A polarization-insensitive phase-type LCOS device

Abstract

This invention relates to a polarization-insensitive phase-type LCOS device, comprising a glass substrate layer, a common electrode layer, a liquid crystal layer, a lower surface alignment layer, a passivation layer, a silicon substrate layer, and an electrode layer arranged sequentially. It also includes a liquid crystal metasurface layer disposed above or below the liquid crystal layer, and a waveplate layer disposed between the lower surface alignment layer and the passivation layer. The liquid crystal metasurface layer comprises a subwavelength-scale periodic metasurface structure and a liquid crystal material structure. The waveplate layer is a quarter-waveplate layer. When incident light interacts with the liquid crystal metasurface layer, the metasurface structure excites local optical resonance, enhancing the light field within the liquid crystal region and extending the effective interaction path between the light and the liquid crystal material. Compared with existing technologies, this invention has advantages such as a thin liquid crystal layer, high response speed, high phase depth, and polarization insensitivity.

Description

Technical Field

[0001] This invention relates to a silicon-based liquid crystal device, and more particularly to a polarization-insensitive phase-type LCOS device. Background Technology

[0002] Liquid crystal on silicon (LCOS) devices are a typical type of reflective spatial light modulator, widely used in holographic displays, wavefront modulation, beam deflection, projection displays, optical communications, and programmable optical systems. For example... Figure 1 As shown, a traditional LCOS structure typically includes a glass substrate layer 1, a common electrode layer 2, an upper surface alignment layer 3, a liquid crystal layer 4, a lower surface alignment layer 5, a passivation layer 6, a silicon substrate layer 7, and an electrode layer 8. Incident light enters the liquid crystal layer from above the device, is reflected by the metal electrode, and then exits through the liquid crystal layer again. Its light field modulation function mainly comes from the electrically controlled birefringence effect of the liquid crystal molecules: by applying a voltage between the transparent electrode and the metal reflective electrode, the alignment state of the liquid crystal molecules can be changed, thereby modulating the propagation phase of the incident light.

[0003] However, the complete reliance on the birefringence of liquid crystal materials in traditional LCOS devices leads to numerous limitations. First, the birefringence of liquid crystals makes the device highly sensitive to the polarization state of incident light; only incident light along a specific polarization direction is modulated. Therefore, in practical optical systems, traditional LCOS devices typically require the use of polarizers, polarization beam splitters, or other polarization control elements. This not only increases the system's size, assembly complexity, and manufacturing cost but also hinders further miniaturization and integration of optical systems. Second, to achieve 2π phase modulation, traditional LCOS devices require a relatively thick liquid crystal layer to provide sufficient optical path difference. However, a liquid crystal layer several micrometers thick significantly reduces the response speed of liquid crystal molecules to an electric field, making it difficult to meet the high-speed dynamic modulation requirements of the device. Furthermore, a thicker liquid crystal layer also enhances crosstalk between electrodes, thereby reducing the device's modulation accuracy and capability.

[0004] To address the polarization sensitivity issue, existing technologies typically employ two main approaches. The first approach uses special polarization-insensitive liquid crystal materials, such as blue phase liquid crystals. Blue phase liquid crystals exhibit near-optical isotropy when no electric field is applied, thus potentially reducing the device's dependence on the incident polarization state at the material level. However, these materials usually require high driving voltages, while standard CMOS backplanes offer limited driving voltages, making it difficult to meet the operational requirements of practical devices. The second approach uses polarizers or similar devices before the LCOS device to ensure incident light polarization. However, when the system uses LEDs, natural light, or other unpolarized light sources, the polarizer filters out approximately half of the incident light energy, resulting in significant light energy loss. This poses a significant limitation for display systems that prioritize high brightness, low power consumption, and high luminous efficiency, especially for AR / VR near-eye displays, portable projectors, and compact optical systems.

[0005] To address the issues of excessively thick liquid crystal layers and slow response speeds, existing technologies typically employ two approaches. The first approach uses liquid crystal materials with a larger refractive index difference. This approach allows for a reduction in liquid crystal layer thickness while maintaining the same phase modulation depth. However, high birefringence liquid crystal materials often suffer from limitations in material selection, high viscosity coefficients, limited improvement in response speed, and constraints on operating wavelength and temperature stability. Furthermore, their optical performance and electrical actuation characteristics often fail to simultaneously meet the requirements of high-speed, low-voltage, and high-stability devices. Therefore, simply increasing the refractive index difference of the liquid crystal material is insufficient to fundamentally solve the problem of achieving high phase depth modulation under thin liquid crystal layer conditions. The second approach combines liquid crystals with metasurfaces. Utilizing the local resonance characteristics of metasurfaces, the interaction between light and liquid crystal materials is enhanced under extremely thin liquid crystal layer conditions, thereby achieving a higher phase modulation depth. This approach helps reduce liquid crystal layer thickness and improve device response speed. However, existing liquid crystal metasurface solutions typically still exhibit significant polarization sensitivity, and their phase modulation effect depends on the matching relationship between the incident light polarization direction and the anisotropic structure of the metasurface or the orientation of the liquid crystal molecules. When the polarization state of the incident light changes, the phase response and modulation efficiency of the device will decrease significantly.

[0006] Therefore, existing LCOS technology still struggles to simultaneously meet requirements such as polarization insensitivity, low driving voltage, high phase depth, and high response speed. How to improve the response speed of LCOS devices and reduce their dependence on the incident polarization state without introducing high driving voltages and complex external polarization optical components is a pressing technical problem that needs to be solved in the further development of LCOS devices. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art by providing a polarization-insensitive phase-type LCOS device with a thin liquid crystal layer, high response speed, high phase depth, and polarization insensitivity, thus solving the problems of slow response speed and sensitivity to incident polarization state of traditional LCOS devices.

[0008] The objective of this invention can be achieved through the following technical solutions: A polarization-insensitive phase-type LCOS device includes a glass substrate layer, a common electrode layer, a liquid crystal layer, a lower surface alignment layer, a passivation layer, a silicon substrate layer, and an electrode layer arranged sequentially. It also includes a liquid crystal metasurface layer disposed above or below the liquid crystal layer and a waveplate layer disposed between the lower surface alignment layer and the passivation layer. The liquid crystal metasurface layer comprises a subwavelength-scale periodic metasurface structure and a liquid crystal material structure. The waveplate layer is a quarter-waveplate layer. When incident light interacts with the liquid crystal metasurface layer, the metasurface structure excites local optical resonance, enhancing the light field within the liquid crystal region and extending the effective interaction path between the light and the liquid crystal material.

[0009] Furthermore, the structural parameters of the LCOS device are determined based on the target operating wavelength and the refractive index of the liquid crystal material.

[0010] Furthermore, the structural parameters include the geometric dimensions, period, height, and thickness of the liquid crystal metasurface.

[0011] Furthermore, the thickness of the supplementary liquid crystal layer is sufficient to enable the LCOS device to achieve a high phase modulation depth.

[0012] Furthermore, the liquid crystal material structure is configured to encapsulate the metasurface structure.

[0013] Furthermore, the metasurface structure is a single-layer or multi-layer dielectric metasurface, a metallic metasurface, or a metal-dielectric composite metasurface.

[0014] Furthermore, the fabrication of the liquid crystal metasurface layer specifically includes: An EBL mask is prepared and the metasurface structure is etched out. Liquid crystal is then injected into the metasurface structure to form the liquid crystal material structure.

[0015] Furthermore, the waveplate layer is made of anisotropic material.

[0016] Furthermore, the waveplate layer adopts any one of the following: a single uniform anisotropic material waveplate, a composite material waveplate, a non-resonant birefringent microstructure waveplate, a resonant enhanced metasurface waveplate, or an emerging anisotropic or tunable material waveplate.

[0017] Furthermore, when designing this LCOS device, the metasurface unit structure of the liquid crystal metasurface layer and the waveplate layer material are selected according to the design requirements of response speed and polarization conversion capability.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1) Existing technologies (such as Chinese patent application CN114114770A) mostly involve only liquid crystal phase metasurfaces. This invention integrates a liquid crystal metasurface and a waveplate into an LCOS device, forming a reflective polarization-independent phase-type LCOS device that combines high phase depth modulation capability with polarization insensitivity. The liquid crystal metasurface utilizes local optical resonance of a subwavelength structure to enhance the interaction between light and the liquid crystal material, enabling the device to achieve a large phase modulation depth even with a relatively thin liquid crystal layer. This achieves complete high phase depth coverage and improves the device's response speed. Incident light passes through the liquid crystal metasurface and receives phase modulation, then passes through a quarter-wave plate to reach the metal electrode and is reflected. The reflected light passes through the quarter-wave plate again, and its polarization direction is rotated by 90 degrees relative to its incident direction. Therefore, when linearly polarized light is effectively modulated by the liquid crystal metasurface during incident propagation, its orthogonally polarized component after reflection does not receive the same modulation again; while for incident polarized light orthogonal to it, equivalent phase modulation can be obtained in another stage of the round-trip propagation process. Therefore, light with different incident polarization directions can obtain a consistent and effective phase response, thereby realizing polarization-insensitive modulation of LCOS devices, solving the polarization sensitivity problem of existing technologies, and having a wider range of applications.

[0019] 2) The design of this invention can achieve a certain working bandwidth, rather than a single working wavelength, which has more practical application significance.

[0020] 3) This invention is geared towards phase-type LCOS, with a more flexible phase control dimension, which can realize arbitrary direction deflection of the beam and can be used to generate two-dimensional holograms.

[0021] 4) Unlike existing technologies (such as patent application CN117872639A) where polarization conversion capability originates from metasurface structures, the polarization conversion capability of this invention is not based on a specific metasurface structure, but rather on an anisotropic structure with a broader control mechanism. This structure includes metasurface units or natural anisotropic material layers. The more flexible design of the polarization conversion layer is more suitable for operating requirements with a certain bandwidth compared to a single metasurface deflection conversion scheme. Furthermore, the polarization conversion structure of this invention allows for the selection of optimal design schemes as needed, flexibly choosing between natural anisotropic materials or metasurface unit structures based on requirements such as response speed and polarization conversion capability.

[0022] 5) This invention enables devices to achieve high response speed in an ultra-thin liquid crystal layer, thereby reducing driving voltage and power consumption. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a traditional LCOS structure; Figure 2 This is a schematic diagram of the structure of the present invention; Figure 3 This is an example diagram of the phase modulation depth of the liquid crystal metasurface according to the present invention; Figure 4 This is a schematic diagram comparing the modulation efficiency of the polarization-insensitive device and the polarization-sensitive device of the present invention. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0025] like Figure 2 As shown, this embodiment provides a polarization-insensitive phase-type LCOS device. Based on the conventional LCOS device comprising a glass substrate layer 1, a common electrode layer 2, a liquid crystal layer 4, a lower surface alignment layer 5, a passivation layer 6, a silicon substrate layer 7, and an electrode layer 8, it further includes a liquid crystal metasurface layer 9 disposed above or below the liquid crystal layer 4, and a waveplate layer 10 disposed between the lower surface alignment layer 5 and the passivation layer 6. The liquid crystal metasurface layer comprises a subwavelength-scale periodic metasurface structure and a liquid crystal material structure. The local optical resonance of the subwavelength structure enhances the interaction between light and the liquid crystal material, enabling the device to achieve a large phase modulation depth with a relatively thin liquid crystal layer, thereby achieving high phase depth coverage and improving the device response speed. The waveplate layer is a quarter-waveplate layer. Incident light passes through the liquid crystal metasurface and obtains phase modulation, then passes through the quarter-waveplate to reach the metal electrode and is reflected. The reflected light passes through the quarter-waveplate again, and its polarization direction is rotated by 90 degrees relative to the incident direction. Therefore, when linearly polarized light is effectively modulated by the liquid crystal metasurface during its incident propagation, its orthogonally polarized component after reflection will not receive the same modulation again; while for incident polarized light orthogonal to it, equivalent phase modulation can be obtained in another stage of the round-trip propagation process. Thus, light with different incident polarization directions can obtain a consistent effective phase response, thereby realizing polarization-insensitive modulation of LCOS devices.

[0026] In the aforementioned polarization-insensitive phase-type LCOS device, the glass substrate layer 1 is a dielectric material used to protect the backplane material from environmental pollution or mechanical damage, while maintaining stable optical performance.

[0027] The common electrode layer 2 is made of ITO material and serves as a common grounding electrode. It can be prepared by magnetron sputtering.

[0028] In the liquid crystal metasurface layer 9, a liquid crystal material structure encapsulates the metasurface structure. The metasurface structure can be a single-layer or multi-layer dielectric metasurface, a metal metasurface, or a metal-dielectric composite metasurface, which can provide a large phase depth with extremely low thickness. Furthermore, this layer can be configured with either the metasurface layer on top or the liquid crystal layer on top, depending on the processing requirements.

[0029] Specifically, the fabrication of the liquid crystal metasurface layer includes: An EBL mask is prepared and the metasurface structure is etched out. Liquid crystal is then injected into the metasurface structure to form the liquid crystal material structure.

[0030] The liquid crystal layer 4 is used to supplement the phase depth of the device, ensuring that the device has sufficient phase modulation depth.

[0031] The lower surface alignment layer 5 is made of polyimide material and is used to provide the initial alignment of liquid crystal molecules.

[0032] Specifically, the orientation layer is made of polyimide using PI letterpress transfer technology.

[0033] Waveplate layer 10 is used to achieve a 1 / 4 waveplate effect.

[0034] Specifically, the waveplate layer can be prepared using one of the following methods: 1) Single homogeneous anisotropic material waveplate: This type of waveplate uses the crystal anisotropy of a single homogeneous material to generate birefringence, thus forming a quarter-wave plate, without relying on composite or micro / nano structures. Typical materials include quartz and magnesium fluoride.

[0035] 2) Oriented or composite waveplates: Quarter waveplates are formed by molecular orientation, stretching, polymerization, and doping to create anisotropy. Typical materials include liquid crystal polymers.

[0036] 3) Non-resonant birefringent microstructure waveplates: The material itself is isotropic, but equivalent anisotropy is generated through the shape of the micro / nano structure, such as using one-dimensional subwavelength gratings or other structures with different material densities in different directions. Commonly used materials include silicon, silicon dioxide, and silicon nitride.

[0037] 4) Resonance-enhanced metasurface waveplates: The material itself is isotropic, but the anisotropy is further enhanced by using optical resonance while generating equivalent anisotropy through micro / nano structure shapes. Examples include optical resonance nanopillars, metal-dielectric resonance structures, and plasmon resonance structures. Commonly used materials include silicon, gold, and titanium dioxide.

[0038] 5) Emerging anisotropic or tunable material waveplates: These utilize emerging tunable materials that possess anisotropic, tunable optical properties, or unique responses. Typical materials include graphene and group III-V phase transition materials.

[0039] Passivation layer 6 is a dielectric material used to protect the electrodes from oxidation and to prevent voltage breakdown of the liquid crystal layer. Specifically, a silicon dioxide thin film can be prepared using magnetron sputtering to serve as the passivation protective layer.

[0040] Specifically, the passivation layer can be prepared to a specified thickness using magnetron sputtering or atomic layer deposition.

[0041] The silicon substrate layer 7 is made of amorphous silicon material and is used to provide mechanical support for the device and a substrate for circuit wiring.

[0042] Specifically, the silicon substrate layer is fabricated using CMOS technology.

[0043] The electrode layer 8 is composed of rectangular metal electrodes and is wrapped with a dielectric material. It is used to apply a working voltage to achieve electronically controlled phase modulation of the liquid crystal molecules.

[0044] Specifically, electrode layer 8 can be prepared by magnetron sputtering to form an aluminum film, followed by EBL to prepare a mask and etching it into an electrode array.

[0045] The structural parameters of the aforementioned polarization-insensitive phase-type LCOS device are designed based on the target operating wavelength and the refractive index of the liquid crystal material. Specifically, the structural parameters include the geometric period, height, duty cycle, and liquid crystal layer thickness of the liquid crystal metasurface. Furthermore, during the design of this LCOS device, the metasurface unit structure of the liquid crystal metasurface layer and the waveplate layer material can be flexibly selected according to the design requirements for response speed and polarization conversion capability.

[0046] The working principle of the polarization-insensitive phase-type LCOS device described above is explained below: First, after entering the device, the incident light passes sequentially through the transparent electrode layer, the alignment layer, and the liquid crystal layer, finally reaching the liquid crystal metasurface layer. When the incident light interacts with the liquid crystal metasurface layer, the metasurface structure can excite local optical resonances, enhancing the light field within the liquid crystal region and extending the effective interaction path between the light and the liquid crystal material. Therefore, even with a thin liquid crystal layer, the device can still achieve a large electrically controlled phase modulation depth.

[0047] Under an applied voltage, the orientation of liquid crystal molecules changes, leading to a change in the equivalent refractive index of the liquid crystal layer and the metasurface region. Since the resonant response of the metasurface is highly sensitive to changes in the surrounding refractive index, the change in liquid crystal orientation further causes a change in the metasurface's resonant phase. By using numerical calculation methods based on Maxwell's equations, such as the finite-difference time-domain method and the finite element method, combined with traditional optimization algorithms or neural network optimization design, the geometric dimensions, period, height, and liquid crystal layer thickness of the metasurface can be rationally optimized. Optimizing the reflectivity, polarization conversion rate, and phase depth at different wavelengths allows the device to achieve continuous or quasi-continuous high phase depth modulation within the target voltage range, such as... Figure 3 As shown. In a specific embodiment, the optimized structural parameters are as follows: metasurface period 1050nm, duty cycle 0.15, height 0.775nm, and overall thickness of the liquid crystal metasurface layer 2μm. Compared to traditional LCOS devices that rely on the cumulative optical path difference of a thick liquid crystal layer, this mechanism can achieve complete phase coverage under a thinner liquid crystal layer, thereby helping to reduce the driving voltage, improve the response speed, and weaken the edge field effect and inter-pixel crosstalk in small pixel devices. Furthermore, this design is designed for a specific operating bandwidth, making it applicable to a wider range of scenarios.

[0048] Subsequently, the light modulated by the liquid crystal metasurface continues to propagate downwards, entering the quarter-wave plate layer and reaching the metal reflective electrode. The metal reflective electrode reflects the incident light, causing it to return along its original path. Since the light passes through the quarter-wave plate twice, before and after reflection, the two-way propagation effect of the quarter-wave plate is equivalent to that of a half-wave plate. Therefore, for linearly polarized incident light, the polarization direction of the reflected light will rotate approximately 90° relative to the original incident polarization direction.

[0049] Taking X-polarized incident light as an example, when the incident light first passes through the liquid crystal layer and the liquid crystal metasurface, its polarization direction matches the effective modulation direction of the liquid crystal, thus achieving electrically controlled phase modulation provided by the liquid crystal metasurface. Subsequently, the light passes through a quarter-wave plate, is reflected by the metal reflecting electrode, and passes through the quarter-wave plate again, where its polarization direction is rotated to y-polarization, orthogonal to the original polarization direction. Therefore, in the return path, the light no longer propagates along the original effective modulation direction of the liquid crystal, avoiding repeated acquisition of the same liquid crystal phase modulation. Thus, the X-polarized incident light obtains equivalent one-way phase modulation throughout the entire round-trip propagation process.

[0050] For y-polarized incident light, the situation is complementary to that of x-polarized incident light. In the incident path, the y-polarized light does not match the effective modulation direction of the liquid crystal, therefore no phase modulation or only weak phase modulation occurs. After passing through a quarter-wave plate, being reflected by the metal electrode, and then passing through the quarter-wave plate again, its polarization direction rotates to x-polarization. In the return path, the light matches the effective modulation direction of the liquid crystal and obtains phase modulation equivalent to that of x-polarized incident light. Therefore, different orthogonally linearly polarized incident lights can all obtain effective phase modulation at some stage of their round-trip propagation.

[0051] For incident light with any polarization state, it can be decomposed into an x-polarization component and a y-polarization component. Since these two orthogonal polarization components obtain equivalent one-way phase modulation in the incident or return path, incident light with any polarization can obtain a consistent effective phase response, such as... Figure 4 As shown. Thus, the present invention achieves polarization-insensitive operating speed for LCOS devices.

[0052] In summary, this invention enhances the phase modulation capability of a thin liquid crystal layer through a liquid crystal metasurface and achieves polarization direction rotation through two-way propagation of a quarter-wave plate, enabling the device to simultaneously possess high phase modulation capability and polarization insensitivity under relatively thin liquid crystal layer conditions. This working mechanism can solve the problems of slow response speed, high driving voltage, and liquid crystal modulation dependence on the incident polarization direction caused by thick liquid crystal layers in traditional LCOS devices.

[0053] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A polarization-insensitive phase-type LCOS device, comprising a glass substrate layer, a common electrode layer, a liquid crystal layer, a lower surface alignment layer, a passivation layer, a silicon substrate layer, and an electrode layer sequentially disposed therefrom, characterized in that, It also includes a liquid crystal metasurface layer disposed above or below the liquid crystal layer and a waveplate layer disposed between the lower surface alignment layer and the passivation layer. The liquid crystal metasurface layer includes a subwavelength scale periodic metasurface structure and a liquid crystal material structure. The waveplate layer is a quarter-waveplate layer. When incident light interacts with the liquid crystal metasurface layer, the metasurface structure excites local optical resonance, enhances the light field in the liquid crystal region, and prolongs the effective interaction path between light and the liquid crystal material.

2. The polarization-insensitive phase-type LCOS device according to claim 1, characterized in that, The structural parameters of the LCOS device are determined based on the target operating wavelength and the refractive index of the liquid crystal material.

3. The polarization-insensitive phase-type LCOS device according to claim 2, characterized in that, The structural parameters include the geometric dimensions, period, height, and thickness of the liquid crystal metasurface.

4. The polarization-insensitive phase-type LCOS device according to claim 3, characterized in that, The thickness of the supplementary liquid crystal layer is sufficient to enable the LCOS device to achieve a high phase modulation depth.

5. The polarization-insensitive phase-type LCOS device according to claim 1, characterized in that, The liquid crystal material structure encapsulates the metasurface structure.

6. The polarization-insensitive phase-type LCOS device according to claim 1, characterized in that, The metasurface structure is a single-layer or multi-layer dielectric metasurface, a metallic metasurface, or a metal-dielectric composite metasurface.

7. The polarization-insensitive phase-type LCOS device according to claim 1, characterized in that, The fabrication of the liquid crystal metasurface layer specifically includes: An EBL mask is prepared and the metasurface structure is etched out. Liquid crystal is then injected into the metasurface structure to form the liquid crystal material structure.

8. The polarization-insensitive phase-type LCOS device according to claim 1, characterized in that, The waveplate layer is made of anisotropic material.

9. The polarization-insensitive phase-type LCOS device according to claim 1 or 8, characterized in that, The waveplate layer is made of any one of the following: a single uniform anisotropic material waveplate, a composite material waveplate, a non-resonant birefringent microstructure waveplate, a resonant enhanced metasurface waveplate, or an emerging anisotropic or tunable material waveplate.

10. The polarization-insensitive phase-type LCOS device according to claim 1, characterized in that, When designing this LCOS device, the metasurface unit structure of the liquid crystal metasurface layer and the waveplate layer material are selected according to the design requirements of response speed and polarization conversion capability.

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