Reconfigurable port array for wavelength selective switching

Abstract

The present application relates to a reconfigurable port array for a wavelength selective switch. A reconfigurable polarization rotator is formed by an array of very small liquid crystal (LC) cells (e.g., cells with a width less than 10 μm, referred to as "microcells"), which are hereinafter referred to as "microcells". Each LC microcell can be addressed by an independent voltage input, which independently controls the polarization rotation performed by the associated LC microcell. By defining a group of adjacent microcells to be maintained at the same voltage level, the group can be used to form a polarization rotator window of appropriate size for a first fiber array configuration. When a fiber array of a different configuration is used (e.g., an array with twice the pitch), a group of adjacent LC microcells of different sizes are maintained at a common voltage level to form a reconfigured "window" of new size.

Description

Technical Field

[0001] The present invention relates to the implementation of a wavelength selectable switch (WSS), and more particularly, to using a reconfigurable polarization rotator at a port interface to accommodate connections with optical fiber arrays of various layouts. Background of the Invention

[0002] Wavelength selective switches are widely used in various optical communication systems and have been found to be a ubiquitous component in reconfigurable optical add / drop multiplexers (ROADMs). As typical WSS implementations have evolved, polarization diversity components have been included at the interface between the input / output ports and the actual switch elements to reduce polarization-related losses during the switching process.

[0003] The basic polarization diversity component takes the form of a birefringent walk-off plate used in conjunction with a polarization rotator (half-wave plate). The walk-off plate creates a spatial separation between the orthogonal polarizations of the input signal, with the polarization rotator positioned to intercept one of the beams and rotate its polarization by 90°. Since both beams now exhibit the same polarization state, the likelihood of polarization-dependent losses within the WSS is significantly reduced.

[0004] One-dimensional fiber arrays are commonly used to support the coupling of multiple optical signals to various ports of a WSS. While it is possible to use small-sized, separate birefringent walk-off plates and polarization rotators for each port of a WSS, a preferred configuration uses a combination of a single, monolithic walk-off plate and a single, monolithic polarization rotator to operate all beams in parallel. The polarization rotator is formed as alternating "windows" with 90° rotation and 0° rotation, with each pair of windows sized to align with an associated fiber in the coupling fiber array. Functionally, the fixed size and position of each polarization rotator window determines the physical size of the fiber array that can be coupled to the WSS. Thus, if there are any subsequent changes to the fiber array arrangement (e.g., an array with a different pitch, or an array with a gap between an input port and a set of output ports), a completely new optical interconnect configuration needs to be built with the modified port spacing / size of the new fiber array.

[0005] Depending on the level of integration in a given component, a change in the fiber array configuration may require rework of other components in the WSS to accommodate the change. SUMMARY OF THE INVENTION

[0006] The present invention is directed to implementations of wavelength selective switches (WSSs), and more particularly, to the use of reconfigurable polarization rotators at port interfaces to accommodate connections to various configurations of optical fiber arrays.

[0007] The reconfigurable polarization rotator is formed from an array of very small liquid crystal (LC) cells (i.e., cells with a width less than 10 μm and preferably no greater than 8 μm), which are hereinafter referred to as "microcells". Each LC microcell is addressable by an independent voltage input that independently controls the polarization rotation performed by the associated LC microcell. By defining a group of adjacent microcells to be held at the same voltage level, the group can be used to form a polarization rotator window of the appropriate size for a given fiber array configuration. When a fiber array of a different configuration is used (e.g., an array with twice the pitch), a group of adjacent LC microcells of different sizes are held at a common voltage level to form a reconfigured "window" of new size.

[0008] The ability to reconfigure the association between multiple groups of LC micro-cells and the input / output ports of the associated fiber arrays also allows a given WSS to be reconfigured for different implementations without having to change any physical components of the WSS. For example, a "twin" 1xN WSS (typically a paired arrangement of a 1xN WSS and an Nx1 WSS) can be reconfigured into a 1x2N WSS by controlling the grouping of individual LC micro-cells in forming associated polarization rotator windows.

[0009] Exemplary embodiments may take the form of a reconfigurable port interface for a given WSS having a plurality of optical signal coupling ports, at least one port for receiving an optical input signal and at least one port for transmitting an optical output signal. The port interface itself is formed to include a birefringent walk-off plate and a polarization rotator array having individually addressable LC cells. The birefringent walk-off plate is disposed adjacent to the plurality of optical signal coupling ports, the birefringent walk-off plate performing spatial separation of orthogonal polarizations of the optical input signal and spatial recombination of parallel polarizations of the optical output signal. The polarization rotator array is positioned to intercept optical signals exiting and entering the birefringent walk-off plate and includes a plurality of LC microcells, each individual LC microcell being individually addressable by a control voltage input to provide one of: a 90° polarization rotation via a first applied voltage and a 0° polarization rotation via a second applied voltage. A plurality of control electrodes are coupled to the plurality of LC microcells in a one-to-one relationship, wherein a first selected plurality of groups of adjacent LC microcells are held at a first applied voltage to construct a 90° polarization window, and a second selected plurality of groups of adjacent LC microcells are held at a second applied voltage to construct a 0° polarization window.

[0010] Another embodiment can be defined as a reconfigurable polarization rotator array, which includes: a plurality of LC microcells (each individual LC microcell can be individually addressed by a control voltage input to provide one of a 90° polarization rotation and a 0° polarization rotation, and the plurality of LC microcells all present a same width W of less than 10 microns); a plurality of control electrodes, which are coupled to the plurality of LC microcells in a one-to-one relationship; and a window configuration controller, which is coupled to the plurality of control electrodes and applies an appropriate voltage to each of the plurality of control electrodes in response to a window reconstruction command to define selected groups of adjacent microcells, thereby forming a transmission window and providing a predetermined polarization rotation to a light beam passing through the transmission window.

[0011] Yet another embodiment of the invention relates to the ability to reconfigure the application of a given WSS (e.g., as a "twin" pair of 1xN WSS, a "quad" group of 1x(N / 4) WSS) by controlling the voltage applied to each individual LC microcell to define the characteristics of each individual port.

[0012] Other and further embodiments and aspects of the invention will become apparent during the following discussion and by reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Referring now to the drawings, wherein like numerals represent like parts throughout the various views:

[0014] Figure 1 is a side view of a prior art WSS illustrating the use of polarization diversity to reduce polarization dependent losses within a switching function;

[0015] Figure 2 is a front view of an exemplary prior art quartz plate used as a polarization rotator in a prior art WSS;

[0016] Figure 3 An array of prior art liquid crystal (LC) cells with fixed rotation that can be used as polarization rotators in a prior art WSS is shown;

[0017] Figure 4 An exemplary reconfigurable optical coupling interface arrangement formed in accordance with the present invention is shown to provide coupling between various input / output port arrangements and switching components of a given WSS, forming a 1x3 WSS;

[0018] Figure 5 is a diagram showing the definition of "pitch", which is used to define the core-to-core spacing between adjacent optical fibers, and the center-to-center spacing between adjacent ports of a WSS;

[0019] Figure 6 is a detailed depiction of a reconfigurable LC polarization rotator array formed by a large number of small-sized LC microcells (microcell width is approximately 5-8 μm);

[0020] Figure 7 The reconfigurable LC polarization rotator array is shown based on controlling the voltage applied to the array. Figure 4 The arrangement is restructured to provide an interface for a 1x6 WSS;

[0021] Figure 8 The invention shows the use of a reconfigurable LC polarization rotator array to adjust the spacing (gap) between defined ports and to provide an arrangement with two different pitches, wherein Figure 8 (a) shows a 1x6 WSS port arrangement, and Figure 8 (b) shows a 1x3 WSS port arrangement in combination with a pair of spaced-apart ports (possibly for transmitting monitoring signals);

[0022] Fig. 9 shows a "twin" 1xN WSS including the reconfigurable LC polarization rotator array of the present invention; and

[0023] Fig.10 Shown based on Fig. 9 Identical components of a 1x2N WSS with an array of LC polarization rotators reconstructed according to the principles of the present invention. Detailed Description

[0024] Figure 1 is a simplified cross-sectional view of a prior art optical coupling interface 1 formed to utilize polarization diversity to address issues associated with polarization dependent losses within a wavelength selective switch (WSS) module. The presence of an uncontrolled polarization of a propagating free-space beam may result in optical losses occurring as the beam propagates through a switch structure between a given input port and a defined output port. Polarization diversity refers to the separation / recombination of the orthogonal polarization states of the input beams so that a single controlled polarization beam propagates through the switch. By applying polarization diversity to construct a single beam of fixed polarization state, the WSS can use polarization sensitive components and also provide a switch that exhibits very small polarization dependent losses.

[0025] The optical coupling interface 1 comprises a set of four optical ports (at Figure 12, 3, 4 and 5 in FIG. 1 ), which will be used with a 1x3 WSS (a set of three input ports and one output port, or a single input port and a set of three output ports). The optical coupling interface 1 includes a birefringent walk-off plate 6 and a polarization rotator 7 (sometimes a polarization rotator is called a "half-wave plate" because its function is to rotate the polarization of a light beam propagating through the plate by 90°). The birefringent walk-off plate 6 is a reciprocal device whose function is to rotate the polarization of a light beam propagating through the plate by 90°. Figure 1 When propagating from left to right in the view of Figure 1 According to its reciprocity property, the birefringent walk-off plate 6 is used to recombine (i.e., spatially superimpose) a pair of spatially separated sub-beams (with V polarization and H polarization) to form a single output beam (with V polarization component and H polarization component) having V polarization component and H polarization component. Figure 1 ). A polarization rotator 7 is disposed adjacent to the birefringent walk-off plate 6 and is positioned to align with the sub-beam having one of the polarization states. The polarization rotator 7 functions in a manner known in the art to rotate the polarization state of the sub-beam passing through its thickness (e.g., from "H" to "V"), thereby providing a "single polarization" input to the subsequent switch engine components of the WSS.

[0026] In many arrangements, the polarization rotator 7 is formed from a quartz plate whose thickness will effect a 90° polarization rotation of the propagating beam. Figure 1 In the multi-port arrangement shown, a monolithic (single) quartz plate having a length L sufficient to interact with each port may be used. Figure 2 is a front view of an exemplary quartz embodiment of a prior art polarization rotator 7. As shown, a single piece of quartz 8 is used to form a monolithic structure having a plurality of openings 9 built through the thickness of the quartz 8. The openings 9 are used to allow a beamlet of a first polarization state (e.g., "vertical") to pass unimpeded while rotating a beamlet of an orthogonal polarization ("horizontal") by 90° so that both beamlets have the same polarization when entering various switch engine components (not shown) within the WSS.

[0027] The openings 9 in the quartz 8 are typically constructed using a mechanical cutting process which, unfortunately, has been found to cause undesirable cracking in surrounding portions of the quartz crystal structure. Furthermore, mechanical cutting processes are limited in being able to reliably construct openings of relatively small size (e.g., less than about 10 μm). The spacing between adjacent openings may also be somewhat variable, which can cause problems when attempting to align the windows with an associated optical fiber array. Another alternative to using a monolithic crystal with machined openings is to use multiple small size quartz plates, each of which is positioned and aligned to intercept a single beam (a fairly labor intensive approach that is subject to misalignment and other manufacturing difficulties).

[0028] Instead of using a quartz-based polarization rotator, a liquid crystal (LC) array can be used as a polarization rotator array. A pair of LC cells is associated with each port, and a separate electrical bias is applied to each cell and used to provide a 90° polarization rotation or a 0° polarization rotation to a sub-beam passing through the associated cell. Figure 3 An array of LC cells is shown (in side view). Each cell of this prior art configuration is also referred to as a "window," with each sub-beam passing through its own window. The process of manufacturing the LC array allows relatively small windows to be formed with greater precision than machined quartz plates. These improvements allow precise alignment with signal ports. However, it has been found that the fixed window size inherent in the prior art LC-based polarization rotators limits the number of ports that can be used and the spacing (pitch) between adjacent ports. Therefore, the physical limitations of the LC window size require that a new interface be built for each different fiber array design that is developed. In most cases, as the fiber array layout changes, an entirely new WSS needs to be manufactured to accommodate the changes in input / output beam positions.

[0029] In order to solve these problems, a reconfigurable optical interface between various fiber array layouts and WSS formed according to the principles of the present invention is proposed. Figure 4 An exemplary reconfigurable optical coupling interface arrangement 10 formed in accordance with the present invention and based on an implementation of a reconfigurable LC polarization rotator array 12 is shown, which allows connection to a variety of different port configurations.

[0030] For discussion purposes, the arrangement 10 is shown as having Figure 1 1. Here, the ports include a single input port 16 and a set of three output ports 18-1, 18-2, 18-3. A birefringent walk-off plate 20 is used in the same manner as discussed above to provide controlled spatial separation between orthogonal polarizations of propagating sub-beams in the optical coupling interface arrangement 10. The spacing P (commonly referred to herein and elsewhere as the "pitch") is defined as the spacing between adjacent beams entering / exiting adjacent ports.

[0031] Figure 5 How to define the pitch of an associated optical fiber array and how to use this pitch to define the pitch of optical ports coupled to individual optical fibers in the array is shown. Here, multiple optical fibers F are positioned in V-grooves formed in a support plate S. The core region of each optical fiber is shown, and the pitch P is defined as the spacing between adjacent core regions. Depending on the physical formation of the V-groove (or similar fiber support configuration), the pitch P can be different, depending on the type of optical fiber, the size of the core region, the fiber diameter, etc.

[0032] Continue to discuss Figure 4 In the illustrated exemplary embodiment of the invention, a reconfigurable LC polarization rotator array 12 is formed of a plurality of very small (narrow) LC cells (e.g., on the order of 5-8 μm; possibly even smaller), hereinafter referred to as LC "microcells." Each LC microcell 14 is individually addressable (and thus reconfigurable between providing a 90° polarization rotation or a 0° polarization rotation) in a one-to-one manner by an array of applied voltages. Thus, groups of adjacent microcells can be held at the same voltage potential to form a single "window" for rotating (or passing) a light beam that passes through a defined group of LC microcells.

[0033] exist Figure 4 In the exemplary embodiment of FIG. 1 , a group of four LC microcells 14-1, 14-2, 14-3, and 14-4 are maintained at a first voltage (denoted as V 90 ), which first voltage provides a 90° polarization rotation for a sub-beam propagating through the set of microcells. This set is defined as a first polarization rotator window 22-1, and is used to rotate the polarization of the walk-off beam from the input port 16. A second window 22-2 is also associated with the input port 16 and is similarly defined by a set of four individual LC microcells 14, where the set of microcells is held at a second voltage associated with a 0° polarization rotation (denoted as V 0 ) so that the polarized sub-beam continues to propagate along the original polarization axis (i.e., without rotation). It is to be understood that Figure 4 The group of four microcells shown is for illustration purposes only; in practice, a greater number (eg, 10 or more) of such microcells may be grouped together to define a window of appropriate size.

[0034] exist Figure 4 In the illustrative example of FIG. 1 , it is assumed that the switch engine components associated with the WSS are configured such that an incident light beam from input port 16 is directed to output port 18-1. A first output window 22-3 (also formed by a group of four individual LC microcells) is defined as being associated with output port 18-1, wherein the group of LC microcells are all held at a voltage V 90 , the voltage V90 A 90° polarization rotation is provided to rotate one of the sub-beams applied as input to the group of LC microcells. An adjacent group of four LC microcells is grouped together to define a second output window 22-4 (where the group is held at an appropriate voltage V 0 To provide a 0° polarization rotation). After the rotation is performed by the first output window 22-3, a pair of spatially separated orthogonal sub-beams pass through the birefringent walk-off plate 20, which is used in this direction to spatially recombine the two polarization / sub-beams and direct the combination as an output beam to the output port 18-1. Although not specifically listed, it should be understood that a pair of output windows are also constructed for each of the remaining output ports 18-2 and 18-3.

[0035] Figure 6 is a more detailed depiction of a reconfigurable LC polarization rotator array 12, showing a plurality of LC microcells 14 (where each microcell may be approximately 5-8 μm in width). Figure 6 Also shown are a plurality of electrodes 24 associated with the LC microcells 14 in a one-to-one relationship. Specifically, each electrode 24-i provides a specific bias voltage to its associated LC microcell 14-i as controlled by a window configuration controller 26. The "commands" input to the controller 26 define the specific port arrangement to be constructed, including the number of individual ports, the spacing (pitch) between adjacent ports, the window size (which may include the number of individual LC microcells 14 to be grouped together to form a window), the gaps to be positioned between the ports, etc. It should be understood that the use of a separate component as a window configuration controller is merely exemplary, and any technique for applying appropriate voltages to individual LC microcells may be used.

[0036] Figure 6 The dashed outline A represents the grouping of a first set of LC microcells 14 together to form a first window, and the dashed outline "B" represents the grouping of a second set of LC microcells 14 together to form a second window. The gap between the two windows is shown here as being formed by a pair of LC microcells (14-x, 14-y) that are not actuated. In this case, the window configuration controller 26 is used to set the first bias voltage V for establishing a 90° polarization rotation to 90 is sent to the LC microcells 14 forming window A. The LC microcells 14 of window B (associated with 0° polarization rotation) are similarly controlled by the window configuration controller 26, wherein in this case, the window configuration controller 26 provides a second bias voltage V to the set of LC microcells 14 forming window B. 0Because each individual, small-sized LC microcell 14 is individually controllable, the window size, port configuration, port pitch, etc. can be adjusted via the window configuration controller 26 (or any other suitable arrangement for addressing the individual LC microcells), as necessary for use with a variety of different fiber array configurations.

[0037] Figure 7 One possible reconfiguration of the LC microcells 14 within the polarization rotator array 12 is shown, which implements a different number of ports, performing different functions, to take advantage of the Figure 4 Here, a 1x6 WSS can utilize the arrangement 10 by changing the grouping of the LC microcells 14 to adjust to a different (smaller) pitch (shown here as P') and a different number of ports that interact with the rest of the system. Figure 7 In the arrangement of FIG. 6 , a single input port 60 is defined as the center-most port, and two sets of output ports (62-1 to 62-3 and 62-4 to 62-6) are positioned above and below the input port 60, respectively. This is a common configuration used in many WSS implementations to minimize the beam steering angle required to properly couple the input port to the selected output port. Advantageously, the reconfiguration capability of the LC microcell array of the present invention allows for Figure 4 1x3 WSS arrangement and Figure 7 Changing between 1x6 WSS arrangements is quick and easy without changing any physical components.

[0038] For this particular embodiment, the reconfigurable polarization rotator array 12 is controlled (via the window configuration controller 26) such that (with Figure 4 Only one pair of adjacent LC microcells 14 are grouped together to form a window (as opposed to the grouping of four adjacent LC microcells 14 in the arrangement of FIG. 1 ). By simply adjusting the individual voltages provided to each LC microcell 14-i, the port interface is easily adjusted to accommodate different fiber arrays (seven fibers, as opposed to four fibers), with different pitches between adjacent fibers. Obviously, this is only one possible reconfiguration; any grouping of adjacent LC microcells 14 can be used to allow a given set of ports to be aligned with the signal paths.

[0039] Figure 8 Another advantage of utilizing a reconfigurable polarization rotator formed from an array of LC microcells in accordance with the principles of the present invention is shown. In this example, the ability to address individual LC microcells 14 allows the same WSS switch engine component (not shown) to communicate with two different fiber arrays configured for different purposes. Figure 8(a) shows a first port configuration 63, which includes a 1x6 port arrangement with the same pitch PA between each port. In this case, the appropriate set of LC micro-units 14 is controlled to provide a 90° polarization rotation, where these sets are spaced a certain amount that provides alignment with the pitch PA of the port configuration 63.

[0040] Figure 8 (b) shows a different port configuration, in this case including a first set 65 of ports that function as input and output ports of the 1x3 WSS. A second set 67 of ports includes a pair of ports 67-1, 67-2 that may be spaced apart to improve certain characteristics of the optical performance of the switch (e.g., reducing crosstalk between adjacent ports, reducing polarization dependent losses, etc.), including a pair of ports for sending / receiving switch monitoring information, or various other possibilities. In this arrangement, the 1x3 WSS is shown with Figure 8 63 of (a). A gap G is shown in the space between ports 65 and 67, defining a second pitch PB between port 67-1 and port 67-2. In accordance with the present invention, such reconfiguration can be readily provided by identifying different sets of individual LC micro-cells 14 that need to be aligned with port 67. Obviously, this is just an example; the ability to independently address each LC micro-cell provides great flexibility in accommodating fiber arrays of different configurations.

[0041] Advantageously, reconfigurable LC microcell polarization rotator arrays formed in accordance with the present invention may also be used in applications where a given WSS is "reconfigured." For example, control of the reconfigurable polarization rotator array allows a "twin" 1xN WSS to be reused as a 1x2N WSS. Fig. 9 and Fig.10 shows how this reconstruction occurs.

[0042] Fig. 9 A dual 1xN WSS 70 is shown, so named because two independent signal sources use the same switching hardware simultaneously (each source maintains a defined polarization) by using signals propagating along orthogonal axes. Here, a 1xN port arrangement 72 including a single input port 74 and a plurality of output ports 76 in number N is configured to maintain the "H" polarization state. An accompanying Nx1 port arrangement 78 completes a twin arrangement operating along an orthogonal "V" polarization state, arrangement 78 being shown including a single output port 80 and a plurality of input ports 82 in number N. A single birefringent walk-off plate 84 is shown positioned beyond the twin configuration of the 1xN port arrangement 72 and the Nx1 port arrangement 78. The walk-off plate 84 is used in the manner described above to provide spatial separation between the two polarization states of the propagating optical beamlets.

[0043] A reconfigurable LC polarization rotator array 86 (formed by a large number of individual, small-sized LC microcells 88) is shown positioned adjacent to the birefringent walk-off plate 84. A window configuration controller 90 is used to provide an individual voltage (optionally V 90 or V 0 ), so that the polarization windows are sized and aligned for each port. The ability to utilize the same WSS elements (e.g., polarization beam splitter 94 and switch engine 96) in a twin 1xN comes from applying "polarization diversity" to the arrangement. That is, the 1xN WSS 72 is configured to utilize beams propagating in a first polarization direction (defined here as "horizontal"), while the Nx1 WSS 78 is configured to utilize beams propagating in a second orthogonal polarization direction (defined here as "vertical"). By maintaining orthogonality between the free-space beams associated with each WSS, two independent arrangements can share the same switching elements.

[0044] According to the principles of the present invention, the reconfigurable LC polarization rotator array 86 is controlled to provide the desired polarization diversity. By addressing each individual LC microcell 88 with appropriate voltage levels, it is possible to achieve polarization diversity using a single walk-off plate and a single polarization rotator array.

[0045] Fig.10 shows the Fig. 9 The 1x2N WSS 100 is formed of the same components as the twin 1xN WSS. Here, the first port 74 is defined as a single input port, and the remaining ports (2N, or 2N+1) are used as output ports. To achieve this reconstruction, the window configuration controller 90 modifies the voltage applied to the LC microcells 88 so that adjacent windows (of the same size as for the "twin" arrangement) have alternating polarizations. Thus, in this "reconfiguration", a single polarization state is used within the WSS, and (as with Fig. 9 The number of possible output ports associated with a given input port is doubled compared to the configuration of

[0046] like Fig. 9 and Fig.10 As shown, an external "command" input can be used to instruct the controller 90 for a particular input / output port arrangement, as desired. In accordance with the principles of the present invention, each individual LC microcell 88 is individually addressable, and commands to the controller 90 are used to determine the particular LC microcell to be activated and the particular voltage (V 90 or V 0 ).

[0047] The principles of the present invention described above with respect to reconfiguring a twin 1xN WSS into a 1x2N WSS may also be used to reconfigure a twin 1xN WSS into a "quaternary" arrangement of a 1x(N / 2) WSS.

[0048] Those skilled in the art will recognize that the present invention is not limited to what is specifically shown and described above. On the contrary, the scope of the present invention includes the combination and sub-combination of the various features described above and variations and modifications of the present invention, which will occur to those skilled in the art after reading the above description and are not in the prior art.

Claims

1. A reconfigurable port interface for a wavelength selective switch (WSS), the reconfigurable port interface comprising: a plurality of optical signal coupling ports, at least one port for receiving an optical input signal and at least one port for sending an optical output signal; a birefringent walk-off plate disposed adjacent to the plurality of optical signal coupling ports, the birefringent walk-off plate performing spatial separation of orthogonal polarizations of the optical input signals and spatial recombination of parallel polarizations of the optical output signals; and a polarization rotator array positioned to intercept optical signals exiting and entering the birefringent walk-off plate, the polarization rotator array comprising: a plurality of liquid crystal microcells, each individual liquid crystal microcell being individually addressable by a control voltage input to provide one of: a 90° polarization rotation via a first applied voltage and a 0° polarization rotation via a second applied voltage; and a plurality of control electrodes coupled to the plurality of liquid crystal microcells in a one-to-one relationship, wherein a first selected plurality of groups of adjacent liquid crystal microcells are maintained at the first applied voltage to construct a 90° polarization window, and a second selected plurality of groups of adjacent liquid crystal microcells are maintained at a second applied voltage to construct a 0° polarization window, Wherein, the window reconstruction command defining the specific port arrangement of the wavelength selective switch includes the spacing between adjacent ports and the window size, wherein the window size includes the number of individual liquid crystal microunits to be grouped together to form a window, and the specific port arrangement is a reconfigurable port arrangement controlled by the multiple control electrodes.

2. The reconfigurable port interface according to claim 1, wherein: A first group of adjacent liquid crystal microcells is controlled to present a 90° polarization rotation to form a first window with a defined size and position for accommodating a first sub-beam of a propagating input signal or an output signal, while a second group of adjacent liquid crystal microcells near the first group is controlled to present a 0° polarization to form a second window with the defined size for accommodating a second sub-beam of the propagating input signal or the output signal.

3. The reconfigurable port interface according to claim 1, wherein: The interface also includes: A window configuration controller is coupled to the plurality of control electrodes and, in response to the window reconfiguration commands, determines the identification of individual liquid crystal microcells required to provide a 90° polarization rotation or a 0° polarization rotation for a given arrangement of the plurality of optical signal coupling ports.

4. The reconfigurable port interface according to claim 3, wherein: The polarization rotator array is configured to associate a pair of transmission windows with each optical coupling port, the pair of transmission windows comprising a first transmission window formed by a first group of adjacent liquid crystal microcells controlled to exhibit a 90° polarization rotation and a second transmission window formed by a second group of adjacent liquid crystal microcells controlled to exhibit a 0° polarization rotation.

5. The reconfigurable port interface according to claim 3, wherein: The window reconfiguration command also includes a port array size.

6. The reconfigurable port interface according to claim 1, wherein: Each liquid crystal microcell has the same width W, where W is less than 10 micrometers.

7. The reconfigurable port interface according to claim 5, wherein: The liquid crystal microcell width W is in the range of 5-8 microns.

8. A reconfigurable polarization rotator array, comprising: a plurality of liquid crystal microcells, each individual liquid crystal microcell being individually addressable by a control voltage input to provide one of a 90° polarization rotation and a 0° polarization rotation, the plurality of liquid crystal microcells all exhibiting a same width W of less than 10 microns; a plurality of control electrodes coupled to the plurality of liquid crystal microcells in a one-to-one relationship; as well as a window configuration controller coupled to the plurality of control electrodes and, in response to a window reconfiguration command, applying an appropriate voltage to each of the plurality of control electrodes to define a selected plurality of groups of adjacent liquid crystal microcells to form a transmission window and provide a predetermined polarization rotation to a light beam passing through the transmission window, Wherein, the window reconstruction command defining a specific port arrangement of the wavelength selective switch includes the spacing between adjacent ports and the window size, wherein the window size includes the number of individual liquid crystal microunits to be grouped together to form a window, and the specific port arrangement is a reconfigurable port arrangement controlled by the multiple control electrodes.

9. The reconfigurable polarization rotator array according to claim 8, wherein: The window reconfiguration command also includes a port array size.

10. A reconfigurable wavelength selective switch, comprising: A plurality of ports, N in number, for receiving and transmitting optical signals of predetermined wavelengths; a switch engine for controlling connections between input ports and output ports within the plurality of ports, the number of which is N; and A reconfigurable port interface is provided between the plurality of ports (N in number) and the switch engine, the reconfigurable port interface comprising: a birefringent walk-off plate disposed adjacent the plurality of ports, the birefringent walk-off plate performing spatial separation of orthogonal polarizations of optical input signals and spatial recombination of parallel polarizations of optical output signals; and a polarization rotator array positioned to intercept optical signals exiting and entering the birefringent walk-off plate, the polarization rotator array comprising a plurality of liquid crystal microcells and a plurality of control electrodes, each individual liquid crystal microcell being individually addressable by a control voltage input to provide one of: a 90° polarization rotation via a first applied voltage and a 0° polarization rotation via a second applied voltage, the plurality of control electrodes being coupled to the plurality of liquid crystal microcells in a one-to-one relationship, wherein a first selected plurality of groups of adjacent liquid crystal microcells are held at the first applied voltage to construct a 90° polarization window, and a second selected plurality of groups of adjacent liquid crystal microcells are held at the second applied voltage to construct a 0° polarization window, Wherein, the window reconstruction command defining the specific port arrangement of the reconfigurable wavelength selective switch includes the spacing between adjacent ports and the window size, wherein the window size includes the number of individual liquid crystal microunits to be grouped together to form a window, and the specific port arrangement is a reconfigurable port arrangement controlled by the multiple control electrodes.

11. The reconfigurable wavelength selective switch according to claim 10, wherein: The interface also includes: a window configuration controller coupled to the plurality of control electrodes and, in response to the window reconfiguration command, determines the identification of individual liquid crystal microcells required to provide a 90° polarization rotation or a 0° polarization rotation for a given arrangement of a plurality of optical signal coupling ports of the reconfigurable port interface.

12. The reconfigurable wavelength selective switch according to claim 10, wherein: The reconfigurable port interface is controlled to define the plurality of ports, N in number, as twin WSSs, each WSS having N / 2 ports.

13. The reconfigurable wavelength selective switch according to claim 10, wherein: The reconfigurable port interface is controlled to define the plurality of ports, numbered N, as a 1xN WSS having a single input port and a plurality of selectable output ports, numbered (N-1).

14. The reconfigurable wavelength selective switch according to claim 10, wherein: The reconfigurable port interface is controlled to define the plurality of ports, the number of which is N, as an Nx1 WSS having a single output port and a plurality of selectable input ports, the number of which is (N-1).

15. The reconfigurable wavelength selective switch according to claim 10, wherein: The reconfigurable port interface is controlled to define the plurality of ports, N in number, as a set of four independent wavelength selective switches, each wavelength selective switch having N / 4 ports.

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