A face type calibration device and method of a spatial light modulator based on an LCOS chip

Abstract

The application discloses a surface type calibration device and method of a spatial light modulator based on an LCOS chip, wherein a calibration light path in the calibration device comprises a collimator, a polarizer, an X direction lens group, a grating, a Y direction lens group and a half-wave plate group; the emitted light is divided into first linearly polarized light and second linearly polarized light through the polarizer, and the light paths of the first linearly polarized light and the second linearly polarized light are perpendicular to each other; the second linearly polarized light passes through the first half-wave plate and the light path is the same as that of the first linearly polarized light, thereby obtaining third linearly polarized light; the third linearly polarized light passes through the X direction lens group, the grating, the Y direction lens group and the second half-wave plate in the light path, thereby obtaining fourth linearly polarized light; the fourth linearly polarized light is decomposed into fifth linearly polarized light and sixth linearly polarized light with equal amplitudes, the polarization direction of the fifth linearly polarized light is the same as that of the first linearly polarized light, the polarization direction of the sixth linearly polarized light is the same as that of the second linearly polarized light, the fifth linearly polarized light and the sixth linearly polarized light generate a phase difference on the LCOS chip, and the surface type of the spatial light modulator is calibrated according to the phase difference result.

Description

Technical Field

[0001] This invention belongs to the field of optical technology, and more specifically, relates to a surface calibration device and method for a spatial light modulator based on an LCOS chip. Background Technology

[0002] Spatial light modulators based on LCOS chips generally consist of an LCOS chip and a driving circuit. Depending on the fabrication process of the LCOS chip, they can be divided into amplitude-type and phase-type spatial light modulators. Amplitude-type spatial light modulators can modulate the amplitude of light and are used in optical projection; phase-type spatial light modulators can modulate the phase of light and are used in beam shaping, digital holography, and diffraction optics such as blazed gratings. Existing surface calibration methods often use laser interferometers, which are complex to align, expensive to use, and have poor calibration accuracy.

[0003] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a surface calibration device and method for a spatial light modulator based on an LCOS chip. The purpose is to calculate the gray level and phase modulation depth curve of different regions of the LCOS chip through optical path test recording data, and to solve the technical problem of the difficulty in quantifying the surface calibration of the LCOS chip by applying the same gray level modulation phase to the LCOS chip.

[0005] To achieve the above objectives, according to one aspect of the present invention, a surface profile calibration device based on a spatial light modulator using an LCOS chip is provided. The calibration optical path 200 in the calibration device includes a collimator 201, a polarizer 202, an X-direction lens group 203, a grating 204, a Y-direction lens group 205, and a half-wave plate group 206, wherein:

[0006] The light emitted from the incident port of the collimator 201 is divided into a first linearly polarized light and a second linearly polarized light by the polarizer 202. The light path of the first linearly polarized light is along the X direction, and the light path of the second linearly polarized light is along the Y direction.

[0007] After the second linearly polarized light passes through the first half-wave plate 2061 in the half-wave plate group 206, the optical path of the second linearly polarized light is in the same direction as the optical path of the first linearly polarized light, and together they obtain the third linearly polarized light with the optical path along the X direction.

[0008] The third linearly polarized light passes through the X-direction lens group 203, the grating 204, the Y-direction lens group 205, and the second half-wave plate 2062 in the half-wave plate group 206 in the optical path to obtain a fourth linearly polarized light that deviates from the X-direction and the Y-direction by 45° respectively.

[0009] The fourth linearly polarized light is decomposed into a fifth linearly polarized light and a sixth linearly polarized light with equal amplitude. The polarization direction of the fifth linearly polarized light is the same as that of the first linearly polarized light, along the X direction, and the polarization direction of the sixth linearly polarized light is the same as that of the second linearly polarized light, along the Y direction.

[0010] The fifth and sixth linearly polarized rays are incident on the LCOS chip 210 of the spatial light modulator 110 and generate a phase difference on the LCOS chip 210. The surface profile of the spatial light modulator 110 is calibrated by the result of the phase difference.

[0011] As a further improvement and supplement to the above solution, the present invention also includes the following additional technical features.

[0012] Preferably, the spatial light modulator 110 in the calibration device includes an LCOS chip 210 and an SLM driver circuit 105, wherein:

[0013] A tunable laser 101, a circulator 102, and a calibration optical path 200 are sequentially arranged before the LCOS chip 210.

[0014] A power meter 103 and a processing unit 104 are sequentially connected after the circulator 102.

[0015] The processing unit 104 is connected to the SLM driving circuit 105;

[0016] The emitted light from the tunable laser 101 becomes linearly polarized light after passing through the circulator 102 and the calibration optical path 200, and then is incident on the LCOS chip 210.

[0017] After the LCOS chip 210 processes the phase of the linearly polarized light, the reflected light passes sequentially through the calibration optical path 200, the collimator 201, and the circulator 102 before entering the power meter 103, where the power meter 103 records the optical power value.

[0018] The processing unit 104 performs calculations and analyses based on the optical power value, and controls the SLM driving circuit 105 to calibrate the spatial light modulator 110 according to the calculation results.

[0019] Preferably, the circulator 102 includes a first port, a second port, and a third port arranged sequentially in a clockwise direction, wherein:

[0020] The circulator 102 is connected to the tunable laser 101 through the first port;

[0021] The circulator 102 is connected to the collimator 201 through the second port;

[0022] The circulator 102 is connected to the power meter 103 through the third port.

[0023] Preferably, the first half-wave plate 2061 in the half-wave plate group 206 is a 45° half-wave plate; the second half-wave plate 2062 in the half-wave plate group 206 is a 22.5° half-wave plate.

[0024] Preferably, the X-direction lens group 203 includes a first X-direction lens 2031, a second X-direction lens 2032, and a third X-direction lens 2033, wherein:

[0025] The first X-direction lens 2031 and the second X-direction lens 2032 are placed in front of the grating 204 to disperse the third linearly polarized beam onto the grating 204;

[0026] The third X-direction lens 2033 is placed after the grating 204, and the third X-direction lens 2033 is used to focus the X-direction light emitted by the grating 204 onto the surface of the LCOS chip 210.

[0027] Preferably, the Y-direction lens group 205 includes a first Y-direction lens 2051 and a second Y-direction lens 2052, wherein:

[0028] The first Y-direction lens 2051 is placed after the grating 204, and the Y-direction light emitted by the grating 204 is focused by the first Y-direction lens 2051.

[0029] The second Y-direction lens 2052 is placed between the first Y-direction lens 2051 and the grating 204. The second Y-direction lens 2052 is used to expand and disperse the light path in the Y direction and incident it onto the surface of the LCOS chip 210.

[0030] According to another aspect of the present invention, a method for surface profile calibration of a spatial light modulator based on an LCOS chip is provided, employing the calibration apparatus as described in the first aspect, the calibration method comprising:

[0031] After setting the wavelength of the tunable laser 101, the optical power value P of the power meter 103 is recorded when the spatial light modulator 110 is powered off.

[0032] The grayscale levels are loaded onto the LCOS chip 210 in sequence, and the power value Pi is recorded for each grayscale level i. The grayscale level-IL curve is obtained based on P and Pi.

[0033] The coordinate system carrying the gray level-IL curve uses gray level and insertion loss IL as two dimensional coordinate scalars.

[0034] The gray level-phase modulation depth curve is calculated based on the gray level-IL curve.

[0035] The grayscale values ​​that need to be loaded for each area of ​​the LCOS chip 210 are found using a preset phase modulation depth. The corresponding grayscale values ​​are loaded onto the areas of the LCOS chip 210 to obtain a surface pattern with a consistent phase modulation depth across the entire surface, thereby achieving surface pattern calibration of the LCOS chip 210.

[0036] Preferably, the method for calculating the grayscale level-IL curve includes:

[0037] When the spatial light modulator 110 is set according to N gray levels and X*Y resolution, gray levels are sequentially loaded onto the LCOS chip 210. Power values ​​Pi are recorded for each gray level i, and a gray level-IL curve is obtained based on P and Pi, specifically including:

[0038] The processing unit 104 controls the SLM driving circuit 105 to set the X*Y pixels of the LCOS chip 210 to the same gray level, and traverses N states from 0 to N-1.

[0039] Each time the processing unit 104 sets a grayscale control state for an LCOS chip 210, it reads the optical power value once through the power meter 103 and records it as Pi, i = 0, 1, 2, ..., N-1;

[0040] Subtracting P from each Pi yields the insertion loss IL for each gray level i. The IL values ​​of N gray levels form the gray level-IL curve.

[0041] Preferably, the method for calculating the grayscale level-phase difference curve includes:

[0042] When the third linearly polarized light passes through the second half-wave plate 2062, it becomes the fourth linearly polarized light;

[0043] The fourth linearly polarized light is decomposed into a fifth and a sixth linearly polarized light with equal amplitude. After passing through the LCOS chip 210, the fifth linearly polarized light has a phase difference of δi relative to the sixth linearly polarized light. The fifth and sixth linearly polarized light reflected back from the LCOS chip 210, after passing through the calibration optical path 200, will have a transmittance change due to the δi phase difference (cos(δi)). i / 2)) 2 Combining the gray level-IL curve, the processing unit (104) obtains the gray level-phase difference curve.

[0044] Where: i represents the gray level of the LCOS chip 210, and the coordinate system carrying the gray level-phase difference curve uses gray level and phase difference as two-dimensional coordinate scalars respectively.

[0045] Preferably, the step of calculating the grayscale level-phase modulation depth curve based on the grayscale level-IL curve specifically involves:

[0046] Combining the grayscale level-IL curve and the phase difference δ i Using the conversion formula between ILi and i, the phase difference δ corresponding to each gray level i is calculated. i ;

[0047] Using the phase difference δ0 of gray level 0 as a reference, the phase difference δ of each gray level i is... i Subtracting δ0 yields the phase modulation depth corresponding to each gray level i, and thus the gray level-phase modulation depth curve is obtained.

[0048] Wherein, ILi represents the insertion loss caused by the change in gray level; for any gray level i, ILi is obtained by subtracting the inherent insertion loss of the system from the corresponding IL value.

[0049] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0050] This invention provides a surface calibration device and method for a spatial light modulator based on an LCOS chip. By recording data from optical path tests, the grayscale level and phase modulation depth curves of different regions of the LCOS chip are calculated. Then, the grayscale level that makes the phase modulation depth of the entire LCOS chip the same in each region is found in these curves, and the grayscale level is applied to the LCOS chip to make the phase modulation depth of the entire LCOS chip consistent, thus completing the surface calibration.

[0051] This invention uses a power meter as a measuring device to record optical power, calculate IL, and then calculate the corresponding phase or transmittance. Compared with the method of using charge-coupled devices to record interference intensity, the data is easier to obtain, the accuracy is higher, the algorithm is simpler, the calibration accuracy and speed are faster, and the calibration cost is lower.

[0052] This invention uses a processing unit to control the SLM and read the power meter, forming a closed-loop system that can automatically and quickly perform surface calibration of the SLM. Attached Figure Description

[0053] Figure 1This is a schematic diagram of the surface calibration device for a spatial light modulator based on an LCOS chip in this invention;

[0054] Figure 2 This is a schematic diagram of the surface calibration device for a spatial light modulator based on an LCOS chip in this invention;

[0055] Figure 3 This is a schematic diagram of the surface calibration device for a spatial light modulator based on an LCOS chip in this invention;

[0056] Figure 4 This is a schematic diagram of the optical path of light incident on the LCOS chip in the Y direction in this invention;

[0057] Figure 5 This is a schematic diagram of the optical path of light incident on the LCOS chip in the X direction in this invention;

[0058] Figure 6 This is a schematic diagram of the light spot arrangement on the LCOS chip in this invention;

[0059] Figure 7 This is a schematic diagram of the grayscale level-IL curve in the surface calibration method of the spatial light modulator based on the LCOS chip in this invention;

[0060] Figure 8 This is a schematic diagram of the grayscale level-phase modulation depth curve in the surface calibration method of the spatial light modulator based on the LCOS chip in this invention.

[0061] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0062] 101-Tunable laser; 102-Circulator; 103-Power meter; 104-Processing unit; 105-SLM drive circuit; 200-Calibration optical path; 201-Collider; 202-Polarizer; 203-X-direction lens group; 2031-First X-direction lens; 2032-Second X-direction lens; 2033-Third X-direction lens; 204-Grating; 205-Y-direction lens group; 2051-First Y-direction lens; 2052-Second Y-direction lens; 206-Half-wave plate group; 2061-First half-wave plate; 2062-Second half-wave plate; 210-LCOS chip. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0064] In the description of this invention, the terms "inner", "outer", "longitudinal", "lateral", "upper", "lower", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and do not require that this invention must be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0065] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0066] Example 1:

[0067] This embodiment provides a surface profile calibration device based on a spatial light modulator using an LCOS chip. The calibration optical path 200 in the calibration device includes a collimator 201, a polarizer 202, an X-direction lens group 203, a grating 204, a Y-direction lens group 205, and a half-wave plate group 206, wherein:

[0068] The light emitted from the incident port of the collimator 201 is divided into a first linearly polarized light and a second linearly polarized light by the polarizer 202. The light path of the first linearly polarized light is along the X direction, and the light path of the second linearly polarized light is along the Y direction.

[0069] After the second linearly polarized light passes through the first half-wave plate 2061 in the half-wave plate group 206, the optical path of the second linearly polarized light is in the same direction as the optical path of the first linearly polarized light, and together they obtain the third linearly polarized light with the optical path along the X direction.

[0070] The third linearly polarized light passes through the X-direction lens group 203, the grating 204, the Y-direction lens group 205, and the second half-wave plate 2062 in the half-wave plate group 206 in the optical path to obtain a fourth linearly polarized light that deviates from the X-direction and the Y-direction by 45° respectively.

[0071] The fourth linearly polarized light is decomposed into a fifth linearly polarized light and a sixth linearly polarized light with equal amplitude. The polarization direction of the fifth linearly polarized light is the same as that of the first linearly polarized light, along the X direction, and the polarization direction of the sixth linearly polarized light is the same as that of the second linearly polarized light, along the Y direction.

[0072] The fifth and sixth linearly polarized rays are incident on the LCOS chip 210 of the spatial light modulator 110 and generate a phase difference on the LCOS chip 210. The surface profile of the spatial light modulator 110 is calibrated by the result of the phase difference.

[0073] Based on the surface profile calibration device for the spatial light modulator based on the LCOS chip provided in Embodiment 1, the calibration principle is as follows: In the calibration optical path 200, the light emitted from the incident port of the collimator 201 is converted into two orthogonal linearly polarized beams, a first linearly polarized beam and a second linearly polarized beam, by the polarizer 202. The first linearly polarized beam is along the horizontal direction of the optical path. Figure 4 As shown, in the x-direction, 0°, the second linearly polarized light is along the vertical direction. Figure 5 As shown, the second linearly polarized light is 90° in the y-direction. Then, the second linearly polarized light is adjusted from the y-direction to the x-direction linearly polarized light by the first half-wave plate 2061. In this way, both the first and second linearly polarized lights are x-direction linearly polarized lights, which are combined to form the third linearly polarized light in the x-direction. Figure 4 The x-direction is shown as 0°.

[0074] The polarization direction of the polarizer 202 is at 45±3° with the optical axis of the liquid crystal molecules inside the LCOS chip 210. In this embodiment, 45° is selected.

[0075] The third linearly polarized light then passes through the X-direction lens group 203, grating 204, Y-direction lens group 205, and second half-wave plate 2062. Grating 204 disperses the emitted light from collimator 201 according to wavelength. The third linearly polarized light is adjusted from the x-direction to 45° linearly polarized light by the second half-wave plate 2062, resulting in the fourth linearly polarized light at 45°. The fourth linearly polarized light is decomposed into a fifth linearly polarized light with equal amplitude (0° in the x-direction) and a sixth linearly polarized light with equal amplitude (90° in the y-direction). The fifth and sixth linearly polarized lights are incident on the LCOS chip 210, creating a phase difference. After reflection by the LCOS chip 210, the fifth linearly polarized light will have a δ phase difference relative to the sixth linearly polarized light. i The phase difference of the LCOS grayscale level is i. Then, the LCOS chip 210 reflects the fifth and sixth polarized light back through the calibration optical path 200. After passing through the calibration optical path 200, the transmittance will change due to the phase change, which will be (cos(δ)). i / 2)) 2 The reflected light is coupled to the power meter 103 via the circulator 102 for reception. The processing unit 104 calculates the grayscale level-phase modulation depth curves corresponding to different wavelengths of light emitted from different incident ports of the collimator 201, such as... Figure 8 As shown, the phase modulation depth corresponding to each gray level is obtained based on the phase difference of the optical power value P0. The phase of the fifth and sixth line polarizers is adjusted according to the gray level to make them consistent. The various areas of the LCOS chip 210 are calibrated to complete the gray level consistency calibration between different surface areas of the LCOS chip 210.

[0076] In this first embodiment, in order to calibrate the spatial light modulator 110, in conjunction with the embodiments of the present invention, there is also a preferred implementation scheme, specifically, as follows: Figure 1 As shown, the spatial light modulator 110 in the calibration device includes an LCOS chip 210 and an SLM driver circuit 105, wherein:

[0077] A tunable laser 101, a circulator 102, and a calibration optical path 200 are sequentially arranged before the LCOS chip 210.

[0078] A power meter 103 and a processing unit 104 are sequentially connected after the circulator 102.

[0079] The processing unit 104 is connected to the SLM driving circuit 105.

[0080] Based on the above calibration device, the calibration process is as follows:

[0081] The emitted light from the tunable laser 101 becomes linearly polarized light after passing through the circulator 102 and calibration optical path 200, and then enters the LCOS chip 210. The LCOS chip 210 processes the phase of the linearly polarized light, thus changing the phase of the light. The reflected light then passes through the calibration optical path 200 and the circulator 102 before entering the power meter 103, where the power meter 103 records the optical power value. The processing unit 104 performs calculations and analysis based on the optical power value, and controls the SLM drive circuit 105 to calibrate the spatial light modulator 110 according to the calculation results.

[0082] In this embodiment of the invention, calibration is performed on different wavelengths emitted from different incident ports of the collimator 201. By adjusting the grayscale curve, the grayscale level of the phase-type SLM is made linearly related to the phase modulation depth. Therefore, during actual calibration, the processing unit 104 controls the SLM driving circuit 107 to load grayscale levels onto the LCOS chip 210. Each time grayscale levels are loaded, the power meter 103 records the optical power value. Based on the optical power value, the corresponding insertion loss (IL) is calculated, resulting in the grayscale level-IL curve, as shown below. Figure 7 As shown. Further, the grayscale level-phase difference curve is obtained, as shown... Figure 8 As shown, the SLM calibration is finally completed by combining the grayscale level-phase difference curve. The specific calibration process will be described in Example 2, and will not be repeated here.

[0083] In this embodiment of the invention, the power meter 103 is measured in dBm, because only power values ​​in dBm can be subtracted. The insertion loss IL is calculated by subtracting multiple power values. The specific calculation process will be described in Embodiment 2.

[0084] In this first embodiment, to avoid the interference between emitted and reflected light, in conjunction with the embodiments of the present invention, there is also a preferred implementation scheme, specifically, as follows: Figure 1 As shown, the circulator 102 includes a first port, a second port, and a third port arranged sequentially in a clockwise direction, wherein:

[0085] The circulator 102 is connected to the tunable laser 101 through the first port;

[0086] The circulator 102 is connected to the collimator 201 through the second port;

[0087] The circulator 102 is connected to the power meter 103 through the third port.

[0088] According to the principle of the circulator, the emitted light from the tunable laser 101 enters the circulator 102 through the first port, and can then be output from the second port and enter the collimator 201; while the reflected light enters the circulator 102 through the second port from the collimator 201, and can then be output from the third port and enter the power meter 103.

[0089] In this first embodiment, in order to adjust the first and second linearly polarized beams emitted from the polarizer 202 to be parallel, in conjunction with the embodiments of the present invention, there is also a preferred implementation scheme, specifically, as follows: Figure 2 As shown, in the half-wave plate group 206, the first half-wave plate 2061 adjusts the optical path direction of the second linearly polarized light to be in the same direction as the first linearly polarized light; in the half-wave plate group 206, the second half-wave plate 2062 adjusts the optical path direction of the third linearly polarized light to be 45° different from the optical path direction of the fourth linearly polarized light.

[0090] The first half-wave plate 2061 is a 45° half-wave plate, which adjusts the second linear polarization in the y-direction from 90° to 0° in the x-direction. The second half-wave plate 2062 is a 22.5° half-wave plate, which adjusts the optical path direction of the third linear polarization to be 45° different from that of the fourth linear polarization.

[0091] In this first embodiment, in order to disperse and expand the different wavelengths of light emitted from different incident ports of the collimator 201, in conjunction with the embodiments of the present invention, there is also a preferred implementation scheme, specifically, as follows: Figure 2 As shown, the X-direction lens group 203 includes a first X-direction lens 2031, a second X-direction lens 2032, and a third X-direction lens 2033, wherein:

[0092] The first X-direction lens 2031 and the second X-direction lens 2032 are placed in front of the grating 204 to disperse the third linearly polarized light onto the grating 204. No beam expansion or dispersion is performed on the Y-direction beam.

[0093] The third X-direction lens 2033 is placed after the grating 204, and the third X-direction lens 2033 is used to focus the X-direction light emitted by the grating 204 onto the surface of the LCOS chip 210.

[0094] In this first embodiment, the light of different wavelengths emitted from different incident ports of the collimator 201 is dispersed by the grating 204 according to the wavelength. The light beam before the grating 204 needs to be expanded by the first X-direction lens 2031 and the second X-direction lens 2032. After passing through the grating 204, it is processed in the X and Y directions respectively.

[0095] The X-direction light is focused by the third Y-direction lens 2033 onto different areas of the LCOS chip 210, forming N columns of light spots on the LCOS chip 210 according to wavelength classification, with each column belonging to the same wavelength. In this first embodiment, to coordinate the different wavelengths of light emitted from different incident ports of the collimator 201 in the Y direction, in conjunction with this embodiment, there is also a preferred implementation scheme, specifically, as follows: Figure 2 As shown, the Y-direction lens group 205 includes a first Y-direction lens 2051 and a second Y-direction lens 2052, wherein:

[0096] The first Y-direction lens 2051 is placed after the grating 204, and the Y-direction light emitted by the grating 204 is focused by the first Y-direction lens 2051.

[0097] The second Y-direction lens 2052 is placed between the first Y-direction lens 2051 and the grating 204. The second Y-direction lens 2052 is used to expand and disperse the light path in the Y direction and incident it onto the surface of the LCOS chip 210.

[0098] The Y-direction light emitted by the collimator 201 is first focused by the first Y-direction lens 2051, and then expanded by the second Y-direction lens 2052 to form N columns of light spots on the surface of different regions of the LCOS chip 210. In each column of light spots, the light spots are arranged from top to bottom along the Y direction according to the different incident port positions of the collimator 201, and the light spots can cover the surface of different regions of the LCOS chip 210.

[0099] Example 2:

[0100] Based on the above embodiment 1, this embodiment of the invention provides a surface calibration method for a spatial light modulator based on an LCOS chip, which is performed using the calibration device described in embodiment 1. Before performing SLM calibration using the aforementioned calibration device, it is necessary to determine the relevant parameter information of the spatial light modulator 110. These relevant parameters include whether the spatial light modulator 110 is phase-type, the optical axis direction of the liquid crystal molecules inside the LCOS chip 210, the resolution of the LCOS chip 210, the grayscale level of the SLM driving circuit 105, and the applicable wavelength range of the spatial light modulator 110, etc.

[0101] After determining that the SLM is phase-type and the optical axis direction of the liquid crystal molecules inside the LCOS chip 210 is determined, the polarization direction of the polarizer 202 can be positioned at 45° to the optical axis direction of the liquid crystal molecules inside the LCOS chip 210. After determining the resolution of the LCOS chip 210, it can be determined how the processing unit 104 should control the SLM driving circuit 107. After determining the grayscale level of the SLM driving circuit 107, the calibration accuracy of the spatial light modulator 110 can be determined. After determining the applicable wavelength range of the SLM, the wavelength that the tunable laser 101 needs to be set, as well as other optical components such as the circulator 102, collimator 210, and power meter 103, can be selected for the corresponding wavelength range. Among them, the grayscale level of the SLM driving circuit 105 determines the modulation accuracy; the higher the grayscale level, the higher the modulation accuracy. Commonly used grayscale levels are: 65536 grayscale (16 bits), 4096 grayscale (12 bits), and 256 grayscale (8 bits).

[0102] For ease of explanation, the SLM driver circuit 105 is described in terms of 2568-bit grayscale level, 1920*1040 resolution, and C-band optical communication band of 1530nm~1570nm. As for the calibration of other grayscale levels, other resolutions, and other bands, please refer to the calibration of this embodiment 2.

[0103] This second embodiment provides a surface calibration method for a spatial light modulator based on an LCOS chip, using the calibration device described in the first embodiment. The calibration method provided by this embodiment mainly includes the following steps:

[0104] S101: After setting the wavelength of the tunable laser 101, record the optical power value P of the power meter 103 when the spatial light modulator 110 is powered off.

[0105] according to Figure 2After setting up the SLM calibration optical path, set the center wavelength of the operating band range from the tunable laser 101 to the LCOS chip 210. Taking the applicable band range of the SLM as the C-band as an example, set the wavelength of the tunable laser 101 to the center wavelength of the C-band at 1550nm. Without powering the SLM, record the optical power value P of the power meter 103 for later calculations.

[0106] S102: Gradient levels are loaded onto the LCOS chip 210 in sequence. Power value Pi is recorded for each gray level i, and gray level-IL curve is obtained based on P and Pi.

[0107] The coordinate system supporting the grayscale level-IL curve uses grayscale level and insertion loss IL as two dimensional coordinate scalars. For example... Figure 7 As shown.

[0108] When the spatial light modulator 110 is set according to N gray levels and X*Y resolution, gray levels are sequentially loaded onto the LCOS chip 210. Power values ​​Pi are recorded for each gray level i, and a gray level-IL curve is obtained based on P and Pi, specifically including:

[0109] The processing unit 104 controls the SLM driving circuit 105 to set the X*Y pixels of the LCOS chip 210 to the same gray level, and traverses N states from 0 to N-1.

[0110] Each time the processing unit 104 sets a grayscale control state for an LCOS chip 210, it reads the optical power value once through the power meter 103 and records it as Pi, i = 0, 1, 2, ..., N-1;

[0111] Subtracting P from each Pi yields the insertion loss IL for each gray level i. The IL values ​​of N gray levels form the gray level-IL curve.

[0112] Since the applicable wavelength range of the SLM is the C-band, the wavelength of the tunable laser is set to the center wavelength of the C-band at 1550nm. Based on the above three parameters of the SLM, the processing unit controls the SLM driving circuit to set the 1920*1040 pixels of the LCOS chip to the same gray level, traversing 256 states from 0 to 255. Taking 256 gray levels and 1920*1080 resolution as an example, specifically, the 1920*1080 pixels of the LCOS chip 210 are set to the same gray level, traversing 256 states from 0 to 255, and the optical power values ​​Pi = 0, 1, 2, ..., 255 are recorded respectively. Finally, the IL of the 256 gray levels forms a gray level-IL curve, as shown in the figure. Figure 7As shown in the curve. The coordinate system carrying the gray level-IL curve uses gray level and insertion loss IL as two coordinate scalars.

[0113] like Figure 7 The phase changes from 0 to 2π, (cos(δ) i / 2)) 2 Such as Figure 7 The lowest point shown in the curve. Each time the processing unit 104 sets a grayscale control state for an LCOS chip, it reads the optical power value of the power meter and records it as Pi = 0, 1, 2, ..., 255. The maximum value of Pi recorded under 256 grayscale levels is the inherent loss of the optical path, denoted as P0. Pi minus P0 is the insertion loss corresponding to grayscale level i, hereinafter referred to as IL. The IL of 256 grayscale levels forms the grayscale level-IL curve.

[0114] S103: Calculate the gray level-phase modulation depth curve based on the gray level-IL curve.

[0115] When the third linearly polarized light passes through the second half-wave plate 2062, it becomes the fourth linearly polarized light;

[0116] The fourth linearly polarized light incident on the LCOS chip 210 is decomposed into a fifth and a sixth linearly polarized light with equal amplitude. After passing through the LCOS chip 210, the fifth linearly polarized light has a phase difference δi relative to the sixth linearly polarized light. The fifth and sixth linearly polarized light reflected back from the LCOS chip 210, after passing through the calibration optical path 200, will have a transmittance change due to the δi phase difference (cos(δi)). i / 2)) 2 Combining the grayscale level-IL curve, the processing unit 104 obtains the grayscale level-phase difference curve, as shown below. Figure 8 As shown.

[0117] Where: i represents the gray level of the LCOS chip 210, and the coordinate system carrying the gray level-phase difference curve uses gray level and phase difference as two-dimensional coordinate scalars respectively.

[0118] Combining the grayscale level-IL curve and the phase difference δ i Using the conversion formula between ILi and i, the phase difference δ corresponding to each gray level i is calculated. i ;

[0119] Using the phase difference δ0 of gray level 0 as a reference, the phase difference δ of each gray level i is... i Subtracting δ0 yields the phase modulation depth corresponding to each gray level i, and thus the gray level-phase modulation depth curve is obtained.

[0120] Wherein, ILi represents the insertion loss caused by the change in gray level; for any gray level i, ILi is obtained by subtracting the inherent insertion loss of the system from the corresponding IL value.

[0121] Taking the optical axis direction of the liquid crystal inside the SLM's LCOS chip as 0°, when a gray level i is added to the LCOS chip, the fifth and sixth linearly polarized liquid crystal molecules produce an unusual ray at 0° and an ordinary ray at 90° through birefringence. The phase difference between the fifth and sixth linearly polarized rays is δi. When the incident light passes through a polarizer at a 45° angle to the 0° direction of the liquid crystal molecule's optical axis, it becomes 45° or -45°. The subsequent calculation results are consistent in both cases. Taking 45° as an example, linearly polarized light incident on the LCOS chip can be decomposed into the fifth linearly polarized ray at 0° and the sixth linearly polarized ray at 90° with equal amplitude. After passing through the LCOS chip, the fifth linearly polarized ray will have a phase difference of δi relative to the sixth linearly polarized ray (LCOS gray level i). After passing through the polarizer, the transmittance changes due to the change in polarization state (cos(δi)). i / 2)) 2 By combining the grayscale level-IL curve, the phase difference curves corresponding to the 256 grayscale levels can be calculated. Taking the phase difference of grayscale 0 as the reference, the phase difference of all grayscale levels is subtracted from the phase difference of grayscale 0 to obtain the phase modulation depth corresponding to each grayscale level.

[0122] S104: Find the grayscale that needs to be loaded on each area of ​​the LCOS chip 210 with a preset phase modulation depth, load the corresponding grayscale onto the area of ​​the LCOS chip 210, and obtain a surface pattern with a consistent phase modulation depth across the entire surface, thereby achieving surface pattern calibration of the LCOS chip 210.

[0123] The fifth and sixth linearly polarized light reflected from the LCOS chip will have their transmittance y(i) change due to the polarization state change after passing through the polarizer 202 in the calibration optical path 200. i / 2)) 2 The following conversion formula exists between the transmittance y(i) and IL(i) corresponding to gray level i:

[0124] y(i)=POWER(10,IL(i) / 10)(1)

[0125] Therefore, combining conversion formula 1 and "transmittance y(i) becomes (cos(δ) i / 2)) 2 The phase difference δ can be obtained. i The conversion formula between IL(i) and IL(i) is as follows:

[0126] (cos(δ i / 2)) 2=POWER(10, IL(i) / 10)(2)

[0127] Where IL(i) represents the insertion loss caused by the change in gray level, which is expressed here by... Figure 5 The gray level-IL curve can be used to determine IL(i): for any gray level i, IL(i) is obtained by subtracting the system's inherent insertion loss value (i.e., the maximum value of IL on the gray level-IL curve) from the IL value corresponding to gray level i on the gray level-IL curve. POWER represents a power function, with the first parameter 10 being the base and the second parameter IL(i) / 10 being the power. According to the conversion formula (2), once IL(i) is determined, the corresponding phase difference δ can be calculated. i The corresponding phase modulation depth is then calculated.

[0128] By changing the wavelength of the tunable laser and repeating steps S101-S104, the phase modulation depth curves corresponding to different gray levels in different regions of the LCOS at different wavelengths can be obtained. Then, by switching different ports of collimator 201, the gray-phase modulation depth curves of different regions of the entire LCOS chip can be obtained. The phase modulation depth profile of the entire LCOS chip with a specific gray level can then be analyzed. To ensure consistent phase depth across the entire surface, the phase modulation depth can be fixed, such as to 2π.

[0129] Using the phase difference of the optical power value P0 as a reference, the phase modulation depth corresponding to each gray level is obtained. The input port of the collimator 210 is switched, and each area of ​​the LCOS chip 210 is calibrated to obtain the gray level-phase modulation depth curve of each area of ​​the LCOS chip 210.

[0130] In the grayscale-phase modulation depth curves calculated for different regions of the entire surface, the grayscale values ​​that need to be loaded for different regions are found. Then, the corresponding grayscale values ​​are loaded for the corresponding regions of the LCOS chip 210, and a surface pattern with consistent phase modulation depth can be obtained. This achieves the surface pattern calibration of the LCOS chip.

[0131] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A surface calibration device for a spatial light modulator based on an LCOS chip, characterized in that The calibration light path (200) in the calibration device comprises a collimator (201), a polarizer (202), an X-direction lens group (203), a grating (204), a Y-direction lens group (205) and a half-wave plate group (206), wherein: The light path emitted from the incident port of the collimator (201) is divided into first linearly polarized light and second linearly polarized light by the polarizer (202), the light path of the first linearly polarized light is along the X direction, and the light path of the second linearly polarized light is along the Y direction; After the second linearly polarized light passes through the first half-wave plate (2061) in the half-wave plate group (206), the light path is the same as that of the first linearly polarized light, and the third linearly polarized light along the X direction is obtained together; The third linearly polarized light passes through the X-direction lens group (203), the grating (204), the Y-direction lens group (205) and the second half-wave plate (2062) in the half-wave plate group (206) in the light path, and the fourth linearly polarized light deviated by 45° from the X direction and the Y direction is obtained; The fourth linearly polarized light is decomposed into fifth linearly polarized light and sixth linearly polarized light with equal amplitudes, the polarization direction of the fifth linearly polarized light is the same as that of the first linearly polarized light, along the X direction, and the polarization direction of the sixth linearly polarized light is the same as that of the second linearly polarized light, along the Y direction; The fifth linearly polarized light and the sixth linearly polarized light are incident on the LCOS chip (210) of the spatial light modulator (110) and generate a phase difference on the LCOS chip (210), and the surface shape of the spatial light modulator (110) is calibrated according to the result of the phase difference; The X-direction lens group (203) comprises a first X-direction lens (2031), a second X-direction lens (2032) and a third X-direction lens (2033), the first X-direction lens (2031) and the second X-direction lens (2032) are placed before the grating (204) and are used to expand and disperse the third linearly polarized light to the grating (204); the third X-direction lens (2033) is placed after the grating (204), and the third X-direction lens (2033) is used to focus the X-direction light emitted by the grating (204) to the surface shape of the LCOS chip (210).

2. The face type calibration device of LCOS chip based spatial light modulator according to claim 1, wherein, The spatial light modulator (110) in the calibration device comprises an LCOS chip (210) and an SLM driving circuit (105), wherein: A tunable laser (101), a circulator (102) and a calibration light path (200) are sequentially arranged before the LCOS chip (210); A power meter (103) and a processing unit (104) are sequentially connected and arranged after the circulator (102); The processing unit (104) is connected with the SLM driving circuit (105); The emergent light of the tunable laser (101) becomes linearly polarized light after passing through the circulator (102) and the calibration light path (200), and then is incident on the LCOS chip (210); The LCOS chip (210) processes the phase of linearly polarized light, and the reflected light enters the power meter (103) in sequence through the calibration light path (200), the collimator (201) and the circulator (102), and the light power value is recorded by the power meter (103); The processing unit (104) performs calculation and analysis based on the light power value, and controls the SLM driving circuit (105) to realize the calibration of the spatial light modulator (110) according to the calculation result.

3. The face type calibration device of LCOS chip based spatial light modulator according to claim 2, characterized in that, The circulator (102) comprises a first port, a second port and a third port arranged in sequence in a clockwise direction, wherein: The circulator (102) is connected with the tunable laser (101) through the first port; The circulator (102) is connected with the collimator (201) through the second port; The circulator (102) is connected with the power meter (103) through the third port.

4. The face type calibration device of LCOS chip based spatial light modulator according to claim 3, characterized in that, The first half-wave plate (2061) in the half-wave plate group (206) is a 45° half-wave plate; and the second half-wave plate (2062) in the half-wave plate group (206) is a 22.5° half-wave plate.

5. The face type calibration device of LCOS chip based spatial light modulator according to claim 1, wherein, The Y-direction lens group (205) comprises a first Y-direction lens (2051) and a second Y-direction lens (2052), wherein: The first Y-direction lens (2051) is placed behind the grating (204), and the Y-direction light emitted by the grating (204) is incident on the first Y-direction lens (2051) for focusing; The second Y-direction lens (2052) is placed between the first Y-direction lens (2051) and the grating (204), and the second Y-direction lens (2052) is used to expand and disperse the Y-direction light path to the surface of the LCOS chip (210).

6. A surface calibration method of a spatial light modulator based on an LCOS chip, characterized in that, The calibration device and the calibration method of any one of claims 1-5 are adopted, and the calibration method comprises: After setting the wavelength of the tunable laser (101), the light power value P of the power meter (103) is recorded in the case that the spatial light modulator (110) is powered off; The LCOS chip (210) is loaded with gray scale levels in sequence, the power value Pi corresponding to each gray scale level i is recorded respectively, and the gray scale level-IL curve is obtained according to P and Pi; The coordinate system carrying the gray scale level-IL curve takes the gray scale level and the insertion loss IL as two-dimensional coordinate scalar respectively; The gray scale level-phase modulation depth curve is calculated according to the gray scale level-IL curve; The gray scale level-phase modulation depth curve is calculated according to the gray scale level-IL curve; 7. The method according to claim 6, wherein the method further comprises: determining the position of the LCOS chip based on the image of the LCOS chip and the image of the reference pattern. The gray scale level-phase modulation depth curve is calculated according to the gray scale level-IL curve; The calculation method of the gray scale level-IL curve comprises: When the spatial light modulator (110) is set according to N gray levels and X*Y resolution, gray levels are sequentially loaded onto the LCOS chip (210), and the power value Pi is recorded for each gray level i. The gray level-IL curve is obtained based on P and Pi, specifically including: The processing unit (104) controls the SLM driving circuit (105) to set the X*Y pixels of the LCOS chip (210) to the same gray level, and traverses N states from 0 to N-1. Each time the processing unit (104) sets the grayscale control state of an LCOS chip (210), it reads the optical power value once through the power meter (103) and records it as Pi, i=0,1,2,...,N-1; Subtracting P from each Pi yields the insertion loss IL for each gray level i. The IL values ​​of N gray levels form the gray level-IL curve.

8. The method according to claim 7, wherein, The calculation method for the grayscale level-phase modulation depth curve includes: When the third linearly polarized light passes through the second half-wave plate (2062), it becomes the fourth linearly polarized light; The fourth linearly polarized light is decomposed into a fifth linearly polarized light and a sixth linearly polarized light with equal amplitudes, and the fifth linearly polarized light has a phase difference δi with respect to the sixth linearly polarized light after passing through the LCOS chip (210), and the fifth linearly polarized light and the sixth linearly polarized light reflected on the LCOS chip (210) again pass through the calibration light path (200) and the transmittance becomes (cos (δ i / 2)) due to the phase difference δi. 2 The gray scale level-phase modulation depth curve is obtained by the processing unit (104) in combination with the gray scale level-IL curve. Where: i is the gray level of the LCOS chip (210), and the coordinate system carrying the gray level-phase modulation depth curve uses gray level and phase difference as two-dimensional coordinate scalars respectively.

9. The method according to claim 8, wherein, The grayscale level-phase modulation depth curve is calculated based on the grayscale level-IL curve, specifically as follows: In combination with the gray scale level-IL curve, and the phase difference and the conversion formula of ILi, the phase difference corresponding to each gray scale level i is calculated ; Phase difference at gray scale 0 Phase difference at gray scale i Subtracting Phase modulation depth corresponding to gray scale i is obtained, and further a gray scale level-phase modulation depth curve is obtained. Wherein, ILi represents the insertion loss caused by the change in gray level; for any gray level i, ILi is obtained by subtracting the inherent insertion loss of the system from the corresponding IL value.

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