CN1253300A - Line beam shaping device - Google Patents

Abstract

A linear beam shaping device includes a micro-cylindrical lens, a micro-chip prism stack, a cylindrical lens, a spherical lens and an optical fiber which are sequentially placed in the advancing direction of a linear beam G emitted by a linear light source to be shaped. The most critical shaping element is the micro-chip prism stack, which is formed by closely arranging N micro-prisms to form an equilateral triangle, an isosceles triangle, an isosceles trapezoid, etc., which can make the reflection of the linear beam on its bottom surface a total internal reflection. The shaping device of the present invention is suitable for any linear beam that needs to be shaped, and has the characteristics of not changing the advancing direction of the beam after shaping, being simple in structure and easy to process.

Description

Line beam shaping device

The invention relates to a line beam shaping device made of transmissive elements. It is mainly used for shaping the output light field of the semiconductor laser line array, and can also be used for other beam shaping occasions that change the prolate beam into a circle, such as the shaping of the output light of the slab laser and the laminar shape of the high-power semiconductor laser pump. Laser output light shaping, etc.

Semiconductor lasers have an asymmetrically distributed output light field. In order to greatly increase the power output, many semiconductor lasers can be formed into an array (usually the length of the linear array is 10mm), but at the same time, the asymmetric distribution of the output light field is strengthened many times. Semiconductor lasers exhibit a high divergence of 60° to 90° in the direction perpendicular to the active region, that is, the pn junction, but the light-emitting region is only 1 μm wide, and the beam quality reaches the diffraction limit; while in the direction parallel to the active region, there is only about 10° divergence. Divergence, the light-emitting area has a certain length, especially when it is formed into an array, it is equivalent to a 10mm long-line light source composed of many light-emitting areas intermittently arranged, and the beam quality is extremely poor. The optical invariants (Lagrange quantities) in the two directions differ by thousands of times. Such an extremely asymmetric light beam cannot be gathered into a small spot with a certain depth of focus through the optical system of lens and prism combination, so as to obtain a high enough brightness, which can be transmitted by optical fiber. People have come up with various ways to solve this problem, so as to finally realize the purpose sought by dense semiconductor lasers. You can find a way from the internal structure of the array device, and install a delivery element with a large numerical aperture for each semiconductor laser; you can also find a way from the outside, designing a special optical system to shape and converge the output light field of the array device .

Figure 1 is a kind of light beam recombination by dislocation surface mirror to obtain a roughly symmetrical light field distribution, and then converge into a small light spot with a lens group, which is a shaping light collection device coupled by an optical fiber. It is a German Fraunhofer laser technology. So Dr.K.Du and others proposed that the core technology is a special reflector called "ladder mirror". The array tube of the semiconductor laser in Fig. 1 is that the line beam emitted by the shaped line light source 1 is compressed by the micro-cylindrical lens 2 to compress the so-called fast direction divergence angle, and then the light field structure is reorganized by the stepped mirror 3 to obtain a roughly symmetrical divergent beam, and then Through the combination of the cylindrical lens 4 and the spherical lens 5, it is converged onto the input end surface of the optical fiber 6, and is coupled out through the optical fiber 6. This structure can get a good shaping effect, but the disadvantages are (1) there is an optical path difference between the parts of the light field recombined by the stepped mirror, which needs to be compensated; (2) the processing of the stepped mirror is very difficult; (3) the stepped mirror It is very difficult to realize the high refractive index film layer of the mirror surface.

The object of the present invention is to provide a line beam shaping device, which overcomes the limitations of the above-mentioned prior art, so that the line beam becomes a circular light spot with uniform and symmetrical divergence angles in all directions after being shaped by the shaping device of the present invention. The advancing direction of the light beam does not change, and the shaping device has a simple structure, and the shaping element is easy to process.

The line beam shaping device of the present invention includes a microcylindrical lens 2, a microchip prism stack 3, a cylindrical lens 4, a spherical lens 5 to an optical fiber 6 placed in sequence in the forward direction of the line beam G emitted by the shaped line light source 1 .

In the above-mentioned line beam shaping device of the present invention, the key shaping element of the line beam G is the micro-prism stack 3, which is composed of N micro-prisms 301 closely arranged. The number of microprisms N= _κθs / _θf , where κ is the compression factor of the line beam by the microcylindrical lens 2 placed between the shaped line light source 1 and the microchip prism stack 3, and _θs is the slow divergence direction of the beam The divergence angle of , θ _f is the divergence angle of the fast divergence direction of the beam.

Said microchip prism stack 3 is an equilateral triangle capable of making the reflection of the line beam on its bottom surface c _n be total internal reflection, or an isosceles triangle, or an isosceles trapezoid, or a quadrilateral with two base angles equal.

Accompanying drawing 3 is helpful for explaining the shaping principle of the microplate prism stack 3 used as the shaping element of the present invention. If microprism 301 is symmetrical, or day isosceles triangle, then the light parallel to microprism 301 bottom edge enters microprism 301 from an inclined plane a, when reflecting to another inclined plane b exit through microprism bottom surface c, the outgoing light It is also parallel to the bottom edge of the microprism 301. If what is incident is a group of light rays located in the same plane, and this plane is deflected by an angle θ relative to the bottom surface of the microprism 301, then what is emitted is also a group of light rays located in the same plane, and this plane is deflected by an angle c relative to the bottom surface of the microprism 301 -theta. Therefore, as long as the microprism 301 is rotated 45° around its bottom edge, the parallel light beam extending in the horizontal direction can be changed into extending in the vertical direction. When the reflection of light on the bottom c of the microprism 301 is total internal reflection, the total loss will only depend on the antireflection effect of the two slopes. Therefore, when the microchip prism stack 3 is placed in the optical path, its bottom surface c _n is parallel to the advancing direction of the line beam G emitted by the shaped line light source 1, and the two inclined surfaces a _n and b _n of the incident and outgoing beams It can contain the cross section of all the shaped line beams, that is to say, the beam incident slope a _n and the beam exit slope b _n of the micro-chip prism stack 3 must be larger than the cross section of the shaped line beam. As shown in Figure 4.

As mentioned above, the microprism stack 3 is composed of a plurality of microprisms as shown in FIG. 3, each of which is placed with its base edge rotated by 45°. Therefore, the horizontally oriented line light source is decomposed into many small line light sources, and then transformed into many vertically oriented small line light sources, rearranged along the horizontal direction to form a comb-like distribution. The situation is shown in Figure 4. Therefore, it is required that there is an included angle of 45° between the bottom c of the N microprisms 301 included in the microprism stack 3 and the bottom c _n of the microprism stack 3 .

Assuming that the shaped line light source 1 has a length D and a width d, then the Lagrange quantities in the horizontal and vertical directions are L _horizontal = D·θ _s and L _vertical = d × θ _f . A typical high-power semiconductor laser array has D=10mm in the horizontal direction, and the divergence angle θ _s is about 10°, which is the so-called slow divergence direction; d=1μm in the vertical direction, and the divergence angle θ _f is 60°～90°, This is the so-called fast divergence direction. The difference between L _horizontal and L _vertical is more than 1,000 times. A strip-shaped microcylindrical lens 2 can be used to compress its "fast divergence direction", for example, to become a line beam with a width of several hundred microns and divergence of a fraction of a degree. Such a transformation allows the output beam to enter the shaping device entirely, but does not change the L _vertical . For the L _level , the situation is the same, for example, 10mm can be compressed to 1mm, but the divergence angle will exceed 100°. Assuming that the microcylindrical lens 2 compresses the divergence angle θ _f in the fast direction by κ times, then L _vertical = κ _d × θ _f /κ. If the total width of the microchip prism stack 3 just matches the length of the incident ray source, then the lengths of these small line sources of light that are decomposed and turned into vertical orientations are all D/N, and the divergence angle in the vertical direction is the original The divergence angle θ _s in the horizontal direction. In the horizontal direction, the total width of these small line light sources is the length D of the original line light source, and the divergence angle is the original divergence angle θ _f /κ in the vertical direction (after being compressed by the microcylindrical lens). If the new Lagrange quantity is expressed by adding "'", then there is a relation L' _vertical =D/N×θ _s and L' _horizontal =D× _θf /κ. From this it follows that θ _f /κ = θ _s /N. Properly select the number N of the microchip prism stack 3 and the compression factor κ of the microcylindrical lens 2, so that the Lagrangian quantities in the two directions are close, and the combination of the lens and the prism can be used to focus such a light beam into a small The circular spot, and the divergence angle is uniform and symmetrical in all directions. To achieve fiber coupling output, this amount should also match the core diameter and numerical aperture of the fiber.

The advantage of the present invention is that using the shaping device of the present invention, when the line beam passes through the shaping element—the microchip prism stack 3, the original Lagrangian value is changed, so that the line beam becomes a uniform and symmetrical circular spot with a divergence angle , and not only can be applied to the line beam shaping of the semiconductor laser array, it has become an important shaping device for the development of fiber-coupled output high-power semiconductor laser sources, but also can be applied to other shaping occasions for changing the prolate beam into a circular beam . That is, it can be applied to any line beam that requires shaping.

The beam shaped by the shaping device of the present invention still advances along the original direction after being shaped by the microchip prism stack 3 , and has the characteristic of not changing the advancing direction. That is to say, the shaping device of the present invention does not cause a turning of the propagation direction of the light beam.

The shaping element of the present invention—the microchip prism stack 3 can be made of common optical glass. Only general optical processing, bonding process and coating technology are required. This is much simpler than the step mirror used as the shaping element in the prior art, and there is no need to add a compensating element for the optical path difference in the optical path.

Description of drawings:

Fig. 1 is a schematic diagram of a prior art line beam shaping device in which the shaping element is a stepped mirror.

Fig. 2 is a schematic diagram of the line beam shaping device of the present invention.

FIG. 3 is a schematic diagram of the shaping structure of the microprism 301 in the microprism stack 3 as the shaping element of the present invention.

FIG. 4 is a schematic structural diagram of a micro-prism stack 3 as a shaping element according to the present invention.

The shaping device of the present invention will be further described below in conjunction with the accompanying drawings and examples.

Example 1:

Shaping device as shown in Figure 2. The structure of the microchip prism stack 3 is shown in FIG. 4 . The shaped line light source 1 is a semiconductor laser bar array. The microchip prism 301 is an isosceles right triangle. The length D of the line array of the shaped line light source 1 is 10 mm, and the divergence angle θ _s ≌10°.

所以要求

因为微棱镜301的厚度δ太薄将大大增加加工难度，同时也增加光束损耗。所以，通常取δ＞0.7mm。由此得出要求，微片棱镜堆3的片数N＜15。Assuming that the line light source length D ' not too far away from the light-emitting area is about 12～14mm, when the sheet thickness of the microprism 301 is δ, the total width of the microprism stack 3 is

so request

Because the thickness δ of the microprism 301 is too thin, the processing difficulty will be greatly increased, and the beam loss will also be increased. Therefore, δ>0.7mm is usually taken. This leads to the requirement that the number of microchip prism stacks 3 is N<15.

On the other hand, the distance between the light-emitting area of the shaped line light source 1 and the microcylindrical lens 2 is close to that of the microchip prism stack 3 behind the microcylindrical lens 2, so that the width of the shaped line light source is κd. If this value is too small, it means that the distance between the micro-chip prism stack 3 and the micro-cylindrical lens 2 is small, which will greatly increase the difficulty of installation and adjustment. Therefore, it is generally suitable to set κ>100. According to the above relationship N=κθ _s /θ _f , θ _f =60°～90°, θ _s =10°, it is required that 10<N<15, so in this embodiment, N≌12 is the most suitable value. As a result of the implementation, a uniform and symmetrical circular spot within the divergence angle is obtained.

Example 2:

The shaped line light source 1 is a solid slab laser, and the output line beam G is rectangular, and the Lagrangian quantities in the two directions may differ by tens of times. The length D≌8mm, width d≌3mm, θ _s ≌5°, θ _f ≌0.6° of the shaped line light source 1 do not need to compress θ _f . Therefore, in the device shown in Fig. The microcylindrical lens 2 between the shaped line light source 1 and the micro-prism stack 3 can be removed, that is to say, the compression factor κ=1, and the line beam G can directly enter the micro-prism stack 3 . N≌8 is obtained from the relationship N=κθ _s /θ _f . Considering the unavoidable error when the microprism 301 is disassembled and reassembled, according to the experimental experience, θ _f will be increased, so the actual value of N is slightly smaller than the value calculated above. In this embodiment, N=6 or 5 is most suitable.

Example 3:

The shaped line light source 1 is a sheet-shaped laser. The length D and width d of the line light source are the same as those in Embodiment 2, so the structures of the shaping device and the micro-prism stack 3 of the shaping element are also the same as in Embodiment 2.

The advantages of the present invention are fully illustrated through the above embodiments. like,

Example 2: The output beam of the solid slab laser is rectangular, and the Lagrange quantities in the two directions may differ by dozens of times. The divergence angle difference of tens of times greatly affects the beam transmission and focal depth of convergence. By adopting the invention, the rectangular output light beam of the slab laser is shaped into a uniform and symmetrical circular light spot with a divergence angle, which is similar to the output of the solid rod laser.

As another example, embodiment 3: as a thin sheet-shaped gain medium, the thin-sheet laser is very beneficial to effectively distribute and arrange the laser oscillation direction, pumping direction and rapid heat dissipation direction, so it becomes a new type of high-power semiconductor laser pumped solid-state laser The structure, unfortunately, the output of the laser with this structure is a "strip-shaped" beam. Now the present invention just solves this problem, and finally obtains a good circular beam output.

Claims (5)

1. A line beam shaping device, comprising on the advancing direction of the line beam (G) emitted by the shaping line light source (1), a micro-cylindrical lens (2) placed successively, a cylindrical lens (4), a spherical lens ( 5) To the optical fiber (6), it is characterized in that a microprism formed by N microprisms (301) closely arranged as a key shaping element is placed between the microcylindrical lens (2) and the cylindrical lens (4) heap(3). 2. The line beam shaping device according to claim 1, characterized in that said sheet number N= _κθs / _θf of said microprisms (301) forming the microchip prism stack (3), wherein κ is placed The compression factor of the line beam by the microcylindrical lens (2) between the shaped line light source (1) and the microchip prism stack (3), θ _s is the divergence angle in the slow divergence direction of the beam, and θ _f is the divergence in the fast divergence direction of the beam horn. 3. The line beam shaping device according to claim 1, characterized in that said microchip prism stack (3) is an equilateral triangle capable of making the reflection of the line beam on its bottom surface (c _n ) be total internal reflection, Either an isosceles triangle, or an isosceles trapezoid, or a quadrilateral with equal base angles. 4. The line beam shaping device according to claim 1 or 3, characterized in that when said microchip prism stack (3) is placed in the light path, its bottom surface (c _n ) and the shaped line light source (1) The advancing direction of the emitted line beam (G) is parallel, and the beam incident slope (a _n ) and the beam exit slope (b _n ) are larger than the section of the shaped line beam. 5. according to claim 1 and 2 described line beam shaping devices, it is characterized in that the bottom surface (c) of the N sheet microprisms (301) that said microchip prism stack (3) comprises and microchip prism stack ( 3) There is an included angle of 45° between the bottom surfaces (c _n ).

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