Complex amplitude SLM adaptive optical alignment system and method in perturbed channel environment

Abstract

The application provides a complex amplitude SLM adaptive optical path alignment system and method for aligning a to-be-aligned light beam in a disturbed channel, wherein the to-be-aligned light beam in the disturbed channel is decomposed into target light and reference light after passing through a beam splitter; a wavefront sensor receives the reference light, acquires phase information of the reference light and inputs the phase information into a processor; the processor calculates a superimposed compensation amount of complex amplitude regulation according to an alignment position and generates a phase hologram, and inputs the phase hologram into a liquid crystal controller; the phase hologram comprises a plurality of concentric circles, and is used for simulating a ring-shaped blazed grating of focused light rays at a preset alignment position; a liquid crystal of a phase SLM receives the target light, the liquid crystal controller converts the phase hologram into a control voltage, and controls the liquid crystal to perform alignment output on the target light; and the application can continuously correct and align the light beam transmitted in the disturbed optical channel based on pure phase SLM complex amplitude regulation.

Description

Technical Field

[0001] This invention relates to the fields of optical compensation and underwater wireless optical communication technology, and more specifically, to an adaptive optical path alignment system and method for a spatial light modulator (SLM) oriented towards perturbed channels. Background Technology

[0002] Underwater Optical Wireless Communication (UOWC) is a wireless information transmission method that uses light as a carrier wave. Compared to previous technologies such as underwater acoustic communication, UOWC technology can effectively support high-speed, broadband, and secure wireless transmission services over short to medium distances.

[0003] Because water bodies are easily affected by varying degrees of ocean turbulence, bubbles, salinity gradients, temperature gradients, ocean currents, waves, and sea breezes, this can cause time-varying fluctuations in received light intensity, leading to a significant deterioration in UOWC link performance. For example, to reduce the impact of turbulence disturbances on UOWC systems, researchers have proposed a scintillation suppression technique based on adaptive optics to address the time-varying effects of underwater turbulence. This technique, an active compensation method, can effectively improve signal quality. The adaptive optics system consists of a wavefront detection device and a compensation device. By employing appropriate compensation devices and algorithms, it achieves compensation and correction of incident wavefront aberrations, thereby reducing optical scintillation. This technique has advantages such as real-time phase compensation and dynamic tracking alignment, thus becoming one of the solutions for improving the transmission performance of UOWC systems under underwater disturbance conditions.

[0004] Wavefront compensation devices in adaptive systems include deformable mirrors (DM), digital micromirror devices (DMD), and solid-state mirrors (SLMs). Compared to DM and DMD, SLMs are the most commonly used adaptive components. SLMs are high-speed, high-precision devices with multi-dimensional modulation capabilities, widely used in adaptive optics systems. They are primarily used to provide phase or intensity modulation only, but the direction depends on the polarization state of the incident laser. SLMs can be used to control the amplitude, phase, and / or polarization of the output beam; with the use of high-speed liquid crystal materials, the modulation rate can reach 1 kHz.

[0005] Currently, several studies have explored the application of SLM-based adaptive optics technology for scintillation compensation. For example, in the paper "Y. Baykal, 'Adaptive optics correction of scintillation in underwatermedium,' J. Mod. Opt., vol. 67, no. 3, pp. 220-225, Jan. 2020", the authors represented aberrations caused by turbulence disturbances using a low-order Zernike filter function, and then achieved aberration correction through adaptive optics, and analyzed the impact of aberrations on scintillation. However, the calculation and adjustment of Zernike coefficients are time-consuming, making real-time dynamic compensation difficult. In the paper “Shen Chuan, Liu Kaifeng, Zhang Cheng, et al. Application of programmable Fresnel phase lens in multi-plane holographic projection [J]. Acta Photonica Sinica, vol. 43, no. 5, pp. 94-101, May 2014”, the authors implemented the projection of a specific image using a programmable Fresnel phase lens based on SLM, which can generate corresponding patterns. The programmable Fresnel phase lens used in this scheme can focus the beam, but it cannot customize the focal point at any point on the focal plane.

[0006] Existing patent literature discloses a high-speed adaptive optics ring spot correction system and method based on machine learning. This method establishes a mapping relationship between the morphology of a distorted ring spot and the phase reconstruction coefficients required to correct the distortion by building a learning model. The distorted ring spot to be measured is input into the trained model, and the phase reconstruction coefficients for correcting the distortion are solved. The corrected phase reconstructed from these coefficients is then loaded onto a single-lens laser beam (SLM) to correct the distortion. While this scheme can correct ring spot aberrations using an SLM, its overall approach involves acquiring the distorted spot and then using a machine learning model for correction. During training, it is necessary to exhaustively use all possible distorted spots as the training set, severely limiting the system performance to the model's training accuracy. Since obtaining a complete set of distorted spots is difficult in practical deployments, 100% accurate correction of the distorted spot cannot be achieved, resulting in poor optical correction performance in dynamic environments. Furthermore, this scheme solves the phase reconstruction coefficient of the corresponding distorted phase through machine learning, which is limited to recovering the initial ring spot, but cannot achieve real-time dynamic focusing at any point in different focal lengths and focal planes, making it difficult to support effective tracking and alignment of the optical path.

[0007] In summary, although existing solutions propose adaptive compensation algorithms for SLMs that can iteratively compensate for wavefront distortion and use programmable Fresnel phase lenses to achieve beam focusing control, they still have the following two drawbacks: First, most existing solutions only study the intensity adjustment compensation of the light field through pure phase SLMs, but rarely consider real-time dynamic focusing at arbitrary points in different focal lengths and focal planes, thus making it difficult to achieve effective tracking and alignment of the optical path; second, there are currently few studies on using complex amplitude modulation techniques to achieve wavefront correction and custom optical path alignment on pure phase SLMs, and specific solutions still need to be explored. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies in achieving effective optical path tracking and alignment, this invention provides a complex amplitude SLM adaptive optical path alignment system and method for perturbed channels. This system can perform optical field correction and alignment of beams transmitted in perturbed optical channels, such as UOWC system receiver alignment and phase recovery of optical signals carrying phase information in perturbed channels including turbulence, bubbles, salinity gradients, temperature gradients, ocean currents, waves, and sea breezes. This invention aims to design complex amplitude SLM modulation schemes for these scenarios, enabling pure phase SLMs to simultaneously possess intensity and phase modulation capabilities, and based on this capability, to achieve controlled continuous alignment of photoelectric detectors (PDs).

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0010] An adaptive optical path alignment system for complex amplitude SLM in a disturbed channel is provided for aligning a beam to be aligned in the channel. The system includes a beam splitter, a wavefront sensor, a processor, and a phase-type SLM. The phase-type SLM includes a liquid crystal and a liquid crystal controller. The wavefront sensor, processor, and liquid crystal controller are connected in sequence.

[0011] The beam splitter is used to receive the beam to be aligned and to decompose the beam into a target beam and a reference beam.

[0012] The wavefront sensor is used to receive reference light, acquire the phase information of the reference light, and input it into the processor;

[0013] The processor is used to calculate the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position, generate a phase hologram based on the superposition compensation amount of complex amplitude modulation, and input the phase hologram into the liquid crystal controller.

[0014] In the liquid crystal controller of the phase-type SLM, the phase hologram includes several ring structures with varying gray levels, which are used to simulate a ring-shaped blazed grating that focuses light at a preset alignment position.

[0015] The liquid crystal of the phase-type SLM is used to receive target light, and the liquid crystal controller is used to convert the phase hologram into a control voltage and control the liquid crystal to align the target light. The aligned target light is then focused at a preset alignment position.

[0016] Preferably, the wavefront sensor includes a camera and a microlens array disposed in front of the camera lens, and the camera is connected to a processor.

[0017] Preferably, the camera is a CMOS camera.

[0018] Preferably, the system further includes a photodetector disposed at a preset alignment position for receiving the target light after alignment output and performing photoelectric conversion and post-processing.

[0019] Preferably, the disturbance channel is a UOWC channel, and the disturbance includes any one or more of the following: turbulence, bubbles, salinity gradient, temperature gradient, ocean current, ocean waves, and sea breeze.

[0020] This invention also provides a complex amplitude SLM adaptive optical path alignment method for perturbed channels, the process of which includes the following steps:

[0021] The beam to be aligned in the perturbation channel is split into target light and reference light after passing through the beam splitter;

[0022] The wavefront sensor receives reference light, acquires the phase information of the reference light, and inputs it into the processor;

[0023] The processor calculates the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position, generates a phase hologram based on the superposition compensation amount of complex amplitude modulation, and inputs the phase hologram into the liquid crystal controller.

[0024] In the liquid crystal controller of the phase-type SLM, the phase hologram includes several concentric rings, which are used to simulate the ring-shaped blazed grating that focuses light at a preset alignment position;

[0025] The phase-type SLM receives the target light through its liquid crystal, and the liquid crystal controller converts the phase hologram into a control voltage and controls the liquid crystal to align and output the target light. The aligned target light is then focused at a preset alignment position.

[0026] Preferably, the superimposed compensation amount of the complex amplitude modulation includes the light intensity compensation amount and the phase compensation amount for each point of the phase-type SLM liquid crystal.

[0027] Preferably, the step of the processor calculating the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position specifically includes:

[0028] The processor calculates the phase-type SLM liquid crystal according to the preset alignment position. Light intensity compensation at each point , It is a positive integer, specifically:

[0029]

[0030] in, For phase-type SLM liquid crystals The x and y coordinates of each point The coordinates of the preset alignment point, The vertical distance from the preset alignment point to the surface of the phase-type SLM liquid crystal. The wavelength of the beam to be aligned. Indicates the modulo operation;

[0031] The processor inverts the phase information of the reference light to obtain the wavefront distribution of the beam to be aligned, and obtains the phase-type SLM liquid crystal based on the wavefront distribution of the beam to be aligned. Phase compensation at each point ;

[0032] The superimposed compensation amount of the complex amplitude modulation is specifically expressed as follows:

[0033]

[0034] in, The first phase-type SLM liquid crystal on The superimposed compensation amount of complex amplitude control at each point.

[0035] Preferably, the annular blazed grating simulated by the phase hologram comprises several conical structures sharing a common vertex;

[0036] The longitudinal section of the annular blazed grating is a symmetrical sawtooth shape, and the axis of symmetry is a straight line passing through the vertex and perpendicular to the bottom surface of the annular blazed grating.

[0037] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by the processor, implements the steps in the above method.

[0038] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0039] This invention provides a complex amplitude SLM adaptive optical path alignment system and method for perturbed channels, used to align a beam to be aligned in a perturbed channel. First, the beam to be aligned in the perturbed channel is decomposed into a target beam and a reference beam after passing through a beam splitter. A wavefront sensor receives the reference beam, acquires its phase information, and inputs it into a processor. The processor calculates the superposition compensation amount of the complex amplitude modulation based on the phase information of the reference beam and a preset alignment position, generates a phase hologram based on the superposition compensation amount, and inputs the phase hologram into a liquid crystal controller. In the liquid crystal controller of the phase-type SLM, the phase hologram includes several concentric rings, used to simulate a ring-shaped blazed grating that focuses the light at the preset alignment position. The liquid crystal of the phase-type SLM receives the target beam, and the liquid crystal controller converts the phase hologram into a control voltage and controls the liquid crystal to output the alignment of the target beam. The aligned target beam is focused at the preset alignment position.

[0040] This invention simulates the distribution of a blazed grating focused at a specific location by loading a hologram onto a phase-type SLM and achieves complex amplitude modulation by superimposing an initial phase difference. Driven by an adaptive optics system, this invention can continuously track and align the optical path at a specific location and perform real-time phase compensation. It can be widely used in optical field correction and alignment applications for beams transmitted in disturbed optical channels, such as UOWC system receiver alignment scenarios in disturbed channels like turbulence, bubbles, salinity gradients, temperature gradients, ocean currents, waves, and sea breezes, and phase recovery scenarios for optical signals carrying phase information. Secondly, based on the interference principle of annular blazed gratings, this invention constructs a phase distribution expression that can focus at any focal length and any position in the focal plane. Based on this expression and combined with the coordinates of the desired focusing point, a corresponding phase distribution can be generated. This phase distribution can be used to invert and manufacture special blazed gratings that can focus at specific locations. In addition, the annular blazed grating simulated by this invention has a novel structure. By adjusting the blaze angle, the position of the strongest ring can be changed, thereby controlling where the strongest illumination is obtained on the target plane, providing a new solution for scenarios with special intensity control requirements. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the UOWC adaptive optical path alignment system architecture based on SLM provided in Example 1.

[0042] Figure 2 This is a schematic diagram of the blazed grating provided in Example 2.

[0043] Figure 3 This is a schematic diagram of the annular blazed grating structure provided in Example 2.

[0044] Figure 4 The SLM-controlled optical field provided in Example 2 M Point enhancement diagram.

[0045] Figure 5 This is a schematic diagram of the experimental setup for the first verification experiment provided in Example 3.

[0046] Figure 6 Provided for Example 3 M Phase compensation map and SLM hologram for point coordinates (0,0,0.3).

[0047] Figure 7 This is a schematic diagram of the initial light spot and the light spot after controlled focusing in the first verification experiment provided in Example 3.

[0048] Figure 8 This is an example of a phase hologram corresponding to focusing at an arbitrary point in the second verification experiment provided in Example 3.

[0049] Figure 9 This is a schematic diagram of the controlled movement effect of the light spot in the third verification experiment provided in Example 3. Detailed Implementation

[0050] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0051] To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions;

[0052] It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.

[0053] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0054] Example 1

[0055] This embodiment provides a complex amplitude SLM adaptive optical path alignment system for perturbed channels, used to align a beam to be aligned in a perturbed channel, including: a beam splitter, a wavefront sensor, a processor, and a phase-type SLM; the phase-type SLM includes a liquid crystal and a liquid crystal controller; the wavefront sensor, processor, and liquid crystal controller are connected in sequence;

[0056] The beam splitter is used to receive the beam to be aligned and to decompose the beam into a target beam and a reference beam.

[0057] The wavefront sensor is used to receive reference light, acquire the phase information of the reference light, and input it into the processor;

[0058] The processor is used to calculate the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position, generate a phase hologram based on the superposition compensation amount of complex amplitude modulation, and input the phase hologram into the liquid crystal controller.

[0059] In the liquid crystal controller of the phase-type SLM, the phase hologram includes several ring structures with varying gray levels, which are used to simulate a ring-shaped blazed grating that focuses light at a preset alignment position.

[0060] The liquid crystal of the phase-type SLM is used to receive target light, and the liquid crystal controller is used to convert the phase hologram into a control voltage and control the liquid crystal to align the target light. The aligned target light is focused at a preset alignment position after the alignment output.

[0061] The wavefront sensor includes a camera and a microlens array disposed in front of the camera lens, and the camera is connected to a processor; in this embodiment, the camera is specifically a complementary metal-oxide-semiconductor (CMOS) camera, but other types of cameras may also be used.

[0062] The system also includes a photodetector (PD) set at a preset alignment position, used to receive the target light after alignment output and perform photoelectric conversion and post-processing.

[0063] In this embodiment, the disturbance channel is specifically the UOWC channel, and the disturbance includes several different types of turbulence, bubbles, salinity gradients, temperature gradients, ocean currents, waves, and sea breezes.

[0064] In the specific implementation process, such as Figure 1 As shown, Figure 1 This is a schematic diagram of the SLM-based UOWC adaptive optical path alignment system architecture in this embodiment. The information bits are first coupled to the driving circuit of the light source through a T-type biaser, and then the beam is adjusted into a collimated beam by the first collimating lens group. The signal is then sent out through the UOWC channel. The UOWC channel is composed of disturbed water bodies, with underwater turbulence, bubbles, salinity gradients, temperature gradients, ocean currents, waves, sea breezes, etc., causing disturbances to the beam. After the disturbed beam propagates through the UOWC channel, the beam width is adjusted by the collimating lens group at the receiving end, and then it enters the adaptive compensation unit (i.e., the alignment system in this embodiment).

[0065] Specifically, the light beam is first reflected and then split into a lower-energy reference beam and a higher-energy target beam by a beam splitter according to the beam splitting energy ratio. The reference beam is received by a Shack-Hartmann wavefront sensor for wavefront measurement and light intensity sensing. The wavefront sensor consists of a microlens array in front of the lens and a camera, where the camera includes, but is not limited to, a CMOS camera. The measured wavefront intensity and phase information are transmitted back to the processor. The processor calculates the superposition compensation amount of complex amplitude modulation based on the phase information of the reference beam and the preset alignment position. It generates a phase hologram based on the superposition compensation amount of complex amplitude modulation and inputs the phase hologram into the liquid crystal controller.

[0066] The phase hologram consists of several concentric rings, used to simulate a ring-shaped blazing grating that focuses light rays at a preset alignment position;

[0067] The phase hologram is then converted into a control voltage by the liquid crystal controller, thereby controlling the SLM. After that, the high-energy target light is compensated by the SLM and received by the PD, which then completes the photoelectric conversion and subsequent signal processing.

[0068] This system simulates the distribution of a blazed grating focused at a specific location by loading a hologram onto a phase-type SLM. Driven by an adaptive optics system, it can continuously track and align the optical path at a specific location and perform real-time phase compensation.

[0069] Example 2

[0070] This embodiment provides a complex amplitude SLM adaptive optical path alignment method for perturbed channels, based on the complex amplitude SLM adaptive optical path alignment system for perturbed channels in Embodiment 1, and includes the following steps:

[0071] The beam to be aligned in the perturbation channel is split into target light and reference light after passing through the beam splitter;

[0072] The wavefront sensor receives reference light, acquires the phase information of the reference light, and inputs it into the processor;

[0073] The processor calculates the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position, generates a phase hologram based on the superposition compensation amount of complex amplitude modulation, and inputs the phase hologram into the liquid crystal controller.

[0074] In the liquid crystal controller of the phase-type SLM, the phase hologram includes several concentric rings, which are used to simulate the ring-shaped blazed grating that focuses light at a preset alignment position;

[0075] The phase-type SLM receives the target light through its liquid crystal, and the liquid crystal controller converts the phase hologram into a control voltage and controls the liquid crystal to align and output the target light. The aligned target light is then focused at a preset alignment position.

[0076] The superimposed compensation amount of the complex amplitude modulation includes the light intensity compensation amount and phase compensation amount for each point of the phase-type SLM liquid crystal.

[0077] The processor calculates the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position as follows:

[0078] The processor calculates the phase-type SLM liquid crystal according to the preset alignment position. Light intensity compensation at each point , It is a positive integer, specifically:

[0079]

[0080] in, For phase-type SLM liquid crystals The x and y coordinates of each point The coordinates of the preset alignment point, The vertical distance from the preset alignment point to the surface of the phase-type SLM liquid crystal. The wavelength of the beam to be aligned. Indicates the modulo operation;

[0081] The processor inverts the phase information of the reference light to obtain the wavefront distribution of the beam to be aligned, and obtains the phase-type SLM liquid crystal based on the wavefront distribution of the beam to be aligned. Phase compensation at each point ;

[0082] The superimposed compensation amount of the complex amplitude modulation is specifically expressed as follows:

[0083]

[0084] in, The first phase-type SLM liquid crystal on The superimposed compensation amount of complex amplitude control at each point;

[0085] The annular blazed grating simulated by the phase hologram includes several conical structures sharing a vertex; the longitudinal section of the annular blazed grating is a symmetrical sawtooth shape, and the axis of symmetry is a straight line passing through the vertex and perpendicular to the bottom surface of the annular blazed grating.

[0086] In the specific implementation process, this embodiment is still based on Figure 1The architecture of the UOWC adaptive optical path alignment system based on SLM is described. The beam to be aligned is first reflected and then split into a lower-energy reference beam and a higher-energy target beam by a beam splitter according to the beam splitting energy ratio. The reference beam is received by a wavefront sensor for wavefront measurement and light intensity sensing. The measured wavefront intensity and phase information are transmitted back to the processor. The processor calculates the corresponding compensation amount according to the optimization target of the output light field and converts it into a control voltage through a liquid crystal controller, thereby realizing the control of the SLM. Afterwards, the higher-energy target beam is compensated by the SLM and then received by the PD, which then completes the photoelectric conversion and subsequent signal processing.

[0087] The processing procedure and compensation calculation method in the processor are the focus of this method. How to use reflective pure phase SLM to achieve simultaneous control of intensity and phase is the key technical problem that this method aims to solve. The following is a detailed introduction to the complex amplitude control solution proposed by this method.

[0088] The core of achieving complex amplitude manipulation using a single phase-type SLM lies in the design of the complex amplitude encoding algorithm, i.e., how to simultaneously encode the amplitude and phase information of the optical field into the phase hologram of the SLM. The basic process of loading complex amplitude into the incident light field is described below:

[0089] Input optical field from UOWC channel It can be represented as:

[0090]

[0091] in: It is the intensity component of the input light field. It is the phase component of the input optical field; after SLM compensation, the system's output optical field It can be represented as:

[0092]

[0093] in: It is the intensity component of the output light field. Let be the phase component of the output light field; then, throughout the entire process from the input light to the output light field, the phase hologram loaded when passing through the SLM... The following relationship should be satisfied:

[0094]

[0095] in: , The wave vector of the input light field, The wave vector for the output light field;

[0096] If we ignore the energy absorption and reflection attenuation during the SLM modulation process, then the compensated amount during the SLM modulation process It can be represented as:

[0097]

[0098] This can be further simplified to:

[0099]

[0100] in, For intensity modulation components that need to be implemented using SLM, For the phase compensation components that need to be implemented using SLM;

[0101] The calculation methods for intensity modulation components and phase compensation components will be further introduced below;

[0102] Calculation of intensity modulation components:

[0103] Since phase-type SLMs cannot directly modulate intensity, an indirect modulation technique must be used to achieve intensity modulation on a phase-type SLM, as detailed below:

[0104] As a type of electromagnetic wave, light waves exhibit significant wave characteristics, such as destructive interference and expansion. In optical components, a blazed grating is a special type of grating whose position of strongest interference can be arbitrarily changed; its shape is as follows... Figure 2 As shown, the surface has a sawtooth-like structure, and the angle between the groove plane and the grating plane is the blaze angle. Due to the blaze angle, the diffraction zero order of each grooved plane does not coincide spatially with the interference zero order of other grooved planes. Light energy can be enhanced by setting a specific blaze angle to achieve the desired blaze of a particular order of interference, thus realizing the blaze of that order's spectrum. and It is the angle between the incident ray and the outgoing ray and the normal to the grating plane; the grating equation of a blazed grating defines the first... m When the flash is of the highest caliber, the angle of incidence Reflection angle Grating constant d and light wavelength The relationship between; specifically, when the maximum light intensity and m When the diffraction order coincides, the grating equation is:

[0105] Therefore, by designing different flare angles This allows the diffraction energy of a beam to be concentrated on a specific order, maximizing the diffraction energy of that order.

[0106] In blazed gratings, specific orders of light intensity enhancement can be achieved by changing the blaze angle; the core lies in designing a reasonable... This causes interference phase expansion to occur when all beams are reflected by different grooved planes and reach a specific order; Figure 2 Each groove plane in the image reflects the light beam, thus changing... The optical path delay can be changed; in SLM, the entire reflective panel is composed of a large number of independent liquid crystal molecular units; taking Holoeye LETO-VIS reflective pure phase SLM as an example, its liquid crystal panel is composed of independent liquid crystals with a resolution of 1920×1080, and each area can be controlled individually; therefore, the optical path delay can be changed by adjusting the refractive index of the liquid crystal in this SLM, thereby simulating a structure similar to a blazed grating.

[0107] Since a blazed grating is composed of parallel striped grooved planes, the light intensity after reflection is distributed in a striped pattern according to its order. From the perspective of the UOWC receiver, concentrating the intensity of the highest brightness order on the PD can improve the signal-to-noise ratio of the received signal. Therefore, this method proposes to... Figure 2 The strip-shaped blazed grating shown is a cross-section of which is then surrounded. Figure 2 The cross-section is formed by rotating one end. Figure 3 The diagram shows a circular zigzag grating structure; the grating is circular in shape overall, with a zigzag concentric ring on the upper surface, each zigzag having a specific blaze angle. In actual manufacturing, the blaze angle of each annular serration... The same value can be set, or different values ​​can be set for each one according to requirements; since the light intensity distribution produced by the annular blazed grating is concentric, the blaze angle of each groove plane can be adjusted. It is possible to find the point where the center of the concentric circles is the strongest shining level. Similarly, a circular blazed grating structure can be simulated by loading a holographic phase map using an SLM, and the height from the slot plane to the grating plane at this moment will be simulated by a liquid crystal.

[0108] Therefore, if the beam passing through the UOWC channel is to be reflected by the SLM, then... Figure 4 shown M If the point is at maximum light intensity, it is necessary to ensure that every ray of light reaches its destination after being reflected by the SLM. M The optical path lengths at each point are the same; to simplify the model, we assume here that all incident beams to the SLM have the same phase; to make... M Dots gain interference enhancement, liquid crystal dots on SLM N To the target point M The distance should meet the following conditions:

[0109]

[0110] in, for M Point coordinates, representing the location of the PD center. For SLM LCD N The x and y coordinates of the point For SLM N The equivalent optical path that the liquid crystal should compensate for. Let be the distance from PD to SLM, then:

[0111]

[0112] because Waveforms with phase differences that are integer multiples of each other vibrate in unison, therefore Differences that are integer multiples can be discarded; only those less than a certain value are retained. The part; at this time, N The equivalent optical path of a point can be converted into phase. :

[0113]

[0114] in: Represents the variable a The modulo operation, The wavelength of the incident light is given by the equation at the coordinate point. When focusing, in Figure 4 The phase that needs to be compensated at the origin of the SLM liquid crystal plane; according to the above formula, the phase distribution of the annular blazed grating focused at a specific position can be calculated, and the production and manufacturing of special blazed gratings can be completed; in addition, in the above formula and There is a corresponding relationship: when the required phase difference accuracy for compensation decreases, the tolerance for wavelength increases; for example, assuming the target phase difference of the system is less than... At this point, it is considered acceptable, and the tolerance range for the wavelength is... The system can support a maximum wavelength offset of Multicolor light;

[0115] Once the target point that needs to be aligned has been determined M Location Then, substituting into the above formula, the corresponding holographic phase diagram can be generated point by point. After the above operations, the original incident light will be modulated to converge at... M A beam of light at a point, thus achieving intensity modulation;

[0116] Calculation of phase compensation components:

[0117] The pure phase SLM intensity modulation process described above assumes that the incident beams have the same phase and does not consider the initial phase difference. However, the actual incident beam is affected by underwater disturbances. Under different environmental conditions such as turbulence, bubbles, salinity gradients, temperature gradients, ocean currents, and waves, different disturbance characteristics will appear. This will lead to various situations such as the wavefront phase of the beam passing through the UOWC channel being ahead, behind, jumping, or abrupt. Therefore, the initial phase difference of the beam is generally not zero. In order to make the phase difference zero when all beams reach the receiver, it is necessary to compensate for the initial phase difference.

[0118] exist Figure 1 In the adaptive compensation unit of the UOWC system shown on the right, the received beam subjected to underwater disturbance is split into a higher-energy target beam and a lower-energy reference beam after passing through a beam splitter. The reference beam then enters a Shack-Hartmann wavefront sensor, which can infer the wavefront distribution of the incident light. ;because This is the initial phase carried by the beam after passing through underwater disturbances, therefore, this phase needs to be loaded onto the SLM for compensation during the compensation process;

[0119] Based on the above intensity compensation and phase compensation methods, it is possible to obtain the focused optical field after passing through the underwater channel. M The required compensation phase for the point And the compensation amount for correcting the initial phase difference To achieve simultaneous intensity and phase compensation within the same compensation unit, it is necessary to simultaneously add intensity and phase compensation phase components to the SLM. Therefore, the SLM holographic phase corresponding to complex amplitude compensation... for:

[0120]

[0121] in, The first phase-type SLM liquid crystal on The superimposed compensation amount of complex amplitude control at each point;

[0122] Based on this, once the point to be focused is set... When the coordinates are determined, the equivalent real-time light intensity compensation based on the current incident light can be obtained. and phase compensation amount This means that the equivalent superimposed compensation amount of complex amplitude modulation can be obtained. Load the compensation amount into Figure 1 In the SLM of the adaptive optics system shown, under the real-time compensation operation of the closed-loop adaptive system, complex amplitude modulation can be achieved and the beam can be controlled to continuously point towards the target point under dynamic disturbances. M ;

[0123] This method simulates the distribution of a blazed grating focused at a specific location by loading a hologram onto a phase-type SLM, and achieves complex amplitude modulation by superimposing an initial phase difference. Driven by an adaptive optics system, this method can continuously track and align the optical path at a specific location and perform real-time phase compensation. Secondly, based on the interference principle of annular blazed gratings, this invention constructs a phase distribution expression that can focus at any focal length and any position in the focal plane. Based on this expression and combined with the coordinates of the desired focusing point, a corresponding phase distribution can be generated. This phase distribution can be used to invert and manufacture special blazed gratings that can focus at a specific location. In addition, the annular blazed grating simulated by this method has a novel structure. By adjusting the blaze angle, the position of the strongest ring can be changed, thereby controlling where the strongest illumination is obtained on the target plane, providing a new solution for scenarios with special intensity control requirements.

[0124] Example 3

[0125] This embodiment provides three verification experiments to verify the effectiveness of the complex amplitude SLM adaptive optical path alignment system and method for disturbed channels proposed in Embodiments 1 and 2;

[0126] This embodiment uses an uncollimated beam to represent non-ideal incident light passing through an underwater channel (the uncollimated beam generates a non-ideal spot upon reaching the SLM surface). An experimental setup based on an SLM with concentric circular blazed grating distribution is constructed, and the target point is changed. M The coordinate values ​​are used to generate the corresponding phase hologram, test whether the beam is controlled and detect whether the position of the actual light spot matches the target point, thereby completing the experimental verification.

[0127] In the specific implementation process, the following are established: Figure 5 The experimental setup shown uses a 532nm laser diode as the light source. Without collimation, the light beam passes through a lens, an attenuator, a polarizer, an aperture, and an SLM before entering a CMOS camera. This embodiment uses a Daheng ME2P-1230-23U3M / C CMOS camera. By controlling the SLM to control the non-ideal beam, focusing and deflection of the beam can be achieved, thus demonstrating the performance of this scheme. This embodiment controls the beam to focus, defocus, and deviate by a certain displacement by loading a corresponding holographic phase map onto the SLM.

[0128] In the first verification experiment, the distance between the SLM and the CMOS camera was set to... z = 0.3m, and set M The coordinates of the point are (0,0,0.3); zThe value of is related to the shape and size of the UOWC system receiver and can be set according to the needs of the underwater application scenario; in this case, the pre-compensated phase and SLM phase hologram obtained by the complex amplitude compensation algorithm are as follows: Figure 6 As shown; the calculated Figure 6 (b) The phase hologram is loaded onto the SLM, and the non-ideal beam will be drawn from... Figure 7 (a) The irregular, non-uniform light spot becomes focused and points towards the target point. M The light spot, such as Figure 7 As shown in (b); it can be seen that for any target point M This method can achieve focusing of the light spot at any position;

[0129] In the second verification experiment, SLM and CMOS cameras were selected at different distances and were not located in... z Target point on the axis M The phase hologram; specifically, Figure 8 (a) is z = Focusing on non-at a distance of 0.5 meters z A phase hologram generated at the point (0.002, 0.0015, 0.5) on the axis. Figure 8 (b) is z = Focusing on non-at a distance of 2 meters z A holographic phase map is generated at the point (-0.0015, -0.001, 2) on the axis. Based on the focal length of the focal point and the changes in horizontal and vertical displacement, this method can generate the corresponding holographic phase map in real time and dynamically, ensuring that the received optical signal is always aligned with the center of the PD.

[0130] In the third verification experiment, under the influence of this method, the received signal spot was controlled to shift in four directions (up, down, left, and right) from the origin, and was tracked and aligned in real time. The experimental results are as follows: Figure 9 As shown;

[0131] The above verification experiment can verify that at any given point M When the position is determined, the equivalent phase is calculated. Furthermore, by utilizing SLM modulation, it is possible to focus an uncollimated beam at any point; thus, it can be seen that the method is feasible to achieve beam intensity modulation in pure phase SLM; on this basis, by taking the initial phase difference of the beam into the compensation amount, it is possible to achieve joint compensation of intensity and phase, that is, to achieve optical path alignment by complex amplitude modulation on SLM.

[0132] In the above description, the same or similar labels correspond to the same or similar parts;

[0133] The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0134] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. 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 claims of the present invention.

Claims

1. A complex amplitude SLM adaptive optical path alignment system for perturbed channels, used to align a beam to be aligned in a perturbed channel, characterized in that, include: Beam splitter, wavefront sensor, processor, and phase-type SLM; The phase-type SLM includes a liquid crystal and a liquid crystal controller; the wavefront sensor, processor, and liquid crystal controller are connected in sequence. The beam splitter is used to receive the beam to be aligned and to decompose the beam into a target beam and a reference beam. The wavefront sensor is used to receive reference light, acquire the phase information of the reference light, and input it into the processor; The processor is used to calculate the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position. The superposition compensation amount of complex amplitude modulation includes the light intensity compensation amount and the phase compensation amount for each point of the phase-type SLM liquid crystal. The specific steps of the processor calculating the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position are as follows: The processor calculates the phase-type SLM liquid crystal according to the preset alignment position. Light intensity compensation at each point , It is a positive integer, specifically: in, For phase-type SLM liquid crystals The x and y coordinates of each point The coordinates of the preset alignment point, The vertical distance from the preset alignment point to the surface of the phase-type SLM liquid crystal. The wavelength of the beam to be aligned. Indicates the modulo operation; The processor inverts the phase information of the reference light to obtain the wavefront distribution of the beam to be aligned, and obtains the phase-type SLM liquid crystal based on the wavefront distribution of the beam to be aligned. Phase compensation at each point ; The superimposed compensation amount of the complex amplitude modulation is specifically expressed as follows: in, The first phase-type SLM liquid crystal on The superimposed compensation amount of complex amplitude control at each point; A phase hologram is generated based on the superposition compensation amount of the complex amplitude modulation, and the phase hologram is input into the liquid crystal controller; In the liquid crystal controller of the phase-type SLM, the phase hologram includes several ring structures with varying gray levels, which are used to simulate a ring-shaped blazed grating that focuses light at a preset alignment position. The liquid crystal of the phase-type SLM is used to receive target light, and the liquid crystal controller is used to convert the phase hologram into a control voltage and control the liquid crystal to align the target light. The aligned target light is then focused at a preset alignment position.

2. The complex amplitude SLM adaptive optical path alignment system for perturbed channels according to claim 1, characterized in that, The wavefront sensor includes a camera and a microlens array positioned in front of the camera lens, with the camera connected to a processor.

3. The complex amplitude SLM adaptive optical path alignment system for perturbed channels according to claim 2, characterized in that, The camera in question is specifically a CMOS camera.

4. The complex amplitude SLM adaptive optical path alignment system for perturbed channels according to claim 1, characterized in that, The system also includes a photodetector set at a preset alignment position, used to receive the target light after alignment output and perform photoelectric conversion and post-processing.

5. A complex amplitude SLM adaptive optical path alignment system for perturbed channels according to any one of claims 1 to 4, characterized in that, The disturbance channel is specifically a UOWC channel, and the disturbance includes any one or more of the following: turbulence, bubbles, salinity gradient, temperature gradient, ocean current, ocean waves, and sea breeze.

6. A complex amplitude SLM adaptive optical path alignment method for perturbed channels, based on the complex amplitude SLM adaptive optical path alignment system for perturbed channels as described in any one of claims 1 to 5, characterized in that, Includes the following steps: The beam to be aligned in the perturbation channel is split into target light and reference light after passing through the beam splitter; The wavefront sensor receives reference light, acquires the phase information of the reference light, and inputs it into the processor; The processor calculates the superposition compensation amount of complex amplitude modulation based on the phase information of the reference light and the preset alignment position, generates a phase hologram based on the superposition compensation amount of complex amplitude modulation, and inputs the phase hologram into the liquid crystal controller. In the liquid crystal controller of the phase-type SLM, the phase hologram includes several concentric rings, which are used to simulate the ring-shaped blazed grating that focuses light at a preset alignment position; The phase-type SLM receives the target light through its liquid crystal, and the liquid crystal controller converts the phase hologram into a control voltage and controls the liquid crystal to align and output the target light. The aligned target light is then focused at a preset alignment position.

7. The method for adaptive optical path alignment of complex amplitude SLM for perturbed channels according to claim 6, characterized in that, The annular blazed grating simulated by the phase hologram includes several conical structures sharing a vertex; The longitudinal section of the annular blazed grating is a symmetrical sawtooth shape, and the axis of symmetry is a straight line passing through the vertex and perpendicular to the bottom surface of the annular blazed grating.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method of claim 6.

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