SPG cell 720. , Depending on the polarization of the incident light controlled by the LC cell 710, the light beam can be diffracted to be either +1 or -1st order light. Regardless of whether the input light is right-handed or left-handed, the composite elements of LC cell 710 and SPG cell 720 route the light beam in three directions to form a 1x3 optical switch. To do. N groups of LC cells and SPG cells are 1x3^NA type optical switch can be realized.

FIG. 8 shows a specific cross section of an optical switch engine 800 using a composite element of an LC cell and an SPG cell. The optical switch engine 800 can be used as the optical switch engine 608 of the WSS optical system 600. The optical switch engine 800 includes a variable optical attenuator (VOA) 805 including an LC cell 810 connected to a polarizing plate 815, a 1/4 wave plate (QWP) 840, and two consecutive LC cells 810 and an SPG cell 820. It comprises a 1 × 9 type optical switch 830 including a pair consisting of a prism or a mirror 890. These components can be arranged as shown in FIG. 8 or in another suitable order. The LC cell 810 and the SPG cell 820 can have M pixels in a direction orthogonal to the N = 9 beams (direction perpendicular to the paper surface of FIG. 8). In FIG. 8, N is the number of beams corresponding to the number of ports, and M is the number of pixels corresponding to the number of wavelength channels. The LC cell used in the optical engine 800 may be an electrically controlled birefringence (ECB) cell, a twisted nematic (TN) cell, and a vertically oriented (VA) cell.

For brevity, the operating principle of a switch engine is described for one wavelength as illustrated in the cross section of engine 800 in FIG. However, the same operating principle applies to all M pixels.

The input light first passes through the VOA805, which is used to control the attenuation of the light output. By controlling the voltage applied to the LC cell 810, the amount of light output of the VOA 805 can be controlled. QWP840 is used to change the linearly polarized light into circularly polarized light. Next, the light beam passes through two groups of LC cells 810 and SPG cells 820 (1 × 9 type optical switch 830). Therefore, the output beam can have nine different angles with respect to the optical axis. The beam is then reflected by a prism or mirror 890 and, after passing through switch 830, becomes parallel to the optical axis. The optical switch engine 800 is properly designed to allow approximately equal distances between any two adjacent optical paths (nine switching angles). Therefore, the reference fiber array can be used as an optical output port (eg, with nine output ports).

FIG. 9 shows a cross section of another specific optical switch engine 900 using a composite element of an LC cell and an SPG cell. The optical switch engine 900 can be used as the optical switch engine 608 of the WSS optical system 600. The optical switch engine 900 includes a VOA 905 including an LC cell 910 connected to a polarizing plate 915, a pair of LC cells 910 and an SPG cell 920, and a 1 × 7 type optical switch 930 including a second SPG cell 920 in the subsequent stage. And a prism or mirror 890. These components can be arranged as shown in FIG. 9 or in another suitable order. The LC cell 910 and the SPG cell 920 can further have M pixels in a direction orthogonal to N = 7 beams (direction perpendicular to the paper surface of FIG. 9). One difference between the optical switch engine 900 and the optical switch engine 800 is that the optical switch engine 900 realizes a 1 × 7 type optical switch by using one LC cell 910 and two SPG cells 920. Is. In the 1 × 7 type optical switch, the LC cell 910 is used to control the polarization of the light, and the two SPG cells 920 are used to diffract the light at a predetermined angle. Furthermore, the optical switch engine 900 does not include QWP. Instead, the VOA905 LC cell 910 is designed as a switchable quarter wave plate (switching between λ / 4 and 3λ / 4), transforming the linearly polarized light of the incident light into circularly polarized light. To increase the number of optical output ports, more SPG cells 920 can be added to the optical switch engine 900, for example in front of the mirror or prism 990. For example, when there are N SPG cells 920, 1 × (2)^{N + 1}-1) A type optical switch engine may be mounted.

FIG. 10 shows a specific cross section of yet another optical switch engine 1000 using a composite element of an LC cell and an SPG cell. The optical switch engine 1000 can be used as the optical switch engine 608 of the WSS optical system 600. The optical switch engine 1000 includes a VOA 1005 including an LC cell 1010 connected to a polarizing plate 1015, a QWP 1040, a 1 × 8 optical switch 1030 including three SPG cells 1020, and a prism or a mirror 1090. These components can be arranged as shown in FIG. 10 or in another suitable order. These SPG cells 1020 can further have M pixels in a direction orthogonal to N = 8 beams (direction perpendicular to the paper surface of FIG. 10). Unlike the optical switch engines 800 and 900 described above, the optical switch engine 1000 controls the optical diffraction angle using only the SPG cell group 1020 without using the LC cell. After the light beam has passed through VOA1005 and QWP1040, the linearly polarized light of the input beam changes to circularly polarized light. Each SPG cell 1020 can diffract the light beam into two angles. Therefore, if there are N SPG cells, 1 × 2^NA type optical switch engine can be formed.

11a to 11d show different operation modes 1100 of the composite elements of the LC cell and the SPG cell. The LC cell 1110 is arranged in front of the SPG cell 1150 (when viewed from the incident light). LC cells 1110 are used to control or switch the polarization of light, and PPG cells 1150 are used to diffract the light beam in one of two directions, depending on the polarization of the input light. Therefore, the N group consisting of LC cells and PPG cells is 1 × 2.^NA type optical switch can be configured.

As shown in FIGS. 11a and 11d, when VH (eg, a voltage above the threshold) is applied to the LC cell 1110, the polarization of the incident light beam does not change as it passes through the LC cell. As shown in FIGS. 11b and 11c, when no voltage is applied to the LC cell 1110 or when VL (for example, a voltage below the threshold value) is applied to the LC cell 1110, the polarization of the incident light beam is switched between left and right. As shown in FIGS. 11a and 11c, when the incident light on the PPG cell 1150 has right circularly polarized light, the light beam is diffracted into +1 degree light. As shown in FIGS. 11b and 11d, when the incident light on the PPG cell 1150 is left circularly polarized, the light beam is diffracted into -1st order light.

FIG. 12 shows a specific cross section of an optical switch engine 1200 using a composite element of an LC cell and an SPG cell. The optical switch engine 1200 can be used as the optical switch engine 608 of the WSS optical system 600. The optical switch engine 1200 includes a VOA 1205 including an LC cell 1210 connected to a polarizing plate 1215, a 1 × 4 optical switch 1230 including a pair consisting of two consecutive LC cells 1210 and a PPG cell 1250, and a prism or mirror 1290. And. These components can be arranged as shown in FIG. 12 or in another suitable order. These LC cells 1210 and PPG cells 1250 can have M pixels in a direction orthogonal to N = 4 beams (direction perpendicular to the paper surface of FIG. 12). Similar optical switches can be designed to have any number of output ports by stacking and coalescing the required number of LC and PPG pairs.

FIG. 13 shows a specific method 1300 for operating an optical switch engine using an LC cell and an SPG cell. For example, method 1300 is performed using any of the optical switch engines 800, 900, and 1000. In step 1310, the incident light beam is polarized to left or right circularly polarized light. For example, QWP840 or 1040, or electrically switchable (by applying a voltage) LC, is used to convert a linearly polarized incident light beam into circularly polarized light. In step 1320, the circularly polarized light beam is diffracted using at least one SPG cell. The direction of rotation of the polarized light of the diffracted light beam is further switched. For example, the circularly polarized light can be electrically switched between the counterclockwise direction and the clockwise direction of the 1 × 9 type optical switch 830, and the first LC810 (or the LC910 of the 1 × 7 type optical switch 930) can be electrically switched. ) Is switched, and then it is diffracted to the corresponding angle by the next stage SPG820 (or 920) which is electrically switchable. In another example, the circularly polarized light is diffracted directly at the corresponding angle by the electrically switchable first SPG 1020 of the 1x8 optical switch 1030.

FIG. 14 shows a specific method 1400 for operating an optical switch engine using an LC cell and a PPG cell. For example, method 1400 is carried out using an optical switch engine 1200. In step 1410, the incident light beam is polarized to left or right circularly polarized light. For example, an electrically switchable LC is used to convert a linearly polarized incident light beam into circularly polarized light. In step 1420, the circularly polarized light beam is diffracted using at least a pair of LC and PPG cells. The direction of rotation of the polarized light of the diffracted light beam is further switched. For example, circularly polarized light is switched between counterclockwise and clockwise using an electrically switchable first LC1210 of a 1x4 optical switch 1230, followed by electrical switching. It is diffracted to the corresponding angle by the possible next stage SPG1250.

Although the present invention has been described with reference to exemplary embodiments, this description should not be construed in a limited sense. Various variations and combinations of the exemplary embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art by reference to the description. Accordingly, the appended claims include all such modifications or embodiments.