Silicon-based liquid crystal devices, wavelength selective switches, and optical add-drop multiplexers

Abstract

Embodiments of the present application provide a silicon-based liquid crystal device, a wavelength selective switch and an optical add-drop multiplexer, and relate to the technical field of optical devices, and the insertion loss fluctuation of the optical signal emitted by the silicon-based liquid crystal device is small. The silicon-based liquid crystal device comprises a silicon substrate, a liquid crystal layer arranged on the silicon substrate, and at least one super surface layer arranged between the silicon substrate and the liquid crystal layer; the super surface layer comprises a plurality of unit cells arranged in an array; in a first direction, the center position of a group of unit cells in a plurality of groups of unit cells distributed continuously is non-periodically distributed in the first direction, and the first direction is the phase gradient direction of the super surface layer; and / or, the center position of the group of unit cells is non-periodically distributed in a second direction, and the second direction is perpendicular to the phase gradient direction on the super surface layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical devices, and particularly relates to a liquid crystal on silicon (LCoS) device, a wavelength selective switch and an optical add / drop multiplexer. BACKGROUND

[0002] An optical communication system is a widely used communication system. In the optical communication system, an optical add / drop multiplexer (OADM) is usually used to realize add wavelength or drop wavelength of optical signals of different wavelengths. The optical add / drop multiplexer does not need to convert optical signals into electrical signals, thereby effectively reducing the cost and power consumption of the optical communication system.

[0003] The core component of the optical add / drop multiplexer is a wavelength selective switch (WSS). The wavelength selective switch is used to receive a multiplexed optical signal formed by multiplexing optical signals of different wavelengths, and transmit optical signals of a predetermined wavelength in the multiplexed optical signal to a predetermined port, thereby realizing the function of selecting optical signals of the predetermined wavelength in the multiplexed optical signal.

[0004] At present, the wavelength selective switch based on the liquid crystal on silicon (LCoS) device is most widely used. The wavelength selective switch based on the liquid crystal on silicon device usually modulates the phase of optical signals of a predetermined wavelength by using the liquid crystal on silicon device, so that the transmission direction of the optical signals of the predetermined wavelength is changed. However, the insertion loss fluctuation of the optical signals emitted by the existing liquid crystal on silicon device is large, thereby limiting the performance of the wavelength selective switch based on the liquid crystal on silicon device. SUMMARY

[0005] Embodiments of the present application provide a liquid crystal on silicon device, a wavelength selective switch and an optical add / drop multiplexer. The insertion loss fluctuation of the optical signals emitted by the liquid crystal on silicon device is small.

[0006] In a first aspect, a silicon-based liquid crystal device is provided. The silicon-based liquid crystal device includes a silicon substrate, a liquid crystal layer disposed on the silicon substrate, and at least one metasurface layer disposed between the silicon substrate and the liquid crystal layer. In the at least one metasurface layer, any one of the metasurface layers includes an array of a plurality of unit cells. Specifically, in a first direction, the metasurface layer includes a plurality of groups of unit cells that are continuously distributed, and in one group of unit cells, the center positions of each of the unit cells are non-periodically distributed in the first direction, which is a phase gradient direction of the metasurface layer. And / or, in one group of unit cells, the center positions of each of the unit cells are non-periodically distributed in a second direction, which is perpendicular to the phase gradient direction on the metasurface layer. In the silicon-based liquid crystal device, due to the non-periodic distribution of the center positions of each of the unit cells in one group of unit cells in the first direction and / or the non-periodic distribution of the center positions of each of the unit cells in one group of unit cells in the second direction, the phase plane formed by one group of unit cells tends to be an ideal phase plane, thereby reducing the insertion loss fluctuation of the light signal emitted by the silicon-based liquid crystal device and the insertion loss fluctuation of the wavelength selective switch using the silicon-based liquid crystal device.

[0007] Optionally, the one group of unit cells includes N unit cells, and N is a positive integer greater than or equal to 2. In the one group of unit cells, the distance P between the center position of the first unit cell and the center position of the Nth unit cell in the first direction satisfies the following formula: where θ is the diffraction angle of the +1 order diffraction light of the metasurface layer, and λ is the wavelength of the incident light of the metasurface layer. In this optional manner, the distance between the center position of the first unit cell and the center position of the Nth unit cell in the one group of unit cells in the metasurface layer can be determined by the diffraction angle of the +1 order diffraction light of the metasurface layer and the wavelength of the incident light of the metasurface layer. When multiple groups of unit cells need to be disposed on the metasurface layer, the size of each of the multiple groups of unit cells can be set to be the same, thereby reducing the process difficulty of manufacturing the multiple groups of unit cells.

[0008] Optionally, the one group of unit cells includes N unit cells, and N is a positive integer greater than or equal to 2. In the first direction, the i-th unit cell in the N unit cells and the i-th reference position in N reference positions have a first displacement amount, and the N first displacement amounts are of a size that makes the diffraction efficiency of the +1 order diffraction light of the metasurface layer greater than a first threshold value, i∈[1,N], and the N reference positions are periodically distributed in the first direction. In this optional manner, the N first displacement amounts are set to make the diffraction efficiency of the +1 order diffraction light of the metasurface layer greater than the first threshold value. Exemplarily, when the number of unit cells included in the one group of unit cells is different, the first threshold value can be adaptively changed, thereby increasing the diffraction efficiency of the metasurface layer.

[0009] Optionally, the group of unit cells includes N unit cells, N being a positive integer greater than or equal to 2. In the second direction, the i-th unit cell in the N unit cells has a second displacement from the reference line parallel to the first direction, and the N second displacements have a magnitude such that the diffraction efficiency of the +1 order diffracted light of the metasurface layer is greater than a second threshold, i∈[1, N]. In this optional manner, the N second displacements are set to make the diffraction efficiency of the +1 order diffracted light of the metasurface layer greater than the second threshold. Exemplarily, the second threshold can be adaptively changed when the number of unit cells included in the group of unit cells is different, thereby increasing the diffraction efficiency of the metasurface layer.

[0010] Optionally, the group of unit cells includes N unit cells, N being a positive integer greater than or equal to 2. In the second direction, the i-th unit cell in the N unit cells has a second displacement from the reference line parallel to the first direction, and the N second displacements have a magnitude such that the diffraction efficiency of the +1 order diffracted light of the metasurface layer is greater than a second threshold, i∈[1, N]. In this optional manner, the N second displacements are set to make the diffraction efficiency of the +1 order diffracted light of the metasurface layer greater than the second threshold. Exemplarily, the second threshold can be adaptively changed when the number of unit cells included in the group of unit cells is different, thereby increasing the diffraction efficiency of the metasurface layer. satisfies the relationship: wherein A1 is a constant. The N reference positions are periodically distributed in the first direction. In this optional manner, the N unit cells have a first displacement standard deviation σ1 from the N reference positions in the first direction, and the N unit cells have a first displacement average value from the N reference positions in the first direction satisfies the relationship: Exemplarily, A1 is greater than or equal to 20 nanometers (nm), thereby increasing the diffraction efficiency of the metasurface layer.

[0011] Optionally, the group of unit cells includes N unit cells, N being a positive integer greater than or equal to 2. In the second direction, the i-th unit cell in the N unit cells has a second displacement from the reference line parallel to the first direction, and the N second displacements have a magnitude such that the diffraction efficiency of the +1 order diffracted light of the metasurface layer is greater than a second threshold, i∈[1, N]. In this optional manner, the N second displacements are set to make the diffraction efficiency of the +1 order diffracted light of the metasurface layer greater than the second threshold. Exemplarily, the second threshold can be adaptively changed when the number of unit cells included in the group of unit cells is different, thereby increasing the diffraction efficiency of the metasurface layer. satisfies the relationship: wherein A2 is a constant. In this optional manner, the N unit cells have a second displacement standard deviation σ2 from the reference line parallel to the first direction, and the N unit cells have a second displacement average value from the reference line parallel to the first direction satisfies the relationship: Exemplarily, A2 is greater than or equal to 20 nm, thereby increasing the diffraction efficiency of the metasurface layer.

[0012] Optionally, the silicon-based liquid crystal device further includes a reflective layer disposed between the silicon substrate and the at least one metasurface layer.

[0013] In a second aspect, a wavelength selective switch is provided, including a reflective structure, a wave divider, and a silicon-based liquid crystal device according to any one of the above first aspect; the wave divider is coupled to the silicon-based liquid crystal device through the reflective structure.

[0014] Thirdly, an optical add-drop multiplexer is provided, comprising a plurality of wavelength selection switches as described in the second aspect above.

[0015] The technical effects of either the second or third aspect can be found in the technical effects of the first aspect, which will not be repeated here. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an optical communication system;

[0017] Figure 2 This is a schematic diagram of an optical add-drop multiplexer.

[0018] Figure 3 This is a schematic diagram of a wavelength selective switch;

[0019] Figure 4 This is a schematic diagram of the structure of a silicon-based liquid crystal device provided in an embodiment of this application;

[0020] Figure 5 for Figure 4 A schematic diagram of the metasurface layer in a silicon-based liquid crystal device is shown.

[0021] Figure 6 for Figure 5 A schematic diagram of a set of unit cells in the metasurface layer is shown;

[0022] Figure 7 for Figure 6 A schematic diagram of the phase plane formed by a set of unit cells in the metasurface layer shown. Figure 1 ;

[0023] Figure 8 for Figure 6 A schematic diagram of the phase plane formed by a set of unit cells in the metasurface layer shown. Figure 2 ;

[0024] Figure 9 for Figure 6 Wavefront energy analysis diagram of a set of unit cells in the metasurface layer shown;

[0025] Figure 10 This is a schematic diagram of the structure of a silicon-based liquid crystal device provided in another embodiment of this application;

[0026] Figure 11 for Figure 10 The diagram shows the structure of the metasurface layer in the silicon-based liquid crystal device. Figure 1 ;

[0027] Figure 12 for Figure 11Structure diagram of a set of unit cells in the illustrated metasurface layer;

[0028] Figure 13 Structure diagram of a set of unit cells in the illustrated metasurface layer; Figure 10 Structure diagram of a set of unit cells in the illustrated metasurface layer; Figure 2 ;

[0029] Figure 14 Structure diagram of a set of unit cells in the illustrated metasurface layer; Figure 13

[0030] Figure 15 Structure diagram of a set of unit cells in the illustrated metasurface layer; Figure 10 Structure diagram of a set of unit cells in the illustrated metasurface layer; Figure 3 ;

[0031] Figure 16 Structure diagram of a set of unit cells in the illustrated metasurface layer; Figure 15

[0032] Figure 17 Wavefront energy analysis diagram of a set of unit cells in the metasurface layer;

[0033] Figure 18 Flowchart for making the set of unit cells illustrated in Figure 12 ;

[0034] Figure 19 Flowchart for making the set of unit cells illustrated in Figure 14 ;

[0035] Figure 20 Schematic diagram of incident light and diffracted light in the metasurface layer in the illustrated silicon-based liquid crystal device. Figure 10 DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0037] ​​​Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In the embodiments of the application, "at least one" means one or more, "multiple" means two or more. "And / or" describes the associated relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the following three cases: A exists alone, A and B exist together, B exists alone, where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects. "At least one of the following" or the like means any combination of the items, including single item or any combination of multiple items. For example, at least one of a, b or c can represent a, b, c, a and b, a and c, b and c, or a, b and c, where a, b and c can be singular or plural. In addition, in the embodiments of the application, "first", "second", and the like do not limit the quantity and order.

[0038] In addition, in the embodiments of the application, the orientation terms such as "upper", "lower", and the like are defined with respect to the orientation in which the components in the drawings are placed, and it should be understood that these directional terms are relative concepts, which are used for relative description and clarification, and can be changed accordingly according to the change of the orientation in which the components are placed in the drawings.

[0039] In the embodiments of the application, the words "exemplary" or "for example" are used to mean serving as an example, instance, or illustration. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the application should not be construed as being more preferred or advantageous than other embodiments or design schemes. Rather, the use of the words "exemplary" or "for example" is intended to present relevant concepts in a concrete manner.

[0040] The technical solutions in the embodiments of the application will be described below with reference to the drawings.

[0041] Figure 1 A schematic structural diagram of an optical communication system 10 is shown in FIG. 1. As shown in FIG. 1, the optical communication system 10 includes an access room 11 and an optical add-drop multiplexing system 12 (such as an optical add-drop multiplexing system 12a, an optical add-drop multiplexing system 12b, and an optical add-drop multiplexing system 12c shown in FIG. 2). Figure 1 Figure 1 Figure 1 ​​The networking mode of the access room 11 and the optical add / drop multiplexing system 12 in the illustrated optical communication system 10 is ring networking. The line-side optical signal transmitted in the optical communication system 10 is output from the access room 11 and passes through any one of the optical add / drop multiplexing systems 12 in a clockwise or counterclockwise direction. Specifically, the line-side optical signal can be generated by the access room 11, or the line-side optical signal can be an optical signal transmitted by another optical communication system and received by the access room 11. The line-side optical signal transmitted in the optical communication system 10 is usually combined by using wavelength division multiplexing (WDM) technology to improve the communication capacity and communication rate of the optical communication system 10, and thus the line-side optical signal contains optical signals of multiple different wavelengths.

[0042] Each optical add / drop multiplexing system 12 supports two-way optical signal transmission, Figure 1 Suppose that the two directions are westward w and eastward e, the line-side optical signal can be transmitted from eastward e to westward w or from westward w to eastward e in the optical add / drop multiplexing system 12. In addition, each optical add / drop multiplexing system 12 is also connected to a local communication device. Specifically, the optical add / drop multiplexing system 12 includes an optical add / drop multiplexer (OADM), and the upper wave port and / or the lower wave port of the optical add / drop multiplexer are connected to the local communication device. The local communication device generates an upper wave optical signal of a predetermined wavelength, transmits the upper wave optical signal of the predetermined wavelength to the upper wave port of the optical add / drop multiplexer, and the optical add / drop multiplexing system 12 combines the upper wave optical signal of the predetermined wavelength into the line-side optical signal. Alternatively, the local communication device also receives one or more optical signals of different wavelengths from the line-side optical signal transmitted from the lower wave port of the optical add / drop multiplexer.

[0043] It should be noted that the embodiments of the present application do not limit the networking mode of the access room 11 and the optical add / drop multiplexing system 12.

[0044] Specifically, referring to the enlarged schematic view of the site optical layer of the optical add / drop multiplexing system 12a shown in the dashed box of Figure 1 Suppose that the line-side optical signal transmitted in the optical communication system 10 passes through any one of the optical add / drop multiplexing systems 12 in a clockwise direction, then in the optical add / drop multiplexing system 12a, the first line-side optical signal is transmitted from eastward e to westward w through the site optical layer (as shown by "1" in Figure 1 The optical signal of wavelength λa in the first line-side optical signal can be dropped to the local communication device to form a lower wave optical signal of wavelength λa (as shown by "2" in Figure 1"5") ; the local communication device can generate an add wavelength signal with wavelength λa, combine the add wavelength signal with wavelength λa with the other wavelength signals in the first line-side optical signal except the wavelength λa, generate a second line-side optical signal and transmit the second line-side optical signal to the west direction w (as shown in Figure 1 "3"). Assuming that the line-side optical signals transmitted in the optical communication system 10 pass through any one of the optical add / drop multiplexing systems 12 in a counterclockwise direction, in the optical add / drop multiplexing system 12a, the first line-side optical signal is transmitted from the west direction w to the east direction e (as shown in Figure 1 "2") ; wherein the optical signal with wavelength λb in the first line-side optical signal can be dropped to the local communication device to form a dropped optical signal with wavelength λb (as shown in Figure 1 "4") ; the local communication device can generate an add wavelength signal with wavelength λb, combine the add wavelength signal with wavelength λb with the other wavelength signals in the first line-side optical signal except the wavelength λb, generate a second line-side optical signal and transmit the second line-side optical signal to the east direction e (as shown in Figure 1 "6").

[0045] As can be seen, in the optical communication system 10, each optical add / drop multiplexing system 12 needs to implement add and drop of a single or multiple wavelengths of optical signals, while also needs to ensure the non-blocking pass-through of other wavelengths of optical signals. Specifically, it is generally achieved by setting an optical add / drop multiplexer in the optical add / drop multiplexing system to implement the add and drop of a single or multiple wavelengths of optical signals, while also implementing the non-blocking pass-through of other wavelengths of optical signals.

[0046] At present, the optical add / drop multiplexers set in the optical add / drop multiplexing system include fixed optical add / drop multiplexers (FOADMs) and reconfigurable optical add / drop multiplexers (ROADMs). Among them, the FOADMs can only add and drop fixed wavelengths of optical signals and cannot be dynamically adjusted. The ROADMs can dynamically adjust the wavelengths of the added and dropped optical signals, and thus can improve the flexibility of the optical add / drop multiplexing system.

[0047] Specifically, Figure 2 A structure schematic diagram of an optical add / drop multiplexer 20 is shown in FIG. 2. Figure 2 As shown, a typical colorless (C), directionless (D) and contentionless (C) optical add / drop multiplexer 20 includes a line-side assembly 21 and a customer-side assembly 22. As shown inFigure 2 As shown, the line side component 21 in the optical add-drop multiplexer 20 can implement the transmission of optical signals of any wavelength from one line direction to another line direction; the customer side component 22 in the optical add-drop multiplexer 20 can implement the downwaving of optical signals of predetermined wavelengths in any line direction to local communication devices, and the upwaving of optical signals of predetermined wavelengths generated by the local communication devices to any line direction. Among them, the line side component 21 includes a plurality of wavelength selective switches (WSSs), and the plurality of wavelength selective switches are cross-connected, thereby realizing the transmission of any wavelength from one line direction to another line direction. Figure 2 The line side component shown specifically includes three WSSs, which are WSS1, WSS2 and WSS3. The WSS1, WSS2 and WSS3 are cross-connected, specifically, one port of the WSS1 is connected with one port of the WSS2, one port of the WSS1 is connected with one port of the WSS3, and one port of the WSS2 is connected with one port of the WSS3.

[0048] In some other embodiments, Figure 2 The optical add-drop multiplexer 20 shown also includes more functional devices, for example, the optical add-drop multiplexer 20 also includes an optical amplifier, the optical amplifier is coupled with the wavelength selective switch, and the optical amplifier can amplify the optical signals transmitted to the wavelength selective switch or amplify the optical signals output by the wavelength selective switch.

[0049] Figure 3 A structure schematic diagram of a wavelength selective switch 30 is shown in FIG. 3. As shown, the wavelength selective switch 30 is implemented based on a liquid crystal on silicon (LCoS) device. Specifically, referring to FIG. 4, the wavelength selective switch 30 includes a reflective structure 32, a wave divider 33 and a liquid crystal on silicon device 34; among them, the wave divider 33 and the liquid crystal on silicon device 34 are coupled through the reflective structure 32. Exemplarily, the wavelength selective switch 30 also includes a fiber array 31, the fiber array 31 is coupled with the reflective structure 32, and the fiber array 31 is used to receive the optical signals transmitted to the wavelength selective switch 30 and output the optical signals generated by the wavelength selective switch 30. Figure 3 As shown, the wavelength selective switch 30 is implemented based on a liquid crystal on silicon (LCoS) device. Specifically, referring to FIG. 4, the wavelength selective switch 30 includes a reflective structure 32, a wave divider 33 and a liquid crystal on silicon device 34; among them, the wave divider 33 and the liquid crystal on silicon device 34 are coupled through the reflective structure 32. Exemplarily, the wavelength selective switch 30 also includes a fiber array 31, the fiber array 31 is coupled with the reflective structure 32, and the fiber array 31 is used to receive the optical signals transmitted to the wavelength selective switch 30 and output the optical signals generated by the wavelength selective switch 30. Figure 3 As shown, the wavelength selective switch 30 is implemented based on a liquid crystal on silicon (LCoS) device. Specifically, referring to FIG. 4, the wavelength selective switch 30 includes a reflective structure 32, a wave divider 33 and a liquid crystal on silicon device 34; among them, the wave divider 33 and the liquid crystal on silicon device 34 are coupled through the reflective structure 32. Exemplarily, the wavelength selective switch 30 also includes a fiber array 31, the fiber array 31 is coupled with the reflective structure 32, and the fiber array 31 is used to receive the optical signals transmitted to the wavelength selective switch 30 and output the optical signals generated by the wavelength selective switch 30.

[0050] Specifically, referring to FIG. 5, the wavelength selective switch 30 includes a reflective structure 32, a wave divider 33 and a liquid crystal on silicon device 34; among them, the wave divider 33 and the liquid crystal on silicon device 34 are coupled through the reflective structure 32. Exemplarily, the wavelength selective switch 30 also includes a fiber array 31, the fiber array 31 is coupled with the reflective structure 32, and the fiber array 31 is used to receive the optical signals transmitted to the wavelength selective switch 30 and output the optical signals generated by the wavelength selective switch 30. Figure 3As shown, the fiber array 31 includes the fiber F1, the fiber F2, the fiber F3 and the fiber F4. The fiber F1 in the fiber array 31 is configured to receive the combined optical signal Sadd transmitted to the wavelength selective switch 30, and transmit the combined optical signal Sadd to the reflection structure 32, where the combined optical signal Sadd includes the optical signal S1 with the wavelength λ1 and the optical signal S2 with the wavelength λ2; the reflection structure 32 reflects the combined optical signal Sadd to the wavelength demultiplexer 33; the wavelength demultiplexer 33 is configured to demultiplex the combined optical signal Sadd to generate the optical signal S1 and the optical signal S2, and transmit the optical signal S1 and the optical signal S2 to the reflection structure 32, where the optical signal S1 and the optical signal S2 are transmitted to different positions of the reflection structure 32; the reflection structure 32 is configured to reflect the optical signal S1 to the first region of the liquid crystal on silicon device 34, and reflect the optical signal S2 to the second region of the liquid crystal on silicon device 34; the first region of the liquid crystal on silicon device 34 is configured to perform phase modulation on the optical signal S1 to generate the optical signal S3, and transmit the optical signal S3 to the reflection structure 32; the reflection structure 32 is configured to transmit the optical signal S3 to the fiber F2 in the fiber array 31; the fiber F2 in the fiber array 31 is configured to output the optical signal S3; the second region of the liquid crystal on silicon device 34 is configured to perform phase modulation on the optical signal S2 to generate the optical signal S4, and transmit the optical signal S4 to the reflection structure 32; the reflection structure 32 is configured to transmit the optical signal S4 to the fiber F3 in the fiber array 31; the fiber F3 in the fiber array 31 is configured to output the optical signal S4.

[0051] For example, the reflection structure 32 can be a cylindrical mirror. The wavelength demultiplexer 33 can be an optical grating.

[0052] For example, the wavelength selective switch based on the liquid crystal on silicon device is usually designed as a polarization dependent architecture, because the liquid crystal in the liquid crystal on silicon device can only perform phase modulation on the optical signal with the first polarization direction. In the wavelength selective switch with the polarization dependent architecture, two single-polarization optical signals need to be generated according to the received optical signal, and the two single-polarization optical signals are transmitted to the liquid crystal on silicon device through different transmission paths, which increases the optical path complexity of the wavelength selective switch and causes relatively large polarization dependent loss (PDL).

[0053] In order to reduce the optical path complexity and the polarization dependent loss of the wavelength selective switch, more and more wavelength selective switches are designed as a polarization independent architecture. In the wavelength selective switch with the polarization independent architecture, the liquid crystal on silicon device is a polarization independence-liquid crystal on silicon (PI_LCoS) device.

[0054] Figure 4 This is a schematic diagram of the structure of the silicon-based liquid crystal device 40 provided in the embodiments of this application, as shown below. Figure 4 As shown, the silicon-based liquid crystal device 40 is specifically a polarization-independent silicon-based liquid crystal device. The polarization-independent silicon-based liquid crystal device 40 includes a silicon substrate 41, a reflective layer 42 disposed on the silicon substrate 41, a metasurface layer 43 disposed on the reflective layer 42, a liquid crystal layer 44 disposed on the metasurface layer 43, and a transparent electrode capping layer 45 disposed on the liquid crystal layer 44. The liquid crystal layer 44 includes a plurality of liquid crystal molecules 440, which can perform phase modulation on light signals with a polarization direction of a first direction. The metasurface layer 43 includes a plurality of unit cells 430 arranged in an array.

[0055] Specifically, the silicon substrate 41 includes a driving circuit. When a voltage is applied to the driving circuit in the silicon substrate 41, the liquid crystal molecules 440 in the liquid crystal layer 44 will be deflected under the action of the voltage. The liquid crystal molecules 440 can perform phase modulation on the light signal with the first polarization direction transmitted through the liquid crystal molecules 440. At this time, assuming that the light signal S5 is incident on the polarization-independent silicon liquid crystal 40, the light signal S5 includes a light signal S51 with the first polarization direction and a light signal S52 with the second polarization direction. The first polarization direction and the second polarization direction are different. Specifically, the first polarization direction and the second polarization direction can be orthogonal. The light signal S5 is transmitted to the liquid crystal layer 44 through the transparent electrode cover layer 45. The liquid crystal molecules 440 in the liquid crystal layer 44 perform phase modulation on the light signal S51 in the light signal S5, but do not perform phase modulation on the light signal S52 in the light signal S5. Subsequently, the light signal S5 passes through the metasurface layer 43 and the reflective layer 42, and is then reflected to the liquid crystal layer 44. In this process, the metasurface layer 43 adjusts the polarization direction of the optical signal S51 in the optical signal S5 to the second polarization direction, and the metasurface layer 43 adjusts the polarization direction of the optical signal S52 in the optical signal S5 to the first polarization direction. This causes the liquid crystal molecules 440 in the liquid crystal layer 44 to perform phase modulation on the optical signal S52 in the optical signal S5, while the liquid crystal molecules 440 in the liquid crystal layer 44 do not perform phase modulation on the optical signal S51 in the optical signal S5, thus generating the optical signal S6. The optical signal S6 is emitted through the transparent electrode cover plate 45.

[0056] Specifically, when the optical signal S5 is incident on the polarization-independent silicon-based liquid crystal 40, the liquid crystal molecules 440 in the liquid crystal layer 44 perform a phase modulation on the optical signal S51 in the optical signal S5. When the optical signal is emitted, the liquid crystal molecules 440 in the liquid crystal layer 44 perform a phase modulation on the optical signal S52 in the optical signal S5, thereby generating the optical signal S6, which is emitted from the polarization-independent silicon-based liquid crystal 40.

[0057] Figure 5for Figure 4 The schematic diagram of the metasurface layer 43 in the silicon-based liquid crystal device 40 shown is as follows: Figure 5 As shown, the metasurface layer 43 includes multiple unit cells 430 arranged in an array. Specifically, Figure 5 The metasurface layer 43 shown includes unit cells 430 arranged in a 3-row × 16-column array. Each row of unit cells arranged along the x-axis comprises multiple sets of unit cells. Specifically, Figure 5 The row of unit cells arranged along the x-axis shown includes two sets of unit cells. Each set of unit cells constitutes a phase plane that varies from 0 to 2π. This phase plane acts on the optical signal whose polarization direction is changed output by the metasurface layer 43. The center positions of each set of unit cells are periodically distributed along the x-axis and periodically distributed along the y-axis.

[0058] For example, since the size of cell 430 is on the order of micrometers or nanometers, cell 430 is also referred to as a micro-nano structure.

[0059] Figure 6 for Figure 5 The schematic diagram of a set of unit cells in the metasurface layer 43 shown is as follows: Figure 6 As shown, where, Figure 6 The illustrated set of unit cells comprises eight unit cells 430. The centers of these unit cells are periodically distributed along the x-axis, specifically, the distance between the centers of any two adjacent unit cells 430 along the x-axis is equal. The centers of the unit cells are also periodically distributed along the y-axis, specifically, the center of each unit cell 430 lies on the line y = a along the y-axis. The eight unit cells 430 in this set are specifically elliptical in shape, and each unit cell 430 has a major axis and a minor axis. The angle between the major axes of cells 430-1, 430-2, 430-3, and 430-4 and the major axis (x-axis) of the liquid crystal molecule 440 is -45 degrees (rotated 45 degrees counterclockwise along the x-axis). The angle between the major axes of cells 430-5, 430-6, 430-7, and 430-8 and the major axis (x-axis) of the liquid crystal molecule 440 is 45 degrees (rotated 45 degrees clockwise along the x-axis).

[0060] For example, refer to Figure 6As shown, cell 430-1 and cell 430-5 have the same size. Specifically, the major axis of cell 430-1 is equal to the major axis of cell 430-5, and the minor axis of cell 430-1 is equal to the minor axis of cell 430-5. Cell 430-1 corresponds to a (1 / 4)π phase value in the phase plane, and cell 430-1 corresponds to a (5 / 4)π phase value in the phase plane. Cells 430-2 and 430-6 have the same dimensions. Cell 430-2 corresponds to the (2 / 4)π phase value in the phase plane, and cell 430-6 corresponds to the (6 / 4)π phase value in the phase plane. Cells 430-3 and 430-7 have the same dimensions. Cell 430-3 corresponds to the (3 / 4)π phase value in the phase plane, and cell 430-7 corresponds to the (7 / 4)π phase value in the phase plane. Cells 430-4 and 430-8 have the same dimensions. Cell 430-4 corresponds to the π phase value in the phase plane, and cell 430-8 corresponds to the 2π phase value in the phase plane.

[0061] Figure 7 for Figure 6 A schematic diagram of the phase plane formed by a group of unit cells in the metasurface layer 43 shown. Figure 1 Ideally, Figure 6 The phase plane formed by a set of unit cells shown is as follows Figure 7 As shown. The phase plane formed by this set of unit cells is an ideal phase plane. When a light signal incident at any position onto the ideal phase plane has a changed polarization direction, it will be diffracted out by rotating by an angle α.

[0062] However, refer to Figure 6 As shown, in reality, the deflection directions of unit cells 430-4 and 430-5 change abruptly, and the nearest-neighbor interaction between unit cells 430-4 and 430-5 is affected, so that the phase plane formed by this set of unit cells is a non-ideal phase plane. Figure 8 for Figure 6 A schematic diagram of the phase plane formed by a group of unit cells in the metasurface layer 43 shown. Figure 2 ,like Figure 8 As shown, the phase plane actually formed by this set of unit cells is uneven, causing the first portion of the incident light signal whose polarization direction changes to be diffracted by an angle α, the second portion by an angle β, and the third portion by an angle γ. This reduces the diffraction efficiency of the light signal diffracted by the angle α in the metasurface layer. Figure 9 for Figure 6 Wavefront energy analysis of a set of unit cells in metasurface layer 43 is shown. Figure 9 As shown, in the case of Figure 6When the wavefront energy analysis is performed on the set of unit cells shown, the wavefront energy analysis diagram includes an energy valley region, and the presence of the energy valley region makes the insertion loss fluctuation of the light signal emitted by the polarization-independent liquid crystal on silicon 40 larger, and the insertion loss fluctuation of the wavelength selective switch using the polarization-independent liquid crystal on silicon 40 larger.

[0063] To this end, an embodiment of the present application provides a liquid crystal on silicon device, in particular a polarization-independent liquid crystal on silicon device, which has a smaller insertion loss fluctuation.

[0064] Figure 10 The structural schematic diagram of the liquid crystal on silicon device 50 provided for another embodiment of the present application is shown in Figure 10 , wherein the liquid crystal on silicon device 50 includes a silicon substrate 51, a liquid crystal layer 55 disposed on the silicon substrate 51, and at least one metasurface layer disposed between the silicon substrate 51 and the liquid crystal layer 55. The liquid crystal layer 55 includes a plurality of liquid crystal molecules 550, which can perform phase modulation on a light signal with a first polarization direction, for example. Figure 10 The at least one metasurface layer includes a metasurface layer 54, as shown in Figure 10 When the at least one metasurface layer includes a plurality of metasurface layers 54, as shown in

[0065] The metasurface layer 54 includes a plurality of unit cells 540 arranged in an array, as shown in Figure 10 In a first direction, in a set of unit cells, the center positions of each unit cell are non-periodically distributed in the first direction, and the first direction is the phase gradient direction of the metasurface layer 54; and / or in a set of unit cells, the center positions of each unit cell are non-periodically distributed in a second direction, and the second direction is perpendicular to the phase gradient direction on the metasurface layer 54. The plurality of unit cells 540 arranged in an array in the metasurface layer 54 are coated, for example, and the material for coating the plurality of unit cells 540 arranged in an array includes one or more of the following: silica, silicon nitride, and other low-refractive dielectric materials. The material of the unit cells 540 includes one or more of the following: amorphous silicon, titanium dioxide, and other dielectric materials, gold, silver, and other metal materials.

[0066] The metasurface layer 54 in the liquid crystal on silicon device 50 shown in Figure 11 , for example, includes a plurality of unit cells 540 arranged in an array, and the center positions of each unit cell in a set of unit cells are non-periodically distributed in a first direction, and the first direction is the phase gradient direction of the metasurface layer 54. Figure 10 The structural schematic diagram of the metasurface layer 54 in the liquid crystal on silicon device 50 shown in Figure 1 , for example, includes a plurality of unit cells 540 arranged in an array, and the center positions of each unit cell in a set of unit cells are non-periodically distributed in a first direction, and the first direction is the phase gradient direction of the metasurface layer 54. Figure 11As shown, the metasurface layer 54 includes 3 rows * 16 columns of unit cells 540 distributed in an array. Among them, the first direction is specifically the x-axis direction, and the second direction is specifically the y-axis direction. In the x-axis direction, there are 2 groups of continuously distributed unit cells. Among them, each group of unit cells forms a phase surface that changes from 0 to 2π in the x-axis direction, and this phase surface acts on the optical signal whose polarization direction changes when output from the metasurface layer 54. The x-axis direction is also called the phase gradient direction of the metasurface layer 54, and the y-axis direction is perpendicular to the x-axis direction on the metasurface layer 54. Among them, Figure 11 The 3 rows * 16 columns of unit cells 540 shown are specifically 6 groups of unit cells, and these 6 groups of unit cells are the same. Among them, in any group of unit cells, the central positions of each unit cell are non-periodically distributed in the x-axis direction, and in any group of unit cells, the central positions of each unit cell are periodically distributed in the y-axis direction.

[0067] Specifically, Figure 12 is Figure 11 a schematic structural diagram of a group of unit cells in the metasurface layer 54 shown. As Figure 12 shown, a group of unit cells includes 8 unit cells 540, and the central positions of these 8 unit cells 540 are non-periodically distributed along the x-axis direction. Specifically, among the 8 unit cells, there are unit cells 540-1, unit cells 540-2, and unit cells 540-3 distributed in sequence along the x-axis; in the x-axis direction, there is a first distance between the central position of unit cell 540-1 and the central position of unit cell 540-2; there is a second distance between the central position of unit cell 540-2 and the central position of unit cell 540-3; the first distance and the second distance are not equal. Specifically, referring to Figure 12 shown, in the x-axis direction, the distances between the central positions of any two adjacent unit cells 540 among the 8 unit cells are not equal. In some other embodiments, in the x-axis direction, it can be that there are s pairs of adjacent unit cells 540 in a group of unit cells whose central positions have a first distance, and the central positions of other pairs of adjacent unit cells 540 have a second distance, and the first distance and the second distance are not equal, 0 < s < N - 1, where N is the number of unit cells included in a group of unit cells. Among them, when a group of unit cells does not satisfy the following condition 1, it means that the central positions of each unit cell in a group of unit cells are non-periodically distributed along the x-axis direction; condition 1 is: in the x-axis direction, the distances between the central positions of any two adjacent unit cells in a group of unit cells are equal.

[0068] Specifically, referring to Figure 12 shown, the central positions of the 8 unit cells 540 are periodically distributed along the y-axis direction. Specifically, in the y-axis direction, the central positions of the 8 unit cells 540 are located on the line y = b, where the line y = b is parallel to the x-axis.

[0069] Exemplarily, Figure 13 is Figure 10Structure diagram of a group of unit cells in the metasurface layer 54 shown in the silicon-based liquid crystal device 50 Figure 2 As shown in the structure diagram of the metasurface layer 54 shown in the silicon-based liquid crystal device 50 Figure 13 The metasurface layer 54 includes an array of 3 rows * 16 columns of unit cells 540, where the first direction is specifically the x-axis direction, and the second direction is specifically the y-axis direction. In the x-axis direction, there are two groups of unit cells that are continuously distributed, where each group of unit cells forms a phase plane that changes from 0 to 2π in the x-axis direction. The x-axis direction is the phase gradient direction of the metasurface layer 54, and the y-axis direction is perpendicular to the x-axis direction on the metasurface layer 54. Among them, Figure 13 The 3 rows * 16 columns of unit cells 540 shown are specifically 6 groups of unit cells, and the 6 groups of unit cells are the same. The center positions of each unit cell in any group of unit cells are periodically distributed in the x-axis direction, and the center positions of each unit cell in any group of unit cells are non-periodically distributed in the y-axis direction.

[0070] Specifically, Figure 14 As shown in the structure diagram of a group of unit cells in the metasurface layer 54 shown in the silicon-based liquid crystal device 50 Figure 13 As shown in the structure diagram of a group of unit cells in the metasurface layer 54 shown in the silicon-based liquid crystal device 50 Figure 14 As shown in the structure diagram of a group of unit cells in the metasurface layer 54 shown in the silicon-based liquid crystal device 50

[0071] Specifically, referring to Figure 14 As shown in the structure diagram of a group of unit cells in the metasurface layer 54 shown in the silicon-based liquid crystal device 50 Figure 14 As shown in the structure diagram of a group of unit cells in the metasurface layer 54 shown in the silicon-based liquid crystal device 50

[0072] Exemplarily, the first displacement amount can be positive or negative, and the second displacement amount can be positive or negative. Figure 14 As shown in the placement position of the set of unit cells, in the y-axis direction, when the center position of the unit cell 540-1 is located above the reference line of y=b, the first displacement amount between the center position of the unit cell 540-1 and the reference line of y=b is positive; in the y-axis direction, when the center position of the unit cell 540-1 is located below the reference line of y=b, the first displacement amount between the center position of the unit cell 540-1 and the reference line of y=b is negative. When the center position of the unit cell 540-2 is located above the reference line of y=b, the second displacement amount between the center position of the unit cell 540-2 and the reference line of y=b is positive; in the y-axis direction, when the center position of the unit cell 540-2 is located below the reference line of y=b, the second displacement amount between the center position of the unit cell 540-2 and the reference line of y=b is negative.

[0073] Exemplarily, Figure 15 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50, Figure 10 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50, Figure 3 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50, Figure 15 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50, Figure 15 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50,

[0074] Exemplarily, Figure 16 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50, Figure 15 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50, Figure 16 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50,

[0075] Exemplarily, Figure 16 As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50, As shown in the structure of the set of unit cells in the metasurface layer 54 of the silicon-based liquid crystal device 50,

[0076] In some embodiments, the metasurface layer 54 includes an array of 3 rows * 16 columns of unit cells 540, and includes two sets of unit cells continuously distributed along the x-axis. Therefore, the 3 rows * 16 columns of unit cells 540 includes 6 sets of unit cells, and any one of these 6 sets of unit cells can be... Figure 12 A set of unit cells, or Figure 14 A set of unit cells, or Figure 16 The set of unit cells shown is not limited to the embodiments of this application.

[0077] For example, in Figure 10 In the silicon-based liquid crystal device shown, since the center position of each cell in a set of cells is non-periodic in the first direction, and / or the center position of each cell in a set of cells is non-periodic in the second direction, the phase plane formed by the set of cells can be made to approach the ideal phase plane, thereby reducing the insertion loss fluctuation of the optical signal emitted by the silicon-based liquid crystal device 50, and reducing the insertion loss fluctuation of the wavelength selection switch of the silicon-based liquid crystal device 50.

[0078] For example, refer to Figure 10 As shown, the silicon-based liquid crystal device 50 further includes a reflective layer 52 disposed between the silicon substrate 51 and at least one metasurface layer. Exemplarily, the material of the reflective layer 52 includes one or more of the following: conductive materials such as aluminum and gold. In some embodiments, the reflective layer 52 is specifically a reflective film coated on the silicon substrate 51.

[0079] In other embodiments, reference is made to Figure 10 As shown, the silicon-based liquid crystal device 50 further includes a transparent electrode cover plate 56 disposed on the liquid crystal layer 55. The silicon substrate 51 includes a driving circuit. When a voltage is applied to the driving circuit in the silicon substrate 51, the driving circuit and the transparent electrode cover plate 56 apply a first voltage to the liquid crystal molecules 550 in the liquid crystal layer 55. Under the action of the first voltage, the liquid crystal molecules 550 in the liquid crystal layer 55 deflect, thereby modulating the phase of the optical signal transmitted through the liquid crystal layer 55.

[0080] In other embodiments, reference is made to Figure 10 As shown, the silicon-based liquid crystal device 50 further includes a passivation layer 53 disposed between the reflective layer 52 and at least one metasurface layer. The presence of the passivation layer 53 can improve the diffraction efficiency of the at least one metasurface layer, and the material of the passivation layer 53 is a low-refractive-index dielectric material.

[0081] For example, Figures 11 to 16 The unit cell 540 shown is specifically illustrated as an elliptical shape. In other embodiments, the shape of the unit cell 540 can also be a rectangle, a T-shape, a cross, or other different shapes. The embodiments of this application do not limit this.

[0082] Exemplarily, Figure 17 is a wavefront energy analysis diagram of a set of unit cells in the metasurface layer 54. As shown in Figure 17 , when wavefront energy analysis is performed on a set of unit cells in the metasurface layer 54 shown in Figure 12 or Figure 14 or Figure 16 , the energy distribution in the wavefront energy analysis diagram is uniform, and the energy trough area shown in Figure 9 is significantly reduced.

[0083] Exemplarily, the center positions of the unit cells in the set of unit cells are non-periodically distributed in the x-axis direction. That is, in the first direction, the i-th unit cell in the set of unit cells has a displacement di from the i-th reference position in the N reference positions, and the N displacement amounts di are such that the diffraction efficiency of the +1 order diffracted light of the metasurface layer 54 is greater than a first threshold value, and the N reference positions are periodically distributed in the first direction. Specifically, the set of unit cells can be designed by the following steps to make the center positions of the unit cells in the set of unit cells non-periodically distributed in the x-axis direction.

[0084] Exemplarily, Figure 18 is a flowchart for manufacturing the set of unit cells shown in Figure 12 . As shown in Figure 18 , the first step is to construct a set of N unit cells, and the center positions of the N unit cells are periodically distributed in the x-axis direction and periodically distributed in the y-axis direction. Exemplarily, as shown in Figure 18 , specifically, 8 unit cells are constructed, and the center positions of the 8 unit cells are periodically distributed in the x-axis direction and periodically distributed in the y-axis direction. Among them, the 8 unit cells constitute a phase plane with a change of 0 to 2π, and the i-th unit cell in the 8 unit cells corresponds to a phase value in the phase plane, i∈[1,8]. Among them, the phase value corresponding to the i-th unit cell in the phase plane is related to the long axis size of the i-th unit cell, the short axis size of the i-th unit cell, and the angle between the long axis direction of the i-th unit cell and the long axis direction of the liquid crystal molecules 550 in the liquid crystal layer 55.

[0085] ​For example, the center positions of the 8 cells are periodically arranged in the x-axis direction, and the distance between the center positions of any two adjacent cells in the x-axis direction is equal. Specifically, in the x-axis direction, the center position of the 1st cell is at the position of x=c1, the center position of the 2nd cell is at the position of x=c2, the center position of the 3rd cell is at the position of x=c3, the center position of the 4th cell is at the position of x=c4, the center position of the 5th cell is at the position of x=c5, the center position of the 6th cell is at the position of x=c6, the center position of the 7th cell is at the position of x=c7, and the center position of the 8th cell is at the position of x=c8. The 8 reference positions are the position of x=c1, the position of x=c2, the position of x=c3, the position of x=c4, the position of x=c5, the position of x=c6, the position of x=c7, and the position of x=c8. The center positions of the 8 cells are periodically arranged in the y-axis direction. Specifically, in the y-axis direction, the center positions of the 8 cells are on the reference line parallel to the x-axis, y=b.

[0086] Generally, when designing N cells to form a phase plane varying from 0 to 2π, N is an even number, the angle between the long axis of the first N / 2 cells and the long axis (x-axis) of the liquid crystal molecules 550 in the liquid crystal layer 55 is -45 degrees (rotated counterclockwise by 45 degrees along the x-axis), the angle between the long axis of the last N / 2 cells and the long axis (x-axis) of the liquid crystal molecules 550 in the liquid crystal layer 55 is 45 degrees (rotated clockwise by 45 degrees along the x-axis); and the long axis and the short axis of the jth cell and the j+N / 2th cell are equal, j∈[1,N / 2].

[0087] Figure 18The second step is as follows: Keeping the shapes of the N unit cells unchanged, a displacement *di* is introduced along the x-axis at the center position of the *i*th unit cell among the N unit cells. After each of the N unit cells moves by the corresponding displacement *di* along the x-axis, the diffraction efficiency of the +1st order diffracted light of the metasurface layer 54 is greater than the first threshold. For example, the displacement *di* can be determined by an algorithm, including any of the following: coordinate search, genetic algorithm, or moving asymptote method, etc. The objective condition of the algorithm is to make the diffraction efficiency of the +1st order diffracted light of the metasurface layer 54 greater than the first threshold. For example, an algorithm can be used to determine the displacement di = d1 of the center position of the first unit cell along the x-axis, the displacement di = d2 of the center position of the second unit cell, the displacement di = d3 of the center position of the third unit cell, the displacement di = d4 of the center position of the fourth unit cell, the displacement di = d5 of the center position of the fifth unit cell, the displacement di = d6 of the center position of the sixth unit cell, the displacement di = d7 of the center position of the seventh unit cell, and the displacement di = d8 of the center position of the eighth unit cell. After determining the displacement di of each of the eight unit cells, the eight unit cells are controlled to move along the x-axis by their corresponding displacement di. The displacement di can be either positive or negative, as shown in the reference. Figure 18 The arrangement of the unit cells shown is such that when the first unit cell needs to move to the right, its displacement *di* is positive; when the first unit cell needs to move to the left, its displacement *di* is negative. After the movement, the centers of the eight unit cells are aperiodically distributed along the x-axis. Specifically, along the x-axis, the center of the first unit cell is at x = c1 + d1, the center of the second unit cell is at x = c2 + d2, the center of the third unit cell is at x = c3 + d3, the center of the fourth unit cell is at x = c4 + d4, the center of the fifth unit cell is at x = c5 + d5, the center of the sixth unit cell is at x = c6 + d6, the center of the seventh unit cell is at x = c7 + d7, and the center of the eighth unit cell is at x = c8 + d8.

[0088] For example, the value of the first threshold is related to the number of unit cells included in a set of unit cells, and the embodiments of this application do not limit the value of the first threshold. For example, when a set of unit cells includes 16 unit cells, the first threshold can be greater than or equal to 90%; when a set of unit cells includes 32 unit cells, the first threshold can be greater than or equal to 95%.

[0089] in, Figure 18 After completing the two steps shown, you will get Figure 12 The set of unit cells shown.

[0090] For example, the center positions of each unit cell in a set of unit cells are aperiodically distributed along the y-axis. This means that, along the y-axis, the i-th unit cell among the N unit cells in the set has a displacement fi with respect to the baseline y=b parallel to the x-axis. These N displacements fi result in the efficiency of the +1st order diffraction light of the metasurface layer 54 being greater than the second threshold. Specifically, a set of unit cells is designed such that the center positions of these unit cells are aperiodically distributed along the y-axis through the following steps.

[0091] For example, Figure 19 To make Figure 14 A flowchart of a set of unit cells is shown. (See attached diagram.) Figure 19 As shown, the first step is to construct a set of N unit cells, where the center positions of each of the N unit cells are periodically distributed along the x-axis and periodically distributed along the y-axis. Wherein, Figure 19 The first step shown is Figure 18 The first step shown is similar and will not be repeated here.

[0092] Figure 19 The second step is as follows: keeping the shape of the N unit cells unchanged, a displacement fi is introduced along the y-axis direction at the center position of the i-th unit cell among the N unit cells. After each of the N unit cells moves along the y-axis by the corresponding displacement fi, the diffraction efficiency of the +1st order diffracted light of the metasurface layer 54 is greater than the second threshold. For example, the displacement fi can be determined by an algorithm, including any of the following: coordinate search, genetic algorithm, or moving asymptote method, etc. The objective condition of the algorithm is to make the diffraction efficiency of the +1st order diffracted light of the metasurface layer 54 greater than the second threshold. For example, an algorithm can be used to determine the displacement fi = f1 of the center position of the first unit cell along the y-axis, the displacement fi = f2 of the center position of the second unit cell, the displacement fi = f3 of the center position of the third unit cell, the displacement fi = f4 of the center position of the fourth unit cell, the displacement fi = f5 of the center position of the fifth unit cell, the displacement fi = f6 of the center position of the sixth unit cell, the displacement fi = f7 of the center position of the seventh unit cell, and the displacement fi = f8 of the center position of the eighth unit cell. After determining the displacement fi of each of the eight unit cells, the eight unit cells are moved along the y-axis by their corresponding displacement fi. The displacement fi can be positive or negative, as shown in the reference. Figure 19The position of the group of unit cells shown, when the first unit cell needs to move upward, the displacement amount f1 of the first unit cell is positive; when the first unit cell needs to move downward, the displacement amount f1 of the first unit cell is negative. After moving, the center positions of the 8 unit cells are non-periodically distributed in the y-axis direction. Specifically, in the y-axis direction, the center position of the first unit cell is at the position of y=b+f1, the center position of the second unit cell is at the position of y=b+f2, the center position of the third unit cell is at the position of y=b+f3, the center position of the fourth unit cell is at the position of y=b+f4, the center position of the fifth unit cell is at the position of y=b+f5, the center position of the sixth unit cell is at the position of y=b+f6, the center position of the seventh unit cell is at the position of y=b+f7, and the center position of the eighth unit cell is at the position of y=b+f8.

[0093] For example, the numerical value of the second threshold value is related to the number of unit cells included in the group of unit cells, and the embodiments of the present application do not limit the numerical value of the second threshold value. For example, when the group of unit cells includes 16 unit cells, the second threshold value can be greater than or equal to 90%; when the group of unit cells includes 32 unit cells, the first threshold value can be greater than or equal to 95%.

[0094] wherein, Figure 19 After the two steps shown are completed, the group of unit cells shown can be obtained Figure 14

[0095] For example, when the center positions of N unit cells in the group of unit cells are non-periodically distributed in the x-axis direction, and the center positions of the N unit cells are non-periodically distributed in the y-axis direction, the design method can be to combine the first step shown with the second step shown, Figure 18 Figure 19 the second step shown.

[0096] For example, the group of unit cells includes N unit cells 540, and N is a positive integer greater than or equal to 2. The distance P between the center position of the first unit cell 540 and the center position of the Nth unit cell 540 in the first direction in the group of unit cells satisfies the following formula one: wherein, θ is the diffraction angle of the +1 order diffracted light of the metasurface layer 54, and λ is the wavelength of the incident light of the metasurface layer 54. Specifically, Figure 20 Figure 10 the schematic diagram of the incident light and the diffracted light of the metasurface layer 54 in the silicon-based liquid crystal device 50 shown. As Figure 20 ​​​As shown, when a light signal S7 with wavelength λ is incident on the metasurface layer 54, the metasurface layer 54 generates a +1st order diffracted light, which is light signal S8, with a diffraction angle of θ. Based on the wavelength of light signal S7 and the diffraction angle θ of light signal S8, the distance between the center positions of the first and Nth cells in a set of unit cells in a metasurface layer 54 along the x-axis can be determined. When multiple sets of unit cells need to be set on the metasurface layer, the size of each set of unit cells can be set to be the same, reducing the difficulty of manufacturing multiple sets of unit cells. In addition, after determining the distance P between the center positions of the first and Nth cells in a set of unit cells along the x-axis, and the value of N, it is also convenient to design the size of a unit cell.

[0097] For example, refer to Figure 12 As shown, a set of unit cells includes N unit cells. The standard deviation σ1 of the displacement of the center positions of the N unit cells relative to the N reference positions in the x-axis direction is equal to the average displacement of the center positions of the N unit cells relative to the N reference positions in the first direction. Satisfying the relation: Wherein, A1 is a constant. The N reference positions are periodically distributed in the first direction. Specifically, A1 can be greater than or equal to 20 nanometers (nm). The value of A1 is related to the fabrication process of the metasurface layer 54, and the embodiments of this application do not limit it.

[0098] Combination Figure 12 and Figure 18 As shown, the formula for calculating the standard deviation σ1 of the displacements of the center positions of the N unit cells relative to the N reference positions along the x-axis is Formula 2: Where N is the number of unit cells in a set of unit cells (540); d i The displacement of the center position of the i-th unit cell relative to the i-th reference position in the x-axis direction (e.g., Figure 18 The displacements di = d1 between the center position of the first unit cell and the first reference position in the x-axis direction in the second step shown are di = d2, ...); Let be the average displacement of the center positions of N unit cells 540 in a set of unit cells relative to N reference positions in the first direction. The calculation formula is shown in Formula 3: Where, x i The value of 540 in the i-th unit cell corresponds to the x-axis direction ( Figure 18In the second step shown, the first unit cell 540 corresponds to the value x = c1 + d1 along the x-axis, the second unit cell 540 corresponds to the value x = c2 + d2 along the x-axis, and so on. i The value corresponding to the i-th reference position among N reference positions in the x-axis direction ( Figure 18 In the first step shown, the first unit cell 540 corresponds to the value x = c1 along the x-axis, the second unit cell 540 corresponds to the value x = c2 along the x-axis, and so on. Where x... i -c i Let d be the displacement d between the center position of the i-th unit cell and the i-th reference position along the x-axis. i ( Figure 18 The displacement d of the center position of the first unit cell relative to the first reference position in the second step shown is along the x-axis. i =d1, the displacement d between the center position of the second unit cell and the second reference position along the x-axis. i =d2…).

[0099] For example, refer to Figure 14 As shown, a set of unit cells includes N unit cells. The standard deviation σ2 of the displacement of the center position of each of the N unit cells from the baseline y = b is equal to the average displacement of the center position of each of the N unit cells from the baseline. Satisfying the relation: Wherein, A2 is a constant. Specifically, A2 can be greater than or equal to 20nm. The value of A2 is related to the fabrication process of the metasurface layer 54, but the embodiments of this application do not limit it.

[0100] Combination Figure 14 and Figure 19 As shown, the formula for calculating the standard deviation σ2 of the displacement of the center positions of the N unit cells relative to the baseline y = b is Formula 4: Where N is the number of unit cells in a set of unit cells (540); f i The displacement of the center position of the i-th unit cell in a set of unit cells relative to the baseline y = b (e.g.) Figure 19 The displacement f of the center position of the first unit cell in the second step shown relative to the baseline y = b i =f1, the displacement f of the center position of the second unit cell relative to the baseline y=b i =f2…); Let be the average displacement of the center positions of N unit cells 540 in a set of unit cells relative to the baseline y = b. The calculation formula is shown in Formula 5: Among them, y i The value of 540 in the i-th unit cell corresponds to the y-axis direction. Figure 19The first cell 540 in the second step shown corresponds to a value y=b+f1 in the y-axis direction, the second cell 540 corresponds to a value y=b+f2 in the y-axis direction, and so on); b is the reference line corresponding to a value y=b in the y-axis direction Figure 19 The y=b shown corresponds to a value y=b in the y-axis direction i -b is the displacement amount f of the center position of the i-th cell from the reference line y=b i Figure 19 The displacement amount f of the center position of the first cell in the second step shown from the reference line y=b is f1, the displacement amount f of the center position of the second cell from the reference line y=b is f2, and so on. i i

[0101] Exemplarily, Figure 10 The silicon-based liquid crystal device 50 shown can be arranged in Figure 3 The silicon-based liquid crystal device 34 shown in the wavelength selective switch 30 is replaced by Figure 3 The silicon-based liquid crystal device 34 shown in the wavelength selective switch 30 is replaced by Figure 3 The insertion loss fluctuation of the wavelength selective switch shown is reduced, and the performance is improved.

[0102] In other embodiments, Figure 10 The silicon-based liquid crystal device 50 shown can also be arranged in a display device as a phase modulator in the display device, so that the display performance of the display device is better.

[0103] Although the present application has been described in connection with specific features and embodiments thereof, it is evident that many modifications and variations of the application will be obvious to those skilled in the art in the light of this teaching. Accordingly, the specification and drawings are to be regarded as illustrative only and the scope of the application is defined by the appended claims. Obviously, many modifications and variations of this application are possible in light of its teachings. It is intended that the scope of the application encompass any and all modifications and variations within the scope of the broadest interpretation of the appended claims. It is therefore submitted that the application will cover any such modifications or variations as fall within the scope of the appended claims and their equivalents.​​​

Claims

1. A silicon-based liquid crystal device, characterized by, The silicon-based liquid crystal device comprises: a silicon substrate, a liquid crystal layer arranged on the silicon substrate, and at least one metasurface layer arranged between the silicon substrate and the liquid crystal layer; the metasurface layer comprises a plurality of unit cells arranged in an array; in a first direction, the center positions of each unit cell in a group of unit cells arranged continuously are non-periodically distributed in the first direction, the first direction being a phase gradient direction of the metasurface layer, so that the diffraction efficiency of +1 order diffracted light of the metasurface layer is greater than a first threshold value; and / or, the center positions of each unit cell in the group of unit cells are non-periodically distributed in a second direction, in the second direction, the displacement between at least one unit cell in the group of unit cells and a reference line parallel to the first direction is greater than 0, so that the diffraction efficiency of +1 order diffracted light of the metasurface layer is greater than a second threshold value; the second direction is perpendicular to the phase gradient direction on the metasurface layer; wherein each group of unit cells forms a phase plane varying from 0 to 2π in the first direction, and the group of unit cells includes two adjacent unit cells with a sudden change in deflection direction.

2. The silicon-based liquid crystal device according to claim 1, wherein θ is the diffraction angle of +1 order diffracted light of the metasurface layer, and λ is the wavelength of incident light of the metasurface layer. The set of unit cells includes N unit cells, N being a positive integer greater than or equal to 2, wherein the distance P between the center position of the first unit cell and the center position of the Nth unit cell in the first direction satisfies the following formula:

3. The silicon-based liquid crystal device according to claim 1 or 2, wherein the group of unit cells comprises N unit cells, N being a positive integer greater than or equal to 2, wherein in the first direction, the i-th unit cell in the N unit cells has a first displacement from the i-th reference position in N reference positions, the N first displacements having a size such that the diffraction efficiency of +1 order diffracted light of the metasurface layer is greater than the first threshold value, i∈[1,N], and the N reference positions are periodically distributed in the first direction.

4. The silicon-based liquid crystal device according to claim 1 or 2, wherein the group of unit cells comprises N unit cells, N being a positive integer greater than or equal to 2, wherein in the second direction, the i-th unit cell in the N unit cells has a second displacement from a reference line parallel to the first direction, the N second displacements having a size such that the diffraction efficiency of +1 order diffracted light of the metasurface layer is greater than the second threshold value, i∈[1,N]. The silicon-based liquid crystal device further comprises a reflective layer arranged between the silicon substrate and the at least one metasurface layer. The wavelength selective switch comprises a reflective structure, a wave divider, and the silicon-based liquid crystal device according to any one of claims 1-7; the wave divider and the silicon-based liquid crystal device are coupled through the reflective structure. The wavelength selective switch comprises a plurality of wavelength selective switches according to claim 8.

5. The silicon-based liquid crystal device according to claim 1 or 2, wherein The set of unit cells includes N unit cells, N being a positive integer greater than or equal to 2, wherein the first displacement standard deviation σ1 of the center positions of the N unit cells in the first direction from the N reference positions, and the first displacement average value of the center positions of the N unit cells in the first direction from the N reference positions satisfy the relationship: The relationship is satisfied: wherein A1 is a constant; and the N reference positions are periodically distributed in the first direction.

6. The silicon-based liquid crystal device of claim 1 or 2, wherein, The set of unit cells includes N unit cells, N being a positive integer greater than or equal to 2, wherein the center positions of the N unit cells are respectively displaced from a reference line parallel to the first direction by a second displacement standard deviation σ2, and the center positions of the N unit cells are respectively displaced from a second displacement average value parallel to the reference line by a second displacement average deviation σ2 satisfies the relationship: where A2 is a constant.

7. The silicon-based liquid crystal device of claim 1 or 2, wherein, ​ 8. A wavelength selective switch, characterized by, ​ 9. An optical add / drop multiplexer characterized by comprising: ​

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