WO2023123044A1

WO2023123044A1 - Uniform light spot shaping system

Info

Publication number: WO2023123044A1
Application number: PCT/CN2021/142461
Authority: WO
Inventors: 陈明阳; 沈放; 王钊; 葛倩倩
Original assignee: 江苏大学
Priority date: 2021-12-27
Filing date: 2021-12-29
Publication date: 2023-07-06
Also published as: CN114253001A

Abstract

A uniform light spot shaping system, comprising a quartz optical fiber (1), an end cap (2) and a trapezoidal beam expander (3); an input end face of the end cap (2) is a plane, and an output end face comprises an inner concave lens (4) and an annular plane, the inner concave lens (4) being located at the center of the output end face, and the annular plane surrounding the periphery of the inner concave lens (4); the trapezoidal beam expander (3) is formed by splicing four trapezoidal quartz plates into a tubular structure, the upper bases of the trapezoidal quartz plates forming an input end of the trapezoidal beam expander (3), and the lower bases of the trapezoidal quartz plates forming an output end of the trapezoidal beam expander (3); and the input end face of the end cap (2) is welded to one end of the quartz optical fiber (1), and the annular plane is connected to the input end of the trapezoidal beam expander (3). The uniform light spot shaping system is suitable for shaping high-power laser light, and has a certain continuous operating distance, so that a rectangular uniform light spot may be obtained both at and within the maximum working distance.

Description

A uniform light spot shaping system

technical field

The invention relates to the field of laser shaping, in particular to a uniform light spot shaping system.

Background technique

An important research direction of laser research and application is laser shaping. The laser spot emitted by the laser is generally a circular spot with Gaussian energy distribution, the energy is high in the middle, low at both ends, and the uniformity is very low, but not only in traditional laser thermal processing such as laser quenching, laser cladding, laser alloying and other applications , and in laser energy supply, optical information processing, storage, recording, laser medicine and other applications, there are great requirements on the uniformity of laser energy. In practical applications, especially the demand for spot homogenization of high-power lasers is increasing. The circular spot not only does not match the size of the photocell in the laser energy supply, resulting in low photoelectric conversion efficiency, but also has the problem of mismatching the shape of the working surface in applications such as laser cladding and laser alloying, resulting in low processing efficiency.

In applications such as laser power supply, it is necessary to convert the laser spot into a uniformly distributed large spot that matches the size of the photocell, that is, it is necessary to expand the laser spot and convert it into a uniformly distributed spot. The trapezoidal concentrator is commonly used in the concentrating photovoltaic system to improve the uniformity of the light spot and realize the concentrating. Square spot. However, this system can only obtain a uniform light spot close to the exit of the trapezoidal concentrator, and even a few millimeters away from the exit of the trapezoidal concentrator, the uniformity of the light spot will drop greatly, so that the working surface has to leave the exit of the concentrator. less than a uniform spot; and the system will form a focal point in the trapezoidal concentrator. If the laser power is too high, it will cause air breakdown and the system stability is low, so it is not suitable for high-power laser shaping; moreover , this kind of trapezoidal concentrator has a concentrating effect, and the concentrating ratio is greater than 1, that is, the output spot size is smaller than the input spot size. If a large spot is to be obtained, the light input end of the concentrator must be designed larger, and the concentrator The length had to increase and the system became bulky and unwieldy.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a uniform light spot shaping system, which is suitable for high-power laser shaping, and can obtain rectangular uniform light spots within a range from the output end face to a certain distance.

The present invention achieves the above-mentioned technical purpose through the following technical means.

A uniform spot shaping system, including a silica fiber, an end cap, and a trapezoidal beam expander;

The input end surface of the end cap is a plane, the output end surface includes a concave lens and an annular plane, the concave lens is located at the center of the output end surface, and the annular plane surrounds the concave lens;

The trapezoidal beam expander is spliced by four trapezoidal quartz plates to form a tubular structure, the upper bottom of the trapezoidal quartz plate forms the input end of the trapezoidal beam expander, and the lower bottom of the trapezoidal quartz plate forms the trapezoidal output of the beam expander;

The input end face of the end cap is fused with one end of the quartz optical fiber, and the annular plane is connected with the input end of the trapezoidal beam expander.

Preferably, the end cap is made of pure quartz, the side shape of the end cap is a square truss, the narrow end face of the four prism is the input end face of the end cap, and the wide end face of the four prism is the output end face of the end cap.

Preferably, the diameter of the circular area of the concave lens on the output end surface of the end cap is larger than the diameter of the laser spot emitted on the output end surface of the end cap.

Preferably, the trapezoidal beam expander is composed of four trapezoidal quartz plates, the inner and outer openings of the input end and the output end of the trapezoidal beam expander are square, and the inner opening edge of the input end of the trapezoidal beam expander The length is D _i , the diameter of the circular area of the concave lens on the output end face of the end cap is De, and D _i > _{D e} _.

Preferably, the inner surface of the trapezoidal beam expander is coated with a high reflection film.

Preferably, the inclination angle α of the trapezoidal beam expander needs to satisfy:

and have

Among them, θ is the divergence angle of the laser beam after propagating through the end cap; i is the number of reflections of the laser light in the trapezoidal beam expander, which is a natural number greater than 1; the input side of the trapezoidal beam expander is D _i , and the output The side length of the inner port is D _o , and the ratio of D _o to D _i is the gradient T, which needs to satisfy:

Beneficial effects of the present invention:

1) In the end cap of the present invention, the laser enters the end cap from the optical fiber, since there is no constraint of the fiber cladding, it can be transmitted in free space, effectively increasing the output end surface light field area, thereby reducing the optical power density, so it can effectively Solve the problem of damage to the fiber end face caused by high-power lasers; secondly, the present invention uses concave lenses to replace the convex lenses used in conventional concentrating photovoltaic systems, so that the system of the present invention will not produce laser focus points, and air breakdown caused by high-power lasers can be avoided. Therefore, the present invention is suitable for shaping of high-power lasers.

2) The end cap of the present invention integrates the concave lens and the optical fiber end cap, which is easy to manufacture, and the end cap and the trapezoidal beam expander are directly connected together, the whole system is no longer a separate structure, that is, the system of the present invention is integrated , compact structure, small footprint.

3) The system of the present invention has a certain continuous working distance, and a uniform rectangular spot can be obtained at the maximum working distance and within it. The system parameters can be adjusted according to the actual working distance and spot size, and the distance between the working surface and the trapezoidal beam expander can be set. The distance from the output end face of the device can be obtained to obtain the output spot that meets the requirements.

Description of drawings

FIG. 1 is a schematic structural diagram of a uniform spot shaping system of the present invention.

Fig. 2 is a sectional view of the quadrangular truss structure of the end cap of the present invention.

Fig. 3 is a schematic diagram of the principle of laser propagation in the end cap of the present invention.

Fig. 4 is the light spot three-dimensional figure and the illuminance figure in the concrete embodiment 1 of the present invention, wherein (a) is the light spot figure after the end cap of the laser; , Spot diagram at 6cm.

Fig. 5 is the three-dimensional diagram and the illuminance diagram of the spot in the specific embodiment 2 of the present invention, wherein (a) is the spot diagram after the laser passes through the end cap; (b), (c) are that the distance from the output end of the trapezoidal beam expander is 0 cm respectively , Spot diagram at 5cm.

Fig. 6 is a three-dimensional diagram and an illuminance diagram of the light spot when the distance from the output end of the trapezoidal beam expander is 0 cm in Embodiment 3 of the present invention.

In the figure: 1-silica fiber, 2-end cap, 3-trapezoidal beam expander, 4-concave lens

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

In describing the present invention, it is to be understood that the terms "central", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "axial", The orientation or positional relationship indicated by "radial", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description , rather than indicating or implying that the device or element referred to must have a particular orientation, be constructed and operate in a particular orientation, and thus should not be construed as limiting the invention. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

In the present invention, unless otherwise clearly specified and limited, terms such as "installation", "connection", "connection" and "fixation" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection , or integrally connected; it may be mechanically connected or electrically connected; it may be directly connected or indirectly connected through an intermediary, and it may be the internal communication of two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

A uniform spot shaping system according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

Referring to FIGS. 1 to 3 , a uniform spot shaping system according to an embodiment of the present invention includes a quartz optical fiber 1 , an end cap 2 , and a trapezoidal beam expander 3 .

The end cap 2 is composed of pure quartz. The input end face of the end cap 2 is a plane, and a spherical cap is missing in the center of the output end face to form a concave lens structure, so that the output end face includes a concave lens 4 and a ring plane. The concave lens 4 is located at the center of the output end face, and the ring shape The plane surrounds the concave lens 4 around. Preferably, the diameter of the circular area of the concave lens 4 on the output end surface of the end cap 2 is larger than the diameter of the laser spot emitted on the output end surface of the end cap 2 .

Further, as shown in FIG. 2 , the end cap 2 has a square truss structure, the narrow end face of the four prism is the input end face of the end cap 2 , and the wide end face of the four prism is the output end face of the end cap 2 .

The trapezoidal beam expander 3 is spliced by four trapezoidal quartz plates to form a tubular structure. The upper bottom of the trapezoidal quartz plate forms the input end of the trapezoidal beam expander 3, and the lower bottom of the trapezoidal quartz plate forms the output end of the trapezoidal beam expander 3. The inner and outer openings of the input end and the output end of the trapezoidal beam expander 3 are square, the width of the inner opening of the input end of the trapezoidal beam expander 3 is D _i , and the diameter of the circular area of the concave lens 4 on the output end face of the end cap 2 is is D _e , D _i >D _e . Preferably, the inner surface of the trapezoidal beam expander 3 is coated with a high-reflection film, which can effectively increase the reflectivity of the inner wall of the trapezoidal beam expander 3, thereby improving the shaping effect.

The input end surface of the end cap 2 is fused with one end of the quartz optical fiber 1 , and the annular plane of the end cap 2 is connected with the input end of the trapezoidal beam expander 3 .

The laser light diverges through the concave lens 4 in the end cap 2 and expands the beam through the trapezoidal beam expander 3 to realize the beam expansion function. At the same time, under the combined action of the two, a uniformly distributed square spot is formed. The divergence angle of the laser after propagating in the end cap 2 is:

θ＝θ ₂ -θ ₀

in:

The law of refraction: sinθ ₂ = n ₂ sinθ ₁

NA is the numerical aperture of the fiber, n ₂ is the refractive index of the silica fiber 1 core and the fiber end cap, r _core is the radius of the silica fiber 1 core, R is the curvature radius of the concave lens, and θ ₁ is the edge light of the laser transmitted in the end cap 2 Incident to the angle of incidence of the concave lens 4, θ ₂ is the refraction angle, θ ₀ is the angle between the normal line and the horizontal line made by drawing analysis when the marginal light is incident on the concave lens 4, d is the spot radius when the laser light is transmitted to the concave lens 4, and d ₀ is The length from the input end of the end cap to the concave lens 4.

Preferably, the inclination angle α of the trapezoidal beam expander 3 needs to satisfy:

and have

Among them, θ is the divergence angle of the laser light after it propagates through the end cap 2; i is the number of reflections of the laser light in the trapezoidal beam expander 3, which is a natural number greater than 1, and its value is determined artificially when the trapezoidal beam expander 3 is designed. Generally, when i=2, 3, the system has a higher uniformity of the spot, the larger i is set, the higher the uniformity of the spot, but the length of the trapezoidal beam expander 3 also increases correspondingly, therefore, its value needs to be selected Appropriate value.

Trapezoidal beam expander 3 has the side length of the inner port at the input end as D _i , the side length of the inner port at the output port as D _o , and the ratio of D _o to D _i is the gradient T, which needs to satisfy:

Wherein, the right part of the inequality greater than or equal to the sign is the corresponding bottom aperture of the incident trapezoidal beam expander 3 when the edge light of the laser is reflected for the ith time (that is, the cross-sectional diameter at the reflection point on the inner wall of the trapezoidal beam expander 3 during the ith reflection) and When the ratio of the inner diameter of the input port of the trapezoidal beam expander, the gradient T is the same as the ratio, it just satisfies the i-time reflection condition of the marginal ray, and when the gradient T is greater than this ratio, there will be more Light rays at small angles within the marginal rays of the light participate in reflection, and the output spot is more uniform at this time.

In a uniform spot shaping system of the present invention, after the incident laser light is diverged by the concave lens 4, when the light traces, it can be regarded as the area within the divergence angle is divided into countless light rays, and the edge light rays and the small-angle light rays within the trapezoidal The continuous reflection in the beam expander 3 readjusts the distribution of the light field, the uniformity of the spot is continuously improved, and the angles of each light are also constantly changing. Finally, the overall light distribution can be approximated as that of the laser light, which is slightly larger than the inclination angle of the trapezoidal beam expander 3. The half angle of the divergence angle of α emerges from the output port of the trapezoidal beam expander 3, so within a certain distance from the output port of the system, the light maintains this angular characteristic. Therefore, the system of the present invention has a continuous working distance, within the maximum working distance , the light is emitted in the form of filling the rectangular output port of the entire trapezoidal beam expander 3, so the output spot of the system is rectangular, and a uniform rectangular spot can be obtained. If the output port of the trapezoidal beam expander 3 is changed to other shapes, uniform light spots of corresponding shapes can also be obtained. The larger the number of reflections i is, the more uniform the rectangular uniform spot is obtained. The larger the length H of the trapezoidal beam expander 3, the higher the uniformity.

When designing the trapezoidal beam expander 3, after setting the number of reflections i, the gradient T and the inclination angle α are determined accordingly, and then the length of the inner port side of the output port D _o is set according to the actual application spot size requirements, and the inner port side length of the input port is The length D _i and the length H are determined accordingly.

Preferred embodiment 1: select 20/400 μm single-mode silica fiber 1, NA=0.06, the length of end cap 2 is 20 mm, the side length of input end is 2 mm, the side length of output end is 10 mm; the curvature of concave lens 4 is 0.6, and the diameter is 3.2 mm; The length of the trapezoidal beam expander 3 is 235 mm, the thickness is 2 mm, the side length of the inner opening of the input end is 6 mm, and the side length of the inner opening of the output end is 40 mm. As shown in accompanying drawing 4, Fig. 4 (a) is the three-dimensional diagram and the illuminance diagram of the light spot after the laser beam is refracted by the concave lens 4, it is obvious that the energy distribution is a Gaussian distribution, Fig. 4 (b), (c) is the light spot receiving end surface and the trapezoid The distance from the output end of the beam expander 3 is respectively the three-dimensional diagram and the illuminance diagram of the square uniform light spot of 0cm and 6cm. The size of the light spot is respectively 4cm×4cm and 5.2cm×5.2cm. As the distance increases, the uniformity of the light spot decreases. When the distance between the receiving end face of the light spot and the output end of the trapezoidal beam expander 3 is 15cm, the uniformity of the light spot is 78.3%. The distance between the receiving end face of the light spot and the output end of the trapezoidal beam expander 3 can be between Choose between 15cm.

Preferred embodiment 2: select 100/360 μm multimode silica fiber 1 for use, NA=0.22, the end cap 2 length is 14mm, the side length of the input end is 2mm, and the side length of the output end is 14mm; The concave lens 4 has a curvature of 0.2 and a diameter of 8mm; trapezoidal The length of the beam expander 3 is 400 mm, the thickness is 2 mm, the side length of the inner opening of the input end is 10 mm, and the side length of the inner opening of the output end is 100 mm. As shown in accompanying drawing 5, Fig. 5 (a) is the three-dimensional diagram and the illuminance diagram of the light spot after the laser beam is refracted by the concave lens 4, and the energy distribution is a Gaussian distribution, Fig. 5 (b), (c) are the light spot receiving end face and the trapezoidal expansion The distance between the output end of the beam device 3 is respectively 0cm, 5cm, and the three-dimensional map and the illumination map of the square uniform spot. As the distance between the end face and the output end of the trapezoidal beam expander 3 increases, the uniformity of the spot decreases. When the distance between the receiving end face of the light spot and the output end of the trapezoidal beam expander 3 is 14cm, the uniformity of the spot is 79.4%. 3 The distance of the output end can be selected between 0-14cm.

Preferred embodiment 3: select 100/360 μm multimode silica fiber 1 for use, NA=0.22, end cap 2 length is 14mm, input end side length is 2mm, output end side length is 14mm; concave lens 4 curvature is 0.2, diameter 8mm; trapezoidal The length of the beam expander 3 is 2.1m, the thickness is 2mm, the side length of the inner opening of the input end is 10mm, and the side length of the inner opening of the output end is 1m. The structure and size of the end cap 2 and the silica fiber 1 used in Embodiment 3 and Embodiment 2 are exactly the same, so the three-dimensional diagram and illuminance diagram of the light spot after the laser beam is refracted by the concave lens 4 in Embodiment 3 are shown in Figure 5(a). As shown in accompanying drawing 6, when the distance between the receiving end face of the light spot and the output end of the trapezoidal beam expander 3 is 0cm, the three-dimensional diagram and the illuminance diagram of the square uniform light spot have obtained a large-sized square uniform light spot of 1m * 1m, and the uniformity is 81.3%. Along with the increase of the distance between the receiving end face of the light spot and the output end of the trapezoidal beam expander 3, the uniformity of the light spot will decrease. The spot size is 1.12m×1.12m, and the distance between the receiving end face of the light spot and the output end of the trapezoidal beam expander 3 can be selected between 0-20cm.

In the description of this specification, descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or characteristic is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be construed as limitations to the present invention. Variations, modifications, substitutions, and modifications to the above-described embodiments are possible within the scope of the present invention.

Claims

A uniform spot shaping system, characterized in that it comprises a quartz optical fiber (1), an end cap (2) and a trapezoidal beam expander (3);

The input end surface of the end cap (2) is a plane, and the output end surface includes a concave lens (4) and an annular plane, the concave lens (4) is located at the center of the output end surface, and the annular plane surrounds the concave lens ( 4) around;

The trapezoidal beam expander (3) is spliced by four trapezoidal quartz plates to form a tubular structure, the upper bottom of the trapezoidal quartz plate surrounds the input end of the trapezoidal beam expander (3), and the lower part of the trapezoidal quartz plate The bottom surrounds the output end of the trapezoidal beam expander (3);

The input end face of the end cap (2) is fused with one end of the quartz optical fiber (1), and the annular plane is connected with the input end of the trapezoidal beam expander (3).
The uniform spot shaping system according to claim 1, characterized in that, the end cap (2) is made of pure quartz, the side shape of the end cap (2) is a square truss, and the narrow side of the four prism is The end face is the input end face of the end cap (2), and the wide end face of the square truss is the output end face of the end cap (2).
The uniform light spot shaping system according to claim 1, characterized in that, the diameter of the circular area of the concave lens (4) on the output end surface of the end cap (2) is larger than that emitted to the output end surface of the end cap (2). The diameter of the laser spot.
The uniform spot shaping system according to claim 1, wherein the trapezoidal beam expander (3) is composed of four trapezoidal quartz plates spliced together, and the inner and outer ports of the input end of the trapezoidal beam expander (3) And the inner and outer openings of the output end are square, the inner opening side length of the input end of the trapezoidal beam expander (3) is D i , and the concave lens (4) is on the output end face of the end cap (2) The diameter of the circular area is D e , D i >D e .
The uniform spot shaping system according to claim 1, characterized in that the inner surface of the trapezoidal beam expander (3) is coated with a high reflection film.
The uniform spot shaping system according to claim 5, wherein the tilt angle α of the trapezoidal beam expander (3) needs to satisfy:

and have

Wherein, θ is the divergence angle after the laser beam propagates through the end cap (2); i is the number of reflections of the laser light in the trapezoidal beam expander (3), which is a natural number greater than 1; the input end of the trapezoidal beam expander (3) The side length of the inner port is D i , the side length of the inner port of the output port is D o , and the ratio of D o to D i is the gradient T, which needs to satisfy: