Diffractive optical element for generating linear light spots and manufacturing method thereof

Abstract

The invention provides a diffractive optical element for generating linear light spots and a manufacturing method of the diffractive optical element. The diffractive optical element for generating the linear light spots comprises a diffractive lens capable of shaping Gaussian light spots into the linear light spots, the diffractive lens comprises an incident surface and an emergent surface which are opposite to each other, a three-dimensional phase structure is arranged in the middle of the emergent surface, and the height distribution of the three-dimensional phase structure is h (x, y). The diffraction optical element can shape Gaussian light spots into high-quality linear light spots, and the linear light spots are high in flat top uniformity, high in diffraction efficiency and sharp in edge; the diffractive optical element is simple in structure, simple in manufacturing method, high in photoetching and etching process redundancy and suitable for mass production.

Description

Technical Field

[0001] The present invention relates to the technical field of diffraction optical elements, and in particular to a diffraction optical element for generating a linear light spot and a manufacturing method thereof. Background Art

[0002] With the vigorous development of the optoelectronics industry, laser technology has been widely used in the fields of industry, agriculture, medicine, health, national defense, etc. In the field of laser processing, it is often necessary to shape the shape and intensity distribution of the light spot to adapt to the needs of different scenarios. Linear light spot is one of the common needs. Traditional ways to produce linear light spots include Powell prisms, multi-piece aspheric mirror combinations and cylindrical mirror arrays, but they all have some shortcomings. The linear light spot produced by the Powell prism has uneven intensity distribution at both ends of the long axis; the combination of multiple aspheric mirrors requires a lot of space and is not applicable in the increasingly integrated modern optical system, and the introduction of multiple mirror groups will increase the difficulty of aberration correction; the effect of the conventional cylindrical mirror array to produce a linear light spot is similar to that of the Powell prism. It not only requires precise control of the array period, sag, aspheric coefficient, etc., but also requires the introduction of aspheric coefficients in the generatrix direction, which brings many challenges to actual processing. Summary of the Invention

[0003] In response to the above problems, the present invention proposes a diffractive optical element for generating a linear light spot and a manufacturing method thereof, which can shape a Gaussian light spot into a high-quality linear light spot, and has a simple structure and a simple manufacturing method.

[0004] The technical solution of the present invention is achieved as follows:

[0005] The present invention first proposes a diffractive optical element for generating a linear light spot, comprising a diffractive lens capable of shaping a Gaussian light spot into a linear light spot. The diffractive lens comprises an incident surface and an exit surface facing each other, and a three-dimensional phase structure is provided in the middle of the exit surface. The height distribution of the three-dimensional phase structure is h(x, y), and h(x, y) is obtained by the following method:

[0006]

[0007] Where U(x1,y1) represents the incident light field, (x1,y1) represents the coordinate system of the incident light field, U(x0,y0) represents the diffracted light field, (x0,y0) represents the coordinate system of the diffracted light field, z is the diffraction distance, k is the incident light wave vector, λ is the incident light wavelength, and F represents Fourier transform;

[0008]

[0009] Where I0 is the incident light intensity, (x,y) is the coordinate system of the Gaussian spot location, and w is the beam waist radius;

[0010] According to the phase difference and the optical path difference Δh, namely:

[0011]

[0012] Set a random phase distribution As the initial phase of the diffractive optical element, multiply the formula (2) by the random phase Then substitute U(x1, y1) into formula (1), that is, replace U(x1, y1) with I(x, y), calculate the diffracted light field U(x0, y0), keep the phase distribution of U(x0, y0) unchanged, replace the amplitude of U(x0, y0) with the target light field amplitude, and perform inverse Fourier transform to obtain the input light field U(x1, y1) again. Replace the amplitude of the input light field U(x1, y1) with the amplitude (I0) of the Gaussian spot in formula (3) 0.5 , and then continue to calculate according to formula (1), repeat this process iteratively, and finally the phase distribution of the required diffractive optical element can be extracted from U(x1,y1)

[0013] According to the material refractive index n of the diffractive optical element, it can be calculated:

[0014]

[0015] According to formula (4), we can get the phase distribution The corresponding height distribution h(x,y) is:

[0016]

[0017] Furthermore, the diffraction lens is a single-piece integrated lens.

[0018] Furthermore, the diffraction lens is a plane lens.

[0019] Furthermore, the diffraction lens is a fused quartz lens.

[0020] Furthermore, the three-dimensional phase structure is formed on the emission surface by etching.

[0021] Furthermore, the height of the three-dimensional phase structure varies in a range of 0 μm to 1.162 μm.

[0022] Furthermore, the pixel size of the three-dimensional phase structure is 1 μm×10 μm, and the distribution range is 10 mm×10 mm.

[0023] The present invention also proposes a method for manufacturing a diffractive optical element for generating a linear light spot, comprising the following steps:

[0024] A. Clean the surface of the diffraction lens and then apply a layer of photoresist on the output surface;

[0025] B. Import the calculated height distribution data into the laser direct writing device to form a height distribution grayscale map;

[0026] C. Adjust the laser spot size, laser head scanning direction speed, step direction, resolution, exposure upper and lower limits of the height distribution grayscale map, and exposure dose parameters to perform 3D grayscale exposure. After development, a three-dimensional structure mask is produced on the photoresist layer.

[0027] D. Dry-etch the plastic mask from top to bottom through ion beam etching, and transfer the mask pattern to the output surface of the diffraction lens to form the final three-dimensional phase structure.

[0028] Beneficial effects of the present invention:

[0029] 1. The diffraction optical element of the present invention can shape a Gaussian light spot into a high-quality linear light spot with high flat top uniformity, high diffraction efficiency and sharp edges.

[0030] 2. The diffractive optical element of the present invention has a simple structure and a simple manufacturing method. The photolithography and etching processes have high redundancy and are suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 is a three-dimensional schematic diagram of Example 1;

[0033] Figure 2 This is a schematic front view of Example 1;

[0034] Figure 3 It is a right side schematic diagram of Example 1;

[0035] Figure 4 is the input Gaussian spot intensity distribution diagram in Example 1;

[0036] Figure 5 is the phase distribution diagram in Example 1;

[0037] Figure 6 is a height distribution diagram of the three-dimensional phase structure in Example 1;

[0038] Figure 7 Schematic diagram of the manufacturing process of the diffractive optical element in Example 1;

[0039] Figure 8 Schematic diagram of the optical path in Example 1;

[0040] Figure 9 This is the intensity distribution diagram of the output linear light spot in Example 1;

[0041] Figure 10 This is a cross-sectional diagram of the middle part of the x-dimension of the linear spot intensity distribution in Example 1;

[0042] Figure 11 This is a cross-sectional diagram of the middle of the y-dimension of the linear spot intensity distribution in Example 1.

[0043] The reference numbers in the figure are: 1-diffraction lens, 2-exit surface, 3-incident surface, 5-three-dimensional phase structure. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0045] A diffractive optical element for generating a linear light spot includes a diffractive lens capable of shaping a Gaussian light spot into a linear light spot. The diffractive lens includes an incident surface and an exit surface relative to each other. A three-dimensional phase structure is provided in the middle of the exit surface. The height distribution of the three-dimensional phase structure is h(x, y). h(x, y) is obtained by the following method:

[0046]

[0047] Where U(x1,y1) represents the incident light field, (x1,y1) represents the coordinate system of the incident light field, U(x0,y0) represents the diffracted light field, (x0,y0) represents the coordinate system of the diffracted light field, z is the diffraction distance, k is the incident light wave vector, λ is the incident light wavelength, and F represents Fourier transform;

[0048]

[0049] Where I0 is the incident light intensity, (x,y) is the coordinate system of the Gaussian spot location, and w is the beam waist radius;

[0050] According to the phase difference and the optical path difference Δh, namely:

[0051]

[0052] Set a random phase distribution As the initial phase of the diffractive optical element, multiply the formula (2) by the random phase Then substitute U(x1, y1) into formula (1), that is, replace U(x1, y1) with I(x, y), calculate the diffracted light field U(x0, y0), keep the phase distribution of U(x0, y0) unchanged, replace the amplitude of U(x0, y0) with the target light field amplitude, and perform inverse Fourier transform to obtain the input light field U(x1, y1) again. Replace the amplitude of the input light field U(x1, y1) with the amplitude (I0) of the Gaussian spot in formula (3) 0.5 , and then continue to calculate according to formula (1), repeat this process iteratively, and finally the phase distribution of the required diffractive optical element can be extracted from U(x1,y1)

[0053] According to the material refractive index n of the diffractive optical element, it can be calculated:

[0054]

[0055] According to formula (4), we can get the phase distribution The corresponding height distribution h(x,y) is:

[0056]

[0057] Furthermore, the diffraction lens is a plane lens.

[0058] Furthermore, the diffraction lens is a fused quartz lens.

[0059] Furthermore, the three-dimensional phase structure is formed on the emission surface by etching.

[0060] Furthermore, the height of the three-dimensional phase structure varies in a range of 0 μm to 1.162 μm.

[0061] Furthermore, the pixel size of the three-dimensional phase structure is 1 μm×10 μm, and the distribution range is 10 mm×10 mm.

[0062] A method for manufacturing a diffractive optical element for generating a linear light spot comprises the following steps:

[0063] A. Clean the surface of the diffraction lens and then apply a layer of photoresist on the incident surface;

[0064] B. Import the calculated height distribution data into the laser direct writing device to form a height distribution grayscale map;

[0065] C. Adjust the laser spot size, laser head scanning direction speed, step direction, resolution, exposure upper and lower limits of the height distribution grayscale map, and exposure dose parameters to perform 3D grayscale exposure. After development, a three-dimensional structure mask is produced on the photoresist layer.

[0066] D. Dry-etch the plastic mask from top to bottom through ion beam etching, and transfer the mask pattern to the output surface of the diffraction lens to form the final three-dimensional phase structure.

[0067] Example 1

[0068] A diffraction optical element for generating a linear light spot includes a diffraction lens 1 capable of shaping a Gaussian light spot into a linear light spot. The diffraction lens 1 includes an incident surface 3 and an exit surface 2 relative to each other. A three-dimensional phase structure 5 is provided in the middle of the exit surface 2. The diffraction lens 1 is a single-piece integrated lens, specifically a plane lens, made of fused quartz, such as Figure 1 、 Figure 2 and Figure 3 shown.

[0069] The three-dimensional phase structure 5 controls the incident light wavefront by transmitting the phase. The corresponding phase distribution is obtained by calculating the Fresnel diffraction process of the light wave in free space based on the iterative Fourier transform algorithm. The Fresnel diffraction formula in Fourier form is:

[0070]

[0071] Among them, U(x1,y1) represents the incident light field, (x1,y1) represents the coordinate system of the incident light field, U(x0,y0) represents the diffracted light field, (x0,y0) represents the coordinate system of the diffracted light field, z is the diffraction distance, k is the incident light wave vector, λ is the incident light wavelength, and F represents Fourier transform.

[0072] The input light spot is a Gaussian light spot with a wavelength of 532 nm and a beam waist diameter of 6 mm. Figure 4 As shown, its intensity distribution satisfies the following formula:

[0073]

[0074] Where I0 is the incident light intensity, (x, y) is the coordinate system of the Gaussian spot location, and w is the beam waist radius. The phase image pixel size is set to 1 μm × 10 μm and the distribution range is set to 10 mm × 10 mm. The pixel size and distribution range can be changed according to specific needs.

[0075] At the beginning of the calculation, a random phase distribution needs to be constructed As the initial phase of the diffraction element, the phase distribution is continuously optimized through the iterative algorithm. is composed of values ​​randomly distributed between 0 and 2π, so Not unique.

[0076] Multiply formula (2) by the random phase Substitute U(x1,y1) into formula (1), replacing I(x,y) with U(x1,y1), and calculate the diffracted light field U(x0,y0). Keeping the phase distribution of U(x0,y0) unchanged, replace the amplitude of U(x0,y0) with the target light field amplitude and perform an inverse Fourier transform to obtain the input light field U(x1,y1).

[0077] Replace the amplitude of the input light field U(x1,y1) with the amplitude of the Gaussian spot (I0) in formula (3) 0.5 , and then continue to calculate according to formula (1).

[0078] Repeat the above process iteratively, and finally the phase distribution of the required diffraction element can be extracted from U(x1,y1) Should Essentially, it is optimized

[0079] According to the phase difference and the optical path difference Δh, namely:

[0080]

[0081] According to the material refractive index n, it can be calculated:

[0082]

[0083] According to formula (4), we can get the phase distribution The corresponding height distribution h(x,y) is:

[0084]

[0085] The range of the value of is from -Π to Π, such as Figure 5 As shown, according to λ = 532nm and n = 1.458, the corresponding height h(x,y) is calculated to range from 0μm to 1.162μm, and the height distribution corresponding to each point position is as follows Figure 6 shown.

[0086] like Figure 7 As shown, a method for manufacturing a diffractive optical element for generating a high-quality linear light spot comprises the following steps:

[0087] A. Clean the surface of the diffraction lens and then evenly coat the incident surface with 1.8 μm thick photoresist.

[0088] B. Import the calculated height distribution data into the laser direct writing device to form a height distribution grayscale map; Figure 4 As shown, the grayscale image is identified as 4096 levels, which is approximately a continuous distribution;

[0089] C. Adjust the laser spot size, laser head scanning direction speed, step direction, resolution, upper and lower exposure limits of the height distribution grayscale map, and exposure dose parameters to perform 3D grayscale exposure. After development, a three-dimensional structure mask is produced on the photoresist layer. After development, a scaled height distribution h(x,y) is obtained on the photoresist layer. The scale is determined by the etching selectivity ratio of the photoresist and fused silica.

[0090] D. Dry-etch the plastic mask from top to bottom through ion beam etching, and transfer the mask pattern to the output surface of the diffraction lens to form the final three-dimensional phase structure.

[0091] The preparation time of the entire process is less than 5h / tablet.

[0092] Adjust the direction of the incident laser to be perpendicular to the surface of the component, from the non-structured surface of the component to the structured surface of the component, and the incident spot position hits the center of the three-dimensional phase structure. The overall optical path diagram is as follows Figure 8 shown.

[0093] The output linear spot is as follows Figure 9 As shown, it is a linear light spot of 300mm×3mm.

[0094] The area with light intensity above 50% is defined as the effective area of ​​the light spot. The data of the area with intensity above 50% of the output linear light spot are extracted, and the diffraction efficiency is calculated to be 91.8%.

[0095] The area with light intensity above 90% is defined as the top area of ​​the spot. The data of the area with intensity above 90% of the output linear spot is extracted. The RMS value of the intensity distribution in this area is calculated to be 96.2%, which meets the flat-top spot characteristics. The uniformity calculation formula is:

[0096]

[0097] The unilateral gradual change area is used to characterize the sharpness of the edge of the output light spot, which is defined as the length from the edge light intensity rising from 13.5% to 90%. The middle section of the output linear light spot is extracted from the x-dimension and y-dimension respectively, as shown in Figure 10 and Figure 11 As shown, the calculated unilateral gradual change areas of the major axis and minor axis are 500 μm and 400 μm respectively.

[0098] In summary, the present invention has a simple structure, occupies a small space, has high processing redundancy, and realizes a linear light spot with high flat top uniformity, high diffraction efficiency, and sharp edges, and is a high-quality linear light spot.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A diffractive optical element for generating a linear light spot, characterized in that: The invention comprises a diffraction lens capable of shaping a Gaussian spot into a linear spot. The diffraction lens comprises an incident surface and an exit surface relative to each other. A three-dimensional phase structure is provided in the middle of the exit surface. The height distribution of the three-dimensional phase structure is h(x, y). h(x, y) is obtained by the following method: Where U(x1,y1) represents the incident light field, (x1,y1) represents the coordinate system of the incident light field, U(x0,y0) represents the diffracted light field, (x0,y0) represents the coordinate system of the diffracted light field, z is the diffraction distance, k is the incident light wave vector, λ is the incident light wavelength, and F represents Fourier transform; Where I0 is the incident light intensity, (x,y) is the coordinate system of the Gaussian spot location, and w is the beam waist radius; According to the phase difference and the optical path difference Δh, namely: Set a random phase distribution As the initial phase of the diffractive optical element, multiply the formula (2) by the random phase Then substitute U(x1, y1) into formula (1), that is, replace U(x1, y1) with I(x, y), calculate the diffracted light field U(x0, y0), keep the phase distribution of U(x0, y0) unchanged, replace the amplitude of U(x0, y0) with the target light field amplitude, and perform inverse Fourier transform to obtain the input light field U(x1, y1) again. Replace the amplitude of the input light field U(x1, y1) with the amplitude (I0) of the Gaussian spot in formula (3) 0.5 , and then continue to calculate according to formula (1), repeat this process iteratively, and finally the phase distribution of the required diffractive optical element can be extracted from U(x1,y1) According to the material refractive index n of the diffractive optical element, it can be calculated: According to formula (4), we can get the phase distribution The corresponding height distribution h(x,y) is:

2. The diffractive optical element for generating a linear light spot according to claim 1, wherein: The diffraction lens is a single-piece integrated lens.

3. The diffractive optical element for generating a linear light spot according to claim 2, wherein: The diffraction lens is a plane lens.

4. The diffractive optical element for generating a linear light spot according to claim 3, wherein: The diffraction lens is a fused quartz lens.

5. The diffractive optical element for generating a linear light spot according to claim 1, wherein: The three-dimensional phase structure is formed on the emission surface by etching.

6. The diffractive optical element for generating a linear light spot according to claim 1, wherein: The height of the three-dimensional phase structure varies in a range from 0 μm to 1.162 μm.

7. The diffractive optical element for generating a linear light spot according to claim 1, wherein: The pixel size of the three-dimensional phase structure is 1 μm×10 μm, and the distribution range is 10 mm×10 mm.

8. A method for manufacturing a diffractive optical element for generating a linear light spot, characterized in that: The following steps are involved: A. Clean the surface of the diffraction lens and then apply a layer of photoresist on the output surface; B. Import the calculated height distribution data into the laser direct writing device to form a height distribution grayscale map; C. Adjust the laser spot size, laser head scanning direction speed, step direction, resolution, exposure upper and lower limits of the height distribution grayscale map, and exposure dose parameters to perform 3D grayscale exposure. After development, a three-dimensional structure mask is produced on the photoresist layer. D. Dry-etch the plastic mask from top to bottom through ion beam etching, and transfer the mask pattern to the output surface of the diffraction lens to form the final three-dimensional phase structure.

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