Silicon-based liquid crystal and wavelength selective switch

Abstract

The invention relates to the technical field of optical communication, in particular to a liquid crystal on silicon and a wavelength selective switch, and aims to provide an LCoS device capable of realizing polarization independence and reducing the problem of secondary crosstalk caused by deflection unconverted residues, so that the application of the LCoS can be ensured. According to the LCoS, an extra phase is pre-added in a dispersion direction based on a metasurface design or a phase film and other structures; through the pre-added phase, high-frequency deflection is formed for the polarization unconverted light, or the scattering phase deviates the energy of the polarization unconverted light from the crosstalk level, so that the crosstalk of the polarization unconverted light to the polarization converted light is avoided, and the suppression of the secondary crosstalk in the port direction is realized.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and in particular to a silicon-based liquid crystal and a wavelength selective switch. Background Art

[0002] Liquid crystal is a kind of material that has both the fluidity of liquid substances and the orderliness of crystal substances, and is anisotropic in physical properties. Optically, by adjusting the electric field applied to the liquid crystal molecules, the orientation of the liquid crystal molecules can be changed, and its refractive index for light with polarization parallel to the orientation of the liquid crystal molecules can be changed, so that voltage-controlled phase modulation can be achieved.

[0003] A commonly used architecture is to sandwich the liquid crystal between a layer of indium tin oxide (ITO) electrode and a layer of metal reflector pixel array to form a sandwich-like structure. The silicon-based array liquid crystal phase modulator based on this architecture is generally referred to as liquid crystal on silicon (LCoS) or LCoS-spatial light modulation (SLM). The optical wavelength selective switch based on LCoS is one of the most core components of the wavelength selective switch (WSS), which can realize the wavelength crossover function. The important step to realize this function is to modulate the two-dimensional array of the LCoS liquid crystal screen. LCoS is composed of millions of pixels. The main way to modulate LCoS is to adjust the phase of different pixels of LCoS, and the phase of the pixel depends on the size of the voltage loaded on the pixel.

[0004] In the practical application of WSS, it is usually necessary to modulate the polarization in both directions. The current solution is to decompose a beam of light with any polarization direction into two perpendicular polarization beams through a polarization beam splitter, and then use a half-wave plate (HWP) or a quarter-wave plate (QWP) plus a reflector to turn the polarization of one beam to be parallel to the other beam, and then incident on the LCoS. However, this method adds additional components, which makes the optical path complicated, hindering the evolution of WSS to large ports and small sizes, and also increases the cost of the system. Therefore, how to realize a polarization-independent LCoS device is of great research significance. Summary of the invention

[0005] The embodiments of the present application provide a silicon-based liquid crystal and a wavelength selective switch, which are used to provide an LCoS device that can achieve polarization independence and can also reduce the secondary crosstalk problem caused by the residual deflection that is not converted, thereby ensuring the application of LCoS.

[0006] In the first aspect, a silicon-based liquid crystal is provided, which is applied to a wavelength selection switch. The silicon-based liquid crystal includes: a first panel and a second panel arranged opposite to each other; a liquid crystal layer located between the first panel and the second panel; a driving circuit for generating an electric field to control the deflection of the liquid crystal in the liquid crystal layer; and two layers of alignment films, the two layers of alignment films are respectively located on opposite sides of the liquid crystal layer; a reflector layer, located above the first panel, for reflecting the light beam; a polarization conversion layer, located above the reflector and below the two layers of alignment layers, for performing polarization conversion on the light beam after passing through the liquid crystal layer; wherein the polarization conversion layer includes at least two types of supersurface microstructures, and the at least two types of supersurface microstructures are periodically arranged alternately.

[0007] By including at least two types of microstructures in the metasurface structure, different modulation effects on polarization-converted light and polarization-unconverted light can be achieved, so that the polarization-unconverted light passing through the LCoS can deviate from the polarization-converted light, thereby reducing the secondary crosstalk effect of the polarization-unconverted light on the polarization-converted light.

[0008] In one possible design, the silicon-based liquid crystal has N pixel areas, the reflector layer includes N reflectors corresponding one-to-one to the N pixel areas, and N is a positive integer; the N reflectors correspond one-to-one to the N groups of metasurface microstructures; wherein a group of metasurface microstructures includes a class of metasurface microstructures.

[0009] Through this design, more accurate processing of polarization-unconverted light can be achieved, thereby better reducing the secondary crosstalk effect of polarization-unconverted light on polarization-converted light.

[0010] In one possible design, the light beam after polarization conversion includes polarization-converted light and polarization-unconverted light; the silicon-based liquid crystal has N pixel areas, the driving circuit has a first voltage control value in the first pixel area, and has a second voltage control value in the second pixel area; the second pixel area is an adjacent pixel area of ​​the first pixel; the first voltage control value and the second voltage control value are determined based on the phase modulation values ​​of the first type of metasurface microstructure and the second type of metasurface structure.

[0011] By using the phase compensation of the phase modulation by the liquid crystal layer, the polarization converted light can be restored to the phase at the time of incidence after passing through the LCoS, thereby reducing the impact on the polarization converted light.

[0012] Based on the above design, in a possible embodiment, the first voltage control value includes phase compensation for a first phase modulation value; wherein the first phase modulation value is used to indicate the phase modulation value of the first type of microstructure to the polarization converted light; the second voltage control value includes phase compensation for a second phase modulation value; wherein the second phase modulation value is used to indicate the phase modulation value of the second type of microstructure to the polarization converted light.

[0013] Based on the above design, in another possible embodiment, the polarization conversion layer includes two types of metasurface microstructures; the second voltage control value includes phase compensation for a third phase modulation value; wherein the third phase modulation value is used to indicate the sum of the first phase modulation value of the polarization conversion light by the first type of microstructure and the second phase modulation value of the polarization conversion light by the second type of microstructure.

[0014] In a possible design, the supersurface microstructure is an elliptical cylindrical microstructure, and different types of supersurface microstructures have different sizes.

[0015] In the second aspect, another silicon-based liquid crystal is also provided, which is applied to a wavelength selection switch. The silicon-based liquid crystal includes: a first panel and a second panel arranged opposite to each other; a liquid crystal layer located between the first panel and the second panel; a driving circuit for generating an electric field to control the deflection of the liquid crystal in the liquid crystal layer; and two layers of alignment films, the two layers of alignment films are respectively located on opposite sides of the liquid crystal layer; a reflector layer, located above the first panel, for reflecting the light beam; a polarization conversion layer, located above the reflector and below the two layers of alignment layers, for performing polarization conversion on the light beam after passing through the liquid crystal layer; wherein the light beam after polarization conversion includes polarization-converted light and polarization-unconverted light; a phase film layer, located above the reflector, for performing the same phase modulation on the polarization-converted light and the polarization-unconverted light.

[0016] In the silicon-based liquid crystal, considering that the polarization-unconverted light has twice the optical path length relative to the polarization-converted light, an additional pre-phase in the dispersion direction is introduced through the phase film, and then the phase is compensated by the phase diagram, so that the secondary crosstalk caused by the polarization-unconverted light can be reduced. In addition, the structure has the characteristics of easy processing.

[0017] In a possible design, the phase film is a high-frequency phase film. In a possible design, the high-frequency phase film is a sinusoidal grating phase film, a triangle wave phase film, or a square wave phase film.

[0018] In a third aspect, an embodiment of the present application further provides a wavelength selection switch, which may include a silicon-based liquid crystal as introduced in the first aspect or any possible design in the first aspect, or may include a silicon-based liquid crystal as introduced in the second aspect or any possible design in the second aspect.

[0019] Since the wavelength selection switch in the third aspect includes the silicon-based liquid crystals of each design in the first aspect, it also has the technical effects brought by each design in the first aspect, or includes the silicon-based liquid crystals of each design in the second aspect, it also has the technical effects brought by each design in the second aspect, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of a wavelength selective switch structure applicable to an embodiment of the present application;

[0021] Figure 2 for Figure 1 A schematic diagram of the structure of the liquid crystal on silicon of the wavelength selective switch shown;

[0022] Figure 3 for Figure 2 Schematic diagram of liquid crystal rotation in silicon-based liquid crystal shown;

[0023] Figure 4 It is a schematic diagram of the structure of a silicon-based liquid crystal;

[0024] Figure 5 is a schematic diagram of the structure of another type of silicon-based liquid crystal;

[0025] Figure 6 A possible system architecture diagram of WSS provided in an embodiment of the present application;

[0026] Figure 7 One of the structural schematic diagrams of a PI-LCoS provided in an embodiment of the present application;

[0027] Figure 8 A schematic diagram of the structure of a metasurface structure provided in an embodiment of the present application;

[0028] Fig. 9 A second structural diagram of a PI-LCoS provided in an embodiment of the present application;

[0029] Fig.10 A third structural diagram of a PI-LCoS provided in an embodiment of the present application;

[0030] Fig.11 This is a fourth structural diagram of a PI-LCoS provided in an embodiment of the present application. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described in detail below in conjunction with the drawings in the embodiments of the present application.

[0032] LCoS has a wide range of application scenarios. It is not only one of the key technologies for display devices such as projectors and projection TVs, but also plays a very important role as a phase modulation device in application scenarios such as WSS. Especially with the development of optical network communications, the application market of WSS is gradually increasing, and the demand for lower cost and higher performance WSS is becoming more and more urgent.

[0033] As an example, Figure 1 The structure diagram of a wavelength selective switch (WSS) 100 applicable to an embodiment of the present application is shown. The wavelength selective switch 100 can be applied to a reconfigurable optical add-drop multiplexer (ROADM). The wavelength selective switch 100 includes a liquid crystal on silicon 1, and the liquid crystal on silicon 1 (LCoS) serves as an optical switching engine of the wavelength selective switch 100, and is used to achieve a phase modulation effect to independently control the diffraction deflection direction of light beams incident to different regions of the liquid crystal on silicon 1.

[0034] The wavelength selective switch 100 may further include at least one input port 101 (e.g., input optical fiber), at least one output port group corresponding to the input port 101, a polarization conversion unit 103, a wavelength division multiplexer 104 (e.g., a diffraction grating), and a lens 105. Each output port group includes at least two output ports 102 (e.g., output optical fibers). Figure 1 As shown, the beam transmission path in the figure is a reversible path. The multi-wavelength signal forms an input beam through the input port 101. The input beam is converted into a linear polarized light corresponding to the working polarization state of the silicon-based liquid crystal 1 by the polarization conversion unit 103. The linear polarized light is incident on the wavelength division multiplexer 104, and the wavelength division multiplexer 104 disperses each wavelength at different angles, and then the dispersed light beam is converted into a parallel light beam by the lens 105 to be incident on different positions of the silicon-based liquid crystal 1. Light beams of different wavelengths are focused on different areas of the silicon-based liquid crystal 1 and are diffracted and deflected. The diffracted light beams are restored to their original polarization states by the polarization conversion unit 103, and light beams of different wavelengths are coupled to their respective target output ports 102. Since the diffraction and deflection directions of light beams of different wavelengths are individually controlled by different areas on the silicon-based liquid crystal 1, the silicon-based liquid crystal 1 can switch any wavelength combination to any of the output ports 102. Among them, the wavelength selection switch 100 also includes a reflector 106, which is used to reflect light.

[0035] In addition to the above structural units, the wavelength selective switch may also include a controller or a processor for selectively configuring a bit sequence to drive pixels in a silicon-based liquid crystal, thereby controlling the optical output in the port direction. The controller or processor may be implemented by hardware, software, firmware, or any combination thereof. For example, the controller or processor may utilize one or more processors, digital signal processors, application specific integrated circuits, field programmable gate arrays, discrete logic, or any combination thereof. When the controller or processor is partially implemented in software, the device may store computer executable instructions for the software in a suitable, non-transitory computer-readable storage medium and may use one or more processors in hardware to execute the instructions to run the technical solution of the present invention.

[0036] Figure 2 A physical structure diagram of the above-mentioned silicon-based liquid crystal is provided. The silicon-based liquid crystal can be applied to the wavelength selection switch 100. The silicon-based liquid crystal 1 can be used to diffract an incident light beam in a linear polarization state to form a deflected light beam. The silicon-based liquid crystal 1 is a polarization-sensitive device that can only work in one polarization direction (i.e., the working polarization direction), and the polarization direction of the incident light beam is the working polarization direction of the silicon-based liquid crystal 1. The silicon-based liquid crystal 1 includes a first panel 11, a second panel 12, a liquid crystal layer 13, a driving circuit 14, and two layers of alignment films 15. The first panel 11 and the second panel 12 are arranged opposite to each other. The first panel 11 is parallel to the second panel 12. The first panel 11 can be a silicon backplane panel, and the second panel 12 can be a transparent glass cover plate. The liquid crystal layer 13 is located between the first panel 11 and the second panel 12, and contains many liquid crystal molecules, which will deflect when a voltage is applied to the electrode layer. The driving circuit 14 is used to generate an electric field to control the deflection of the liquid crystal in the liquid crystal layer 13. Two alignment films 15 are respectively located on opposite sides of the liquid crystal layer 13. That is, one of the alignment films 15 is located between the liquid crystal layer 13 and the first panel 11, and the other alignment film 15 is located between the liquid crystal layer 13 and the second panel 12. The alignment films 15 are used to make the liquid crystal in the liquid crystal layer 13 have an initial orientation.

[0037] As an example, the driving circuit 14 includes a first electrode layer 141 and a second electrode layer 142. The first electrode layer 141 is located between the liquid crystal layer 13 and the first panel 11. The second electrode layer 142 is located between the liquid crystal layer 13 and the second panel 12. The first electrode layer 141 and the second electrode layer 142 can be indium tin oxide (ITO) electrode layers. Specifically, the first electrode layer 141 is formed on the side of the first panel 11 facing the liquid crystal layer 13, the second electrode layer 142 is formed on the side of the second panel 12 facing the liquid crystal layer 13, and the two layers of the alignment film 15 are located between the first electrode layer 141 and the second electrode layer 142. When the first electrode layer 141 and the second electrode layer 142 are powered on, the liquid crystal deflection in the liquid crystal layer 13 is controlled by a vertically-aligned (VA) driving mode.

[0038] Please refer to Figure 2 and Figure 3 When a voltage is applied to the first electrode layer 141 and the second electrode layer 142 to form an electric field between the first electrode layer 141 and the second electrode layer 142, the liquid crystal in the liquid crystal layer 13 will deflect (the deflection plane is Figure 3 XY plane, i.e., a plane perpendicular to the first panel 11), wherein X represents the wavelength direction (also referred to as the "dispersion direction" in the present embodiment), Y represents the phase period 2π (or can also be understood as the direction of the optical path), and Z represents the port direction (or can also be referred to as the "switching direction", "exchange direction", etc.). In one example, the liquid crystal in the liquid crystal layer 13 is composed of Figure 3 The state deflection of the middle left figure is Figure 3 The state in the middle right figure, that is, the long axis of the liquid crystal is deflected from a direction roughly parallel to the first panel 11 to a direction roughly perpendicular to the first panel 11, and this application is explained using this as an example. In another embodiment, the long axis of the liquid crystal in the liquid crystal layer 13 may also be deflected from a direction roughly perpendicular to the first panel 11 to a direction roughly parallel to the first panel 11. Since liquid crystal is a birefringent material, the deflection of the liquid crystal will bring about a change in the equivalent refractive index, thereby achieving a phase modulation effect. At the same time, the deflection angle of the liquid crystal molecules is related to the magnitude of the voltage applied to the first electrode layer 141 and the second electrode layer 142, so different phase modulation amounts can be achieved by applying different voltages, which is also the principle of phase modulation of pixels in a two-dimensional array of silicon-based liquid crystals.

[0039] Limited by the optoelectronic properties of the liquid crystal itself, general LCoS devices are polarization-dependent, and only light with a polarization direction parallel to the orientation of the liquid crystal molecules can be modulated. However, in the actual application of WSS, we need to modulate polarization in both directions. The current solution is mainly to decompose a beam of light with any polarization direction into two perpendicular polarization beams through a polarization beam splitter, and then use a half-wave plate (HWP) or a quarter-wave plate (QWP) plus a reflector to turn the polarization of one of the beams parallel to the other, and then incident on the LCoS. This method adds additional devices, which makes the optical path complicated; it hinders the evolution of WSS to large ports and small sizes; at the same time, it also increases the cost of the system. Therefore, how to realize a polarization-independent LCoS device has become a very critical issue.

[0040] In one possible implementation, Figure 4 This is a schematic diagram of the physical structure of another type of silicon-based liquid crystal. The structure of ordinary LCoS is generally to add liquid crystal to a layer of ITO electrode and a layer of metal reflector pixel array to form a Figure 4 The sandwich structure shown in FIG. 1 is another possible embodiment. Figure 5 is a schematic diagram of the physical structure of another silicon-based liquid crystal, Figure 4 The difference between the schematic diagram of liquid crystal on silicon shown is that Figure 4 The silicon-based liquid crystal shown includes a sub-wavelength grating structure or a super surface structure, or a polymer, added above the reflector layer to form a QWP polarization conversion layer, and the optical axis of the QWP is 45 degrees to the LCoS orientation direction. Figure 5 In the structure shown, the incident polarized light will be converted into perpendicularly polarized light by the QWP after reflection.

[0041] As a possible example, when the light that the liquid crystal can modulate is s light, the incident light with polarization s can be modulated when passing through the liquid crystal, but after being converted into p light by the QWP polarization conversion layer, the reflected p light cannot be modulated by the liquid crystal; it can be understood that the optical path of this incident light is modulated into a phase modulation of one times the height of the liquid crystal.

[0042] As another possible example, when the light that the liquid crystal can modulate is s-light, the incident light with polarization p cannot be modulated when passing through the liquid crystal, but after being converted into s-light by the QWP polarization conversion layer, the reflected s-light can be modulated by the liquid crystal; it can be understood that the optical path modulation of this incident light is also a phase modulation of one times the height of the liquid crystal. It can be understood that no matter what polarization state the incident light has, when it passes through the liquid crystal Figure 5 The LCoS structure shown will experience a phase modulation of one times the liquid crystal height, thereby achieving polarization-independent phase modulation.

[0043] However, due to factors such as micro-nanostructure processing, wavelength bandwidth required by WSS and micro-nanostructure design, Figure 5 The actual QWP polarization conversion layer in the LCoS structure shown cannot completely convert the incident light into reflected light with vertical polarization, but there is a part of the polarization that is not converted. This part of the residual amount will introduce a secondary crosstalk problem in the application of WSS. For example, when the light that the liquid crystal can modulate is s light, and the incident light is also s light, after passing through the QWP polarization conversion layer, there may be some polarized but unconverted s light that can still be modulated by the liquid crystal after reflection. The optical path of this part of the s light is modulated into a phase modulation of twice the height of the liquid crystal, resulting in a secondary crosstalk problem.

[0044] In view of this, an embodiment of the present application provides an LCoS. In the LCoS, an additional phase (referred to as "pre-added phase" in the embodiment of the present application) is pre-added in the dispersion direction based on a metasurface design or a phase film or other structure; through this pre-added phase, a high-frequency deflection or scattering phase is formed for the polarization-unconverted light to deviate its energy from the crosstalk level, thereby avoiding the crosstalk of the polarization-unconverted light to the polarization-converted light, thereby achieving the suppression of the secondary crosstalk in the port direction.

[0045] Figure 6 A possible system architecture diagram of WSS provided for an embodiment of the present application. The system may include at least: a fiber array (FA), two dispersion direction lenses, a port direction main lens, a grating and a polarization-independent (PI)-LCoS. Among them, the light beam coming out of the FA port is shaped by the dispersion direction lens unit and then incident on the PI-LCoS. In addition, light of different wavelengths in the light beam can be split by the grating and thus hit different areas on the PI-LCoS; then, the corresponding phase diagram is loaded on each area on the PI-LCoS to achieve that the light of a certain wavelength channel is deflected to the designated port after passing through the port direction main lens, thereby achieving wavelength switching.

[0046] In some other possible embodiments, in some traditional WSS structures, an additional polarization splitter component is added to the right of FA or the left of PI-LCoS to first decompose the incident polarized light into two beams of orthogonal polarization, and then adjust the polarization of the two beams of light to be parallel to the liquid crystal orientation through HWP or QWP plus a reflector. Then, the two beams of light are incident on different areas of PI-LCoS, so that the modulation of the two polarizations can be achieved. However, when the WSS structure is introduced, Figure 6After the PI-LCoS shown in the figure, the WSS architecture removes the polarization splitter component and can more effectively utilize PI-LCoS to achieve a lower cost and smaller size WSS structure. As the core component in ROADM, WSS can dynamically add or drop service wavelengths through remote reconfiguration without manual fiber adjustment, thereby achieving wavelength reconstruction of the wavelength division multiplexing (WDM) system and flexible scheduling of services. This is of great significance for realizing all-optical networking, flexible scheduling of ultra-large capacity services, and fully transparent transmission of services.

[0047] The PI-LCoS provided in the embodiment of the present application can be applied to a WSS without a polarization splitter component, for example Figure 6 In the WSS system architecture shown.

[0048] In an optional implementation, the pre-phase in the dispersion direction of PI-LCoS proposed in the embodiment of the present application can be realized through the structure of the metasurface polarization conversion layer; wherein the metasurface structure provided in the embodiment of the present application can be composed of at least two microstructures, so that the deviation of the polarization unconverted light can be realized through the gradient phase, thereby reducing the secondary crosstalk. For example, the contents of the following embodiments 1 and 2 are introduced.

[0049] In another optional implementation, the pre-phase in the dispersion direction of PI-LCoS proposed in the embodiment of the present application can be realized by the structure of the phase film; wherein, since the polarization unconverted light has a double optical path and the polarization converted light has a single optical path, the polarization unconverted light can be deviated by the phase film, thereby reducing the secondary crosstalk. For example, the content introduced in the following embodiment 3.

[0050] Embodiment 1

[0051] Figure 7 A schematic diagram of the structure of a PI-LCoS provided in an embodiment of the present application. The PI-LCoS may include at least: glass, an ITO electrode, two alignment layers, a liquid crystal layer, a reflector, a silicon-based backplane, and a metasurface polarization conversion layer 701; it can be understood that the metasurface polarization conversion layer 701 is used to represent Figure 5 The QWP polarization conversion layer shown adopts a metasurface structure.

[0052] The glass surface has a layer of ITO electrode transparent to the selected wavelength. The ITO electrode and a metal reflector electrode of a pixel array above the silicon-based backplane can form a pair of voltage-driven electrodes acting on the liquid crystal; and the liquid crystal layer is sandwiched between the pair of electrodes after being aligned by the alignment layer. In some possible embodiments, by adjusting the voltage value of each pixel in the pixel array, the liquid crystal above each pixel position can be oriented accordingly, so that the phase adjustment of each pixel can be achieved; wherein each pixel corresponds to a reflector.

[0053] The metasurface polarization conversion layer 701 is located above the metal mirrors of the pixel array. Figure 7 The metasurface polarization conversion layer 701 shown may adopt a metasurface structure, which may have the following phase constraints:

[0054] (1) Supersurface structures can include two types of microstructures, as well as Figure 7 The periodic arrangement of ABAB is shown.

[0055] In some possible embodiments, the metasurface on each column of pixel array in the dispersion direction is the same type A microstructure, or the same type B microstructure; it can also be understood that the system period is 2 pixel widths in the dispersion direction.

[0056] In other embodiments, the correspondence between the metasurface structure in the metasurface polarization conversion layer 701 and the pixel array is not limited.

[0057] By using a metasurface structure including two types of microstructures, different modulation effects on polarization-converted light and polarization-unconverted light can be achieved, so that the polarization-unconverted light passing through the LCoS can deviate from the polarization-converted light, thereby reducing the secondary crosstalk effect of the polarization-unconverted light on the polarization-converted light.

[0058] (2) For both Type A and Type B metasurface microstructures, the optical axis forms an angle of 45 degrees with the liquid crystal direction, so that the two components of the incident light with polarization parallel and perpendicular to the optical axis of the metasurface have a phase difference of about 180 degrees after being reflected, and most of the incident light is converted into another polarization perpendicular to the optical axis and then reflected, thereby achieving the effect of polarization conversion.

[0059] (3) The phase modulation of reflected light by the type A metasurface microstructure and the type B metasurface microstructure is different. Figure 7 As shown, after the incident light is polarized, it includes polarization-converted light and polarization-unconverted light.

[0060] For example, the phase modulation of polarization-converted light by the type A metasurface microstructure can be expressed as The phase modulation of the type A metasurface microstructure for polarization-unconverted light can be expressed as The phase modulation of polarization-converted light by the type B metasurface microstructure can be expressed as The phase modulation of the type B metasurface microstructure for polarization-unconverted light can be expressed as In an optional embodiment, the phase difference of the polarization converted light may satisfy And, the phase difference of the polarization unconverted light can satisfy

[0061] (4) Considering that the phase modulation of polarization-converted light by the type A metasurface microstructure can be expressed as The polarization conversion light can be compensated by voltage control of the liquid crystal.

[0062] In an optional embodiment, the voltage control of the liquid crystal in the pixel column where the type A metasurface structure is located can be expressed as: In order to achieve phase compensation for the phase modulation of the type A metasurface microstructure. Similarly, the voltage control of the liquid crystal by the pixel column where the type B metasurface structure is located can be expressed as To achieve phase compensation for the phase modulation of the Class B metasurface microstructure.

[0063] Exemplarily, polarization-converted light passes through Figure 7 After the metasurface polarization conversion layer 701 is shown, it can be expressed as the following formula 1-1:

[0064]

[0065] For example, polarization-unconverted light passes through Figure 7 After the metasurface polarization conversion layer 701 is shown, it can be expressed as the following formula 1-2:

[0066]

[0067] According to the above formulas 1-1 and 1-2, the phase of the polarization-converted light after passing through the metasurface polarization conversion layer 701 can be restored to The total phase modulation of the polarization-unconverted light is It can be understood that for polarization-unconverted light, the The phase is changed to achieve the goal of deviating the energy of the crosstalk order from the zero order in the dispersion direction, realizing the deviation of the polarization-unconverted light relative to the polarization-converted light, thereby reducing the secondary crosstalk.

[0068] In another optional embodiment, the voltage control of the liquid crystal by the pixel column where the type A metasurface structure is located can also be expressed as At this time, the voltage control of the liquid crystal by the pixel column where the type B metasurface structure is located can be expressed as It can be understood that when the selected metasurface structure satisfies There is no need to perform phase compensation and the phase diagram can be loaded normally.

[0069] In some possible embodiments, Figure 8 A schematic diagram of a super surface structure provided in an embodiment of the present application. For example, the super surface structure may be in an elliptical cylindrical shape and made of silicon material.

[0070] Optionally, the period of the Class A metasurface microstructure may be d=850nm, the height may be h=400nm, the angle between the optical axis and the X direction may be 45°, and there may be four structures in the Y direction forming a class and located on the same column of the pixel array. In a possible embodiment, the major and minor axes of the Class A structure may be implemented as: r1=140nm, r2=270nm.

[0071] Optionally, the period of the Class B metasurface microstructure can also be d=850nm, the height can also be h=400nm, the angle between the optical axis and the X direction is 45°, and there can be four structures in the Y direction that form a class and are located on the same column of the pixel array. In a possible embodiment, the major and minor axes of the Class B structure can be implemented as: r1=170nm, r2=250nm.

[0072] from Figure 8 It can be seen that the metasurface structure can be periodically arranged in the Y direction by multiple type A microstructures and multiple type B microstructures, and can be extended in the X direction.

[0073] In the above optional embodiment, the electromagnetic simulation results of the phase difference of the type A metasurface microstructure and the type B metasurface microstructure for polarization converted light are: The electromagnetic simulation results for the phase difference of the polarization-unconverted light are:

[0074] In addition, according to the results of electromagnetic simulation, even without liquid crystal compensation, the additional insertion loss introduced by this structure is only about 0.4dB, but the isolation of the secondary crosstalk can be improved by more than 30dB, exceeding the 25dB isolation requirement for WSS applications; when liquid crystal compensation is added, the insertion loss can be further optimized to about 0.2dB.

[0075] It should be noted that Figure 8 This is only an example of a possible metasurface structure. The number of Type A microstructures and Type B microstructures can be determined based on the period, microstructure size, LCoS size, etc., and this application does not limit this.

[0076] Through the super surface structure provided in the first embodiment above, by Figure 8 The metasurface structure shown is parameter-designed, and a periodic arrangement is formed by using Class A and Class B metasurface structures. The Class A and Class B metasurface structures have different modulation effects on polarization-converted light and polarization-unconverted light, thereby effectively reducing the secondary crosstalk caused by the presence of polarization-unconverted light.

[0077] Embodiment 2

[0078] Fig. 9 A schematic diagram of the structure of a PI-LCoS provided in an embodiment of the present application. The PI-LCoS may include at least: glass, an ITO electrode, two alignment layers, a liquid crystal layer, a reflector, a silicon-based backplane, and a metasurface polarization conversion layer 901; it can be understood that the metasurface polarization conversion layer 901 is used to represent Figure 5 The QWP polarization conversion layer shown uses a metasurface structure. Figure 7 The same or similar points will not be repeated here; the difference is that the metasurface polarization conversion layer 901 can also be used as follows Fig. 9 The microstructures shown include four types of microstructures, namely, type A, type B, type C and type D, and are arranged in a periodic manner. It can be understood that in this embodiment, every 4 columns of pixels form a period in the dispersion direction.

[0079] The phase constraints of the metasurface polarization conversion layer 901 may include: the phase difference of the four types of metasurface structures ABCD for polarization-converted light is less than 0.5π; and the phase of the polarization-unconverted light forms a gradient from 0 to 2π, which can also be understood as the blazed grating phase in the dispersion direction, thereby achieving the deflection of the polarization-unconverted light to the negative first order in the dispersion direction to reduce the secondary crosstalk.

[0080] It should be noted that although Figure 7 The supersurface structure includes two types of microstructures: Fig. 9 It is introduced that the metasurface structure includes four types of microstructures. The embodiments of the present application do not limit the number of categories of metasurface structures, for example, more types of microstructures may be included, such as three, five or more types. In addition, the phase of the polarized unconverted light provided in the embodiments of the present application may not be limited to the blazed grating phase, but may also be other high-frequency phase changes such as the sinusoidal grating phase, so as to achieve the effect of deviating the polarized unconverted light energy from the zero order of the dispersion direction.

[0081] Embodiment 3

[0082] Fig.10 A schematic diagram of the structure of a PI-LCoS provided in an embodiment of the present application. The PI-LCoS may include the following Figure 5In the various structures shown, a phase film can also be inserted at any position above the metal reflector of the pixel array, for example Fig.10 The example shown is that the phase film is inserted between the glass and the ITO electrode, or for example, the phase film can also be inserted above the reflector (or below the QWP polarization conversion layer), above the QWP polarization conversion layer, below the ITO electrode, etc. Among them, the phase modulation of the phase film on the polarization converted light and the polarization unconverted light is the same, assuming that the phase modulation of the phase film on the polarization converted light is expressed as The phase modulation of the phase film on the polarization unconverted light is expressed as but In addition, the structure has the following phase constraints: the phase in the dispersion direction is approximately continuously changing and high-frequency; and the phase difference between adjacent pixels in each column should be less than 0.5π to facilitate liquid crystal compensation.

[0083] Considering that the light beam passes through the phase film twice, the phase that the liquid crystal needs to compensate should be twice the phase added by the phase film. Therefore, the control phase added by the liquid crystal can be adjusted as shown in the following formula 2-1:

[0084]

[0085] It can be understood that at this time, the total phase modulation of the polarization converted light is still The total phase modulation for the polarization unconverted light becomes as shown in the following formula 2-2:

[0086]

[0087] It can also be understood that there is still residual in the dispersion direction The high-frequency phase of the polarization-unconverted light can be deviated from the polarization-converted light, reducing the influence of the polarization-unconverted light on the polarization-converted light, thereby reducing the secondary crosstalk.

[0088] In a possible embodiment, the phase film 1001 may be a sinusoidal grating phase film. Fig.11 A schematic diagram of the structure of a PI-LCoS provided in an embodiment of the present application. Fig.11 The sinusoidal grating phase film shown has high transmittance for the selected wavelength, which can be expressed as follows:

[0089] Formula 3-1:

[0090]

[0091] Here, T is larger than the size of a pixel.

[0092] The liquid crystal is controlled by voltage, and the adjusted phase is shown in the following formula 3-2:

[0093]

[0094] Based on the above formula 3-1 and formula 3-2, and considering that the light beam passes through the phase film twice, the total modulation phase of the polarization converted light after passing through the liquid crystal with the phase shown in formula 3-2 and passing through the sinusoidal grating phase film twice as shown in formula 3-1 is

[0095] Based on the above formula 3-1 and the above formula 3-2, and considering that the light beam passes through the phase film twice, the total phase modulation of the polarization unconverted light is It can be understood that for polarization-unconverted light, a sinusoidal grating phase in the dispersion direction is still retained on the basis of secondary crosstalk, so as to deviate the energy of the crosstalk order from the zero order in the dispersion direction, realize the deviation of polarization-unconverted light relative to polarization-converted light, and thus reduce the secondary crosstalk.

[0096] It should be noted that, in some other possible embodiments, the phase film 1001 may also be a grating phase film in other shapes such as a triangle wave or a square wave and having a continuously changing high-frequency phase.

[0097] It should also be noted that the QWP polarization conversion layer in Example 3 can adopt a supersurface structure such as that in Example 1 or Example 2, or a module that can realize the polarization conversion function by adopting a supersurface structure with a uniform microstructure, a sub-wavelength grating structure or a polymer, etc., and the present application does not limit this.

[0098] The structure provided in the third embodiment can reduce the secondary crosstalk caused by the unconverted polarization light by introducing an additional pre-phase in the dispersion direction through the sinusoidal grating phase film and then compensating the phase with the phase diagram. In addition, the structure is easy to process.

[0099] The present application also provides a WSS, which at least includes the silicon-based liquid crystals introduced in the above embodiments. In an optional embodiment, the WSS may also include an input port, an output port, a polarization conversion unit, a wavelength division multiplexer, a lens, a reflector, etc. In another optional embodiment, the WSS may also include FA, a dispersion direction lens unit, a port direction main lens, a grating, etc.

[0100] An embodiment of the present application also provides an optical communication device, including the silicon-based liquid crystal introduced in the aforementioned embodiments.

[0101] It should be noted that in the description of the present application, "at least one" refers to one or more, wherein a plurality refers to two or more. In view of this, in the embodiments of the present application, "a plurality" may also be understood as "at least two". "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / ", unless otherwise specified, generally indicates that the associated objects before and after are in an "or" relationship. In addition, it should be understood that in the description of the present application, words such as "first" and "second" are only used for the purpose of distinguishing descriptions, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order.

[0102] It should be noted that in the embodiments of the present application, "coupling" can be understood as electrical connection, and the coupling of two elements can be direct or indirect coupling between the two elements. For example, A and B are connected, which can be either direct coupling between A and B, or indirect coupling between A and B through one or more other elements, such as A and B coupling, or A and C are directly coupled, C and B are directly coupled, and A and B are coupled through C. In some scenarios, "coupling" can also be understood as connection.

[0103] In the various embodiments of the present application, unless otherwise specified or provided for in any logical conflict, the terms and / or descriptions between the different embodiments are consistent and may be referenced to each other, and the technical features in the different embodiments may be combined to form new embodiments according to their inherent logical relationships.

[0104] In this application, the word "exemplary" is used to mean an example, illustration or description. Any embodiment or design described as "exemplary" in this application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Alternatively, it can be understood that the use of the word "exemplary" is intended to present concepts in a specific way and does not constitute a limitation on this application.

[0105] It is to be understood that the various digital numbers involved in the present application are only for the convenience of description and are not intended to limit the scope of the embodiments of the present application. The size of the sequence number of the above-mentioned processes does not mean the order of execution, and the order of execution of each process should be determined by its function and inherent logic. In addition, the terms "including" and "having" and any deformation thereof are intended to cover non-exclusive inclusions, for example, including a series of steps or units. Methods, systems, products or equipment are not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0106] Although the present application has been described in conjunction with specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the spirit and scope of the present application. Accordingly, the present specification and the accompanying drawings are merely exemplary illustrations of the schemes defined by the appended claims, and are deemed to have covered any and all modifications, variations, combinations or equivalents within the scope of the present application.

[0107] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the embodiments of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A silicon-based liquid crystal, applied to a wavelength selective switch, characterized in that: The silicon-based liquid crystal comprises: A first panel and a second panel arranged opposite to each other; a liquid crystal layer, located between the first panel and the second panel; a driving circuit for generating an electric field to control the deflection of liquid crystal in the liquid crystal layer; and Two layers of alignment films, the two layers of alignment films are respectively located on opposite sides of the liquid crystal layer; A reflector layer, located above the first panel, for reflecting the light beam; A polarization conversion layer is located above the reflector and below the two alignment layers, and is used to perform polarization conversion on the light beam after passing through the liquid crystal layer; wherein the polarization conversion layer includes at least two types of supersurface microstructures, and the at least two types of supersurface microstructures are periodically alternately arranged.

2. The silicon-based liquid crystal according to claim 1, characterized in that: The silicon-based liquid crystal has N pixel areas, and the reflector layer includes N reflectors corresponding to the N pixel areas one by one, where N is a positive integer; The N reflectors correspond one-to-one to the N groups of metasurface microstructures; wherein a group of metasurface microstructures includes a type of metasurface microstructures.

3. The silicon-based liquid crystal according to claim 1 or 2, characterized in that: The light beam after polarization conversion includes polarization-converted light and polarization-unconverted light; The silicon-based liquid crystal has N pixel areas, the driving circuit has a first voltage control value in the first pixel area and a second voltage control value in the second pixel area; the second pixel area is an adjacent pixel area of ​​the first pixel; The first voltage control value and the second voltage control value are determined based on the phase modulation values ​​of the first type of metasurface microstructure and the second type of metasurface structure.

4. The liquid crystal on silicon according to claim 3, characterized in that: The first voltage control value includes a phase compensation for a first phase modulation value; wherein the first phase modulation value is used to indicate a phase modulation value of the first type of microstructure on the polarization converted light; The second voltage control value includes a phase compensation for a second phase modulation value; wherein the second phase modulation value is used to indicate a phase modulation value of the second type of microstructure on the polarization converted light.

5. The silicon-based liquid crystal according to claim 3, characterized in that: The polarization conversion layer includes two types of metasurface microstructures; The second voltage control value includes a phase compensation for a third phase modulation value; wherein the third phase modulation value is used to indicate the sum of a first phase modulation value of the polarization converted light by the first type of microstructure and a second phase modulation value of the polarization converted light by the second type of microstructure.

6. The liquid crystal on silicon according to any one of claims 1 to 5, characterized in that: The super surface microstructure is an elliptical columnar microstructure, and different types of super surface microstructures have different sizes.

7. A silicon-based liquid crystal used in a wavelength selective switch, characterized in that: The silicon-based liquid crystal comprises: A first panel and a second panel arranged opposite to each other; a liquid crystal layer, located between the first panel and the second panel; a driving circuit for generating an electric field to control the deflection of liquid crystal in the liquid crystal layer; and Two layers of alignment films, the two layers of alignment films are respectively located on opposite sides of the liquid crystal layer; A reflector layer, located above the first panel, for reflecting the light beam; A polarization conversion layer, located above the reflector and below the two alignment layers, for performing polarization conversion on the light beam after passing through the liquid crystal layer; wherein the light beam after polarization conversion includes polarization-converted light and polarization-unconverted light; The phase film layer is located above the reflector and is used to perform the same phase modulation on the polarization-converted light and the polarization-unconverted light.

8. The liquid crystal on silicon according to claim 7, characterized in that: The phase film is a high-frequency phase film.

9. The liquid crystal on silicon according to claim 8, characterized in that: The high-frequency phase film is a sinusoidal grating phase film, a triangle wave phase film, or a square wave phase film.

10. A wavelength selective switch, characterized in that: include: The liquid crystal on silicon according to any one of claims 1 to 6 or the liquid crystal on silicon according to any one of claims 7 to 9.

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