A phase calibration system and method for a pure phase reflective liquid crystal spatial light modulator

Abstract

The application discloses a system and method for generating stable interference fringes by using a pure phase reflective liquid crystal spatial light modulator, and the system comprises a light source module, a laser collimation filtering and beam expanding module, a pure phase reflective liquid crystal spatial light modulator (SLM) control module and a CCD image acquisition module. The system can generate stable double-hole light spots by loading a gray-scale gradual phase grating on the SLM, replaces the method for generating double-hole light spots by using a photoetching mask in a traditional physical optical interference experiment, and can achieve the final result without the aid of other devices, and is simple and convenient to operate. In addition, compared with traditional interference systems such as a Talbot-Green system and a Mach-Zehnder system, the output interference fringes will not vibrate, and the calculation of the post-stripe movement amount is not affected, and the system has the characteristics of stable operation, flexible control and accurate calculation.

Description

Technical Field

[0001] This invention belongs to the field of optical imaging, and particularly relates to the field of ghost imaging, specifically a phase calibration system and method for a pure phase reflective liquid crystal spatial light modulator. Background Technology

[0002] Liquid crystal spatial light modulators (LC-SLMs) are optical diffraction devices that can control the intensity, phase, frequency, and other characteristics of light waves in one or two dimensions. They are widely used in fields such as optical holographic projection, laser beam shaping, adaptive optics, and coherent wavefront modulation.

[0003] Because the birefringence effect produced by the liquid crystal spatial light modulator is different for light of different wavelengths, that is, the phase modulation effect is different for light of different wavelengths, the liquid crystal spatial light modulator needs to be tested and phase calibrated before use.

[0004] Currently, the main methods used for phase calibration of liquid crystal spatial light modulators are double-slit interference, Mach-Zehnder interference, and Thyman-Green interferometry. The double-slit interference optical path is much more stable than the Mach-Zehnder and Thyman-Green interferometry paths, with less noticeable interference fringe fluctuation. In the double-slit interference path, the traditional method uses a photomask to generate a double-aperture spot. This requires additional components, resulting in a relatively complex structure that is inconvenient to operate and has a high cost. Furthermore, the photomask may have issues such as inaccurate fabrication or unevenness, leading to relatively large calibration errors. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a phase calibration system and method specifically for phase calibration of pure phase reflective liquid crystal spatial light modulators. It can avoid calibration errors caused by inaccurate and uneven processing due to the use of photolithography masks through a relatively simple optical structure, and obtain interference fringes and phase-grayscale curves.

[0006] The technical solution to achieve the purpose of this invention is: a phase calibration system for a pure phase reflective liquid crystal spatial light modulator, the system comprising a light source module, a laser collimation, filtering and beam expanding module, a pure phase reflective liquid crystal spatial light modulator (SLM) control module and an image acquisition module arranged sequentially along the optical axis;

[0007] The light source module is used to provide stable single-longitudinal-mode continuous laser output;

[0008] The laser collimation, filtering, and beam expanding module is used to generate a uniform light spot that can cover the SLM LCD screen and filter scattered light.

[0009] The pure phase reflective liquid crystal spatial light modulator (SLM) control module is used to control the loading of SLM electrical signals and to generate dual-aperture light spots by performing phase hysteresis projection.

[0010] The image acquisition module is used to acquire interference fringe images of the dual-aperture light spots.

[0011] Furthermore, the light source module includes a single-mode laser and an adjustable light attenuator arranged sequentially along the optical axis. The thickness of the thin film on the surface of the adjustable light attenuator is adjustable, so that the single-mode laser emits stable continuous laser light.

[0012] Furthermore, the laser collimation, filtering, and beam expanding module includes a microscope objective, a pinhole, and a lens arranged sequentially along the optical axis; the pinhole is located at both the rear focal plane of the microscope objective and the front focal plane of the lens.

[0013] Furthermore, the pure phase reflective liquid crystal spatial light modulator (SLM) control module includes a half-wave plate, a pure phase liquid crystal spatial light modulator (SLM), a host computer, and a polarizer. The outgoing light from the laser collimation, filtering, and beam expanding module is incident on the pure phase liquid crystal spatial light modulator (SLM) after passing through the half-wave plate, and then reflected by the pure phase liquid crystal spatial light modulator (SLM) before being incident on the polarizer. By adjusting the half-wave plate and the polarizer, the pure phase liquid crystal spatial light modulator (SLM) reaches its maximum modulation degree. Then, the host computer loads the phase psychrogram corresponding to each gray value onto the pure phase liquid crystal spatial light modulator (SLM) to generate the corresponding dual-aperture light spot.

[0014] Furthermore, the image acquisition module includes a focusing lens, a CCD camera, and a host computer; the dual-aperture light spots converge and interfere through the focusing lens, and then the CCD camera acquires the interference fringe image and transmits the interference fringe image to the host computer; by changing the gray value of one of the light spots, the fringe movement is measured based on the interference fringe image to obtain the final calibration result.

[0015] The calibration method based on the above-mentioned phase calibration system for a pure phase reflective liquid crystal spatial light modulator includes the following steps:

[0016] Step 1: Construct a phase calibration system for a pure phase reflective liquid crystal spatial light modulator;

[0017] Step 2: Adjust the adjustable light attenuator to select the desired optical power;

[0018] Step 3: Adjust the position of the microscope objective so that the light spot focused by the microscope objective is directly opposite the pinhole, thus filtering out a uniform laser spot.

[0019] Step 4: Load a phase lattice capable of generating a dual-aperture light spot onto a pure phase liquid crystal spatial light modulator (SLM).

[0020] Step 5: The two light spots are converged by a lens to generate interference. Then, the interference fringe image is acquired by a CCD camera and uploaded to the host computer.

[0021] Step 6: Change the gray value of one of the light spots, obtain the stripe movement corresponding to each gray value, and record it;

[0022] Step 7: The host computer performs data processing and calculation to obtain the phase corresponding to each gray value and plots the curve to complete the calibration.

[0023] Compared with the prior art, the significant advantages of this invention are:

[0024] 1) This invention proposes a method of generating dual-aperture spots by loading corresponding phase holograms onto an SLM, which is simpler in structure and easier to operate than the traditional method of generating dual-aperture spots using photomasks.

[0025] 2) Reduces the use of photomasks, resulting in lower costs.

[0026] 3) This invention uses SLM to generate dual-aperture light spots. Compared with light spots generated using photolithography masks, the light spots are rounder and have smoother edges, and the interference fringes are more uniform in brightness, resulting in more accurate measurement results.

[0027] 4) Compared with traditional interferometric systems such as Thyman-Green and Mach-Zendel, the output interference fringes will not jitter and will not affect the calculation of the fringe shift in the later stage. It has the characteristics of stable operation, flexible control and accurate calculation.

[0028] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the phase calibration optical path system for a pure phase reflective liquid crystal spatial light modulator.

[0030] Figure 2 This is a schematic diagram of the phase lattice applied to the SLM when the target light field distribution is a dual-aperture spot.

[0031] Figure 3 This is a schematic diagram of the target light field as a double-aperture light spot.

[0032] Figure 4 This is a schematic diagram of a dual-hole structure with a gradient of grayscale. From left to right and from top to bottom, the grayscale of the right hole gradually changes. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0034] In one embodiment, combined Figure 1 A phase calibration system for a pure phase reflective liquid crystal spatial light modulator is provided. The system includes a light source module 1, a laser collimation, filtering and beam expanding module 2, a pure phase reflective liquid crystal spatial light modulator (SLM) control module 3, and an image acquisition module 4 arranged sequentially along the optical axis.

[0035] The light source module 1 is used to provide stable single-longitudinal-mode continuous laser output;

[0036] The laser collimation, filtering, and beam expanding module 2 is used to generate a uniform light spot that can cover the SLM LCD screen and filter scattered light.

[0037] The pure phase reflective liquid crystal spatial light modulator (SLM) control module is used to control the loading of SLM electrical signals and to generate dual-aperture light spots by performing phase hysteresis projection.

[0038] The image acquisition module 4 is used to acquire interference fringe images of the dual-aperture light spot.

[0039] Furthermore, in one embodiment, the light source module 1 includes a single-mode laser 5 and an adjustable light attenuator 6 arranged sequentially along the optical axis. The thickness of the thin film on the surface of the adjustable light attenuator 6 is adjustable, so that the single-mode laser 5 emits stable continuous laser light.

[0040] Here, an adjustable light attenuator 6 is used to attenuate optical power. The thickness of the thin film on the surface of the adjustable light attenuator is adjustable, so the reflectance of the surface is also continuously adjustable.

[0041] Preferably, in one embodiment, the single-mode laser 5 is a green semiconductor-pumped solid-state laser with an emission wavelength of 532nm and a power of 400mW.

[0042] Furthermore, in one embodiment, the laser collimation, filtering, and beam expanding module 2 includes a microscope objective 7, a pinhole 8, and a lens 9 arranged sequentially along the optical axis; the pinhole 8 is located at both the rear focal plane of the microscope objective 7 and the front focal plane of the lens 9.

[0043] Preferably, in one embodiment, a microscope objective lens 7 with a magnification of 40x is selected, and a 25μm pinhole 8 and a lens 9 are used to filter the scattered light caused by dust or impurities in the air or on optical components, so as to obtain a light spot with uniform light intensity distribution and a diameter of 7mm.

[0044] Furthermore, in one embodiment, the pure phase reflective liquid crystal spatial light modulator (SLM) control module 3 includes a half-wave plate 10, a pure phase liquid crystal spatial light modulator (SLM) 11, a host computer 13, and a polarizer 14. The outgoing light from the laser collimation, filtering, and beam expanding module 2 is incident on the pure phase liquid crystal spatial light modulator (SLM) 11 after passing through the half-wave plate 10, and then reflected by the pure phase liquid crystal spatial light modulator (SLM) 11 before being incident on the polarizer 14. By adjusting the half-wave plate 10 and the polarizer 14, the pure phase liquid crystal spatial light modulator (SLM) 11 reaches its maximum modulation degree. Then, the host computer 13 loads the phase psychrogram corresponding to each gray value onto the pure phase liquid crystal spatial light modulator (SLM) 11 to generate the corresponding dual-aperture light spot.

[0045] Preferably, in one embodiment, the pure phase liquid crystal spatial light modulator SLM11 is a LETO type product from HOLOEYE GmbH, Germany, with an incident angle not exceeding ±5°.

[0046] Furthermore, in one embodiment, the image acquisition module 4 includes a focusing lens 15, a CCD camera 16, and a host computer 13; the dual-aperture light spots converge and interfere through the focusing lens 15, and then the CCD camera 16 acquires the interference fringe image and transmits the interference fringe image to the host computer 13; the gray value of one of the light spots is changed, and the fringe movement is measured based on the interference fringe image to obtain the final calibration result.

[0047] In one embodiment, a phase calibration method for a pure phase-reflective liquid crystal spatial light modulator is proposed, the method comprising the following steps:

[0048] Step 1: Construct a phase calibration system for a pure phase reflective liquid crystal spatial light modulator;

[0049] Step 2: Adjust the adjustable light attenuator to select the desired light power (light power that will not damage the surface of optical components and will not overexpose the camera);

[0050] Step 3: Adjust the position of the microscope objective so that the light spot focused by the microscope objective is directly opposite the pinhole, thus filtering out a uniform laser spot.

[0051] Step 4: Load a device capable of generating a dual-aperture light spot onto a pure phase liquid crystal spatial light modulator (SLM). Figure 3 The phase diagram shown is as follows Figure 2 As shown;

[0052] Step 5: The two light spots are converged by a lens to generate interference. Then, the interference fringe image is acquired by a CCD camera and uploaded to the host computer.

[0053] Step 6, change the grayscale value of one of the light spots as follows: Figure 4As shown, the amount of stripe movement corresponding to each grayscale value is obtained and recorded;

[0054] Here, step 6 can also be replaced by loading the grayscale image of the grayscale gradient of one of the holes in the pre-prepared double hole pattern onto the SLM, obtaining and recording the stripe movement amount corresponding to each grayscale value.

[0055] Step 7: The host computer performs data processing and calculation to obtain the phase corresponding to each gray value and plots the curve to complete the calibration.

[0056] In summary, this invention proposes a method for generating dual-aperture spots by loading a corresponding phase symmetry image onto an SLM (Self-Device Model). Compared to the traditional method of generating dual-aperture spots using a photomask, this method is structurally simpler and easier to operate, reduces the use of photomasks, and lowers costs. The dual-aperture spots generated by this invention using an SLM are more rounded and have smoother edges than those generated using a photomask, resulting in more uniform interference fringe brightness and ultimately more accurate measurement results.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A phase calibration system for a pure phase-reflective liquid crystal spatial light modulator, characterized in that, The system includes a light source module (1), a laser collimation, filtering and beam expanding module (2), a pure phase reflective liquid crystal spatial light modulator (SLM) control module (3), and an image acquisition module (4) arranged sequentially along the optical axis. The light source module (1) is used to provide stable single-longitudinal-mode continuous laser output; The laser collimation, filtering and beam expanding module (2) is used to generate a uniform light spot that can cover the SLM LCD screen and filter scattered light. The pure phase reflective liquid crystal spatial light modulator (SLM) control module is used to control the loading of SLM electrical signals and to generate dual-aperture light spots by performing phase hysteresis projection. The image acquisition module (4) is used to acquire interference fringe images of the dual-aperture light spot; The pure phase reflective liquid crystal spatial light modulator (SLM) control module (3) includes a half-wave plate (10), a pure phase liquid crystal spatial light modulator (SLM) (11), a host computer (13), and a polarizer (14). The output light of the laser collimation, filtering, and beam expanding module (2) is incident on the pure phase liquid crystal spatial light modulator (SLM) (11) after passing through the half-wave plate (10), and then incident on the polarizer (14) after being reflected by the pure phase liquid crystal spatial light modulator (SLM) (11). By adjusting the half-wave plate (10) and the polarizer (14), the pure phase liquid crystal spatial light modulator (SLM) (11) reaches the maximum modulation degree. Then, the host computer (13) loads the phase symmetry diagram corresponding to each gray value on the pure phase liquid crystal spatial light modulator (SLM) (11) to generate the corresponding dual-aperture light spot. The light source module (1) includes a single-mode laser (5) and an adjustable light attenuator (6) arranged sequentially along the optical axis. The thickness of the thin film on the surface of the adjustable light attenuator (6) is adjustable, so that the single-mode laser (5) emits a stable continuous laser. The laser collimation, filtering and beam expanding module (2) includes a microscope objective (7), a pinhole (8) and a lens (9) arranged sequentially along the optical axis; the pinhole (8) is located at both the back focal plane of the microscope objective (7) and the front focal plane of the lens (9); The pure phase liquid crystal spatial light modulator SLM (11) adopts the LETO type product of HOLOEYE Company of Germany, and the incident angle does not exceed ±5°. The image acquisition module (4) includes a focusing lens (15), a CCD camera (16), and a host computer (13). The dual-aperture light spots converge and interfere through the focusing lens (15), and then the CCD camera (16) acquires the interference fringe image and transmits the interference fringe image to the host computer (13). The gray value of one of the light spots is changed, and the fringe movement is measured based on the interference fringe image to obtain the final calibration result.

2. The phase calibration system for a pure phase-reflective liquid crystal spatial light modulator according to claim 1, characterized in that, The single-mode laser (5) is a green semiconductor-pumped solid-state laser.

3. A calibration method for the phase calibration system of a pure phase reflective liquid crystal spatial light modulator according to any one of claims 1 to 2, characterized in that, The method includes the following steps: Step 1: Construct a phase calibration system for a pure phase reflective liquid crystal spatial light modulator; Step 2: Adjust the adjustable light attenuator to select the desired optical power; Step 3: Adjust the position of the microscope objective so that the light spot focused by the microscope objective is directly opposite the pinhole, thus filtering out a uniform laser spot. Step 4: Load a phase lattice capable of generating a dual-aperture light spot onto a pure phase liquid crystal spatial light modulator (SLM). Step 5: The two light spots are converged and interference is generated by the lens. Then, the interference fringe image is acquired by the CCD camera and uploaded to the host computer. Step 6: Change the gray value of one of the light spots, obtain the stripe movement corresponding to each gray value, and record it; Step 7: The host computer performs data processing and calculation to obtain the phase corresponding to each gray value and plots the curve to complete the calibration.

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