Micro-lens array device for homogenizing array light beams and design method of micro-lens array device

Abstract

The invention relates to a microlens array device for array light beam homogenization and a design method thereof, and belongs to the field of light field regulation and control. On the basis of the idea that light intensity homogenization can be achieved through the soft-edge diaphragm, the micro-lens array with sawtooth-shaped sub-apertures is designed. According to the optical convolution principle, the microlens array can serve as a two-dimensional phase grating, the far field of the microlens array can obtain array distribution, and the light intensity distribution of the far field is modulated by Fourier transform of the small lens, so that the array light beam intensity distribution obtained by using the microlens array with the square sub-aperture is not uniform. According to the micro-lens array with the zigzag sub-apertures, array light beams with uniform light intensity distribution can be obtained. The device does not need complex phase regulation and control, is simple in structure and obvious in advantages, can obtain corresponding array light beams with uniform light intensity distribution by replacing different incident light beams, and is high in operability.

Description

Technical Field

[0001] The invention belongs to the field of light field regulation, and in particular relates to a microlens array device for array light beam homogenization and a design method thereof. Background Art

[0002] A vortex beam is a dark empty light field with a spiral phase structure and a phase singularity at the center of the beam. In 1992, Allen et al. proved that each photon of this beam has The orbital angular momentum (OAM) of a vortex beam is 1, where l is called the topological charge or mode number. Since the modes of the vortex beam are mutually orthogonal, they can form a complete orthogonal basis, which has great potential in breaking through communication capacity. In addition, it also has good application prospects in optical tweezers and optical processing. Compared with a single vortex, vortex arrays show more attractive performance and are expected to have better applications in these fields. For example, in the field of optical communications, multi-channel coded communications can be performed, which can greatly improve the communication rate; in optical tweezers, multiple particles can be captured at one time, and in optical processing, multiple units can be processed simultaneously, greatly improving work efficiency.

[0003] In the above-mentioned application scenarios, the generation of vortex beam arrays is also very important. The common generation methods currently used are mainly spatial light modulators, metasurfaces, and multi-spiral phase plates. Using a spatial light modulator, a vortex beam array is generated by beam shaping, but the spatial light modulator cannot withstand high power and has extremely low diffraction efficiency. Although the use of metasurfaces and multi-spiral phase plates improves the diffraction efficiency, it is expensive, and as the dimension of the vortex array increases, the difficulty of manufacturing the device will also increase. In the Chinese invention application CN202211270724.9 (a method and device for generating a vortex beam array), a microlens array with a square sub-aperture is used to generate a vortex beam. Since the array light field distribution in the far field is modulated by the Fourier transform of the small lens, and the field distribution of the Fourier transform of the small lens with a square sub-aperture is uneven, the generated vortex beam array is not uniformly distributed, which will affect the application of the vortex array. Summary of the invention

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A microlens array device for array light beam homogenization comprises: a microlens array composed of a plurality of sub-lenses; the edge of the sub-aperture of the microlens array is a sawtooth structure, the lengths of the two sides of the sawtooth are equal, and the parameters of the tooth height and tooth width of the sawtooth sub-aperture are modulated to achieve the optimal light homogenization effect of the array light beam.

[0006] A design method of a microlens array device for array light beam homogenization comprises the following steps:

[0007] Step 1: Calculate the period of the microlens array according to the array period of the target array beam;

[0008] Step 2: setting the edge of each sub-aperture of the microlens array to a sawtooth shape, and modulating the tooth height and tooth width of the sawtooth sub-aperture through an optimization algorithm to achieve the best homogenization effect;

[0009] Step 3: Step 1 obtains the period of the lens array, and Step 2 obtains the tooth height and tooth width of the sawtooth sub-aperture. Combining the results of Step 1 and Step 2, the sawtooth edge structures of adjacent sub-apertures are spliced ​​to obtain a microlens array of sawtooth sub-apertures;

[0010] Step 4: After the incident light beam irradiates the sawtooth sub-aperture microlens array, according to the optical convolution principle, an array beam distribution with uniform light intensity distribution is obtained in the far field, and the light beam of each unit in the array is the same as the incident light beam.

[0011] The present invention has the following beneficial effects:

[0012] The present invention changes the sub-aperture edge of the microlens array into a sawtooth shape, and the sub-aperture of the sawtooth edge is a soft-edge aperture, which can achieve a light intensity homogenization effect. Therefore, the sawtooth microlens array can generate an array beam with uniform light intensity distribution.

[0013] (1) The present invention combines a soft-edge aperture with a microlens array to achieve an array beam with uniform light intensity distribution.

[0014] (2) The present invention utilizes the principle of optical convolution to realize array control of any light beam by simply replacing the corresponding incident light beam.

[0015] (3) The present invention can generate array beams without complex phase control, and the device structure is simple and the system is highly efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a single sawtooth subaperture;

[0017] Figure 2 Schematic diagram of a microlens array with sawtooth sub-apertures;

[0018] Figure 3 Schematic diagram of the spiral phase with topological charge number l=1;

[0019] Figure 4Comparison diagram of the vortex beam array generated by the square sub-aperture microlens array and the vortex beam array generated by the sawtooth sub-aperture microlens array; among them, (a) is the vortex beam array generated by the square sub-aperture microlens array, and (b) is the vortex beam array generated by the sawtooth sub-aperture microlens array. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] The following is a brief introduction of a microlens array device for array light beam homogenization of the present invention in conjunction with the accompanying drawings. The microlens array can be regarded as a two-dimensional periodic phase grating, and its transmittance function can be expressed by a comb function, as follows:

[0022] (1)

[0023] In the above formula, is the rectangular coordinate system of the incident plane, is the comb function, is the window function of the lenslet, is an exponential function, is the wave number, , is the laser wavelength, is the side length of each sub-lens, is the focal length of the microlens array, Represents an imaginary number.

[0024] According to the Fourier transform principle, the Fourier transform of the comb function is still a comb function, but the periods are inversely proportional to each other. According to the convolution principle, the product of the incident beam and the comb function is converted into the convolution of the Fourier transform of the incident beam and the comb function after Fourier transform to obtain the array beam. The expression is as follows:

[0025] (2)

[0026] in, is the rectangular coordinate system of the far field plane, is the far-field light field, represents the Fourier transform, represents the incident light field; is the comb function, is the window function of the lenslet, is an exponential function, is the wave number, , is the laser wavelength, is the side length of each sub-lens, is the focal length of the microlens array, Represents an imaginary number.

[0027] From the above formula, it can be seen that the far-field light field is the convolution of the Fourier transform of the incident light field and the comb function, which is an array beam. The relationship between the obtained array beam period τ and the microlens array period d is as follows:

[0028] (3)

[0029] It can also be seen from the above formula that the intensity distribution of the array beam is related to the Fourier transform of the small lens. When the beam passes through a general hard-edge aperture, the straight-edge diffraction effect will affect the uniformity of the light field distribution. Therefore, the microlens array with a square sub-aperture obtains an uneven light field distribution of the array beam. Here, a soft-edge aperture is introduced to obtain a microlens array with a sawtooth sub-aperture to adjust the light intensity distribution. The microlens array with a sawtooth sub-aperture is shown in Figure 2 As shown. Due to the existence of two oblique edges of each sawtooth, the sawtooth soft-edge aperture can convert the straight-edge diffraction distributed along the radial direction into the straight-edge diffraction along the two vertical oblique edges, and further decompose the straight-edge diffraction distributed along the angular direction. Due to the conservation of energy, the straight-edge diffraction distributed along the radial direction will eventually be reduced, thereby reducing the diffraction effect and homogenizing the light field distribution on the diffraction surface.

[0030] The schematic diagram of a single sawtooth sub-aperture in a sawtooth sub-aperture microlens array is shown in Figure 1 As shown, the expression of one side is as follows:

[0031] (4)

[0032] In the above formula, is the inner half length of the sawtooth aperture, is the gear height ratio, is the serial number of each tooth, It refers to the number of teeth on a single side of the sawtooth subaperture. is the tooth height of the sawtooth subaperture, is an intermediate amount.

[0033] The present invention also provides a design method of a microlens array device for homogenizing the array light beam, comprising the following steps:

[0034] Step 1: Calculate the period of the microlens array according to the array period of the target array beam;

[0035] Step 2: setting the edge of each sub-aperture of the microlens array to a sawtooth shape, and modulating the tooth height and tooth width of the sawtooth sub-aperture through an optimization algorithm such as a genetic algorithm, a gradient descent algorithm or a machine learning algorithm to achieve the best homogenization effect;

[0036] Step 3: Step 1 obtains the period of the lens array, and Step 2 obtains the tooth height and tooth width of the sawtooth sub-aperture. Combining the results of Step 1 and Step 2, the sawtooth edge structures of adjacent sub-apertures are spliced ​​to obtain a microlens array of sawtooth sub-apertures;

[0037] Step 4: After the incident light beam irradiates the sawtooth sub-aperture microlens array, according to the optical convolution principle, an array beam distribution with uniform light intensity distribution is obtained in the far field, and the light beam of each unit in the array is the same as the incident light beam.

[0038] The following uses a vortex beam array with a sawtooth sub-aperture microlens array to control uniform light intensity distribution as an example to introduce the implementation of the present invention. The tooth height h of the sawtooth sub-aperture and the number of sawtooth teeth M on a single side will affect the homogenization effect. The present invention uses a genetic algorithm (or a gradient descent algorithm or machine learning or other prior art optimization algorithms) for optimization to obtain the sawtooth sub-aperture tooth height h and the number of sawtooth teeth M on a single side with the best homogenization effect. Then a 3×3 sawtooth sub-aperture microlens array is obtained, such as Figure 2 As shown. Figure 3 As shown, a spiral phase plate is used to generate a vortex beam. The incident Gaussian beam passes through the spiral phase plate and then carries the spiral phase, and a vortex beam can be obtained in the far field. The phase distribution of the microlens array with a sawtooth sub-aperture is loaded by a spatial light modulator. Figure 4 Comparison diagram of the vortex beam array generated by the square sub-aperture microlens array and the vortex beam array generated by the sawtooth sub-aperture microlens array; after the incident beam carrying the spiral phase irradiates the spatial light modulator, the vortex beam array can be observed in the far field, such as Figure 4 Then, the square sub-aperture microlens array is loaded with phase distribution in the same way, and the vortex beam array is observed in the far field, as shown in (b). Figure 4 By comparison, it can be seen that compared with the result of modulating the vortex beam array by the square sub-aperture microlens array, the microlens array after the sawtooth sub-aperture modulation can obtain a vortex beam array with uniform light intensity distribution, and the effect is obvious.

[0039] The present invention combines a soft-edge aperture with a microlens array and utilizes the optical convolution principle. It does not require a complex structure and phase modulation to achieve a uniformly distributed vortex beam array. The device structure is simple and the system is highly efficient. In addition, this embodiment only demonstrates the regulation of the vortex beam array. In fact, arrays of other beams can also be regulated by simply replacing the corresponding incident beam.

[0040] The present invention is not limited to the above-mentioned specific implementation modes. Any modifications and changes to the present invention within the spirit and principle of the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A microlens array device for array beam homogenization, characterized in that: include: A microlens array is composed of a plurality of sub-lenses; the edge of the sub-aperture of the microlens array is a sawtooth structure, the lengths of the two sides of the sawtooth are equal, and the parameters of the tooth height and tooth width of the sawtooth sub-aperture are modulated to achieve the optimal light homogenization effect of the array light beam.

2. The microlens array device for array light beam homogenization according to claim 1, characterized in that: The microlens array is a two-dimensional periodic phase grating, and its transmittance function is expressed as a comb function as follows: （1） in, is the rectangular coordinate system of the incident plane, is the comb function, is the window function of the lenslet, is an exponential function, is the wave number, , is the laser wavelength, is the side length of each sub-lens, is the focal length of the microlens array, Represents an imaginary number.

3. The microlens array device for array light beam homogenization according to claim 1 or 2, characterized in that: The expression of one side of the sawtooth subaperture is as follows: （4） in, is the inner half length of the sawtooth aperture, is the gear height ratio, is the serial number of each tooth, It refers to the number of teeth on one side of the sawtooth subaperture. is the tooth height of the sawtooth subaperture, is an intermediate amount.

4. The microlens array device for array light beam homogenization according to claim 1, characterized in that: The parameters of the tooth height and tooth width of the sawtooth sub-aperture are modulated by an optimization algorithm, which is a genetic algorithm, a gradient descent algorithm or a machine learning algorithm.

5. The microlens array device for array light beam homogenization according to claim 1, characterized in that: The product of the incident light beam and the comb function is converted into the convolution of the Fourier transform of the incident light beam and the comb function after Fourier transformation, and the array light beam is obtained, which is expressed as follows: （2） in, is the rectangular coordinate system of the far field plane, is the far-field light field, represents the Fourier transform, represents the incident light field; is the comb function, is the window function of the lenslet, is an exponential function, is the wave number, , is the laser wavelength, is the side length of each sub-lens, is the focal length of the microlens array, Represents an imaginary number.

6. A design method for a microlens array device for array beam homogenization, characterized in that: The steps include: Step 1: Calculate the period of the microlens array according to the array period of the target array beam; Step 2: setting the edge of each sub-aperture of the microlens array to a sawtooth shape, and modulating the tooth height and tooth width of the sawtooth sub-aperture through an optimization algorithm to achieve the best homogenization effect; Step 3: Step 1 obtains the period of the lens array, and Step 2 obtains the tooth height and tooth width of the sawtooth sub-aperture. Combining the results of Step 1 and Step 2, the sawtooth edge structures of adjacent sub-apertures are spliced ​​to obtain a microlens array of sawtooth sub-apertures; Step 4: After the incident light beam irradiates the sawtooth sub-aperture microlens array, an array beam distribution with uniform light intensity distribution is obtained in the far field, and the light beam of each unit in the array is the same as the incident light beam.

7. The design method of a microlens array device for array light beam homogenization according to claim 6, characterized in that: The microlens array is a two-dimensional periodic phase grating, and its transmittance function is expressed as a comb function as follows: （1） in, is the rectangular coordinate system of the incident plane, is the comb function, is the window function of the lenslet, is an exponential function, is the wave number, , is the laser wavelength, is the side length of each sub-lens, is the focal length of the microlens array, Represents an imaginary number.

8. The design method of a microlens array device for array light beam homogenization according to claim 6, characterized in that: In step 2, the expression for one side of the sawtooth subaperture is as follows: （4） in, is the inner half length of the sawtooth aperture, is the gear height ratio, is the serial number of each tooth, It refers to the number of teeth on one side of the sawtooth subaperture. is the tooth height of the sawtooth subaperture, is an intermediate amount.

9. The design method of a microlens array device for array light beam homogenization according to claim 6, characterized in that: In step 2, the optimization algorithm is a genetic algorithm, a gradient descent algorithm or a machine learning algorithm.

10. The design method of a microlens array device for array light beam homogenization according to claim 8, characterized in that: In step 4, according to the convolution principle, the product of the incident beam and the comb function is converted into the convolution of the Fourier transform of the incident beam and the comb function after Fourier transformation, and the array beam is obtained, which is expressed as follows: （2） in, is the rectangular coordinate system of the far field plane, is the far-field light field, represents the Fourier transform, represents the incident light field; is the comb function, is the window function of the lenslet, is an exponential function, is the wave number, , is the laser wavelength, is the side length of each sub-lens, is the focal length of the microlens array, Represents an imaginary number.

11. The design method of a microlens array device for array light beam homogenization according to claim 6, characterized in that: In step 1, the required array beam period is With the microlens array period The relational expression is as follows: （3） In the above formula, is the period of the target array beam, is the microlens array period, is the laser wavelength, is the focal length of the Fourier transform lens.

12. The design method of a microlens array device for array light beam homogenization according to claim 6, characterized in that: In step 4, the incident light beam is a vortex light beam, and a vortex light beam array with uniform light intensity distribution is obtained in the far field; the incident light beam is changed to an incident light beam of other modes to obtain a corresponding light beam array.

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