A collimated flat-top Gaussian beam converter

Abstract

The present application belongs to the field of optical devices and proposes a collimated flat-top Gaussian beam converter, comprising: a beam expansion lens group, a polygonal gradient refractive index lens array, an aspheric focusing lens, a polygonal gradient refractive index fiber image transmission bundle, and a collimating element; the beam expansion lens group is used to expand and collimate the incident light, and the expanded and collimated light is incident on the polygonal gradient refractive index lens array. The light output from the polygonal gradient refractive index lens array is focused onto the image-side focal plane of the aspheric focusing lens after passing through the aspheric focusing lens; one end face of the polygonal gradient refractive index fiber image transmission bundle is placed at the image-side focal plane of the aspheric focusing lens, and the other end is placed at the object-side focal plane of the collimating lens. The collimated flat-top beam converter of the present application is capable of converting a non-uniform Gaussian beam emitted by a light source into a flat-top beam, thereby improving the uniformity of light energy distribution in the exposure area and overcoming the defect that the working spot of a traditional Gaussian beam is bright in the center and dark at the edges.

Description

Technical Field

[0001] The present application belongs to the field of optical devices, and in particular to a Gaussian beam converter. Background Art

[0002] With the increasing popularity of laser applications, beam shaping and homogenization are increasingly required in fields such as laser display and lighting, laser medical treatment, laser cleaning, laser cutting and welding, and scientific research. This involves converting a conventional laser Gaussian beam, which has high energy in the center and low energy around the edges, into a flat-top beam with uniform intensity distribution. Common methods for converting Gaussian beams to flat-top beams include beam expansion and apertures, aspheric lens arrays, fly-eye microlens arrays, liquid crystal spatial light modulators, diffractive optical elements, and polygonal homogenizers.

[0003] The first method is to use the beam expansion and aperture method to take a relatively uniform portion of the Gaussian beam in the center area. This method can obtain a relatively uniform flat-top beam, but the use of an aperture will result in high energy loss, which is not a good solution.

[0004] The second method is the aspheric lens group shaping method. Based on the principles of geometric optics, two aspheric lenses are used to form a Kepler telescope structure. Through phase control, it can be collimated into a flat-top beam. In theory, arbitrary wavefront transformation can be achieved. However, this system requires the use of a complex aspheric structure, which has high requirements for processing and detection equipment and is difficult to process. Moreover, this method is only effective for single-mode laser beams. However, in fact, the beams emitted by many laser systems are complex multi-mode laser beams, and the light field intensity distribution changes with time with uncertainty, which makes this method have great application limitations.

[0005] The third method is the compound eye microlens array shaping method. This method uses an aspheric collimating lens to collimate the light source, and then inputs it into the microlens array to split the input light spot wavefront. The split light spots are then gathered and superimposed through a subsequent focusing lens to obtain a uniform light field distribution. The shape of the light spot is related to the shape of the microlens. The more sub-mirrors in the compound eye microlens array, the better the beam homogenization effect. This method enables the multiple sub-beams after segmentation to converge on a specific plane, realizing the homogenization of the Gaussian beam into a flat top, but the flat top beam cannot maintain its original surface shape for long-distance propagation.

[0006] The fourth method is the liquid crystal spatial light modulator shaping method. This method uses computer programming to control the light intensity distribution of each pixel point on the output surface to achieve adjustable light beam spatial shaping. However, the limited pixel size of the liquid crystal and the gap between pixels will affect the shaping effect, which limits the application scenarios.

[0007] The current flat-top Gaussian beam converter is difficult to achieve good flat-top conversion effect and collimation characteristics for beams with complex light field distribution. Summary of the Invention

[0008] In order to solve the technical problems pointed out in the background technology, the following technical solutions are adopted:

[0009] A collimated flat-top Gaussian beam converter is sequentially arranged along the positive direction of the optical axis: a beam expanding lens group, a polygonal gradient refractive index lens array, an aspheric focusing lens, a polygonal gradient refractive index fiber image bundle, and a collimating element; the beam expanding lens group is used to expand and collimate the incident light, the expanded and collimated light is incident on the polygonal gradient refractive index lens array, and the light output from the polygonal gradient refractive index lens array is focused onto the image-side focal plane of the aspheric focusing lens after passing through the aspheric focusing lens; one end face of the polygonal gradient refractive index fiber image bundle is placed at the image-side focal plane of the aspheric focusing lens, and the other end is placed at the object-side focal plane of the collimating lens.

[0010] The working principle of the above device is as follows: the light beam is expanded and collimated through a beam expansion lens group; a closely arranged polygonal gradient refractive index lens array is used to split the wavefront of the light beam with complex light field distribution. The gradient refractive index lenses in the polygonal gradient refractive index lens array are closely arranged without gaps, and Fresnel diffraction will not cause energy loss. The split wavefronts are gathered through an aspheric focusing lens, and the output wavefronts of each gradient refractive index lens are input into a polygonal gradient refractive index fiber image transmission bundle through an aspheric focusing lens. The flat-top beam gathered by the aspheric focusing lens is evenly distributed into the sub-fiber for transmission. After being output from the sub-fiber, it is collimated and combined into a flat-top beam through a collimating lens to achieve long-distance collimated transmission.

[0011] Furthermore, the polygonal gradient refractive index lens array is an array structure in which a plurality of polygonal gradient refractive index lenses are arranged into a polygonal cross section.

[0012] Furthermore, the polygonal gradient-index fiber optic image bundle is composed of a number of polygonal gradient-index fibers with side lengths of 1-5 microns, tightly packed and arranged without gaps into a polygonal cross-section array. The polygonal gradient-index fibers serve as sub-fibers, and through the array arrangement, they form a polygonal gradient-index fiber optic image bundle with light transmission capabilities.

[0013] Preferably, the beam expansion lens assembly comprises a first converging lens and a second converging lens, wherein the image-side focal point of the first converging lens coincides with the object-side focal point of the second converging lens. The first converging lens focuses the incident laser beam into a spherical wave, and the confocal second converging lens adjusts the spherical wave into a plane wave, thereby achieving beam expansion and collimation of the incident laser beam.

[0014] Furthermore, a pinhole filter is provided at the image-side focus of the first converging lens, and the pinhole filter is used to filter out stray light.

[0015] Furthermore, the number of sides of the polygon is 2(n+1), where n is a natural number. For example, when the polygon is a tetrahedron, a hexagon, or an octagon, the refractive index of each polygonal gradient index lens in the polygonal gradient index lens array is symmetrically distributed about the center.

[0016] The collimated flat-top beam converter can convert the non-uniform complex light field beam emitted by the light source into a flat-top beam, thereby improving the uniformity of light energy distribution in the exposure area and overcoming the defect of the traditional Gaussian beam working spot with bright center and dark edges. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : Schematic diagram of collimated flat-top Gaussian beam converter;

[0018] Figure 2 :Schematic diagram of the axial light transmission trajectory and cross-sectional refractive index distribution of the polygonal gradient refractive index lens;

[0019] Figure 3 : Schematic diagram of the quadrilateral gradient refractive index fiber lens array structure and cross-sectional refractive index distribution;

[0020] Among them: 1. Beam expanding lens group; 2. Polygonal gradient refractive index lens array; 3. Aspheric focusing lens; 4. Polygonal gradient refractive index fiber image bundle; 5. Collimating lens. DETAILED DESCRIPTION

[0021] To further clarify the objectives, technical solutions, and advantages of this application, the present application will be further described below with reference to the accompanying drawings. The terms "first" and "second" in this application are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referred to. The term "several" in this application does not specifically limit a specific number, but should be understood as a preset number selected based on a set objective.

[0022] Example 1

[0023] like Figure 1 The collimated flat-top Gaussian beam converter shown is arranged in sequence along the positive direction of the optical axis: a beam expanding lens group 1, a polygonal gradient refractive index lens array 2, an aspheric focusing lens 3, a polygonal gradient refractive index fiber image bundle 4, and a collimating element 5; the beam expanding lens group is used to expand and collimate the incident light, and the expanded and collimated light is incident on the polygonal gradient refractive index lens array. The light output from the polygonal gradient refractive index lens array passes through the aspheric focusing lens and is focused onto the image-side focal plane of the aspheric focusing lens; the light input end face of the polygonal gradient refractive index fiber image bundle is placed at the image-side focal plane of the aspheric focusing lens, and the light output end face is placed at the object-side focal plane of the collimating lens.

[0024] When the expanded and collimated light is incident on the polygonal gradient refractive index lens array, each gradient refractive index lens in the polygonal gradient refractive index lens array divides the expanded and collimated light into sub-wavefronts corresponding to the gradient refractive index lens. Each sub-wavefront passes through the aspheric focusing lens and is focused onto the focal plane of the aspheric focusing lens.

[0025] After the expanded and collimated light passes through the polygonal gradient refractive index lens array, each sub-wavefront is focused on the image focal plane by the converging action of the aspheric focusing lens, and a homogenized light beam is obtained at the image focal plane; the homogenized light beam is evenly distributed and input into the polygonal gradient refractive index fiber image bundle. After the light beam is output from each sub-fiber in the polygonal gradient refractive index fiber image bundle, it passes through the collimating element and is collimated and combined into a flat-top beam.

[0026] The refractive index of each polygonal gradient refractive index lens in the polygonal gradient refractive index lens array is distributed in a gradient from the center to the edge, such as Figure 2 As shown, incident light at different angles propagates sinusoidally through the polygonal gradient index lens. This light propagation process repeats at a fixed periodic pattern. If the period is denoted by P, when the polygonal gradient index lens array length L is 0.25P, collimated light entering from one end automatically focuses on the other end. If the polygonal gradient index lens length is an integer multiple of half the period, such as 0.5P, 1P, 1.5P, or 2P, the light exits as parallel light. A polygonal gradient index lens array can be used to achieve functions such as light collimation or image transmission by setting its length to n*0.5P, where n is a natural number.

[0027] like Figure 3 The figure shows a schematic diagram of a quadrilateral gradient refractive index lens array and its cross-sectional refractive index distribution. The figure shows that the array is composed of 10×10 quadrilateral gradient refractive index lenses arranged in a quadrilateral cross-section. The refractive index of each quadrilateral gradient refractive index lens exhibits a gradient distribution that gradually decreases from the center to the edge.

[0028] Example 2

[0029] Based on Example 1, the polygonal gradient refractive index lens array is prepared by the following steps:

[0030] 1) Melt the cesium-containing glass in a platinum crucible at a temperature of 1380-1420 degrees and shape it into cylindrical glass;

[0031] 2) Processing cylindrical glass into a polygonal columnar glass cross section;

[0032] 3) Place the polygonal columnar glass on a drawing machine and draw it into continuous polygonal glass fiber;

[0033] 4) Place the polygonal glass fiber in 500~600°C potassium nitrate molten salt for Cs + -K + Ion exchange, thus forming a polygonal gradient refractive index fiber with a gradually decreasing refractive index from the center to the edge;

[0034] 5) The polygonal gradient refractive index fibers are densely arranged into an array rod with a polygonal cross-section. The array rod is placed in a melt-pressing furnace at 750-850°C for melt pressing to form a polygonal gradient refractive index fiber array mother rod. The polygonal gradient refractive index fiber array mother rod is cut into predetermined lengths and both end faces are polished to produce a polygonal gradient refractive index lens array.

[0035] The polygonal gradient refractive index lens array of this solution has a polygonal cross section, which can effectively reduce the gap between the side walls and improve the filling rate.

[0036] Preferably, the cesium-containing glass is made of the following compounds, with the weight percentage of ingredients being: 40%-60% Cs2O; 25%-40% SiO2; 5%-10% B2O3; 3%-8% Al2O3; 3%-9% ZnO; 5%-10% Na2O+K2O; 0.5%-2% ZrO2; and 3%-5% InF3.

[0037] Cs2O is the main component of glass, which is used to realize the reaction with K in high temperature molten salt. + Ions are replaced by ions to achieve Cs from the center to the edge of the glass fiber + The ion concentration gradually decreases and K + The ion concentration gradually increases. + The unit refractive index of ions in glass is 1.76, K + The unit refractive index of ions in glass is 1.57. + Ions and K in high temperature molten salts + The change in ion concentration gradient caused by ion replacement reduces the refractive index, which in turn causes the refractive index of the glass fiber to gradually decrease from the center to the edge.

[0038] SiO2 is a glass former and the main component of the glass. To ensure that the glass production temperature does not exceed 1450 degrees, the content of this component generally does not exceed 65%; choosing a weight composition of 25%-40% can ensure that the glass melting temperature is between 1380-1420 degrees;

[0039] B2O3 is a flux, ensuring that SiO2 and other glass components can be fully melted into glass;

[0040] Al2O3 and ZnO are glass intermediates, which are used as connecting materials of Si in structure. 4+ ions and Cs+ ions, Na + ions, K + Ions, In 3+ ions such as monovalent and trivalent ions, while ensuring that Cs + Ions and K in molten salts + The stability of the overall structure of the glass during the ion exchange process is improved, and the high temperature corrosion resistance of the glass is improved;

[0041] Na2O+K2O monovalent oxides are glass structure network modifiers used to reduce the glass forming temperature. The mixing ratio of these components can regulate the ion exchange temperature and speed of cesium glass;

[0042] ZrO2 is used to improve the anti-crystallization performance during glass drawing or multiple optical fiber drawing processes.

[0043] InF3 for Cs + ions, Na + ions, K + The bridging of monovalent network modifier ions such as ions ensures the stability of the glass network structure and improves the chemical stability of the glass during high-temperature ion exchange. At the same time, the mixing ratio with Cs2O is conducive to regulating the deviation between the refractive index distribution index produced by ion exchange and theoretical calculation.

[0044] As a preferred embodiment: the weight percentage of ingredients is: 42%-55% Cs2O; 25%-33% SiO2; 6%-8% B2O3; 3%-5% Al2O3; 4%-6% ZnO; 5%-8% Na2O+K2O; 1%-2% ZrO2; 3%-5% InF3.

[0045] The advantages of the cesium-containing glass are: high cesium content, through the Cs + Ions and K in high temperature molten salts + The difference in ion concentration gradient caused by ion replacement is large, which makes the refractive index of the glass fiber gradually decrease from the center to the edge, and the color difference is small.

Claims

1. A collimated flat-top Gaussian beam converter, characterized in that Arranged in sequence along the positive direction of the optical axis are: a beam expanding lens group, a polygonal gradient refractive index lens array, an aspheric focusing lens, a polygonal gradient refractive index fiber image transmission bundle, and a collimating element; the beam expanding lens group is used to expand and collimate the incident light, and the expanded and collimated light is incident on the polygonal gradient refractive index lens array. The light output from the polygonal gradient refractive index lens array passes through the aspheric focusing lens and is focused onto the image-side focal plane of the aspheric focusing lens; One end of the polygonal gradient refractive index optical fiber image bundle is placed at the image-side focal plane of the aspheric focusing lens, and the other end is placed at the object-side focal plane of the collimating lens; The polygonal gradient refractive index lens array is an array structure composed of a plurality of polygonal gradient refractive index lenses arranged into a polygonal cross-section; the length of the polygonal gradient refractive index lens array is n*0.5P, where n is a natural number and P is the transmission period of light in the polygonal gradient refractive index lens array; The polygonal gradient refractive index lens array is prepared by the following steps: 1) Melting the cesium-containing glass in a platinum crucible at a temperature of 1380-1420°C and forming it into cylindrical glass; 2) Processing the cylindrical glass into a polygonal columnar glass; 3) The polygonal columnar glass is placed on a drawing machine and drawn into continuous polygonal glass fibers; 4) Place the polygonal glass fiber in 500-600°C potassium nitrate molten salt for Cs + -K + Ion exchange, thus forming a polygonal gradient refractive index fiber with a gradually decreasing refractive index from the center to the edge; 5) Arranging polygonal gradient refractive index fibers tightly into an array rod with a polygonal cross-section, placing the array rod in a melt-pressing furnace at 750-850° C. for melt-pressing to form a polygonal gradient refractive index fiber array mother rod, cutting the polygonal gradient refractive index fiber array mother rod into predetermined lengths, and polishing both end faces of the cut pieces to produce a polygonal gradient refractive index lens array; The cesium-containing glass is made of the following compounds, with the weight percentage of ingredients being: 40%-60% Cs2O; 25%-40% SiO2; 5%-10% B2O3; 3%-8% Al2O3; 3%-9% ZnO; 5%-10% Na2O+K2O; 0.5%-2% ZrO2; and 3%-5% InF3.

2. The collimated flattened Gaussian beam transformer according to claim 1, wherein: The polygonal gradient refractive index optical fiber image transmission bundle is an array structure with a polygonal cross section, which is formed by stacking and arranging a number of polygonal gradient refractive index optical fibers with a cross-sectional side length of 1-5 microns without gaps.

3. The collimated flattened Gaussian beam transformer according to claim 1, wherein: The beam expanding lens group consists of a first converging lens and a second converging lens. The image focus of the first converging lens coincides with the object focus of the second converging lens. The first converging lens focuses the incident laser beam into a spherical wave, and the spherical wave is adjusted into a plane wave by the confocal second converging lens.

4. The collimated flattened Gaussian beam transformer according to claim 3, wherein: A pinhole filter is provided at the image-side focal point of the first converging lens.

5. The collimated flattened Gaussian beam transformer according to claim 1, wherein: The number of sides of the polygon is 2(n+1), where n is a natural number.

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