Novel liquid crystal spatial light modulator and use method

Abstract

The invention discloses a novel liquid crystal spatial light modulator and a use method, relates to the technical field of spatial light modulation, and aims to solve the problems of poor real-time performance, insufficient high-frequency phase distortion compensation, dependence on accurate wavefront detection and the like caused by the fact that an existing liquid crystal on silicon (LCOS) spatial light modulator depends on software algorithm compensation. The modulator comprises a reflection type LCOS device and a transmission type phase compensation layer, the LCOS comprises a CMOS silicon-based backboard, an electrode layer, a liquid crystal layer and other structures, and the phase compensation layer is fixed on the surface of the LCOS device. The application method comprises the following steps: establishing a gray-phase curve through an orthogonal polarization method, obtaining initial phase distribution through a phase shift interference method, and preparing a physical compensation layer through laser direct writing or voltage control to realize phase regulation and control combining physics and an algorithm. Complexity of a compensation algorithm is reduced, light field regulation and control precision and efficiency are improved, and the method is suitable for the fields of holographic display, all-optical communication and the like.

Description

Technical Field

[0001] The present invention relates to the field of spatial light modulation technology, and in particular to a novel liquid crystal spatial light modulator and a use method thereof. Background Art

[0002] Light field manipulation technology uses spatial light modulators to generate light fields with non-uniform amplitude, phase, or polarization distributions, demonstrating significant application value in holographic displays, all-optical communications, and beam shaping. To achieve real-time dynamic manipulation, spatial light modulators typically employ a pixelated structure, independently modulating the wavefronts of light waves at different locations to achieve the target light field distribution. Liquid crystal on silicon (LCOS) spatial light modulators (LCOS), manufactured using CMOS technology, are reflective liquid crystal devices. Their core advantages lie in their high resolution and flexible digital phase manipulation capabilities. By controlling the pixel voltage to change the orientation of liquid crystal molecules, the phase or intensity of the incident light can be precisely modulated, making them a core component of modern light field manipulation.

[0003] However, the phase modulation accuracy and stability of LCOS are limited by existing compensation technologies. The current mainstream solution relies on closed-loop calibration using software algorithms: by detecting the deviation between the output wavefront and the target value, an iterative algorithm is used to optimize the grayscale image loaded into the LCOS to compensate for phase errors introduced by device nonlinear response, temperature drift, manufacturing tolerances, etc. However, this method has inherent flaws: first, the iterative process is time-consuming and difficult to meet the needs of real-time dynamic applications; second, it is highly dependent on stable wavefront detection, and its accuracy is easily disturbed in complex optical paths or dynamic environments; third, it has limited effect on compensating for high-frequency phase distortion caused by physical structural defects (such as pixel edge effects and backplane topography fluctuations). These problems not only limit the performance upper limit of LCOS, but also increase the manufacturing cost and operational difficulty of the device.

[0004] In view of this, this application is hereby filed. Summary of the Invention

[0005] The object of the present invention is to provide a novel liquid crystal spatial light modulator and a method of use thereof to solve the problems mentioned in the above background technology.

[0006] To solve the above technical problems, the present invention provides a novel liquid crystal spatial light modulator, including a reflective modulation device and a transmissive modulation device; the reflective modulation device is a silicon liquid crystal (LCOS), which modulates the phase of the incident light according to the application scenario; the reflective modulation device includes, from bottom to top, a CMOS silicon-based backplane, an aluminum pixel electrode layer, a dielectric reflection layer, a lower orientation layer, a first liquid crystal molecule layer, an upper orientation layer, an ITO electrode layer and a glass substrate; the transmissive modulation device is a phase compensation layer, which is a multi-layer structure fixed to the upper surface of the reflective modulation device, and compensates for the initial phase deviation problem of the silicon liquid crystal (LCOS) device caused by the surface morphology of the silicon-based backplane and the uneven thickness of the liquid crystal cell; the spatial light control device is coated with an anti-reflection layer film on the glass and air interfaces; through the combination of reflective and transmissive modulation devices, the phase deviation of the LCOS device is compensated at the physical level, thereby improving the phase modulation accuracy of the device.

[0007] Furthermore, the material of the dielectric reflective layer is at least one of Si, ZnSe, and GaAs; the dielectric reflective layer is periodically arranged in the short axis and long axis directions of the liquid crystal, with a period of 300-800nm ​​on the long axis and a duty cycle of 50%-80%, a thickness of the high refractive index material of 100-500nm, a width of the dielectric material on the short axis of 100-200nm, and a period of 300-500nm; while enhancing the reflective performance, horizontal orientation of the liquid crystal is achieved, thereby optimizing the modulation effect of the liquid crystal on silicon (LCOS) device.

[0008] Furthermore, the phase compensation layer is a sandwich structure of an upper transparent substrate, an upper orientation layer, a second liquid crystal molecule layer, a lower orientation layer, and a lower transparent substrate; the initial phase distribution of the phase compensation layer is achieved by laser direct writing; physical compensation is achieved for the initial surface phase distribution of the silicon-based liquid crystal (LCOS) device, and phase deviation caused by physical structural defects is specifically addressed.

[0009] Furthermore, the phase compensation layer includes a structure of an upper transparent substrate, an ITO transparent upper electrode layer, an upper alignment layer, a liquid crystal molecule layer, a lower alignment layer, an ITO transparent lower electrode layer, and a lower transparent substrate; an elliptical ring-shaped transparent electrode array is photolithographically prepared on the surface of the upper transparent substrate and evenly distributed in the effective area of ​​the corresponding silicon-based liquid crystal (LCOS) device, each ring-shaped electrode is independently connected to the driving circuit, and a gap area is left between adjacent ring electrodes; the compensation phase distribution can be dynamically adjusted through voltage control to cope with phase drift caused by factors such as temperature.

[0010] Furthermore, the lower substrate of the phase compensation layer and the glass substrate of the liquid crystal on silicon (LCOS) device are made of the same material; thus, the optical diffraction efficiency is improved and the adverse effects caused by interface reflection are reduced.

[0011] A method for using a novel liquid crystal spatial light modulator comprises the following steps: Step 1: Establishing the grayscale-phase modulation curve of the first LCOS device in different phase modulation regions by the orthogonal polarization method. Configure a first laser light source, a first linear polarizer, a first beam splitter, a first LCOS device, a second linear polarizer, and a photodetector. Perform a grayscale voltage scanning operation on multiple spatial coordinate points on the surface of the first LCOS device to generate a grayscale-phase modulation characteristic curve and form a lookup table to feed back to the driving algorithm. Step 2: Measure the reference phase of the first LCOS device by phase-shift interferometry. Configure a Twyman-Green interferometer, including a second laser light source, a beam expansion and collimation module, a polarization module, a second beam splitter, a reference mirror, and an imaging module. Set all pixel units of the second LCOS device to 0 grayscale, and process the interference pattern to obtain an initial surface phase distribution. Step 3: Prepare a phase physical compensation layer according to the initial surface phase distribution, and realize phase physical compensation through the phase compensation layer (107); combine the orthogonal polarization method and the phase shift interferometry method to accurately obtain phase information and perform compensation, thereby improving the accuracy of phase calibration.

[0012] Furthermore, in step 1, the transmission axis of the first linear polarizer is parallel to the initial orientation of the liquid crystal molecules of the first LCOS device, and the transmission axis of the second linear polarizer is orthogonal to the transmission axis of the first linear polarizer at 90°; the photodetector uses an area array CCD camera, and its pixel resolution matches the pixel unit of the first LCOS device; the spatial coordinate points are arranged in a periodic matrix, the number of which is not less than 30, and the maintenance time of each voltage point is greater than 3 times the response time of the liquid crystal; the accuracy and representativeness of the grayscale-phase modulation curve are ensured to provide a reliable data basis for subsequent compensation.

[0013] Furthermore, in step 2, the polarization module makes the polarization direction of the incident light parallel to the initial orientation of the liquid crystal molecules of the second LCOS device; the beam splitter 2 splits the light beam to the reference mirror and the second LCOS device for emission and interference, and adjusts the position of the reference mirror so that the optical path of the two beams is equal; ensures the quality of the interference pattern and improves the accuracy of the initial surface phase distribution measurement.

[0014] Furthermore, in the step three, when the phase physical compensation layer is prepared by laser direct writing, the laser wavefront is modulated by a DMD device and focused on the surface of the photo-aligned material for vector scanning exposure; when prepared by voltage control, a gradient voltage is applied to the elliptical ring-shaped electrode to induce the second liquid crystal layer molecules to produce a compensation phase distribution opposite to the surface phase error of the second LCOS device; two methods of preparing the compensation layer are provided, which are flexibly applicable to different application scenarios and enhance the practicality of the method.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. By combining a reflective LCOS device with a transmissive phase compensation layer, a phase compensation mechanism is constructed that integrates physical and algorithmic aspects. This effectively addresses the inadequate compensation of high-frequency physical structural defects, such as pixel edge effects and backplane topography, by existing software algorithms. This significantly improves the phase modulation accuracy of LCOS. Furthermore, physical compensation reduces the time required for software iterative calibration, breaking through efficiency bottlenecks in real-time dynamic applications, reducing reliance on high-precision wavefront detection, and enhancing stability in complex environments.

[0016] 2. The phase compensation layer is fabricated using either laser direct writing or voltage control, flexibly addressing phase deviations caused by manufacturing tolerances and temperature drift, adapting to diverse application scenarios. By matching the phase compensation layer with the LCOS substrate material, interfacial reflection losses are reduced and optical diffraction efficiency is improved. This solution reduces hologram computational complexity and device cost, and has broad practical application in a variety of fields, including holographic displays, all-optical communications, and laser processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a novel liquid crystal spatial light modulator, which includes a transmissive modulation device and a reflective modulation device; Figure 2 The orthogonal polarization method of the present invention is used to calibrate the LCOS response. (a) Schematic diagram of the optical path; (b) Relationship between light intensity and grayscale after compensation; (c) Grayscale phase modulation curve after compensation; Figure 3 Schematic diagram of the optical path of the interferometry method of the present invention. (a) Schematic diagram of the optical path of the Twyman-Green interferometer; (b) Initial phase diagram of the LCOS device at zero grayscale before compensation; (c) Phase distribution diagram after compensation through the physical compensation layer; Figure 4 Schematic diagram of the ITO electrode structure in the phase compensation layer according to the second embodiment of the present invention.

[0018] In the picture: 100, CMOS silicon backplane; 101, aluminum pixel electrode layer; 102, dielectric reflective layer; 103, lower alignment layer; 104, first liquid crystal molecule layer; 105, upper alignment layer; 106, ITO electrode layer; 107, phase compensation layer; 108, anti-reflection layer; 201, laser light source 1; 202, beam expander; 203, first linear polarizer; 204, beam splitter 1; 205, aperture; 206, first LCOS device; 207, linear translation stage; 208, second linear polarizer; 209, Fourier lens; 210, photodetector; 301. Second laser light source; 302. Beam expansion and collimation module; 303. Polarization module; 304. Second beam splitter; 305. Reference mirror; 306. Second LCOS device; 307. 4f system; 308. Imaging module. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] See also Figures 1-4 The present invention provides a technical solution: a new liquid crystal spatial light modulator and a method of use, comprising: Example 1: A new type of liquid crystal spatial light modulator, such as Figure 1 As shown, it is a multi-layer structure, characterized in that it includes, from bottom to top, a CMOS silicon-based backplane 100, an aluminum pixel electrode layer 101, a dielectric reflective layer 102, a lower orientation layer 103, a first liquid crystal molecule layer 104, an upper orientation layer 105, an ITO electrode layer 106, a phase compensation layer 107 and an anti-reflection layer 108 thin film.

[0021] First, an LCOS driving circuit is fabricated on the surface of a single-crystal silicon substrate using a conventional CMOS process to form a CMOS silicon-based backplane 100. Subsequently, a metal reflective layer and a low-refractive-index oxide protective layer are sequentially deposited. The metal reflective layer is then etched using micromachining methods such as photolithography and nanoimprinting to prepare an aluminum pixel electrode layer 101. The pixel electrode has a gap area of ​​100-300nm.

[0022] A high-refractive-index dielectric reflective layer 102 is prepared on the surface of the aluminum pixel electrode layer 101. The material of the dielectric reflective layer 102 is Si, ZnSe or GaAs, and is periodically arranged in the short and long axis directions of the liquid crystal: the period on the long axis is 300-800nm, the duty cycle is 50%-80%, and the thickness of the high-refractive-index material is 100-500nm; the width of the dielectric material on the short axis is 100-200nm, and the period is 300-500nm. This structure can simultaneously enhance reflection and achieve horizontal orientation of the liquid crystal.

[0023] A lower alignment layer 103 is fabricated on the surface of the dielectric reflective layer 102 by rubbing a polyimide (PI) film (about 20 nm thick) to produce grooves. Subsequently, a first liquid crystal molecule layer 104, an upper alignment layer 105, and an ITO electrode layer 106 are sequentially arranged, wherein the upper alignment layer 105 is also fabricated by rubbing the PI film.

[0024] The phase compensation layer 107 has a sandwich structure of first and second glass substrates: a photosensitive polymer film is spin-coated on the upper and lower surfaces of the first glass substrate, and an ITO electrode layer 106 is plated thereon. The ITO electrode layer 106 is photolithographically processed to form a periodic arrangement along the long axis of the liquid crystal molecules. The ITO width in each period is 6-8μm, and the gap between adjacent ITO layers is 200-300nm. An upper alignment layer 105 is formed on the surface of the ITO electrode layer 106, and grooves in the PI film are used to align the liquid crystal molecules along the long axis when no voltage is applied. An anti-reflection layer 108 is plated on the upper and lower surfaces of the second glass substrate, and a PI film alignment layer (approximately 20nm thick) is prepared by friction.

[0025] The silicon-based backplane is bonded to the first glass substrate, and the first glass substrate is bonded to the second glass substrate. Spacer particles are evenly mixed in the frame glue to control the thickness of the upper and lower liquid crystal layers. The frame is sealed with a dispensing machine and an opening is reserved. The liquid crystal is poured and then sealed.

[0026] The method of using the device is as follows: Step 1: Establish the grayscale-phase modulation curve of the first LCOS device 206 by the orthogonal polarization method. Figure 2 As shown in (a), a laser light source 201, a beam expander 202, a first linear polarizer 203, a beam splitter 204, an aperture 205, a first LCOS device 206, a linear translation stage 207, a second linear polarizer 208, a Fourier lens 209, and a photodetector 210 are configured; the transmission axis of the first linear polarizer 203 is parallel to the initial orientation of the liquid crystal molecules of the first LCOS device 206, and the transmission axis of the second linear polarizer 208 is 90° perpendicular to it; the photodetector 210 uses a planar array CCD camera, and the pixel resolution matches the pixel unit of the first LCOS device 206; 50 spatial coordinate points arranged in a periodic matrix are selected on the surface of the first LCOS device 206, and grayscale voltage scanning is performed. The maintenance time of each voltage point is greater than 3 times the response time of the liquid crystal, and a grayscale-phase modulation curve is generated and fitted into a lookup table (LUT) to feed back to the driving algorithm. The intensity and phase modulation after compensation vary with the grayscale value, respectively, as shown in FIG. Figure 2 (b) and Figure 2 (c) Display.

[0027] Step 2: Measure the reference phase of the first LCOS device 206 by phase-shift interferometry. Set all pixels of the first LCOS device 206 to 0 grayscale and configure the Twyman-Green interferometer ( Figure 3a), including a second laser light source 301 (633nm HeNe laser), a beam expansion and collimation module 302, a polarization module 303, a second beam splitter 304, a reference mirror 305, a 4f system 307, and an imaging module 308; the polarization module 303 makes the polarization direction of the incident light parallel to the initial orientation of the liquid crystal molecules of the first LCOS device 206, and the second beam splitter 304 splits the light beam into the reference mirror 305 and the second LCOS device 306. The position of the reference mirror 305 is adjusted to make the optical path lengths of the two beams equal to form interference, as shown in FIG. Figure 3 As shown in b, the imaging module 308 captures and processes the interference pattern to obtain the initial surface phase distribution at 0 grayscale.

[0028] Step 3: Prepare the physical phase compensation layer. The 325nm HeCd laser wavefront is modulated by the DMD device, and then focused onto the surface of the photosensitive polymer film of the phase compensation layer 107 after being expanded and collimated by a high numerical aperture objective lens. Scanning and exposing according to the preset compensation phase pattern vector induces the molecular alignment of the photo-aligned material. Liquid crystal is poured between the first and second glass substrates and sealed. The first LCOS device 206 is set to 0 grayscale again, as shown in FIG. Figure 3 As shown in c, interferometer measurement shows that the initial phase distribution after compensation is approximately planar, and the spatial phase error does not exceed λ / 16.

[0029] Example 2: The difference between this embodiment and the first embodiment lies in the structure and preparation method of the phase compensation layer 107, which are as follows: The phase compensation layer 107 includes an upper transparent substrate, an ITO transparent upper electrode layer, an upper alignment layer 105, a liquid crystal molecule layer, a lower alignment layer 103, an ITO transparent lower electrode layer and a lower transparent substrate. An elliptical ring-shaped transparent electrode array is prepared on the surface of the first glass substrate (upper transparent substrate) by photolithography and is evenly distributed in the effective area of ​​the second LCOS device 306. Each ring-shaped electrode is independently connected to the driving circuit, and a gap area (such as ) is left between adjacent ring-shaped electrodes. Figure 4 shown).

[0030] ITO transparent upper / lower electrode layers are respectively coated on the upper surface of the first glass substrate and the lower surface of the second glass substrate (lower transparent substrate), and the PI film upper orientation layer 105 and lower orientation layer 103 (about 20nm thick) are prepared by friction method, so that the liquid crystal molecules are aligned along the long axis when no voltage is applied.

[0031] After the substrates are bonded and liquid crystal is injected, a gradient voltage is applied to the elliptical ring-shaped electrode to generate a non-uniform electric field in the second liquid crystal layer, inducing the liquid crystal molecules to produce a compensating phase distribution opposite to the surface phase error of the second LCOS device 306; when factors such as temperature cause the surface phase to drift, the gradient voltage is adjusted by the driving circuit to optimize the compensation effect.

[0032] In the method of use, steps 1 and 2 are the same as those in embodiment 1, and step 3 replaces laser direct writing with voltage control, and the rest of the operations are the same.

Claims

1. A novel liquid crystal spatial light modulator, characterized in that: Including reflective modulation devices and transmissive modulation devices; The reflective modulation device is a silicon-based liquid crystal, which modulates the phase of incident light according to an application scenario; the reflective modulation device comprises, from bottom to top, a CMOS silicon-based backplane (100), an aluminum pixel electrode layer (101), a dielectric reflection layer (102), a lower orientation layer (103), a first liquid crystal molecule layer (104), an upper orientation layer (105), an ITO electrode layer (106), and a glass substrate; The transmissive modulation device is a phase compensation layer (107) having a multi-layer structure and fixed on the upper surface of the reflective modulation device, and performs phase compensation on the initial phase deviation problem of the silicon-based liquid crystal device caused by the surface morphology of the silicon-based backplane and the uneven thickness of the liquid crystal box; The spatial light control device is coated with an anti-reflection layer (108) thin film on both the glass and air interfaces.

2. The novel liquid crystal spatial light modulator according to claim 1, characterized in that: The material of the dielectric reflection layer (102) is at least one of Si, ZnSe, and GaAs; the dielectric reflection layer (102) is periodically arranged in the short axis and long axis directions of the liquid crystal, the period on the long axis is 300-800 nm, the duty cycle is 50%-80%, the thickness of the high refractive index material is 100-500 nm, the width of the dielectric material on the short axis is 100-200 nm, and the period is 300-500 nm.

3. The novel liquid crystal spatial light modulator according to claim 1, characterized in that: The phase compensation layer (107) is a sandwich structure comprising an upper transparent substrate, an upper orientation layer (105), a second liquid crystal molecule layer, a lower orientation layer (103), and a lower transparent substrate; the initial phase distribution of the phase compensation layer (107) is achieved by laser direct writing.

4. The novel liquid crystal spatial light modulator according to claim 1, wherein: The phase compensation layer (107) comprises an upper transparent substrate, an ITO transparent upper electrode layer, an upper orientation layer (105), a liquid crystal molecule layer, a lower orientation layer (103), an ITO transparent lower electrode layer, and a lower transparent substrate. An elliptical ring-shaped transparent electrode array is photolithographically prepared on the surface of the upper transparent substrate and is evenly distributed in the effective area of ​​the corresponding silicon-based liquid crystal device. Each ring-shaped electrode is independently connected to a drive circuit, and a gap area is left between adjacent ring-shaped electrodes.

5. The novel liquid crystal spatial light modulator according to claim 1, characterized in that: The lower substrate of the phase compensation layer (107) and the glass substrate of the silicon-based liquid crystal device are made of the same material.

6. A method for using a novel liquid crystal spatial light modulator, characterized in that: The following steps are involved: Step 1: establishing a grayscale-phase modulation curve of the first LCOS device (206) in different phase modulation areas by an orthogonal polarization method, configuring a laser light source (201), a first linear polarizer (203), a beam splitter (204), a first LCOS device (206), a second linear polarizer (208) and a photodetector (210), selecting a plurality of spatial coordinate points on the surface of the first LCOS device (206) to perform a grayscale voltage scanning operation, generating a grayscale-phase modulation characteristic curve and forming a lookup table to feed back to a driving algorithm; Step 2: measuring the reference phase of the first LCOS device (206) by phase-shift interferometry, configuring a Twyman-Green interferometer, including a second laser light source (301), a beam expansion and collimation module (302), a polarization module (303), a second beam splitter (304), a reference mirror (305), and an imaging module (308), setting all pixel units of the second LCOS device (306) to 0 grayscale, and processing the interference pattern to obtain an initial surface phase distribution; Step 3: Prepare a phase physical compensation layer according to the initial surface phase distribution, and realize phase physical compensation through the phase compensation layer (107).

7. The method for using the novel liquid crystal spatial light modulator according to claim 6, wherein: In the step 1, the light transmission axis of the first linear polarizer (203) is parallel to the initial orientation of the liquid crystal molecules of the first LCOS device (206), and the light transmission axis of the second linear polarizer (208) is orthogonal to the light transmission axis of the first linear polarizer (203) at 90 degrees; the photodetector (210) adopts a planar array CCD camera, and its pixel resolution matches the pixel unit of the first LCOS device (206); the spatial coordinate points are arranged in a periodic matrix, the number of which is not less than 30, and the maintenance time of each voltage point is greater than 3 times the response time of the liquid crystal.

8. The method for using the novel liquid crystal spatial light modulator according to claim 6, wherein: In the second step, the polarization module (303) makes the polarization direction of the incident light parallel to the initial orientation of the liquid crystal molecules of the second LCOS device (306); the second beam splitter (304) splits the light beam to the reference mirror (305) and the second LCOS device (306) for emission and interference, and adjusts the position of the reference mirror (305) so that the optical paths of the two beams are equal.

9. The method for using the novel liquid crystal spatial light modulator according to claim 6, wherein: In the step three, when the phase physical compensation layer is prepared by laser direct writing, the laser wavefront is modulated by a DMD device and focused on the surface of the photo-aligned material for vector scanning exposure; when the phase physical compensation layer is prepared by voltage control, a gradient voltage is applied to the elliptical ring-shaped electrode to induce the second liquid crystal layer molecules to produce a compensation phase distribution opposite to the surface phase error of the second LCOS device (306).

Images