An optical waveguide-based laser beam shaping system and method

Abstract

The application relates to a kind of laser beam shaping systems and methods based on optical waveguide, belong to beam shaping technology.It includes semiconductor laser from left to right sequentially arranged, fast axis collimating lens, slow axis collimating lens, beam expander system, focusing lens and optical waveguide;Fast axis collimating lens is plano-convex cylindrical lens, for collimating the fast axis direction of light beam;Slow axis collimating lens is plano-convex cylindrical lens, for collimating the slow axis direction of light beam;Beam expander system includes preceding plano-concave cylindrical lens and following plano-convex cylindrical lens, for expanding the light beam width of slow axis direction to be consistent with the light beam width of fast axis direction;Focusing lens is plano-convex lens, for focusing light beam to optical waveguide input end;The input end section of optical waveguide is rectangle, and the output end section is circular, for shaping rectangular light spot into circular light spot.In the application, light beam is transmitted in optical waveguide efficiently, and gradually shaped into circular light beam through transition structure.

Description

A laser beam shaping system and method based on optical waveguides Technical Field

[0001] This invention pertains to beam shaping technology, and more specifically, relates to a laser beam shaping system and method based on optical waveguides. Background Technology

[0002] Semiconductor lasers play a vital role in modern technology, possessing advantages such as small size, light weight, high electro-optical conversion efficiency, high reliability, and long lifespan. They are widely used in military, communications, medical, and materials processing fields.

[0003] Semiconductor lasers have certain defects in beam quality, mainly manifested in large divergence angles in the fast and slow axes and asymmetrical far-field distribution. Before practical application, beam shaping technology is needed to improve these beam characteristics so that their beam quality and transmission characteristics meet the application requirements.

[0004] To address the beam quality difference between the fast and slow axes of semiconductor laser output beams, beam shaping techniques can be employed to optimize beam characteristics. Coupled to a circular optical fiber using optical elements is a common and effective solution. Through collimation and focusing, the laser beam can be effectively coupled into the fiber. While optical fibers are axisymmetric and have consistent light-receiving capabilities in all directions, the coupled beam is typically a rectangular spot with significant differences in the beam parameter product (BPP) between the fast and slow axes. At the fiber coupling point, the beam width along the fast axis is much smaller than that along the slow axis. This mismatch between the rectangular spot and the circular space of the fiber results in low space utilization at the fiber input, wasting considerable angle and space resources and significantly reducing the brightness of the output beam. To reduce brightness loss, multiple single-tube semiconductor lasers are typically stacked along the fast axis to increase the BPP, thereby filling the space at the fiber input and improving power and brightness. However, fast-axis stacking requires high precision, significantly increasing system complexity and adjustment difficulty, which is detrimental to cost control and reliability improvement in practical applications. Summary of the Invention

[0005] This invention addresses the technical problems existing in the prior art by providing a beam shaping system and method for semiconductor lasers. The system collimates the output beam of the semiconductor laser and couples it into an optical waveguide with a rectangular input end face and a circular output end face. The output beam of the semiconductor laser effectively fills the rectangular input end of the optical waveguide, and the laser beam entering the waveguide is shaped into a circular spot at the output end. This invention achieves efficient beam transmission within the optical waveguide and gradually shapes the beam into a circular beam through a transition structure.

[0006] According to a first aspect of the present invention, a laser beam shaping system based on an optical waveguide is provided, comprising a semiconductor laser, a fast-axis collimating lens, a slow-axis collimating lens, a beam expanding system, a focusing lens, and an optical waveguide arranged sequentially from left to right;

[0007] The semiconductor laser is used to output a beam;

[0008] The fast-axis collimating lens is a plano-convex cylindrical lens used to collimate the beam along the fast axis, thereby reducing the divergence angle along the fast axis.

[0009] The slow-axis collimating lens is a plano-convex cylindrical lens used to collimate the beam along the slow axis, thereby reducing the divergence angle along the slow axis.

[0010] The beam expanding system includes a front plano-concave cylindrical lens and a rear plano-convex cylindrical lens for expanding the beam width in the fast axis direction to match the beam width in the slow axis direction.

[0011] The focusing lens is a plano-convex lens, used to focus the light beam onto the input end of the optical waveguide;

[0012] The optical waveguide has a rectangular cross-section at its input end and a circular cross-section at its output end. The rectangular input end cross-section and the circular output end cross-section of the optical waveguide have the same cross-sectional area, so that the beam parameter product of the optical waveguide remains unchanged. The optical waveguide is used to shape a rectangular light spot into a circular light spot.

[0013] Preferably, the region between the rectangular input section and the circular output section of the optical waveguide is a transition region, and the transition profile of the transition region adopts an exponential function transition:

[0014]

[0015] Where w begin (x,y) represents the waveguide width distribution on the rectangular cross-section at the input end of the optical waveguide, w end (x,y) is the waveguide width distribution on the circular cross-section of the output end of the optical waveguide, L is the length of the transition region of the optical waveguide, z is the coordinate of the length direction of the optical waveguide, and W(x,y,z) is the waveguide width distribution on the cross-section corresponding to the z coordinate.

[0016] Preferably, the spot size at the input end of the optical waveguide is smaller than the rectangular input end cross-sectional size of the optical waveguide, the beam width in the slow axis direction of the input beam of the optical waveguide is smaller than the long side of the rectangular input end cross-section, and the beam width in the fast axis direction of the input beam of the optical waveguide is smaller than the short side of the rectangular input end cross-section.

[0017] Preferably, the beam parameter product of the incident light at the input end of the optical waveguide in the slow axis direction is greater than that in the fast axis direction, and the beam parameter product in the slow axis direction is less than that of the optical waveguide.

[0018] According to another aspect of the present invention, a method for beam shaping using the aforementioned optical waveguide-based laser beam shaping system is provided, comprising:

[0019] The output beam of the semiconductor laser passes sequentially through a fast-axis collimating lens, a slow-axis collimating lens, a slow-axis beam expander, a focusing lens, and an optical waveguide.

[0020] When the collimated light spot is incident on the beam expander system, the light spot size D2 in the fast axis direction after passing through the beam expander system is obtained;

[0021]

[0022] Where f1 is the focal length of the plano-concave cylindrical lens in the beam expander system, f2 is the focal length of the plano-convex cylindrical lens in the beam expander system, and D1 is the spot radius along the fast axis after collimation along the fast axis and the slow axis.

[0023] The focusing lens focuses the expanded beam so that the focused beam can be coupled to the input end of the optical waveguide.

[0024] After being focused, the light spot reaching the input end of the optical waveguide is rectangular. The rectangular light spot coupled into the optical waveguide passes through the transition region of the optical waveguide and outputs a circular beam at the output end of the optical waveguide.

[0025] Preferably, the beam reaching the input end of the optical waveguide after focusing has equal divergence angles along its fast axis and slow axis, and the beam divergence angle θ at the input end of the optical waveguide is... in Smaller than the maximum receiving angle θ of the optical waveguide Max This achieves coupling;

[0026] The θ Max The numerical aperture NA and θ of the optical waveguide are obtained through calculation. Max The relationship is:

[0027]

[0028] Where n0 is the air refractive index, n1 is the fiber core refractive index, and n2 is the cladding refractive index; when the beam couples into the optical waveguide, the incident angle is less than or equal to θ. Max The light rays undergo total internal emission at the core-cladding interface, thus being confined to propagate within the core; when the incident angle is greater than θ Max The light rays are eventually lost due to refraction.

[0029] Compared with existing technologies, the beneficial effects of the laser beam shaping system based on optical waveguide provided by this invention are:

[0030] (1) The laser beam shaping system based on optical waveguide of the present invention includes an optical waveguide with a rectangular cross section at the input end and a circular cross section at the output end. The rectangular end face of the optical waveguide can efficiently receive the laser beam, avoiding the brightness loss problem caused by the difference in beam parameter product (BPP) in the fast axis and slow axis directions of the output beam of the semiconductor laser. For high-power wide-area semiconductor lasers with a large stripe width, the brightness of the beam is increased by about an order of magnitude compared to direct coupling into the optical fiber.

[0031] (2) The present invention adopts fixed optical components, including fast-axis collimating lens, slow-axis collimating lens, beam expander system, focusing lens and optical waveguide, with no moving parts, simple device structure, low system complexity, simple and quick debugging process, and long-term stability, which is suitable for a variety of high-requirement application scenarios.

[0032] (3) The optical waveguide of this invention employs pulsed laser etching technology to form a region of minute refractive index variation inside the glass, thereby precisely controlling the transition shape of the waveguide structure. The light beam achieves efficient transmission in the optical waveguide, and is gradually shaped into a circular beam through the transition structure. During the shaping process, the cross-sectional area of ​​the transition region remains essentially unchanged, avoiding energy loss caused by higher-order mode excitation and mode conversion, and ensuring that the shaped beam possesses excellent symmetry and beam quality. Attached Figure Description

[0033] Figure 1 is an overall schematic diagram of a laser beam shaping system based on an optical waveguide according to the present invention.

[0034] Figure 2 is a schematic diagram of the optical waveguide structure of a laser beam shaping system based on an optical waveguide according to the present invention.

[0035] Figure 3 is a schematic cross-section of the optical waveguide input end of a laser beam shaping system based on an optical waveguide according to the present invention.

[0036] Figure 4 is a cross-sectional view of the optical waveguide structure of a laser beam shaping system based on an optical waveguide according to the present invention.

[0037] Figure 5 is a simulation diagram of the beam spot after passing through the beam expander system in a laser beam shaping system based on optical waveguide according to the present invention.

[0038] Figure 6 is a simulation diagram of the focused laser beam after beam shaping in a laser beam shaping system based on an optical waveguide according to the present invention.

[0039] Figure 7 is a schematic diagram showing the power variation of a laser beam shaping system based on an optical waveguide according to the present invention as a function of transmission distance.

[0040] Figure 8 is a schematic diagram of the output beam of a laser beam shaping system based on an optical waveguide according to the present invention.

[0041] Among them: 1-semiconductor laser, 2-fast axis collimating lens, 3-slow axis collimating lens, 4-beam expander system, 5-focusing lens, 6-optical waveguide. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0043] The present invention discloses a laser beam shaping system based on an optical waveguide, comprising, from left to right, a semiconductor laser, a fast-axis collimating lens, a slow-axis collimating lens, a slow-axis beam expanding system, a focusing lens, and an optical waveguide;

[0044] A semiconductor laser, wherein the output beam of the semiconductor laser serves as a light source, and is generally an asymmetric spot, typically a non-ideal elliptical spot;

[0045] A fast-axis collimating lens, which is a plano-convex cylindrical lens, is used to collimate the beam along the fast axis and reduce the divergence angle along the fast axis.

[0046] A slow-axis collimating lens, which is a plano-convex cylindrical lens, is used to collimate the light beam along the slow axis and reduce the divergence angle along the slow axis.

[0047] The slow-axis beam expander system is a Galilean telescope system consisting of a plano-concave cylindrical lens and a plano-convex cylindrical lens, used to expand the beam width in the slow-axis direction to match the beam width in the fast-axis direction.

[0048] A focusing lens, which is a plano-convex lens, is used to focus a light beam onto the input end of an optical waveguide;

[0049] An optical waveguide is used to convert a rectangular light spot into a circular light spot. The optical waveguide has a rectangular cross-section at the input end and a circular cross-section at the output end. The rectangular cross-section is used to efficiently receive the laser beam coupled into the optical waveguide and gradually shape the beam into a circular light spot through a transition region.

[0050] In some embodiments, the cross-sectional area of ​​the transition region remains essentially unchanged during the transition of the optical waveguide from a rectangular cross-section to a circular cross-section, so as to ensure that the beam parameter product (BPP) of the optical waveguide remains unchanged.

[0051] In some embodiments, the transition profile of the optical waveguide during the transition process can adopt a linear transition, a cosine function transition, or an exponential function transition. Specifically, the exponential function transition is as follows:

[0052]

[0053] Where w begin (x,y) represents the waveguide width distribution on the rectangular cross-section at the input end of the optical waveguide, w end (x,y) is the waveguide width distribution on the circular cross-section of the output end of the optical waveguide, L is the length of the transition region of the optical waveguide, z is the coordinate of the length direction of the optical waveguide, and W(x,y,z) is the waveguide width distribution on the cross-section corresponding to the z coordinate.

[0054] In some embodiments, the spot size at the input end of the optical waveguide is slightly smaller than the rectangular input end cross-sectional size of the optical waveguide, the beam width of the input beam in the slow axis direction is smaller than the long side of the rectangular fiber core, and the beam width of the input beam in the fast axis direction is smaller than the short side of the rectangular fiber core.

[0055] In some embodiments, the divergence angle of the light spot along the fast axis at the input end of the optical waveguide is equal to the divergence angle along the slow axis, and the divergence angle of the light spot is less than the maximum receiving angle of the optical waveguide, ensuring that the light beam can be coupled efficiently.

[0056] In some embodiments, the beam parameter product (BPP) of the incident light at the input end of the optical waveguide in the slow axis direction is greater than that in the fast axis direction, and the beam parameter product in the slow axis direction is slightly smaller than that of the optical waveguide.

[0057] In an exemplary embodiment of the present invention, the system has a beam shaping function, which can be used to solve the brightness loss problem caused by the difference in beam parameter product between the fast axis and slow axis directions of the output beam of a semiconductor laser, thereby improving the beam coupling efficiency. Figure 1 is an overall schematic diagram of a laser beam shaping system based on an optical waveguide provided by an embodiment of the present invention. As shown in Figure 1, the beam shaping system of this embodiment includes: a semiconductor laser 1, a fast-axis collimating lens 2, a slow-axis collimating lens 3, a beam expander 4, a focusing lens 5, and an optical waveguide 6.

[0058] Semiconductor laser 1 is a 960nm laser used to provide the light source required by the system.

[0059] The fast-axis collimating lens 2 is a plano-convex cylindrical lens used to collimate the fast-axis direction of the output beam of the semiconductor laser in order to reduce the divergence angle in the fast-axis direction.

[0060] The slow-axis collimating lens 3 is a plano-convex cylindrical lens used to collimate the slow-axis direction of the output beam of the semiconductor laser in order to reduce the divergence angle in the slow-axis direction.

[0061] The fast-axis beam expander system 4 is a Galilean telescope system consisting of a front plano-concave cylindrical lens and a rear plano-convex cylindrical lens. It is used to adjust the beam size. When the collimated beam D1 is incident on the beam expander system, the beam size D2 in the fast-axis direction after passing through the beam expander system can be obtained.

[0062]

[0063] Where f1 is the focal length of the plano-concave cylindrical lens in the beam expander system, f2 is the focal length of the plano-convex cylindrical lens in the beam expander system, and D1 is the spot radius along the fast axis after collimation along the fast axis and the slow axis.

[0064] Focusing lens 5 is a plano-convex lens used to focus the expanded beam, enabling the focused beam to be accurately and efficiently coupled to the input end of the optical waveguide. The shape and divergence angle of the focused beam meet the receiving requirements of the optical waveguide, thereby ensuring coupling efficiency and beam transmission performance.

[0065] Optical waveguide 6 is an optical waveguide structure etched within glass using pulsed laser writing technology. In embodiments of this invention, glass is selected as the material substrate, and femtosecond laser writing technology is employed. Utilizing the high energy, high power, and short pulse width of femtosecond lasers, a minute region of refractive index variation is precisely formed within the glass through nonlinear absorption and localized heating, thereby forming an optical waveguide structure. By controlling parameters such as the pulse width, energy, and focusing position of the femtosecond laser, complex three-dimensional optical waveguide structures can be formed within the optical waveguide material. A variable cross-section optical waveguide is an optical waveguide structure formed based on multiple scan stacking. Its cross-sectional shape can be adjusted to optimize light transmission characteristics. By changing the cross-sectional shape of the waveguide, optical properties such as mode distribution, dispersion characteristics, and transmission loss can be adjusted to meet the needs of different application scenarios. Through femtosecond laser direct writing technology, the required geometry can be precisely etched with a spacing of 0.8 μm between adjacent tracks, enabling the fabrication of rectangular to circular optical waveguides.

[0066] In an embodiment of the present invention, FIG1 illustrates a plan view of the beam shaping system according to this embodiment shaping the beam in the fast axis and slow axis directions.

[0067] In an embodiment of the present invention, the optical waveguide transitions from rectangular to circular, as shown in Figure 2. The input end cross-section of the optical waveguide is rectangular, and the output end cross-section is circular, as shown in Figure 3. The cross-sectional profile of the transition region of the optical waveguide is in the form of an exponential function, and the cross-sectional view of the transition region is shown in Figure 4. The width of the fiber core in the transition region can adopt a linear transition, a cosine function transition, or an exponential function transition; and the cross-sectional area of ​​the transition region remains basically unchanged during the transition process, thus maintaining the stability of the beam parameter product (BPP) while keeping the refractive indices of the fiber core and cladding constant. This design can ensure that the energy loss of the beam during the transition from rectangular to circular is reduced during the transmission process within the optical waveguide, improving the energy utilization efficiency of the beam, while avoiding energy loss caused by the excitation of higher-order modes and the inter-mode conversion due to the uneven transition, significantly improving the shaping effect of the system.

[0068] In an embodiment of the present invention, a Galilean telescope system is used as the beam expander system 4. This system consists of a plano-concave cylindrical lens and a plano-convex cylindrical lens, used to adjust the spot size of the output beam of the semiconductor laser along the fast axis. Precise beam expansion ensures that the spot radius along the fast axis is approximately equal to that along the slow axis, creating conditions for subsequent efficient coupling. A simulation diagram of the spot after beam expansion is shown in Figure 5.

[0069] In this embodiment of the invention, the focusing lens 5 is a plano-convex lens, which focuses the laser beam processed by the beam expanding system 4, enabling the beam to be efficiently coupled to the input end of the optical waveguide. After focusing, the beam spot reaching the input end of the optical waveguide is rectangular. The beam width along the slow axis of the input beam is smaller than the long side of the rectangular fiber core, and the beam width along the fast axis of the input beam is smaller than the short side of the rectangular fiber core. Simultaneously, the beam spot size along the fast and slow axes is equal after processing by the beam expanding system 4, ensuring that the divergence angles of the laser beam reaching the input end of the optical waveguide are equal in both the fast and slow axes, and guaranteeing that the beam divergence angle θ at the input end of the optical waveguide is achieved. in Smaller than the maximum receiving angle θ of the optical waveguide Max This achieves efficient coupling. θ Max The numerical aperture NA of the optical waveguide and θ can be calculated. Max The relationship is:

[0070]

[0071] Where n0 is the air refractive index, n1 is the fiber core refractive index, and n2 is the cladding refractive index. When the beam couples into the optical waveguide, the incident angle is less than or equal to θ. Max The light rays undergo total internal emission at the core-cladding interface, thus being confined to propagate within the core; when the incident angle is greater than θMax The light rays are eventually lost due to refraction.

[0072] Figure 6 shows a simulation of the spot of the semiconductor laser output beam at the input end of the optical waveguide after being focused by focusing lens 5. The spot is rectangular and has the characteristic that the divergence angles in the fast axis and slow axis directions are equal.

[0073] The above model was established using Matlab simulation to simulate the transmission characteristics of the semiconductor laser output beam in the optical waveguide. The simulation results show that the power changes stably with the transmission distance, as shown in Figure 7, demonstrating the reliability and effectiveness of the system design. Furthermore, the laser beam output from the waveguide is an ideal circular spot, as shown in Figure 8. The rectangular spot coupled into the optical waveguide, after passing through the transition region, outputs a circular beam at the output end of the waveguide. This verifies that the waveguide structure has good beam shaping capabilities. This design not only improves the beam transmission efficiency but also ensures the uniformity and symmetry of the beam at the output end, which is crucial for improving the accuracy and quality of the semiconductor laser output beam.

[0074] This invention provides an innovative semiconductor laser output beam shaping system based on optical waveguides. It employs optical components such as a fast-axis collimating lens, a slow-axis collimating lens, a beam expander, a focusing lens, and an optical waveguide. Through precise optical design and optimization, it successfully shapes the semiconductor laser output beam from a rectangle into a circle, effectively solving the brightness loss problem caused by the difference in beam percentage (BPP) between the fast and slow axes in traditional technologies, thus improving the brightness of the output beam. The system also has the advantages of simplicity and stability.

[0075] Example

[0076] In this embodiment, the simulated semiconductor laser has a light-emitting surface of (200×1)μm, and its fast and slow axes have a divergence angle of 40°×15°. The fast-axis collimating lens is model GLH15-8x4-004, the slow-axis collimating lens is model GLH15-12x10-015-NIR, the plano-concave cylindrical lens in the beam expander system is model NCY108112-B, the plano-convex cylindrical lens is model CY108117-B, and the focusing lens is model CX20608-AB. The simulated waveguide rectangular input end has a long side length of 1200μm and a short side length of 100μm, adopts an exponential function transition form, has a transition region length of 10mm, a core refractive index of 1.51, a cladding refractive index of 1.50, a waveguide NA of 0.173, and a maximum divergence angle that can be received is approximately 10°. By using a beam shaping device to shape the beam of the monolithic semiconductor laser, the brightness is increased by about 9.8 times compared to traditional coupling into an optical fiber, and the energy loss during transmission is less than 2%.

[0077] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser beam shaping system based on optical waveguides, characterized in that, The system comprises, from left to right, a semiconductor laser, a fast-axis collimating lens, a slow-axis collimating lens, a beam expander, a focusing lens, and an optical waveguide. The semiconductor laser is used to output a light beam. The fast-axis collimating lens is a plano-convex cylindrical lens used to collimate the light beam along the fast axis, thereby reducing the divergence angle along the fast axis. The slow-axis collimating lens is also a plano-convex cylindrical lens used to collimate the light beam along the slow axis, thereby reducing the divergence angle along the slow axis. The beam expander includes a front plano-concave cylindrical lens and a rear plano-convex cylindrical lens, used to expand the beam width along the fast axis to match the beam width along the slow axis. The focusing lens is a plano-convex lens used to focus the light beam onto the input end of the optical waveguide. The input end cross-section of the optical waveguide is rectangular, and the output end cross-section is circular. The cross-sectional areas of the rectangular input end cross-section and the circular output end cross-section of the optical waveguide are the same to keep the beam parametric product of the optical waveguide constant. The optical waveguide is used to shape the rectangular light spot into a circular light spot. The region between the rectangular input end cross-section and the circular output end cross-section of the optical waveguide is a transition region, and the transition profile of the transition region adopts an exponential function transition. Where w begin (x,y) represents the waveguide width distribution on the rectangular cross-section at the input end of the optical waveguide, w end (x,y) is the waveguide width distribution on the circular cross-section of the output end of the optical waveguide, L is the length of the transition region of the optical waveguide, z is the coordinate of the length direction of the optical waveguide, and W(x,y,z) is the waveguide width distribution on the cross-section corresponding to the z coordinate.

2. The laser beam shaping system based on optical waveguide as described in claim 1, characterized in that, The spot size at the input end of the optical waveguide is smaller than the rectangular input end cross-sectional size of the optical waveguide. The beam width in the slow axis direction of the input beam of the optical waveguide is smaller than the long side of the rectangular input end cross-section, and the beam width in the fast axis direction of the input beam of the optical waveguide is smaller than the short side of the rectangular input end cross-section.

3. The laser beam shaping system based on optical waveguide as described in claim 1, characterized in that, The incident light at the input end of the optical waveguide has a beam parameter product in the slow axis direction that is greater than its beam parameter product in the fast axis direction, and the beam parameter product in the slow axis direction is less than the beam parameter product of the optical waveguide.

4. A method for beam shaping using a laser beam shaping system based on optical waveguides according to any one of claims 1-3, characterized in that, include: The output beam of the semiconductor laser passes sequentially through a fast-axis collimating lens, a slow-axis collimating lens, a slow-axis beam expander, a focusing lens, and an optical waveguide. When the collimated light spot is incident on the beam expander system, the light spot size D2 in the fast axis direction after passing through the beam expander system is obtained; Where f1 is the focal length of the plano-concave cylindrical lens in the beam expander system, f2 is the focal length of the plano-convex cylindrical lens in the beam expander system, and D1 is the radius of the light spot along the fast axis after collimation along the fast axis and slow axis. The focusing lens focuses the expanded beam so that the focused beam can be coupled to the input end of the optical waveguide. The light spot that reaches the input end of the optical waveguide after focusing is rectangular. The rectangular light spot coupled into the optical waveguide passes through the transition region of the optical waveguide and outputs a circular beam at the output end of the optical waveguide.

5. The beam shaping method as described in claim 4, characterized in that, After focusing, the beam reaching the input end of the optical waveguide has equal divergence angles along its fast axis and slow axis, and the beam divergence angle θ at the input end of the optical waveguide is... in Smaller than the maximum receiving angle θ of the optical waveguide Max Thus achieving coupling; the θ Max The numerical aperture NA and θ of the optical waveguide are obtained through calculation. Max The relationship is: Where n0 is the air refractive index, n1 is the fiber core refractive index, and n2 is the cladding refractive index; when the beam couples into the optical waveguide, the incident angle is less than or equal to θ. Max The light rays undergo total internal emission at the core-cladding interface, thus being confined to propagate within the core; when the incident angle is greater than θ Max The light rays are eventually lost due to refraction.

Images