CN115268093A - Collimating flat-top Gaussian beam converter - Google Patents

Abstract

The application belongs to the optical device field, provides a collimation flat-top Gaussian beam converter, includes: the system comprises a beam expanding lens group, a polygonal gradient refractive index lens array, an aspheric focusing lens, a polygonal gradient refractive index optical fiber image transmission beam and a collimating element; the beam expanding lens group is used for expanding and collimating incident light, the expanded and collimated light is incident to the polygonal gradient index lens array, and the light output from the polygonal gradient index lens array is focused to an image focal plane of the aspheric focusing lens after passing through the aspheric focusing lens; one end face of the polygonal gradient refractive index optical fiber image transmission beam is placed at an image space focal plane of the aspheric focusing lens, and the other end face of the polygonal gradient refractive index optical fiber image transmission beam is placed at an object space focal plane of the collimating lens. The collimation flat-top beam converter can convert non-uniform Gaussian beams emitted by a light source into flat-top beams, improves the distribution uniformity of light energy in an exposure area, and overcomes the defect that the center bright edge of a working light spot of the traditional Gaussian beam is dark.

Description

Collimating flat-top Gaussian beam converter

Technical Field

The application belongs to the field of optical devices, and particularly relates to a Gaussian beam converter.

Background

With the popularization of laser application, shaping and homogenizing of light beams are required in the fields of laser display and illumination, laser medical treatment, laser cleaning, laser cutting, welding, scientific research and the like, namely, a conventional laser Gaussian beam with high middle energy and low surrounding energy is converted into a flat-top beam with uniformly distributed light intensity. The former common modes for converting Gaussian beams into flat-topped beams include beam expanding and diaphragm adding, aspheric lens group, fly-eye micro lens array, liquid crystal spatial light modulator, diffractive optical element, polygonal homogenizing rod and the like.

First, a relatively uniform flat-top beam can be obtained by using a beam expanding and diaphragm adding method to obtain a relatively uniform partial beam in the central region of a gaussian beam, but the use of a diaphragm causes high energy loss, and is not a good solution.

Secondly, an aspheric lens group shaping method is based on a geometrical optics principle, a Keplerian telescope structural form is formed by two aspheric lenses, and the Keplerian telescope structural form can be collimated into a flat-top beam through phase regulation and control, so that any wavefront transformation can be realized theoretically; the method only has good effect on single-mode laser beams, but actually, the beams emitted by many laser systems are complex multi-mode laser beams, and the variation of the light field intensity distribution along with time has uncertainty, so that the method has great application limitation.

And thirdly, a fly-eye micro-lens array shaping method, which is characterized in that a light source is collimated by using an aspheric collimating lens, then the light source is input into a micro-lens array to segment the wave surface of an input light spot, and the segmented light spots are gathered and superposed through a subsequent focusing lens, so that homogenized light field distribution is obtained, and the shape of the light spot is related to the shape of the micro-lens. The more the number of the sub-lenses of the fly-eye micro-lens array is, the better the light beam homogenization effect is. The method enables the plurality of divided sub-beams to be gathered on a specific plane, and the Gaussian beam is homogenized into a flat top, but the flat top beam cannot keep long-distance propagation of the original surface.

And fourthly, a liquid crystal spatial light modulator shaping method, which utilizes computer programming to control the light intensity distribution of each pixel point of the output surface to realize adjustable light beam spatial shaping, but the shaping effect is influenced by the limited pixel size of liquid crystal and the gaps among the pixels, so that the application scene is limited.

The existing flat-top Gaussian beam converter is difficult to realize better flat-top conversion effect and collimation characteristic for the beams with complex light field distribution.

Disclosure of Invention

In order to solve the technical problems pointed out in the background technology, the following technical scheme is adopted:

a collimation flat-top Gaussian beam converter is sequentially provided with the following components in the positive direction of an optical axis: the system comprises a beam expanding lens group, a polygonal gradient refractive index lens array, an aspheric focusing lens, a polygonal gradient refractive index optical fiber image transmission beam and a collimating element; the beam expanding lens group is used for expanding and collimating incident light, the expanded and collimated light is incident to the polygonal gradient index lens array, and the light output from the polygonal gradient index lens array is focused to an image focal plane of the aspheric focusing lens after passing through the aspheric focusing lens; one end face of the polygonal gradient refractive index optical fiber image transmission beam is placed at an image space focal plane of the aspheric focusing lens, and the other end face of the polygonal gradient refractive index optical fiber image transmission beam is placed at an object space focal plane of the collimating lens.

The working principle of the device is as follows: the light beam is expanded and collimated by a beam expanding lens group; the method comprises the steps of adopting a tightly arranged polygonal gradient refractive index lens array to segment wave surfaces of light beams with complex light field distribution, tightly arranging seamless gradient refractive index lenses in the polygonal gradient refractive index lens array, avoiding energy loss caused by Fresnel diffraction, collecting the segmented wave surfaces through an aspheric focusing lens, inputting the emergent wave surfaces of the gradient refractive index lenses into polygonal gradient refractive index optical fiber image transmission beams through the aspheric focusing lens, uniformly distributing flat-top light beams collected by the aspheric focusing lens into sub-optical fibers for transmission, and collimating and combining the flat-top light beams into the flat-top light beams through a collimating lens after being output from the sub-optical fibers, thereby realizing long-distance collimating transmission.

Furthermore, the polygonal gradient index lens array is an array structure with a polygonal cross section formed by arranging a plurality of polygonal gradient index lenses.

Furthermore, the polygonal gradient refractive index optical fiber image transmission beam is of an array structure with a polygonal cross section formed by arranging a plurality of polygonal gradient refractive index optical fibers with the side length of 1-5 microns in a gapless close packing manner. The polygonal gradient refractive index optical fiber is used as a sub-optical fiber and is arranged in an array to form the polygonal gradient refractive index optical fiber image transmission bundle with the light transmission function.

Preferably, the beam expanding lens group is composed of a first converging lens and a second converging lens, and an image space focal point of the first converging lens coincides with an object space focal point of the second converging lens. The first converging lens focuses the incident laser beam into spherical waves, and the spherical waves are adjusted into plane waves through the second converging lens arranged in a confocal mode, so that beam expansion and collimation of the incident laser beam are achieved.

Furthermore, an aperture filter is arranged at the image space focus of the first converging lens. The aperture filter is used for filtering stray light.

Further, the number of sides of the polygon is: 2 (n + 1) pieces, wherein n is a natural number. For example, when the refractive index of the polygonal gradient index lens array is four, six or octagonal, the refractive index of each polygonal gradient index lens in the polygonal gradient index lens array is distributed symmetrically with respect to the center.

The collimation flat-top light beam converter can convert the non-uniform complex light field light beam emitted by the light source into the flat-top light beam, so that the light energy distribution uniformity in the exposure area is improved, and the defect that the bright edge at the center of the working light spot of the traditional Gaussian beam is dark is overcome.

Drawings

FIG. 1: a principle diagram of a collimating flat-top Gaussian beam converter;

FIG. 2: the schematic diagram of the light ray transmission track and the cross-section refractive index distribution of the polygonal gradient refractive index lens axis;

FIG. 3: a schematic diagram of refractive index distribution of the quadrilateral gradient refractive index fiber lens array structure and the cross section;

wherein: 1. a beam expanding lens group; 2. a polygonal gradient index lens array; 3. an aspherical focusing lens; 4. polygonal gradient refractive index optical fiber image transmission bundle; 5. a collimating lens.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more clear, the present application will be further described in detail with reference to the accompanying drawings. Hereinafter, the terms "first" and "second" in the present application are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. The "plurality" described herein is not particularly limited to specific ones, but should be understood as a preset number selected according to a set target.

Example one

The collimated flat-top gaussian beam converter shown in fig. 1 is sequentially arranged along the positive direction of the optical axis as follows: the device comprises a beam expanding lens group 1, a polygonal gradient refractive index lens array 2, an aspheric focusing lens 3, a polygonal gradient refractive index optical fiber image transmission beam 4 and a collimating element 5; the beam expanding lens group is used for expanding and collimating incident light, the expanded and collimated light is incident to the polygonal gradient index lens array, and the light output from the polygonal gradient index lens array is focused to an image focal plane of the aspheric focusing lens after passing through the aspheric focusing lens; the light input end surface of the polygonal gradient refractive index optical fiber image transmission beam is arranged at the image space focal plane of the aspheric focusing lens, and the light output end surface is arranged at the object space focal plane of the collimating lens.

When the light which is subjected to beam expanding and collimating enters the polygonal gradient refractive index lens array, each gradient refractive index lens in the polygonal gradient refractive index lens array divides the light which is subjected to beam expanding and collimating into wavelet surfaces corresponding to the gradient refractive index lens, and each wavelet surface is focused to a focal plane of the aspheric surface focusing lens after passing through the aspheric surface focusing lens.

After the light which is expanded and collimated passes through the polygonal gradient refractive index lens array, each wavelet surface is focused on an image focal plane through the convergence action of an aspheric focusing lens, and homogenized light beams are obtained at the image focal plane; the homogenized light beams are uniformly distributed and input into the polygonal gradient refractive index optical fiber image transmission bundle, and the light beams are output from each sub-optical fiber in the polygonal gradient refractive index optical fiber image transmission bundle, then pass through the collimating element and are collimated and combined into flat-top light beams.

As shown in fig. 2, incident light rays with different incident angles are transmitted forwards in the polygonal gradient refractive index lens according to a sine rule, the light ray transmission process is repeated according to a fixed period rule, if the period is denoted as P, when the length L of the polygonal gradient refractive index lens array is 0.25P, collimated light is incident from one end, and the light rays are automatically focused on the other end face; if the length of the polygonal gradient index lens is selected to be integral multiples of a half period, such as 0.5P, 1P, 1.5P, 2P, the light rays exit as parallel light. The polygon gradient index lens array can be used, the length of the polygon gradient index lens array is set to be n x 0.5P, and functions of light collimation or image transmission and the like are achieved, wherein n is a natural number.

As shown in fig. 3, which is a schematic diagram of a refractive index distribution of a quadrilateral gradient index lens array and a cross section thereof, it can be seen that the array is formed by arranging 10 × 10 quadrilateral gradient index lenses in a quadrilateral way in which the cross section is a quadrilateral, wherein the refractive index of each quadrilateral gradient index lens shows a gradient distribution in which the refractive index gradually decreases from the center to the edge.

Example two

On the basis of the first embodiment, the polygonal gradient index lens array is prepared by the following steps,

1) Melting cesium-containing glass in a platinum crucible at a temperature of 1380-1420 ℃, discharging and forming into cylindrical glass;

2) Processing the cylindrical glass into cylindrical glass with a polygonal cross section;

3) Putting the polygonal columnar glass on a wire drawing machine for wire drawing to form continuous polygonal glass fibers;

4) Putting the polygonal glass fiber into potassium nitrate molten salt with the temperature of 500-600 ℃ for Cs ⁺ -K ⁺ Ion-exchanging to form a polygonal gradient index fiber with a gradually decreasing refractive index from the center to the edge;

5) The method comprises the steps of closely arranging polygonal gradient refractive index fibers into array rods according to the mode that the cross sections of the polygonal gradient refractive index fibers are polygonal, putting the array rods into a melting furnace with the temperature of 750-850 ℃ for melting to form a polygonal gradient refractive index fiber array female rod, cutting the polygonal gradient refractive index fiber array female rod according to a preset length, and polishing two cut end faces to obtain the polygonal gradient refractive index lens array.

The cross section of the polygonal gradient refractive index lens array is polygonal, so that gaps between the side walls can be effectively reduced, and the filling rate is improved.

The preferable cesium-containing glass is prepared from the following compounds in percentage by weight: 40% -60% of Cs ₂ O；25%-40%SiO ₂ ；5%-10%B ₂ O ₃ ；3%-8%Al ₂ O ₃ ；3%-9%ZnO；5%-10%Na ₂ O+K ₂ O；0.5%-2%ZrO ₂ ；3%-5%InF ₃ 。

Cs ₂ O is a main component of the glass and is used for realizing K in high-temperature molten salt ⁺ Ion replacement is carried out on ions to realize the Cs from the center to the edge of the glass fiber ⁺ Gradual decrease in ion concentration and K ⁺ The ion concentration gradually increases. Due to Cs ⁺ The unit refractive index of ions in the glass is 1.76, K ⁺ Ion has a unit refractive index of 1.57 in glass and passes Cs in glass ⁺ Ion and K in high temperature molten salt ⁺ The refractive index is reduced due to ion concentration gradient change caused by ion replacement, so that the refractive index is gradually reduced from the center to the edge of the glass fiber on the whole;

SiO ₂ is a glass forming body, is a main component of the glass, and generally has the content of 65 percent or less for ensuring that the glass production temperature does not exceed 1450 percent; 25 to 40 weight percent of the glass is selected to ensure that the glass melting temperature is 1380 to 1420 ℃;

B ₂ O ₃ as a flux, ensure SiO ₂ And other glass components can be sufficiently fused into a vitreous body;

Al ₂ O ₃ ZnO is a glass intermediate and structurally acts as a linking Si ⁴⁺ Ions and Cs ⁺ Ion, na ⁺ Ion, K ⁺ Ions, in ³⁺ Ion-like bridges of monovalent and trivalent ions while ensuring Cs ⁺ K in ions and molten salts ⁺ The stability of the whole structure of the glass in the ion exchange process of ions improves the high-temperature corrosion resistance of the glass;

Na ₂ O+K ₂ the O-univalent oxide is a glass structure network modifier and is used for reducing the glass forming temperature, and the mixing proportion of the components can regulate and control the ion exchange temperature and speed of the cesium glass;

ZrO ₂ the method is used for improving the devitrification resistance in the glass drawing or multiple optical fiber drawing processes.

InF ₃ For Cs ⁺ Ion, na ⁺ Ion, K ⁺ The bridging of ions of the univalent network modifier such as ions ensures the stable structure of the glass network, improves the chemical stability of the glass during high-temperature ion exchange, and simultaneously reacts with Cs ₂ The mixing proportion of O is beneficial to regulating and controlling the deviation between the refractive index distribution index generated by ion exchange and theoretical calculation.

Preferably, the method comprises the following steps: the weight percentage of the ingredients is as follows: 42% -55% of Cs ₂ O；25%-33%SiO ₂ ；6%-8%B ₂ O ₃ ；3%-5%Al ₂ O ₃ ；4%-6%ZnO；5%-8%Na ₂ O+K ₂ O；1%-2%ZrO ₂ ；3%-5%InF ₃ 。

The cesium-containing glass has the advantages that: high cesium content, passing Cs in the glass ⁺ Ion and K in high temperature molten salt ⁺ The ion concentration gradient change difference caused by ion replacement is large, so that the gradual reduction range of the refractive index from the center to the edge of the glass fiber is large as a whole, and the chromatic aberration is small.

Claims (8)

1. The utility model provides a collimation flat-top gaussian beam converter which characterized in that sets gradually along the positive direction of optical axis: the device comprises a beam expanding lens group, a polygonal gradient refractive index lens array, an aspheric focusing lens, a polygonal gradient refractive index optical fiber image transmission beam and a collimating element; the beam expanding lens group is used for expanding and collimating incident light, the expanded and collimated light is incident to the polygonal gradient index lens array, and the light output from the polygonal gradient index lens array is focused to an image focal plane of the aspheric focusing lens after passing through the aspheric focusing lens; one end face of the polygonal gradient refractive index optical fiber image transmission beam is placed at an image space focal plane of the aspheric focusing lens, and the other end face of the polygonal gradient refractive index optical fiber image transmission beam is placed at an object space focal plane of the collimating lens.

2. The collimated flattop gaussian beam transformer of claim 1, wherein: the polygonal gradient refractive index lens array is an array structure with a polygonal cross section formed by arranging a plurality of polygonal gradient refractive index lenses.

3. The collimated flat-topped gaussian beam transformer of claim 1, wherein: the polygonal gradient refractive index optical fiber image transmission beam is of an array structure with a polygonal cross section formed by tightly stacking and arranging a plurality of polygonal gradient refractive index optical fibers with the side length of the cross section of 1-5 micrometers in a gapless manner.

4. The collimated flat-topped gaussian beam transformer of claim 1, wherein: the beam expanding lens group consists of a first converging lens and a second converging lens, the image space focus of the first converging lens is superposed with the object space focus of the second converging lens, the first converging lens focuses the incident laser beam into spherical waves, and the spherical waves are adjusted into plane waves through the second converging lens which is arranged in a confocal mode.

5. The collimated flat-topped gaussian beam transformer of claim 4, wherein: an aperture filter is arranged at the image space focus of the first convergent lens.

6. The collimated flat-topped gaussian beam transformer of claim 1, wherein: the number of the polygon sides is: 2 (n + 1) pieces, wherein n is a natural number.

7. The collimated flat-topped gaussian beam transformer of claim 1, wherein: the length of the polygonal gradient index lens array is n x 0.5P, wherein n is a natural number, and P is a transmission period of light rays in the polygonal gradient index lens array.

8. The collimated flat-topped gaussian beam transformer of claim 1, wherein: the polygonal gradient index lens array is prepared by the following steps,

1) Melting cesium-containing glass in a platinum crucible at 1380-1420 ℃, discharging and forming into cylindrical glass;

2) Processing the cylindrical glass into cylindrical glass with a polygonal cross section;

3) Putting the polygonal columnar glass on a wire drawing machine for wire drawing to form continuous polygonal glass fiber;

4) Placing the polygonal glass fiber into potassium nitrate molten salt at 500-600 ℃ for Cs ⁺ -K ⁺ Ion-exchanging to form a polygonal gradient index fiber with a gradually decreasing refractive index from the center to the edge;

5) The method comprises the steps of closely arranging polygonal gradient refractive index fibers into array rods according to the mode that the cross sections of the polygonal gradient refractive index fibers are polygonal, putting the array rods into a melting furnace with the temperature of 750-850 ℃ for melting to form a polygonal gradient refractive index fiber array female rod, cutting the polygonal gradient refractive index fiber array female rod according to a preset length, and polishing two cut end faces to obtain the polygonal gradient refractive index lens array.

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