Device for realizing complex amplitude light field regulation and control based on spatial light modulator
阅读说明：本技术 一种基于空间光调制器实现复振幅光场调控的装置 (Device for realizing complex amplitude light field regulation and control based on spatial light modulator ) 是由 余亚中 艾计安 李普杰 范晓燕 于 2020-06-22 设计创作，主要内容包括：本发明公开了一种基于空间光调制器实现复振幅光场调控的装置。对激光器出射的高斯光束进行准直、偏振调节和扩束处理,扩束后的光束经分光镜分成两路,一路光束经空间光调制器进行光场调控,对调制后的出射光束进行空间滤波处理,选取一级衍射分量,在相位图的共轭像平面上得到特殊空间结构光场。将生成光场与另一路未经调制的光束进行空间干涉,通过干涉原理可以恢复生成光场的相位分布信息。利用峰值信噪比对光场的强度分布质量进行评价,以目标光场的强度分布为参考图像,PSNR值越大,生成光场与目标光场的强度分布越相似。该装置结构简单,易于调整,可以产生任意复振幅光场,并通过图像采集系统对光场的强度和相位分布进行分析评价。(The invention discloses a device for realizing complex amplitude light field regulation and control based on a spatial light modulator. The Gaussian beam emitted by the laser is collimated, polarized and expanded, the expanded beam is divided into two paths by the spectroscope, one path of beam is subjected to light field regulation and control by the spatial light modulator, the modulated emitted beam is subjected to spatial filtering, a first-order diffraction component is selected, and a light field with a special spatial structure is obtained on a conjugate image plane of a phase diagram. The generated light field and the other path of unmodulated light beam are subjected to spatial interference, and phase distribution information of the generated light field can be recovered through an interference principle. And evaluating the intensity distribution quality of the light field by utilizing the peak signal-to-noise ratio, wherein the greater the PSNR value is, the more similar the intensity distribution of the generated light field and the target light field is by taking the intensity distribution of the target light field as a reference image. The device has simple structure and easy adjustment, can generate any complex amplitude light field, and analyzes and evaluates the intensity and phase distribution of the light field through the image acquisition system.)
1. A device for realizing complex amplitude light field regulation and control based on a spatial light modulator is characterized by comprising a semiconductor laser (1), a single-mode optical fiber (2) with a polarization controller, a collimating lens (3), a polarizer (4), a beam expander (5), a spectroscope A (6), the spatial light modulator (7), a reflector A (8), a Fourier transform lens A (9), a small hole filtering device (10), a Fourier transform lens B (11), a spectroscope B (12), an image acquisition device (13) and a reflector B (14);
the Gaussian beam emitted by the semiconductor laser (1) is transmitted through a section of single-mode optical fiber (2) with a polarization controller, the collimation lens (3) is used for collimating the light beam emitted by the optical fiber, then the polarization adjustment is carried out, the polarization state of the input light beam is jointly adjusted and controlled by the optical fiber polarization controller and the polarizer (4), the polarization state of the transmitted light in the single-mode optical fiber is changed by adjusting the optical fiber polarization controller, the polarizer (4) controls the polarization state of the optical fiber output light field, and the light field incident to the liquid crystal spatial light modulator (7) has a specific polarization direction and a higher power value;
the beam expander (5) expands the beam to match a liquid crystal panel of the spatial light modulator, the linearly polarized light after expansion passes through the spectroscope A (6), one path of light beam is obliquely incident on the liquid crystal spatial light modulator (7) to be subjected to phase modulation, the inclination angle of the SLM is adjusted firstly, the incident light beam is obliquely incident on the central position of the SLM at a small angle, then the spatial position of an emergent light path is changed by the reflector A (8), and an output light beam with modulation information is reflected by the reflector A (8) and then sequentially passes through the Fourier transform lens A (9), the small-hole filtering device (10), the Fourier transform lens B (11), the spectroscope B (12) and the image acquisition device (13);
loading a phase hologram on a liquid crystal spatial light modulator (7), then finely adjusting a reflector A (8) to enable a first-order diffraction component to pass through an optical axis of a 4f system consisting of a Fourier transform lens A (9) and a Fourier transform lens B (11), then adjusting the size of an aperture diaphragm to ensure that only the positive first-order diffraction component passes through, reflecting an unmodulated light beam reflected by a spectroscope A (6) to a spectroscope B (12) through a reflector B (14) to interfere with a modulated light beam, recording intensity information of an interference light field through an image acquisition device (13), and recovering phase distribution information of a generated light field through an interference principle.
2. The device for realizing complex amplitude light field regulation based on the spatial light modulator as claimed in claim 1, wherein the polarization direction of the polarizer 4 is consistent with the arrangement direction of the liquid crystal molecules of the spatial light modulator 7.
3. The device for realizing complex amplitude light field regulation based on the spatial light modulator according to claim 1, wherein the distance between the spatial light modulator (7) and the Fourier transform lens A (9) through the reflector A (8) is the lens focal length.
4. The device for realizing complex amplitude light field regulation based on the spatial light modulator as claimed in claim 1, wherein the pinhole filter device (10) ensures that the positive first order diffraction component passes through at the focal position of the Fourier transform lens A (9); the image acquisition device (13) is arranged on a focal plane of the Fourier transform lens B (11), namely a conjugate image plane of the hologram, and is used for acquiring light field information.
5. The apparatus according to claim 1, wherein the phase-type spatial light modulator is used to implement complex amplitude modulation by simultaneously encoding amplitude and phase information into a phase function, and encoding a common complex amplitude function:
wherein the content of the first and second substances,
the complex amplitude function is expressed as a pure phase function:
（2）；
wherein the content of the first and second substances,is related to the desired amplitude distributionAn associated phase modulation function, and，is a linear phase grating;
and (3) expanding the phase function, and selecting a first-order diffraction component to obtain:
（3）；
neglecting the exponential terms, obtaining a phase modulation function through numerical inversion, wherein the finally loaded computed hologram expression is as follows:
（4）；
the light field quality evaluation selects peak signal-to-noise ratio (PSNR) as an objective standard for measuring image distortion or noise level, represents the ratio of the maximum possible power of a signal to destructive noise power influencing the representation precision of the signal, and for two monochromatic images I and K of m × n, if one is similar to the other in noise, two-dimensional matrix data of the image are collected and normalized and recorded as
PSNR is then defined as:
（6）；
whereinMaximum pixel value possible for the picture; and evaluating the intensity distribution of the generated light field by utilizing the peak signal-to-noise ratio (PSNR), and taking the intensity distribution of the target light field as a reference image, wherein the larger the PSNR value between the target light field and the reference image, the smaller the image distortion is represented, and the more similar the intensity distribution of the generated light field and the target light field is.
Technical Field
The invention relates to the field of light field regulation, in particular to a device for realizing complex amplitude light field regulation based on a spatial light modulator.
Background
The conventional Gaussian beam is integrated into a special light field with certain intensity and phase distribution, and due to the unique physical effect and phenomenon of the beam, the light field attracts wide attention in the optical field. The traditional refraction type device, namely the geometric optical lens is difficult to generate a space structure light field, if a light field meeting specific space distribution is required to be obtained, a diffraction type device is required to be used for carrying out space modulation on an incident beam, wherein the liquid crystal space light modulator has extremely strong flexibility due to programmable control, and can realize dynamic fine regulation and control of a laser mode field.
The liquid crystal spatial light modulator performs phase modulation on the determined linearly polarized light by controlling the electro-optic effect of liquid crystal molecules in the liquid crystal spatial light modulator, and the deflection of the liquid crystal molecules can be controlled by changing the voltage of a pixel unit so as to change the birefringence of the liquid crystal molecules, so that controllable phase delay is introduced. The commercial liquid crystal spatial light modulator is generally of a pure phase type, can only regulate and control the spatial phase of an input light field, and is suitable for the light field which can be obtained by an analytical method. Starting from a target light field, a transfer function is constructed through a correct and appropriate calculation mode, and a phase diagram needing to be loaded on the spatial light modulator can be obtained by solving phase distribution required by light field regulation. When the light beam is transmitted in a free space, the transmission characteristic is mainly characterized by amplitude, phase and polarization multi-parameters, and the light field generated by pure-phase single-parameter regulation has single spatial distribution, so that the generation of a complex light field is greatly limited.
The phase and amplitude of an incident light field can be independently controlled by combining two cascaded spatial light modulators with a polarization sensitive device, but the method has complex experimental device and relatively difficult experimental operation. In practical applications, it is therefore desirable to generate an arbitrary complex amplitude light field based on a single phase type spatial light modulator and evaluate the light field quality.
Disclosure of Invention
The invention aims to provide a device for realizing complex amplitude light field regulation and control based on a spatial light modulator, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention adopts the following technical scheme: a device for realizing complex amplitude light field regulation and control based on a spatial light modulator comprises a semiconductor laser, a single-mode optical fiber with a polarization controller, a collimating lens, a polarizer, a beam expanding lens, a spectroscope A, the spatial light modulator, a reflector A, a Fourier transform lens A, a small hole filtering device, a Fourier transform lens B, a spectroscope B, an image acquisition device and a reflector B; the Gaussian beam emitted by the semiconductor laser is transmitted through a section of single-mode optical fiber with a polarization controller, the collimation lens is used for collimating the emergent beam of the optical fiber, then the polarization adjustment is carried out, the polarization state of the input beam is jointly regulated and controlled by the optical fiber polarization controller and the polarizer, the polarization state of the transmitted light in the single-mode optical fiber is changed by regulating the optical fiber polarization controller, the polarizer controls the polarization state of the optical fiber output light field, and the light field incident to the liquid crystal spatial light modulator has a specific polarization direction and a higher power value;
the beam expander carries out beam expansion processing on a light beam to match a liquid crystal panel of the spatial light modulator, linearly polarized light after being expanded passes through the spectroscope A, one path of the light beam is obliquely incident on the liquid crystal spatial light modulator to be subjected to phase modulation, the inclination angle of the SLM is adjusted firstly, so that the incident light beam is obliquely incident on the central position of the SLM at a small angle, then the spatial position of an emergent light path is changed by the reflector A, and an output light beam with modulation information is reflected by the reflector A and then sequentially passes through the Fourier transform lens A, the small hole filtering device, the Fourier transform lens B, the spectroscope B and the image acquisition device;
loading a phase hologram on a liquid crystal spatial light modulator, then finely adjusting a reflector A to enable a first-order diffraction component to pass through an optical axis of a 4f system consisting of a Fourier transform lens A and a Fourier transform lens B, then adjusting the size of an aperture diaphragm to ensure that only a positive first-order diffraction component passes through, reflecting an unmodulated light beam reflected by a spectroscope A to the spectroscope B through the reflector B to interfere with a modulated light beam, recording intensity information of an interference light field through an image acquisition device, and recovering phase distribution information of a generated light field through an interference principle.
The polarization direction of the polarizer is consistent with the arrangement direction of liquid crystal molecules of the spatial light modulator 7.
The distance between the spatial light modulator and the Fourier transform lens A through the reflector A is the focal length of the lens.
The pinhole filter device is arranged at the focus position of the Fourier transform lens A and ensures that the positive first-order diffraction component passes through; the image acquisition device is arranged on a focal plane of the Fourier transform lens B, namely a conjugate image plane of the hologram, and is used for acquiring light field information.
The complex amplitude regulation and control realized by using the phase type spatial light modulator needs to simultaneously encode the amplitude and phase information into a phase function, and encode a common complex amplitude function:
（1）；
wherein the content of the first and second substances,representing the distribution of the amplitudes to be coded,represents a phase distribution;
the complex amplitude function is expressed as a pure phase function:
（2）；
wherein the content of the first and second substances,is related to the desired amplitude distribution
and (3) expanding the phase function, and selecting a first-order diffraction component to obtain:
neglecting the exponential terms, obtaining a phase modulation function through numerical inversion, wherein the finally loaded computed hologram expression is as follows:
light field quality assessmentSelecting peak signal-to-noise ratio (PSNR) as an objective standard for measuring image distortion or noise level, representing the ratio of the maximum possible power of a signal to destructive noise power influencing the representation accuracy of the signal, and if one of two monochromatic images I and K of m × n is similar to the other one in noise, acquiring two-dimensional matrix data of the image and carrying out normalization processing, and recording the two-dimensional matrix data as normalized dataThe normalized intensity distribution of the target light field is recorded as
PSNR is then defined as:
（6）；
whereinMaximum pixel value possible for the picture; and evaluating the intensity distribution of the generated light field by utilizing the peak signal-to-noise ratio (PSNR), and taking the intensity distribution of the target light field as a reference image, wherein the larger the PSNR value between the target light field and the reference image, the smaller the image distortion is represented, and the more similar the intensity distribution of the generated light field and the target light field is.
Compared with the prior art, the invention has the beneficial effects that: based on the spatial light modulator, the complex amplitude regulation and control technology is utilized, the regulation and control transformation of any complex amplitude light field is realized, and the application expansibility is realized; the intensity distribution of the space light field is evaluated based on the peak signal-to-noise ratio, and the method is simple and reliable; the modulated light beam generating the space light field interferes with the other path of unmodulated light beam, and the phase information of the light field can be recovered by utilizing the interference principle.
Drawings
FIG. 1 is a schematic diagram of the principle structure of the complex amplitude light field regulation and control and light field quality evaluation device of the present invention;
fig. 2 shows the optical field intensity distribution at different PSNR values for example of a high-order bessel beam.
In the figure: the device comprises a semiconductor laser 1, a single-mode optical fiber 2 with a polarization controller, a collimating lens 3, a polarizer 4, a beam expanding mirror 5, a spectroscope A6, a spatial light modulator 7, a reflector A8, a Fourier transform lens A9, a pinhole filtering device 10, a Fourier transform lens B11, a spectroscope B12, an image acquisition device 13 and a reflector B14.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely explained below with reference to the drawings in the embodiments of the present invention.
As shown in fig. 1, a device for realizing complex amplitude light field regulation based on a spatial light modulator includes a semiconductor laser 1, a single-mode optical fiber 2 with a polarization controller, a collimating lens 3, a polarizer 4, a beam expander 5, a spectroscope a6, a spatial light modulator 7, a reflector A8, a fourier transform lens a9, a pinhole filtering device 10, a fourier transform lens B11, a spectroscope B12, an image acquisition device 13, and a reflector B14;
the Gaussian beam emitted by the semiconductor laser 1 is transmitted through a section of single-mode optical fiber 2 with a polarization controller, the collimation lens 3 is used for collimating the light beam emitted by the optical fiber, then the polarization adjustment is carried out, the polarization state of the input light beam is jointly adjusted and controlled by the optical fiber polarization controller and the polarizer 4, the polarization state of the transmitted light in the single-mode optical fiber is changed by adjusting the optical fiber polarization controller, the polarizer 4 controls the polarization state of the optical fiber output light field, and the light field incident to the liquid crystal spatial light modulator 7 has a specific polarization direction and a higher power value;
the beam expander 5 expands the beam to match a liquid crystal panel of the spatial light modulator, the linearly polarized light after being expanded passes through the spectroscope A6, one path of light beam is obliquely incident on the liquid crystal spatial light modulator 7 to be subjected to phase modulation, the inclination angle of the SLM is adjusted firstly, the incident light beam is obliquely incident on the central position of the SLM at a small angle, then the reflector A8 is adjusted to change the spatial position of an emergent light path, and an output light beam with modulation information is reflected by the reflector A8 and then sequentially passes through the Fourier transform lens A9, the small hole filtering device 10, the Fourier transform lens B11, the spectroscope B12 and the image acquisition device 13;
loading a phase hologram on the liquid crystal spatial light modulator 7, then finely adjusting a reflector A8 to enable the first-order diffraction component to pass through an optical axis of a 4f system consisting of a Fourier transform lens A9 and a Fourier transform lens B11, then adjusting the size of a pinhole diaphragm to ensure that only the positive first-order diffraction component passes through, reflecting an unmodulated light beam reflected by a spectroscope A6 to a spectroscope B12 through a reflector B14 to interfere with a modulated light beam, recording intensity information of an interference light field through an image acquisition device 13, and recovering phase distribution information of the generated light field through an interference principle.
The polarization direction of the polarizer 4 is consistent with the arrangement direction of liquid crystal molecules of the spatial light modulator 7. The distance between the spatial light modulator 7 and the Fourier transform lens A9 through the reflector A8 is the focal length of the lens. The pinhole filter device 10 ensures that the positive first-order diffraction component passes through at the focus position of the Fourier transform lens A9; the image acquisition device 13 is located in the focal plane of the fourier transform lens B11, i.e. the conjugate image plane of the hologram, and is used for acquiring light field information.
The complex amplitude regulation and control realized by using the phase type spatial light modulator needs to simultaneously encode the amplitude and phase information into a phase function, and encode a common complex amplitude function:
（1）；
wherein the content of the first and second substances,
the complex amplitude function is expressed as a pure phase function:
（2）；
wherein the content of the first and second substances,
and (3) expanding the phase function, and selecting a first-order diffraction component to obtain:
neglecting the exponential terms, obtaining a phase modulation function through numerical inversion, wherein the finally loaded computed hologram expression is as follows:
the light field quality evaluation selects peak signal-to-noise ratio (PSNR) as an objective standard for measuring image distortion or noise level, represents the ratio of the maximum possible power of a signal to destructive noise power influencing the representation precision of the signal, and for two monochromatic images I and K of m × n, if one is similar to the other in noise, two-dimensional matrix data of the image are collected and normalized and recorded asThe normalized intensity distribution of the target light field is recorded as
PSNR is then defined as:
（6）；
wherein
The foregoing is a preferred embodiment of the present invention, and it will be apparent to those skilled in the art that variations, modifications, substitutions and alterations can be made in the embodiment without departing from the principles and spirit of the invention.
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