Metasurface structures, phase-type liquid-crystal-on-silicon panel, and wavelength selective switch

Abstract

A metasurface structure (300) comprising a plurality of metasurface units (330). Each metasurface unit (330) comprises a first nano micro-pillar (311) and a second nano micro-pillar (312), the first nano micro-pillar (311) being an axially symmetric and centrally symmetric pattern, and the second nano micro-pillar (312) being an axially symmetric and centrally symmetric pattern; the vertical projection of each first nano micro-column (311) on a base layer (310) is a first projection (301), and the vertical projection of each second nano micro-pillar (312) on the base layer (310) is a second projection (302), the symmetry axis (11) of the first projection (301) and the symmetry axis (12) of the second projection (302) being symmetrical about a third axis (13); the included angle between the third axis (13) and the dispersion direction of a phase-type liquid-crystal-on-silicon panel (200) is 35°-55°. When light is incident on the metasurface units (330), the wavefront of polarization-converted light reflected by the metasurface units (330) is flat, while the wavefront of light which is not converted by polarization is perturbed, thus reducing the component of the light which is not converted by polarization entering a system optical path, and reducing system crosstalk. Further disclosed are a phase-type liquid-crystal-on-silicon panel (200) and a wavelength selective switch (100). The requirements of the phase-type liquid-crystal-on-silicon panel (200) for manufacturing precision are reduced, and the wavelength selective switch (100) exhibits a high degree of isolation and low crosstalk.

Description

Metasurface structures, phase-type silicon-based liquid crystal panels, wavelength selective switches

[0001] This application claims priority to Chinese patent application filed on May 6, 2024, with application number 202410554180.1 and entitled "Metasurface Structure, Phase-Type Silicon-Based Liquid Crystal Panel, Wavelength Selective Switch", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of optical device technology, and in particular to a metasurface structure, a phase-type silicon-based liquid crystal panel, and a wavelength selective switch. Background Technology

[0003] Liquid crystal on silicon (LCOS) is a type of reflective liquid crystal device with a very small matrix size. This type of liquid crystal device is fabricated on a silicon chip using complementary metal oxide semiconductor (CMOS) technology.

[0004] LCOS can be applied to optical devices that utilize phase modulation of optical signals, such as wavelength selective switches (WSS) or dynamic gain flatness filters (DGFF). The working principle of LCOS is to apply different voltages to different pixels. Due to the birefringence effect of liquid crystals, different voltages correspond to different phase delays, thus forming a grating-like structure. An LCOS consists of a stacked backplane, a periodic metastructure, and a liquid crystal layer. The periodic metastructure functions as a polarization converter, acting equivalent to an ultrathin half-wave plate, thus giving the LCOS device polarization independence. Currently, periodic metasurface structures suffer from crosstalk issues. Summary of the Invention

[0005] This application provides a metasurface structure, a phase-type silicon-based liquid crystal panel, and a wavelength selective switch. The aim is to improve the crosstalk problem of metasurface structures.

[0006] To achieve the above objectives, this application adopts the following technical solution.

[0007] In a first aspect, embodiments of this application provide a metasurface structure. The metasurface structure includes a substrate layer, a filling layer, and a plurality of metasurface units. The filling layer is stacked on top of the substrate layer. The plurality of metasurface units are located between the substrate layer and the filling layer. Each metasurface unit includes a plurality of first nanopillars and a plurality of second nanopillars arranged sequentially; the vertical projection of the first nanopillars on the substrate is a first projection; the first projection is a non-centrosymmetric figure symmetrical about a first axis; the vertical projection of the second nanopillars on the substrate is a second projection; the second projection is a non-centrosymmetric figure symmetrical about a second axis; the first axis and the second axis are not parallel, and the first projection and the second projection are symmetrical about a third axis. Thus, when a light beam is transmitted to the metasurface unit, since the first axis and the second axis are not parallel, and since the first projection and the second projection are symmetrical about the third axis, the first nanopillars and the second nanopillars can be regarded as structures with inconsistent orientations on the substrate. The first and second nanopillars can perturb the light beam transmitted to the metasurface unit, reducing the unpolarized light component in the light beam reflected by the metasurface structure and entering the working optical path (e.g., into the grating). This reduces the interference of unpolarized light on polarized light and lowers the crosstalk of the metasurface structure, thereby reducing the crosstalk of the phase-type silicon-based liquid crystal panel.

[0008] In conjunction with the first aspect, in some feasible ways, the angle between the first axis and the second axis is less than or equal to 20°. Thus, the first and second nanopillars are oriented close to each other on the substrate. In other words, the first and second nanopillars have the same shape and extend in similar directions. The metasurface composed of these two nanopillars can achieve polarization conversion and reduction of crosstalk.

[0009] In conjunction with the first aspect, in some feasible ways, the first projection is rectangular or elliptical. The first nanopillar, projected as rectangular or elliptical, allows the metasurface structure to eliminate the unpolarized light component and reduce crosstalk between the unpolarized light and the polarized light.

[0010] In conjunction with the first aspect, in some feasible ways, the first projection is a quadrilateral with an arc-shaped transition at the intersection of its two sides. The first nanopillar, projected as a quadrilateral with an arc-shaped transition at the intersection of its two sides, enables the metasurface structure to eliminate the component of unpolarized light and reduce crosstalk between unpolarized light and polarized light.

[0011] In conjunction with the first aspect, in some feasible ways, the phase of multiple metasurface units decreases sequentially for polarized light with the polarization direction of the first direction. Thus, the multiple metasurface units can construct a phase gradient for the phase-polarized converted light, separating the polarized light reflected by the metasurface structure with a polarization direction orthogonal to the first direction from the polarized light with the polarization direction of the first direction. This further reduces the component of unpolarized light in the beam reflected by the metasurface structure and entering the working optical path (e.g., into the grating).

[0012] Secondly, embodiments of this application provide a metasurface structure. The metasurface structure includes a substrate layer, a filling layer, and a plurality of metasurface units. The filling layer is stacked with the substrate layer. The plurality of metasurface units are located between the substrate layer and the filling layer; each metasurface unit includes a plurality of first nanopillars and a plurality of second nanopillars arranged along the dispersion direction of the metasurface structure. The dimensions of the first nanopillars along a first direction are L1 and L2, respectively; the dimensions of the first nanopillars along the first direction are L3 and L4, respectively; the first and second directions are perpendicular to each other and both are perpendicular to the thickness direction of the substrate; L1 is greater than L3, and L4 is less than L2. Thus, the dimension of the first nanopillar along one direction is greater than the dimension of the second nanopillar along that direction, and the dimension of the first nanopillar along another direction is smaller than the dimension of the second nanopillar along that direction. When the light beam is transmitted to the metasurface unit, the metasurface unit, which includes multiple first nanopillars and multiple second nanopillars, can reduce the component of unpolarized light, reduce the interference of unpolarized light on polarized light, and reduce the crosstalk of metasurface structure 3.

[0013] In conjunction with the second aspect, in some feasible ways, the first nanopillar is cuboid in shape, and the second nanopillar is cuboid in shape.

[0014] In conjunction with the second aspect, in some feasible ways, the phase of multiple metasurface units for polarized light with the polarization direction of the first direction decreases sequentially.

[0015] Thirdly, embodiments of this application provide a metasurface structure. The metasurface structure includes a substrate layer, a filling layer, and multiple metasurface units. The filling layer is stacked on top of the substrate layer. The multiple metasurface units are located between the substrate layer and the filling layer. The metasurface units include a first array group and a second array group arranged sequentially; wherein the period of the first array group is less than λ0 / n, the period of the second array group is less than λ0 / n, and the periods of the first array group and the second array group are different; λ0 is the vacuum wavelength, and n is the refractive index of the filling layer. Thus, the metasurface units include two array groups with different arrangement periods. This can reduce the component of unpolarized light, reduce the interference of unpolarized light on polarized light, and reduce signal crosstalk.

[0016] In conjunction with the third aspect, in some feasible ways, along the dispersion direction, the phase of multiple metasurface units for polarized light with the polarization direction of the first direction decreases sequentially.

[0017] Fourthly, embodiments of this application provide a phase-type silicon-based liquid crystal panel. The phase-type silicon-based liquid crystal panel includes a liquid crystal layer and any of the metasurface structures provided in the first aspect. The filling layer is located between the substrate layer and the liquid crystal layer; the angle between the third axis and the dispersion direction of the phase-type silicon-based liquid crystal panel is 35° to 55°. Thus, the phase-type silicon-based liquid crystal panel can effectively suppress unconverted polarization light. When the phase-type silicon-based liquid crystal panel is used in a wavelength-selective switch, it can improve the isolation of the wavelength-selective switch and reduce crosstalk of the optical signal.

[0018] Fifthly, embodiments of this application provide a phase-type silicon-based liquid crystal panel. The phase-type silicon-based liquid crystal panel includes a liquid crystal layer and any of the metasurface structures provided in the second aspect above; the filling layer is located between the substrate layer and the liquid crystal layer; the angle between the first direction and the dispersion direction of the phase-type silicon-based liquid crystal panel is 35° to 55°. Thus, the phase-type silicon-based liquid crystal panel can effectively suppress unconverted polarization light. When the phase-type silicon-based liquid crystal panel is used in a wavelength-selective switch, it can improve the isolation of the wavelength-selective switch and reduce crosstalk of the optical signal.

[0019] Sixthly, embodiments of this application provide a phase-type silicon-based liquid crystal panel. The phase-type silicon-based liquid crystal panel includes a liquid crystal layer and any of the metasurface structures provided in the third aspect above; the filling layer is located between the substrate layer and the liquid crystal layer.

[0020] In a seventh aspect, embodiments of this application provide a wavelength selective switch. The wavelength selective switch includes: a grating and any one of the phase-type silicon-based liquid crystal panels provided in the fourth, fifth, and sixth aspects described above; the grating is used to emit multiple single-wavelength lights, and the phase-type silicon-based liquid crystal panel is used to deflect the multiple single-wavelength lights at an angle. Because the phase-type silicon-based liquid crystal panel has low crosstalk, the processing accuracy requirements of the phase-type silicon-based liquid crystal panel are reduced, the processing difficulty is lowered, and the processing tolerance is improved. The wavelength selective switch including this phase-type silicon-based liquid crystal panel has the advantages of high isolation and low crosstalk. Attached Figure Description

[0021] Figure 1a is a schematic diagram of the structure of an optical communication network provided in an embodiment of this application.

[0022] Figure 1b is a schematic diagram of the structure of multiple wavelength selection switches connected together.

[0023] Figure 2 is a schematic diagram of a wavelength selective switch.

[0024] Figure 3 is a schematic diagram of a phase-type silicon-based liquid crystal panel.

[0025] Figure 4a is a schematic diagram of the metasurface structure provided in the embodiment of this application.

[0026] Figure 4b is an optical path diagram of a phase-type silicon-based liquid crystal panel provided in an embodiment of this application.

[0027] Figure 5 is a schematic diagram of a metasurface unit and a substrate provided in an embodiment of this application.

[0028] Figure 6 is a schematic diagram of another metasurface unit and substrate provided in an embodiment of this application.

[0029] Figure 7 is a schematic diagram of another metasurface unit and substrate provided in an embodiment of this application.

[0030] Figure 8 is a schematic diagram of another metasurface unit and substrate provided in an embodiment of this application.

[0031] Figure 9 is a schematic diagram of another metasurface unit and substrate provided in an embodiment of this application.

[0032] Figure 10 is a schematic diagram of the structure of a first array group and a second array group provided in an embodiment of this application.

[0033] In the diagram: 10-Optical communication network; 20-Optical network equipment; 100-Wavelength selective switch; 002-Fiber optic array; 003-Microlens; 004-Curved mirror; 005-Lens; 006-Triangular prism; 007-Reflective grating; 200-Phase-type silicon-based liquid crystal panel; 220-First electrode layer; 230-Second electrode layer; 300-Metasurface structure; 310-Substrate layer; 320-Filling layer; 330-Metasurface unit; 311-First nanopillar; 312-Second nanopillar; 301-First projection; 302-Second projection; 11-First axis; 12-Second axis; 13-Third axis; 401-First nanopillar; 402-Second nanopillar; 510-First array group; 520-Second array group; 501-First nanopillar; 502-Second nanopillar; 210-Liquid crystal layer. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the application will now be described in further detail with reference to the accompanying drawings.

[0035] In the following description, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0036] Furthermore, in this application, directional terms such as "upper" and "lower" are defined relative to the orientation of the components shown in the accompanying drawings. It should be understood that these directional terms are relative concepts, used for relative description and clarification, and can change accordingly depending on the orientation of the components in the accompanying drawings.

[0037] Figure 1a is a schematic diagram of the structure of an optical communication network 10 provided in an embodiment of this application. Referring to Figure 1a, the optical communication network 10 includes multiple optical network devices 20. The optical network devices 20 include reconfigurable optical add-drop multiplexers (ROADMs) or optical cross-connects (OXCs), etc. The multiple optical network devices 20 are interconnected through optical channels.

[0038] The network device 20 includes a wavelength selective switch 100, through which wavelength division multiplexing (WDM) technology is implemented between multiple network devices 20. The wavelength selective switch 100 has advantages such as flexible scheduling and ultra-high capacity wavelength scheduling, playing a key role in building optical networks with ultra-high system capacity and ultra-strong node scheduling.

[0039] As shown in Figure 1b, the wavelength selection switch 100 enables wavelength scheduling across different dimensions. The wavelength selection switch 100 has the function of outputting the input wavelength from any output port, thereby enabling the optical network device 20 (as shown in Figure 1a) to configure any wavelength at any port.

[0040] This application embodiment does not limit the number of wavelength selection switches 100 in the optical network device 20. For example, the wavelength selection switches 100 in the optical network device 20 can be one, two, three, four or more.

[0041] Figure 2 is a schematic diagram of a wavelength selective switch 100. Referring to Figure 2, the wavelength selective switch 100 includes an optical fiber array 002, a microlens 003, a curved mirror 004, a lens 005, a triangular prism 006, a reflective grating 007, and a phase-type silicon-based liquid crystal panel 200, which are arranged sequentially along the light propagation path.

[0042] The fiber optic array 002 includes an optical input port and an optical output port. The light beam enters through the optical input port and sequentially passes through the fiber optic array 002, microlens 003, curved mirror 004, lens 005, triangular prism 006, reflective grating 007, and phase-type silicon liquid crystal panel 200 before returning to the optical output port. In Figure 2, the solid line represents the path of the light beam from the optical input port to the phase-type silicon liquid crystal panel 200, and the dashed line represents the path of the light beam from the phase-type silicon liquid crystal panel 200 to the optical output port.

[0043] A light beam propagates from the light input port to a microlens 003. The microlens 003 shapes the beam and converts its angle and height in a preset direction. The beam is then projected onto a curved mirror 004, which has optical power in both the dispersion direction and the preset direction. After collimation, the beam is projected onto a lens 005. Lens 005 compensates for beam aberrations and projects the beam onto a triangular prism 006. The triangular prism 006 disperses the beam and projects it onto a reflective grating 007. The reflective grating 007 splits the beam at different frequencies to obtain multiple single-wavelength beams. The reflective grating 007 guides these single-wavelength beams sequentially through the triangular prism 006 and lens 005 to the curved mirror 004 in different directions. The curved mirror 004 reflects these single-wavelength beams again, focusing them onto the same focal plane. The curved mirror 004 and lens 005 can also be Fourier lenses. The phase-type silicon-based liquid crystal panel 200 deflects the aforementioned multiple single-wavelength lights at different angles, and then transmits the deflected single-wavelength lights back to the optical output port of the fiber array 002 along a reverse path. Thus, single-wavelength signal light of any wavelength in the beam incident from the optical input port can be output from any optical output port. This facilitates the configuration of the signal output from the optical output port. The wavelength selection switch 100 has the advantages of being polarization-independent and having a simple structure.

[0044] Figure 2 illustrates a split-type wavelength selective switch 100. In some embodiments, the wavelength selective switch 100 can be a single integrated component. For example, the reflective grating 007, the curved reflector 004, and the fiber array 002 are all connected to the light-transmitting body. This can reduce the sealing requirements of the wavelength selective switch 100.

[0045] Figure 3 is a schematic diagram of a phase-type silicon-based liquid crystal panel 200. As shown in Figure 3, the phase-type silicon-based liquid crystal panel 200 includes a liquid crystal layer 210 and a metasurface structure 300; the liquid crystal layer 210 and the metasurface structure 300 are stacked.

[0046] In some embodiments, the phase-type silicon-based liquid crystal panel 200 may further include a first electrode layer 220 and a second electrode layer 230. The first electrode layer 220, the liquid crystal layer 210, the metasurface structure 300 layer, and the second electrode layer 230 are stacked.

[0047] This application does not limit the materials of the first electrode layer 220 and the second electrode layer 230. For example, the material of the first electrode layer 220 can be a transparent conductive material, such as indium tin oxide (ITO) or indium zinc oxide (IZO). The first electrode layer 220 allows light to pass through and be transmitted to the liquid crystal layer 210. The material of the second electrode layer 230 can be a metallic material, such as aluminum (Al) or magnesium (MG). The transmittance of the second electrode layer 230 is very low. The first electrode layer 220 and the second electrode layer 230 provide an electric field for the liquid crystal layer 210. By adjusting the magnitude of the electric field, the refractive index of the liquid crystal layer 210 is changed, thereby changing the phase of the single-wavelength light incident on the liquid crystal layer 210.

[0048] The liquid crystal layer 210 is used to change the phase of the light beam incident on the liquid crystal layer 210. The metasurface structure 300 modulates the polarization conversion of light.

[0049] The phase-type silicon-based liquid crystal panel 200 has a dispersion direction, also known as the wavelength direction. During light propagation in the phase-type silicon-based liquid crystal panel 200, the direction of the optical axis is perpendicular to the dispersion direction. The optical axis refers to the centerline of the light beam or the axis of symmetry of the optical system.

[0050] In the example of Figure 3, the metasurface structure 300 performs polarization conversion on the light beam. For instance, when a light beam polarized in the second direction is incident on the phase-type silicon-based liquid crystal panel 200, the metasurface structure 300 converts the light beam polarized in the second direction into a light beam polarized in the first direction. The light beam polarized in the first direction is then transmitted to the grating 007 (as shown in Figure 2). The first and second directions are perpendicular to each other.

[0051] The polarization direction, specifically the first direction, can be either P (parallel) or S (senkrecht) polarization. For example, the metasurface structure 300 converts a beam of light in the P (parallel) polarization state into a beam of light in the S (senkrecht) polarization state. Alternatively, it converts a beam of light in the S polarization state into a P polarization state. The metasurface unit 330 exhibits polarization-independent properties. The aforementioned S polarization state indicates that the polarization direction is perpendicular to the incident plane. The P polarization state indicates that the polarization direction is parallel to the incident plane.

[0052] A portion of the light beam with a polarization direction in the second direction may not be converted by the metasurface structure 300. In other words, the polarization state of a portion of the light beam incident on the phase-type silicon liquid crystal panel 200 is not converted by the metasurface structure 300. In the embodiments of this application, the light beam reflected by the metasurface unit 330 with the same polarization state as the light beam incident on the metasurface unit 330 is defined as "unconverted polarization light". For example, both the light beam incident on the metasurface unit 330 and the light beam reflected by the metasurface unit 330 may be in an S-polarization state, or both may be in a P-polarization state.

[0053] Accordingly, a beam whose polarization state is perpendicular to that of the beam incident on the metasurface unit 330 is defined as a "polarization-converted beam". For example, the beam incident on the metasurface unit 330 is in a P-polarization state and the beam reflected by the metasurface unit 330 is in an S-polarization state, or the beam incident on the metasurface unit 330 is in an S-polarization state and the beam reflected by the metasurface unit 330 is in a P-polarization state.

[0054] Figure 4a is a schematic diagram of the metasurface structure 300 provided in an embodiment of this application. Referring to Figure 4a, the metasurface structure 300 includes: a substrate layer 310, a filling layer 320, and a plurality of metasurface units 330. The substrate layer 310 and the filling layer 320 are stacked; the plurality of metasurface units 330 are located between the substrate layer 310 and the filling layer 320. The dashed lines in Figure 4a are for illustrating the relative positions of the metasurface units 330 and the substrate layer 310, and do not restrict the metasurface units 330 to be located on the surface of the filling layer 320.

[0055] In the example of Figure 4a, multiple metasurface units 330 are arranged in a periodic or superperiodic array. The period of the metasurface units 330 is subwavelength. The period of the metasurface units 330 is the same as or smaller than the operating wavelength.

[0056] In some embodiments of this application, the multiple metasurface units 330 may have the same phase for polarized light with the polarization direction of the first direction. Figure 3 shows an optical path diagram in which the multiple metasurface units 330 have the same phase for polarized light with the polarization direction of the first direction.

[0057] Figure 4b is an optical path diagram of a phase-type silicon-based liquid crystal panel 200 provided in an embodiment of this application. In Figure 4b, the phase of the polarized light with the polarization direction in the first direction is sequentially decreased by multiple metasurface units 330. The polarized light with the polarization direction in the first direction is the beam reflected back to the grating 007 by the metasurface units 330 (as shown in Figure 2). The polarized light with the polarization direction in the first direction (polarization-converted light) reflected by the metasurface units 330 is deflected by the metasurface units 330 and returns to the grating 007. The polarized light with the polarization direction in the second direction (polarization-unconverted light) reflected by the metasurface units 330 is not deflected by the metasurface units 330, and the component returning to the grating 007 is further reduced. In this way, multiple metasurface units 330 can construct a phase gradient for the phase-polarization-converted light, thereby realizing the deflection of the polarization-converted light. This can further reduce the component of the unconverted light in the beam reflected back to the grating 007 by the metasurface units 330, improving the crosstalk and insertion loss problems of the unconverted light.

[0058] For example, along the dispersion direction of the phase-type silicon-based liquid crystal panel 200 (as shown in Figure 3), the phases of the plurality of metasurface units 330 are sequentially increased from 0 to 2π.

[0059] Taking type N of metasurface unit 330 as an example, along the dispersion direction, the phase of the m-th type of metasurface unit 330 satisfies the following equation:

[0060] In some embodiments of this application, the phases of the plurality of metasurface units 330 may also be equal.

[0061] The filling layer 320 serves to protect the metasurface unit 330. Exemplarily, the filling layer 320 comprises a dielectric material with a low refractive index. For example, the material of the filling layer 320 may include silicon oxide, aluminum oxide, or photoresist.

[0062] For example, the surface of the filler layer 320 facing away from the base layer 310 is flat, making the surface of the metasurface structure 300 smoother and easier to bond with other components.

[0063] The substrate layer 310 assists the microstructure in achieving polarization modulation. For example, the material of the substrate layer 310 may include silicon oxide, silicon nitride, or silicon.

[0064] In some embodiments of this application, the liquid crystal layer 210 (as shown in FIG3) and the filler layer 320 are connected to the surface opposite to the substrate layer 310. For example, the surfaces of the liquid crystal layer 210 and the filler layer 320 opposite to the substrate layer 310 are bonded together with optical adhesive.

[0065] In some embodiments of this application, the liquid crystal layer 210 (as shown in FIG3) and the substrate layer 310 are connected to the surface opposite to the filler layer 320. For example, the surfaces of the liquid crystal layer 210 and the substrate layer 310 are bonded together with optical adhesive.

[0066] Figure 5 is a schematic diagram of a metasurface unit 330 and a substrate layer 310 provided in an embodiment of this application. Only one metasurface unit 330 is shown in Figure 5. Referring to Figure 5, the metasurface unit 330 includes multiple first nanopillars 311 and multiple second nanopillars 312. The multiple first nanopillars 311 and multiple second nanopillars 312 are arranged sequentially.

[0067] The vertical projection of the first nanopillar 311 onto the substrate 310 is called the first projection 301. The first projection 301 is a non-centrosymmetric figure symmetrical about the first axis 11. The aforementioned "vertical projection of the first nanopillar 311 onto the substrate 310" refers to the projection of the first nanopillar 311 onto the substrate 310 along the thickness direction of the substrate 310. The rest of the descriptions in the text are similar.

[0068] The aforementioned "multiple first nanopillars 311 and multiple second nanopillars 312 arranged in sequence" means that multiple first nanopillars 311 are arranged first, and then multiple second nanopillars 312 are arranged. The same applies to the sequential arrangement of other positions in this paper.

[0069] The vertical projection of the second nanopillar 312 onto the substrate layer 310 is the second projection 302; the second projection 302 is a non-centrosymmetric figure symmetrical about the second axis 12. The first axis 11 and the second axis 12 are not parallel, and the first projection 301 and the second projection 302 are symmetrical about the third axis 13. Thus, the first nanopillar 311 and the second nanopillar 312 can be considered as structures with the same shape but different orientations.

[0070] Thus, when the light beam is transmitted to the metasurface unit 330, since the first axis 11 and the second axis 12 are not parallel, and since the first projection 301 and the second projection 302 are symmetrical about the third axis 13, the first nanopillars 311 and the second nanopillars 312 can be regarded as structures with inconsistent orientations on the substrate layer 310. The combination of the first nanopillars 311 and the second nanopillars 312 responds to the incident light in such a way that the phase of the polarization-converted light reflected is flat, while the phase of the unconverted light is not flat. This prevents the unconverted component from returning to the system optical path, i.e., from returning to the grating 007 (as shown in Figure 2). In this way, the unconverted component of the light beam reflected back to the grating 007 by the metasurface unit 330 (as shown in Figure 2) is eliminated, reducing the interference of the unconverted light on the polarization-converted light, thereby reducing the crosstalk of the phase-type silicon-based liquid crystal panel 200. Because the component of the unconverted light is reduced, the polarization-converted light can be better utilized to reduce insertion loss.

[0071] Clearly, the phase-type silicon-based liquid crystal panel including the metasurface unit 330 can effectively improve crosstalk and insertion loss problems. It can suppress unconverted polarization light to -30dB while reducing the insertion loss of the phase-type silicon-based liquid crystal panel.

[0072] The aforementioned "component of unpolarized light" refers to the ratio of the energy of the unpolarized light to the energy of the beam reflected by the metasurface unit 330. Similarly, the "component of polarized light" refers to the ratio of the energy of the polarized light to the energy of the beam reflected by the metasurface unit 330.

[0073] In some embodiments of this application, the included angle α between the first axis 11 and the second axis 12 is less than or equal to 20°. Exemplarily, the included angle α between the first axis 11 and the second axis 12 can be 0.5°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 12°, 15°, 18°, or 20°, etc. Thus, the first nanopillar 311 and the second nanopillar 312 are positioned close to each other on the substrate layer 310. In other words, the first nanopillar 311 and the second nanopillar 312 have the same shape and extend in similar directions. This allows for the deflection of polarization-converted light.

[0074] The first nanopillar 311 comprises a dielectric material with a high refractive index. For example, the material of the first nanopillar 311 is amorphous silicon, silicon nitride, or titanium oxide. The material of the second nanopillar 312 is the same as that of the first nanopillar 311.

[0075] In the example of Figure 5, multiple first nanopillars 311 are arrayed. The multiple first nanopillars 311 are arranged in columns, with each column containing multiple first nanopillars 311. The arrangement positions of the first nanopillars 311 are the same between adjacent columns.

[0076] In the example of Figure 5, the distance between two adjacent first nanopillars 311 located in the same column is s1, and the distance between two adjacent first nanopillars 311 located in the same row is s2. s1 and s2 can be the same or different. s1 or s2 can also be referred to as the period of the first nanopillars 311.

[0077] Similarly, the distance between two adjacent second nanopillars 312 located in the same column is s1, and the distance between two adjacent second nanopillars 312 located in the same row is s2. In other words, in the example of Figure 5, the period of the first nanopillar 311 and the period of the second nanopillar 312 are equal.

[0078] Similarly, multiple second nanopillars 312 are arrayed. The multiple second nanopillars 312 are arranged in columns, with each column containing multiple second nanopillars 312. The arrangement of the second nanopillars 312 in adjacent columns is identical.

[0079] In the example of Figure 5, the distance between two adjacent second nanopillars 312 located in the same column is d1, and the distance between two adjacent second nanopillars 312 located in the same row is d2. d1 and d2 can be the same or different. d1 can also be referred to as the period of the second nanopillars 312.

[0080] The embodiments of this application do not limit the dimensions of the first nanopillar 311 along the thickness direction of the substrate layer 310, nor do the embodiments of this application limit the dimensions of the second nanopillar 312 along the thickness direction of the substrate layer 310.

[0081] In the embodiments of this application, the first projection 301 and the second projection 302 have multiple shape options. In the example of Figure 5, the first projection 301 is rectangular, and the second projection 302 is also rectangular. A rectangle is an axially symmetric shape and a non-centrosymmetric shape. The first nanopillar 311 is cuboid, and the second nanopillar 312 is cuboid. The long side of the first nanopillar 311 is parallel to the first axis 11, and the long side of the second nanopillar 312 is parallel to the second axis 12. The long side directions of the first nanopillar 311 and the second nanopillar 312 are different. This can eliminate the component of unpolarized light and reduce crosstalk between unpolarized light and polarized light.

[0082] Figure 6 is a schematic diagram of another metasurface unit 330 and substrate layer 310 provided in an embodiment of this application. The difference between Figure 6 and Figure 5 lies in the different shapes of the first nanopillar 311 and the second nanopillar 312. In the example of Figure 6, the first projection 301 is elliptical, and the second projection 302 is also elliptical. The major axis of the first projection 301 and the major axis of the second projection 302 are the same, but their extension directions are different. The minor axis of the first projection 301 and the minor axis of the second projection 302 are the same, but their extension directions are different.

[0083] In the example of Figure 6, the angle between the major axis of the first nanopillar 311 and the major axis of the second nanopillar 312 is greater than 0 and less than or equal to 20°. The major axes of the first nanopillar 311 and the second nanopillar 312 are symmetrical about the third axis 13. In other embodiments, the minor axes of the first nanopillar 311 and the second nanopillar 312 are symmetrical about the third axis 13.

[0084] The metasurface unit 330 in Figure 6 can also eliminate the component of unpolarized light, reduce the interference of unpolarized light on polarized light, and reduce the crosstalk of metasurface structure 300.

[0085] Similarly, in the embodiment shown in Figure 6 where the phase of polarized light with the polarization direction in the first direction is successively decreased by multiple metasurface units 330, the multiple metasurface units 330 can construct a phase gradient for the phase-polarized light, thereby achieving the deflection of the polarized light. This can further reduce the component of unpolarized light in the beam reflected back to grating 007 by the metasurface units 330, improving the crosstalk and insertion loss problems of unpolarized light.

[0086] Figure 7 is a schematic diagram of another metasurface unit 330 and substrate layer 310 provided in an embodiment of this application. The difference between Figure 7 and Figure 5 lies in the different shapes of the first nanopillar 311 and the second nanopillar 312. In the example of Figure 7, the first projection 301 is a quadrilateral with an arc-shaped transition at the intersection of its two sides. In other words, in Figure 7, the first projection 301 can be considered as a quadrilateral with chamfered corners. For example, the first projection 301 is a rectangle with an arc-shaped transition at the intersection of its two sides.

[0087] Similarly, the metasurface unit 330 in the example of Figure 7 can also eliminate the component of unpolarized light, reduce the interference of unpolarized light on polarized light, and reduce the crosstalk of metasurface structure 300.

[0088] As described above, the phase-type silicon-based liquid crystal panel 200 includes a plurality of metasurface units 330. In embodiments where the phase-type silicon-based liquid crystal panel 200 includes the metasurface units 330 shown in FIG. 5, FIG. 6, or FIG. 7, the angle β between the third axis 13 and the dispersion direction of the phase-type silicon-based liquid crystal panel 200 is 35° to 55°. Exemplarily, the angle β between the third axis 13 and the dispersion direction of the phase-type silicon-based liquid crystal panel 200 can be 35°, 36°, 38°, 40°, 42°, 43°, 44°, or 45°. With β being 35° to 55°, for polarization-converted light, the component of unpolarized light reflected by the first nanopillar 311 and the second nanopillar 312 is relatively small. The phase-type silicon-based liquid crystal panel 200 can effectively suppress unpolarized light. When the phase-type silicon-based liquid crystal panel 200 is used for wavelength selective switching, it can improve the isolation of the wavelength selective switch and reduce crosstalk of optical signals.

[0089] In some embodiments of this application, the metasurface unit 330 may be other structures.

[0090] Figure 8 is a schematic diagram of another metasurface unit 330 and substrate layer 310 provided in an embodiment of this application. Referring to Figure 8, the metasurface unit 330 includes a plurality of first nanopillars 401 and a plurality of second nanopillars 402. The plurality of first nanopillars 401 and the plurality of second nanopillars 402 are arranged sequentially.

[0091] The first nanopillar 401 has a dimension of L1 along the first direction a and a dimension of L2 along the second direction b. The second nanopillar 402 has a dimension of L3 along the first direction a and a dimension of L4 along the second direction b. The first direction a and the second direction b are perpendicular to each other, and both the first direction a and the second direction b are perpendicular to the thickness direction of the substrate layer 310. L1 is greater than L3, and L4 is less than L2.

[0092] Thus, the dimension of the first nanopillar 401 along one direction is larger than the dimension of the second nanopillar 402 along that direction. Furthermore, the dimension of the first nanopillar 401 along another direction is smaller than the dimension of the second nanopillar 402 along that direction. When the light beam is transmitted to the metasurface unit 330, the metasurface unit 330, comprising multiple first nanopillars 401 and multiple second nanopillars 402, can deflect the polarization-converted light while simultaneously eliminating the component of the unpolarized light, reducing the interference of the unpolarized light on the polarization-converted light, and lowering the crosstalk of the metasurface structure 300.

[0093] This application does not limit the ratio of L1 to L3 in its embodiments. In some embodiments, L1 is 1.01 to 1.3 times L3. For example, L1 is 1.01, 1.02, 1.05, 1.08, 1.1, 1.15, 1.2, 1.25, or 1.3 times L3.

[0094] This application does not limit the ratio of L2 to L4 in its embodiments. In some embodiments, the ratio of L2 to L4 is 1.01 to 1.3 times. For example, L2 to L4 can be 1.01 times, 1.02 times, 1.05 times, 1.08 times, 1.1 times, 1.15 times, 1.2 times, 1.25 times, or 1.3 times.

[0095] In the embodiments of this application, L1 can be greater than L2, or less than or equal to L2. In some embodiments, L2 is 0.25 to 0.7 times L1. For example, L2 is 0.25, 0.3, 0.4, 0.5, 0.6, or 0.7 times L1, etc.

[0096] For example, the first nanopillar 401 is cuboid in shape. The dimension of the first nanopillar 401 along the first direction a is the dimension of the first nanopillar 401 along the length direction of the cuboid. The dimension of the first nanopillar 401 along the second direction b is the dimension of the first nanopillar 401 along the width direction of the cuboid.

[0097] The second nanopillar 402 is cuboid in shape. The dimension of the second nanopillar 402 along the first direction a is the dimension of the second nanopillar 402 along the length direction of the cuboid. The dimension along the second direction b is the dimension of the second nanopillar 402 along the width direction of the cuboid.

[0098] In some embodiments of this application, both the first nanopillar 401 and the second nanopillar 402 can be elliptical. For example, the major axis of the first nanopillar 401 is L1, and the minor axis is L2. The major axis of the second nanopillar 402 is L3, and the minor axis is L4.

[0099] As described above, the phase-type silicon liquid crystal panel 200 (as shown in Figure 3) includes multiple metasurface units 330. In the embodiment where the phase-type silicon liquid crystal panel 200 includes the metasurface units 330 shown in Figure 8, the angle between the first direction a and the dispersion direction of the phase-type silicon liquid crystal panel 200 is γ, and the magnitude of the angle γ is 35° to 55°. For example, the magnitude of the angle γ can be 35°, 36°, 38°, 40°, 42°, 43°, 44°, 45°, 46°, 47°, 50°, 52°, 53°, or 55°, etc. In this way, the phase-type silicon liquid crystal panel 200 can effectively suppress unconverted polarization light. When the phase-type silicon liquid crystal panel is used for wavelength selective switching, it can improve the isolation of the wavelength selective switch and reduce crosstalk of optical signals.

[0100] The array arrangement of multiple first nanopillars 401 and multiple second nanopillars 402 shown in Figure 8 are described in Figure 5 above and will not be repeated here.

[0101] In some embodiments of the phase-type silicon-based liquid crystal panel 200, including the metasurface units 330 shown in FIG. 8, the phases of the plurality of metasurface units 330 may also be equal. In some embodiments, the phases of the plurality of metasurface units 330 shown in FIG. 8 for polarized light with a polarization direction of the first direction decrease sequentially. In this way, the component of unpolarized light in the light beam reflected back to the grating 007 by the metasurface units 330 can be further reduced, improving the crosstalk problem and insertion loss problem of unpolarized light.

[0102] Figure 9 is a schematic diagram of another metasurface unit 330 and substrate layer 310 provided in an embodiment of this application. Referring to Figure 9, the metasurface unit 330 includes a first array group 510 and a second array group 520. The first array group 510 and the second array group 520 are arranged along the dispersion direction.

[0103] The period of the first array group 510 is less than λ0 / n, the period of the second array group 520 is less than λ0 / n, and the periods of the first array group 510 and the second array group 520 are different. Here, λ0 is the vacuum wavelength, and n is the refractive index of the filling layer 320 (as shown in Figure 4a). λ0 / n can be considered as the equivalent wavelength of the filling layer 320.

[0104] Thus, the metasurface unit 330 includes two array groups with different arrangement periods. This can deflect polarization-converted light while eliminating the component of unpolarized light, reducing the interference of unpolarized light on polarization-converted light, and lowering signal crosstalk.

[0105] For example, the first array group 510 includes a plurality of first nanopillars 501. The second array group 520 includes a plurality of second nanopillars 502.

[0106] The embodiments of this application do not limit the number of first nanopillars 501 in the first array group 510. The embodiments of this application do not limit the number of second nanopillars 502 in the second array group 520.

[0107] The distance between two adjacent first nanopillars 501 located in the same column is k1, and the distance between two adjacent second nanopillars 502 located in the same row is k2. k1 or k2 can also be referred to as the period of the first nanopillars 501.

[0108] The distance between two adjacent second nanopillars 502 located in the same column is r1, and the distance between two adjacent second nanopillars 502 located in the same row is r2. r1 can also be called the period of the second nanopillars 502.

[0109] In the embodiment shown in Figure 9, k2 and r2 are not equal. k1 and r1 are equal. In some embodiments, k2 is greater than r2. In some embodiments, k2 is less than r2.

[0110] Alternatively, in the embodiment of Figure 9, k2 and r2 are equal. k1 and r1 are not equal. In some embodiments, k1 is greater than r1. In some embodiments, k1 is less than r1.

[0111] In the example of Figure 9, the first nanopillar 501 and the second nanopillar 502 can have the same shape. The shape of the vertical projection of the first nanopillar 501 onto the substrate 310 is not limited. For example, the vertical projection of the first nanopillar 501 onto the substrate 310 can be an axisymmetric figure and a non-centrosymmetric figure.

[0112] In some embodiments, both the first nanopillar 501 and the second nanopillar 502 are cuboid in shape, and the length direction of the first nanopillar 501 and the length direction of the second nanopillar 502 are the same. For example, the dimensions of the first nanopillar 501 and the second nanopillar 502 can be the same.

[0113] In some embodiments, the first nanopillar 501 and the second nanopillar 502 are both elliptical, and the major axis direction of the first nanopillar 501 and the major axis direction of the second nanopillar 502 are the same.

[0114] Figure 10 is a schematic diagram of the structure of a first array group 510 and a second array group 520 provided in an embodiment of this application. The difference between Figure 10 and Figure 9 is that the periods of the first array group 510 and the second array group 520 are different.

[0115] In the embodiment of Figure 10, k2 and r2 are equal, while k1 and r1 are not equal. In some embodiments, k1 is greater than r1. In some embodiments, k1 is less than r1.

[0116] In other words, in the embodiment of FIG10, the column spacing of the plurality of first nanopillars 501 in the first array group 510 is the same as the column spacing of the plurality of second nanopillars 502 in the second array group 520. The row spacing of the plurality of first nanopillars 501 in the first array group 510 is the same as the row spacing of the plurality of second nanopillars 502 in the second array group 520. Thus, two array groups with different arrangement periods can deflect polarization-converted light while eliminating the component of unpolarized light, reducing the interference of unpolarized light on polarization-converted light, and reducing signal crosstalk.

[0117] The phase-type silicon-based liquid crystal panel 200, including the metasurface unit 330 shown in Figure 9 or Figure 10, has low crosstalk, reducing the processing accuracy requirements of the phase-type silicon-based liquid crystal panel 200, lowering the processing difficulty, and increasing the processing tolerance. The wavelength selective switch including this phase-type silicon-based liquid crystal panel 200 has the advantages of high isolation and low crosstalk.

[0118] Similarly, in some embodiments, the phase of the multiple metasurface units 330 shown in FIG9 or FIG10 for polarized light with the polarization direction in the first direction decreases sequentially. This further reduces the component of unconverted polarization light in the beam reflected back to grating 007 by the metasurface units 330, improving crosstalk and insertion loss problems related to unconverted polarization light.

[0119] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A metasurface structure, characterized in that, The metasurface structure includes: basal layer; A filler layer, wherein the filler layer is stacked with the substrate; Multiple metasurface units are located between the substrate layer and the filling layer; Each of the metasurface units includes a plurality of first nanopillars and a plurality of second nanopillars; The vertical projection of the first nanopillar onto the substrate is the first projection; the first projection is a non-centrosymmetric figure about a first axis. The vertical projection of the second nanopillar onto the substrate is the second projection; the second projection is a non-centrosymmetric figure that is symmetric about a second axis; the first axis is not parallel to the second axis, and the first projection and the second projection are symmetric about a third axis.

2. The metasurface structure according to claim 1, characterized in that, The included angle between the first axis and the second axis is less than or equal to 20°.

3. The metasurface structure according to claim 1 or 2, characterized in that, The first projection is a rectangle or an ellipse.

4. The metasurface structure according to claim 1 or 2, characterized in that, The first projection is a quadrilateral with an arc-shaped transition where the two sides intersect.

5. The metasurface structure according to any one of claims 1-4, characterized in that, The phase of the multiple metasurface units decreases sequentially for polarized light with the polarization direction in the first direction.

6. A metasurface structure, characterized in that, The metasurface structure includes: basal layer; A filler layer, wherein the filler layer is stacked with the substrate; Multiple metasurface units are located between the substrate layer and the filling layer; Each of the metasurface units includes a plurality of first nanopillars and a plurality of second nanopillars arranged in sequence; Wherein, the dimension of the first nanopillar along the first direction is L1, and the dimension along the second direction is L2; ​​the dimension of the first nanopillar along the first direction is L3, and the dimension along the second direction is L4; the first direction and the second direction are perpendicular to each other, and both the first direction and the second direction are perpendicular to the thickness direction of the substrate; L1 is greater than L3, and L4 is less than L2.

7. The metasurface structure according to claim 6, characterized in that, The first nanopillar is cuboid in shape, and the second nanopillar is cuboid in shape.

8. A metasurface structure, characterized in that, The metasurface structure includes: basal layer; A filler layer, wherein the filler layer is stacked with the substrate; Multiple metasurface units are located between the substrate layer and the filling layer; Each of the metasurface units includes a first array group and a second array group arranged in sequence; Wherein, the period of the first array group is less than λ0 / n, the period of the second array group is less than λ0 / n, and the periods of the first array group and the second array group are different; λ0 is the vacuum wavelength, and n is the refractive index of the filling layer.

9. A phase-type silicon-based liquid crystal panel, characterized in that, The phase-type silicon-based liquid crystal panel includes: Liquid crystal layer; and The metasurface structure according to any one of claims 1-5; the filling layer is located between the substrate layer and the liquid crystal layer; the angle between the third axis and the dispersion direction of the phase-type silicon-based liquid crystal panel is 35° to 55°.

10. A phase-type silicon-based liquid crystal panel, characterized in that, The phase-type silicon-based liquid crystal panel includes: Liquid crystal layer; and The metasurface structure according to claim 6 or 7; the filling layer is located between the substrate layer and the liquid crystal layer; the angle between the first direction and the dispersion direction of the phase-type silicon-based liquid crystal panel is 35° to 55°.

11. A phase-type silicon-based liquid crystal panel, characterized in that, The phase-type silicon-based liquid crystal panel includes: Liquid crystal layer; and The metasurface structure of claim 8; the filling layer is located between the substrate layer and the liquid crystal layer.

12. A wavelength selective switch, characterized in that, The wavelength selection switch comprises: a grating and a phase-type silicon-based liquid crystal panel as described in any one of claims 9-11; The grating is used to emit multiple single-wavelength lights, and the phase-type silicon-based liquid crystal panel is used to deflect the multiple single-wavelength lights at an angle.

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