Semiconductor laser collimating lens

Abstract

The utility model discloses a collimating lens for semiconductor laser output light beam collimation is constituted by single homogenizing rod mirror or homogenizing rod mirror adds flat convex mirror combination, and the homogenizing rod mirror of core part has the core layer of relatively high refractive index and the cladding of relatively low refractive index, utilizes interface total reflection characteristic to the light beam of semiconductor laser and carries out homogenization and compression divergence angle, obtains collimating light beam output that light beam is close to parallel, the spot shape is close to circular, energy distribution is close to flat top distribution, and this collimating light beam destroys the coherence of light source, cancels the division of "fast axis direction", "slow axis direction", and this light beam can be directly applied and makes optical system structure compact, also can be gathered into optical fiber again through coupling lens.

Description

Technical Field

[0001] This utility model relates to the field of optical processing technology, specifically to a lens for collimating the output beam of a semiconductor laser. Background Technology

[0002] Due to the characteristics of their waveguide structure, semiconductor lasers typically output beams with unequal divergence angles in two orthogonal directions. The divergence angle in the principal direction, for example, is 60° (half-angle 30°, or numerical aperture NA = 0.5), called the fast axis direction, and is usually single-mode output. The divergence angle in the other orthogonal direction, for example, is 8°, and is usually multimode output. To collimate the beam, a fast-axis collimator (FAC) and a slow-axis collimator (SAC) are typically used to collimate the beam in both directions separately, forming a long, narrow beam rather than a near-circular beam. This process is complex and involves high component and assembly costs.

[0003] A beam homogenizer is a device that uses the principle of total internal reflection to confine an internal light beam. It is commonly used in projection, lighting, and solar concentrators. Beam homogenizers are universally applicable to different wavelengths and divergence angles of the light source, and they also have the characteristic of disrupting the coherence of the light source and causing the beam energy distribution to tend towards a flat-top distribution rather than a Gaussian distribution. Therefore, this application proposes a lens for beam collimation of semiconductor lasers based on the beam homogenizer principle. Summary of the Invention

[0004] To address the problems mentioned in the background section, this utility model provides the following technical solution: A collimating lens for a semiconductor laser is characterized by being composed of a single homogenizing rod mirror 2 or a combination of a homogenizing rod mirror 2 and a plano-convex mirror 4. The homogenizing rod mirror 2 has a core layer with a relatively high refractive index and a cladding layer with a relatively low refractive index. It homogenizes the output beam of the semiconductor laser 1 and compresses the divergence angle to obtain a collimated beam output with a beam that is nearly parallel, a spot shape that is nearly circular, and an energy distribution that is nearly flat-topped.

[0005] Furthermore, the aspect ratio of the core layer of the homogenizing rod mirror 2 is not less than 5.

[0006] Furthermore, the two end faces of the uniform light bar mirror 2 are configured as planes or spherical surfaces 3.

[0007] Furthermore, the uniform beam mirror 2 is of uniform diameter or conical in the axial direction, and its cross-section is circular, square, or hexagonal.

[0008] Furthermore, the homogenizing rod mirror 2 has only a core layer and an outer cladding layer of air.

[0009] By adopting the above technical solution, this utility model has the following beneficial effects: The collimating lens for the semiconductor laser in this application is composed of a single uniform beam mirror 2 or a combination of a uniform beam mirror 2 and a plano-convex mirror 4. By utilizing the total internal reflection characteristics of the uniform beam mirror 2 at the interface, the beam of the semiconductor laser 1 is homogenized and the divergence angle is compressed, resulting in a collimated beam output with a nearly parallel beam, a nearly circular spot shape, and a nearly flat-top energy distribution. This collimated beam destroys the coherence of the light source and eliminates the distinction between the "fast axis direction" and the "slow axis direction". This beam can be used directly and makes the optical system structure compact. Alternatively, the beam can be focused into an optical fiber through a coupling lens. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the beam divergence angle of a semiconductor laser beam compressed by a uniform beam mirror. Figure 2 Schematic diagram of adding a plano-convex mirror to a flat-end homogenizing rod mirror; Figure 3 This is a schematic diagram showing that the left end of the homogenizing rod mirror has a spherical surface; Figure 4 This is a schematic diagram of a uniform beam mirror with an axial cone angle. Figure 5 A schematic diagram of a square tower-shaped uniform light bar mirror with a spherical surface; Figure 6 This is a schematic diagram of a collimated beam being converged into an optical fiber via a coupling lens. Detailed Implementation

[0011] The technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. The embodiments described below are exemplary, and the accompanying drawings are not drawn to scale and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0012] like Figure 1 As shown, the semiconductor laser 1 emits a beam of light, which enters the homogenizing rod mirror 2. The left end of the homogenizing rod mirror 2 is a plane and the right end is a spherical surface 3. After being homogenized, the laser beam is collimated and output.

[0013] The homogenizing rod mirror 2 has two layers of materials with different refractive indices. The core layer has a refractive index of n1, and the cladding layer has a refractive index of n2. For example, n1=1.65 and n2=1.45. According to optical principles, total internal reflection occurs at the interface between the core layer and the cladding layer when the incident angle exceeds arcsin(n2 / n1)=61.5°. At this time, the divergence half-angle corresponding to the laser 1 on the left is arc(n1*sin(90-61.5))=51.9°. That is, lasers within 51.9° can be received by the homogenizing rod mirror 2, while the fast axis divergence half-angle of the laser 1 is usually less than 40°.

[0014] In order for the homogenizing rod mirror 2 to achieve a good "homogeneous" effect, it usually needs to have a sufficient length or a sufficient aspect ratio. The aspect ratio is usually not less than 5 times. For example, the equivalent diameter of the core layer of the homogenizing rod mirror 2 is 1.0, while the length of the core layer is 8.0, and the aspect ratio is 8.

[0015] The two end faces of the homogenizing rod lens 2 are usually flat. In order to prevent the homogenizing rod lens 2 from being too long, the right end face of the homogenizing rod lens 2 can be made into a spherical surface 3 with a radius of curvature r to help compress the divergence angle of the output beam. For example, r=3.0 and the total length of the lens l=6.0. In this way, a collimated beam that is close to parallel light output can be obtained at the right end of the homogenizing rod lens 2, and the beam no longer has the distinction between the "fast axis" and the "slow axis". The output is close to a circular light spot, and the energy distribution is closer to a flat-top distribution than the Gaussian distribution.

[0016] Figure 1 This collimating lens is very simple and effective in some applications. For example, in a PM2.5 air dust detection device made using the laser Mie scattering principle, a semiconductor laser is needed to emit a near-infrared, nearly parallel beam with a beam equivalent diameter of about 2.0 mm and an energy distribution close to a flat top. The scattered light from the particles passing through the beam is then received and processed. If the collimating lens of this invention is not used, multiple components such as spherical mirrors, cylindrical mirrors, and apertures are needed to form a collimating optical path, which is more complicated and the detection effect is not good.

[0017] From a manufacturing cost perspective, it's cheaper to add a plano-convex lens in front of the flat end face of the light homogenizer than to make a spherical surface on the end face. Figure 2 As shown, to the right of the homogenizing rod mirror 2 is a plano-convex mirror 4 with a similar geometric aperture. The homogenizing rod mirror 2 and the plano-convex mirror 4 are usually bonded together with adhesive, or they can be separated and fixed in relative position by structural components.

[0018] like Figure 3 As shown, the spherical surface 3 can be placed on the left side of the homogenizing rod mirror 2, that is, the side closer to the laser 1. Similarly, a homogenizing rod mirror 2 with good collimation effect can be designed. That is, the spherical surface 3 can be placed on either side or both sides of the homogenizing rod mirror 2. Both sides of the homogenizing rod mirror 2 can be planes or spheres.

[0019] The homogenizing rod structure can also be conical (tower-shaped), such as... Figure 4 The conical homogenizing rod mirror 6 is shown. Let the equivalent diameter of the left end face of the core rod be di, the equivalent diameter of the right end face be do, the numerical aperture of the left incident end be sinθi, and the numerical aperture of the right exit end be sinθo. When the homogenizing rod mirror 2 has sufficient length, approximately di*sinθi=do*sinθo, that is, the horn opening to the right can compress the beam divergence angle. For example, if di=0.5 and θi=30° on the left side, and do=2.0 on the right side, then θo=7.2°.

[0020] Besides cylindrical pyramidal towers, there can also be square pyramidal towers and hexagonal pyramidal towers, etc. Figure 5 As shown, this is a square-pyramidal homogenizing rod lens 6 with only a core homogenizing rod and a spherical surface 3 on the left end face. In this collimating lens, the spherical surface 3 functions similarly to... Figure 3 The function of the cone-shaped part is similar to Figure 4 Only the core layer can be understood as the cladding being air, and its refractive index n2=1.0.

[0021] In summary, the core component of the collimating lens structure in the above embodiments is the homogenizing rod mirror 2. The homogenizing rod mirror 2 has a core layer with a relatively high refractive index and a cladding layer with a relatively low refractive index. It utilizes the total internal reflection characteristics of the interface to homogenize and compress the divergence angle of the beam from the semiconductor laser 1, thereby obtaining a collimated output beam that is nearly parallel, has a nearly circular spot shape, and has a nearly flat-top energy distribution. The two end faces of the homogenizing rod mirror 2 can be flat or spherical 3, or a plano-convex mirror 4 can be added in front of the flat end face. The homogenizing rod mirror 2 can be of equal diameter or conical in the axial direction, and its cross-section can be circular, square, or hexagonal. It can have only a core layer and an outer cladding layer of air.

[0022] In other applications where it is necessary to focus the light energy into an optical fiber, the collimated beam formed can be coupled by placing a coupling lens at the right end of the homogenizing rod mirror 2. Figure 6 The coupling lens focuses the light beam into fiber 5, which is, for example, a multimode fiber with a core diameter of 50 μm.

[0023] The embodiments of the present invention have been shown and described above. Those skilled in the art may make modifications, substitutions and variations to the embodiments without departing from the principles and spirit of the present invention, but such modifications, substitutions and variations are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A collimating lens for a semiconductor laser, characterized in that, It is composed of a single homogenizing rod mirror (2) or a combination of homogenizing rod mirror (2) and plano-convex mirror (4). The homogenizing rod mirror (2) has a core layer with a relatively high refractive index and a cladding layer with a relatively low refractive index. It homogenizes the output beam of the semiconductor laser (1) and compresses the divergence angle to obtain a collimated beam output with a beam that is close to parallel, a spot shape that is close to circular, and an energy distribution that is close to flat-top distribution.

2. The collimating lens for a semiconductor laser according to claim 1, characterized in that, The aspect ratio of the uniform light bar mirror (2) is not less than 5.

3. The collimating lens for a semiconductor laser according to claim 1, characterized in that, The two end faces of the uniform light bar mirror (2) are set as planes or spheres (3).

4. The collimating lens for a semiconductor laser according to claim 1, characterized in that, The uniform light bar mirror (2) is of equal diameter or conical in the axial direction, and its cross-section is circular, square or hexagonal.

5. The collimating lens for a semiconductor laser according to claim 1, characterized in that, The homogenizing rod mirror (2) has only a core layer and an outer cladding layer of air.

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