Optical fiber type light spot homogenizer

Abstract

The optical fiber type light spot homogenizer comprises a machine frame, a laser source is arranged at one end of the machine frame, a multimode optical fiber corresponding to the laser source is arranged at the other end of the machine frame, the laser source emits a laser beam, the multimode optical fiber receives the laser beam, and the multimode optical fiber is connected with the machine frame. The multi-mode fiber laser is characterized in that the relative refractive index difference section of the inner side of the sunken inner cladding of the multi-mode fiber is in a two-stage step decreasing shape, and the center line of the laser beam and the center of the end face of the multi-mode fiber are aligned and offset in parallel by a section of radial offset. The device is small in size, low in cost, compact in structure, good in homogenization effect and stable in performance, and can be directly seamlessly integrated with an input laser source and an output optical fiber system. The optical fiber type light spot homogenizer assembly and the laser beam shaping system can achieve efficient light spot homogenization within the centimeter-level distance. The system can be applied to a vehicle-mounted laser radar, a vehicle-mounted head-up display, a multimode PON optical splitter, laser medical equipment or laser material processing equipment and the like.

Description

Technical Field

[0001] This invention relates to an optical fiber beam homogenizer, used to convert a beam with non-uniform energy distribution into a beam with uniform energy distribution, belonging to the field of laser beam shaping technology. Background Technology

[0002] Currently, light sources such as VCSELs (Vertical-Cavity Surface-Emitting Lasers) and fiber-coupled semiconductor lasers are widely used in industrial, medical, and consumer electronics fields. However, the energy distribution (i.e., the beam spot) of these lasers typically exhibits a Gaussian distribution, meaning the energy intensity is highest at the center of the spot and gradually decreases towards the edges. In many applications, this non-uniform beam energy distribution is detrimental. For example, in laser material processing (such as laser welding, annealing, or 3D printing), a Gaussian beam can cause overheating or ablation at the center of the material, while the edges are underheated, resulting in uneven processing quality; in laser medicine (such as dermatological treatments), a non-uniform beam spot can lead to inconsistent energy delivery to biological tissues, making it difficult to precisely control the treatment area and depth; in optical sensing and illumination (such as automotive LiDAR, AR head-up displays, or machine vision), a non-uniform illumination beam spot can cause inconsistent brightness or detection sensitivity within the field of view, affecting the accuracy and reliability of the system. To address the aforementioned problems, two main technical solutions exist. The first type utilizes bulk optics, most commonly microlens arrays (MLAs) or diffractive optical elements (DOEs). This approach typically includes a laser source, a collimating lens, a first microlens array, a second microlens array, and a focusing lens. The Gaussian beam is first collimated, then split and superimposed by two microlens arrays, and finally focused onto the target surface to form a uniform spot. However, this approach suffers from large size, complex structure, difficult assembly, high cost, and poor environmental stability. The second type uses standard multimode fiber. To overcome the shortcomings of the first approach, those skilled in the art have attempted to use a section of standard multimode fiber (e.g., OM3 or OM4 fiber) as a homogenizer. The principle is based on mode coupling and dispersion that occur when light propagates through the fiber. However, existing fiber homogenizers have the following drawbacks: the beam needs to travel several meters, tens of meters, or even longer to gradually achieve a "steady-state mode distribution" (EMD), i.e., a uniform output spot. This makes it impossible to manufacture compact optical devices at the centimeter level. On the other hand, the homogenization effect is extremely dependent on the input conditions. In standard optoelectronic packages (such as TOSA), in order to pursue the highest coupling efficiency, the laser source and the optical fiber must be "coaxially aligned". This coaxial alignment will only strongly excite the low-order modes of the optical fiber (such as LP01). Within a short distance (e.g., 5 cm to 50 cm), these low-order modes do not have enough mechanism and distance to couple to the high-order modes, resulting in poor homogenization. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing an optical fiber type spot homogenizer that is not only small in size, low in cost, and compact in structure, but also has good homogenization effect and stable performance.

[0004] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: it includes a frame, a laser source is installed at one end of the frame, and a multimode optical fiber is installed at the other end of the frame corresponding to the laser source. The laser source emits a laser beam, and the multimode optical fiber receives the laser beam. The characteristic feature is that the relative refractive index difference profile of the inner side of the recessed inner cladding of the multimode optical fiber is in the form of a two-step decreasing shape, and the center line of the laser beam is aligned with the center of the end face of the multimode optical fiber and offset by a radial offset amount.

[0005] According to the above scheme, the radial offset is 5µm~15µm.

[0006] According to the above scheme, the multimode optical fiber includes a core layer and a cladding layer. The cladding layer is divided into a recessed inner cladding layer and an outer cladding layer from the inside to the outside. The relative refractive index difference on the inner side of the recessed inner cladding layer decreases in two steps, including a first step layer and a second step layer. The relative refractive index difference Δn3.1 of the first step layer is -0.5% to -0.6%, and the radial thickness on one side is 2µm to 4µm. The relative refractive index difference Δn3.2 of the second step layer is -0.7% to -0.8%, and the radial thickness on one side is 2µm to 4µm.

[0007] According to the above scheme, the core layer includes a main core layer and an auxiliary core layer covering it. The main core layer has a radius of 21.0~26.0μm, and its refractive index profile exhibits a graded refractive index distribution with a refractive index distribution index α of 1.80~2.20. The maximum relative refractive index difference Δn1 of the main core layer is 0.5%~0.6%, and the minimum relative refractive index difference is 0. The auxiliary core layer has a radius of 35~40μm, and its refractive index profile is a diagonal line. Extending downwards from the edge of the main core layer, the angle A between the core layer and the horizontal axis is 50º~85º. The minimum relative refractive index difference Δn2 of the auxiliary core layer is -0.30% to -0.40%. The core layer is successively covered by a recessed inner cladding layer and an outer cladding layer. The radius of the recessed inner cladding layer is 90~100μm, and the relative refractive index difference Δn3 is -0.9% to -1.1%. The outer cladding layer is a pure silica glass layer with a radius of 62.5μm.

[0008] According to the above scheme, the angle A between the refractive index profile of the auxiliary core layer and the horizontal axis is 55º~80º.

[0009] According to the above scheme, the core layer is a fluorine- and germanium-doped silicon dioxide glass layer, and the recessed inner cladding layer is a fluorine-doped silicon dioxide glass layer.

[0010] According to the above scheme, the multimode fiber has an effective mode bandwidth of ≥2000MHz·km at a wavelength of 850nm.

[0011] According to the above scheme, the multimode fiber has an effective mode bandwidth of ≥1500MHz·km at a wavelength of 980nm.

[0012] According to the above scheme, the length L of the multimode optical fiber is 5cm to 50cm.

[0013] According to the above scheme, a ferrule for fixing the optical fiber is provided at the multimode optical fiber installation location at the other end of the rack. The center line of the ferrule hole is aligned with the center line of the laser beam and offset by a radial offset.

[0014] According to the above scheme, the multimode fiber end is inserted into the ferrule and fixed in the ferrule by adhesive bonding.

[0015] According to the above scheme, the laser source is a laser emitter, which is mounted on a support at one end of the frame. The support is a fine-tuning support, equipped with left-right fine-tuning and up-down fine-tuning.

[0016] According to the above scheme, the ferrule is installed on the ferrule holder at the other end of the frame. The ferrule holder is a fine-tuning ferrule holder, which is equipped with left and right fine-tuning devices and up and down fine-tuning devices.

[0017] The beneficial effects of this invention are as follows: 1. By offsetting the central axis of the multimode fiber core with the central axis of the laser beam of the laser source, a "controlled offset" coupling structure is formed, breaking the symmetry of the input beam. This forcibly and efficiently excites a large number of higher-order modes in the multimode fiber. Subsequently, when these excited higher-order modes and lower-order modes propagate together in the fiber segment with the "stepped decreasing profile," the stepped profile induces efficient mode coupling and energy exchange, enabling the optical field to quickly reach a steady-state mode distribution. This close integration of the offset excitation structure with the stepped refractive index function of the fiber ensures that the energy of the Gaussian beam is rapidly and fully redistributed during short-distance transmission, thereby forming a uniform flat-top beam at the output end. 2. It is small in size, low in cost, compact in structure, has good homogenization effect, and stable performance. It can be seamlessly integrated with the input laser source and output fiber system. It is a fiber-type beam homogenizer assembly and laser beam shaping system that can achieve efficient beam homogenization within a centimeter (cm) distance. The system can be applied to vehicle-mounted LiDAR (Light Detection and Ranging), vehicle-mounted HUD (Head-Up Display), multimode PON beam splitters, laser medical equipment, or laser material processing equipment, etc. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the working principle of the present invention.

[0019] Figure 2 This is a schematic diagram of the controlled offset coupling structure of the present invention.

[0020] Figure 3This is a schematic diagram of the relative refractive index difference of the multimode optical fiber of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0022] The device includes a frame, with a laser source (such as a VCSEL laser) mounted at one end. A multimode fiber is mounted at the other end of the frame, corresponding to the laser source. The laser source emits a laser beam, and the multimode fiber receives the laser beam. A ferrule is provided at the multimode fiber mounting location at the other end of the frame to fix the fiber. The glass portion of the fiber is inserted into the central end hole of the ferrule. The centerline of the ferrule hole is aligned with and parallel to the centerline of the laser beam, offset radially by a certain amount. That is, the end face of the multimode fiber is perpendicular to the fiber's central axis and perpendicular to the input laser beam. The refractive index difference profile of the inner cladding of the multimode fiber exhibits a two-step decreasing pattern. The centerline of the laser beam is aligned with and parallel to the center of the multimode fiber end face, offset radially by a certain amount, ranging from 5µm to 15µm, and more specifically from 8µm to 12µm. The multimode fiber comprises a core layer and a cladding layer. The core layer includes a main core layer and an auxiliary core layer covering it. The main core layer has a radius of 21.0~26.0 μm, a graded refractive index profile, a refractive index distribution index α of 1.80~2.20, a maximum relative refractive index difference Δn1 of 0.5%~0.6%, and a minimum relative refractive index difference of 0. The auxiliary core layer has a radius of 35~40 μm, and its refractive index profile is a diagonal line extending downwards from the edge of the main core layer, with an angle A of 50º~85º with the horizontal axis. The minimum relative refractive index difference Δn2 of the auxiliary core layer is... The cladding, ranging from -0.30% to -0.40%, consists of a recessed inner cladding and an outer cladding, arranged sequentially from the inside out. The radius of the recessed inner cladding is 90–100 μm, and the relative refractive index difference Δn3 is -0.9%–-1.1%. The relative refractive index difference on the inner side of the recessed inner cladding decreases in a two-step manner, including a first-step layer and a second-step layer. The relative refractive index difference Δn3.1 of the first-step layer is -0.5% to -0.6%, and the radial thickness on one side is 2 µm to 4 µm. The relative refractive index difference Δn3.2 of the second-step layer is -0.7% to -0.8%, and the radial thickness on one side is 2 µm to 4 µm. The outer cladding is a pure silica glass layer with a radius of 62.5 μm.

[0023] Figure 1 This is a schematic diagram illustrating the working principle and structure of the fiber-optic beam homogenizer of the present invention. It includes a laser source and its output laser beam (Gaussian beam), a multimode fiber, and an output beam (homogenized beam).

[0024] To verify the technical effects of the present invention, the following embodiments and comparative examples were carried out.

[0025] Example 1: Fiber profile: The relative refractive index difference Δn3.1 of the first step layer is -0.55%, and the width is 3.0 µm; the relative refractive index difference Δn3.2 of the second step layer is -0.75%, and the width is 3.0 µm; fiber length L: 10 cm; coupling structure: the centerline of the laser beam is aligned with the center of the multimode fiber end face and offset by a radial offset of 10 µm.

[0026] Test Results: With an input VCSEL laser beam (@980nm), the offset structure excited a large number of higher-order modes, and the stepped profile rapidly brought the light field to a steady-state distribution within 10cm. Output spot uniformity: 88% (flat-topped distribution, see...) Figure 1 right).

[0027] Comparative example: Fiber profile: The same stepped fiber profile as in Embodiment 1 of the present invention is used; Fiber length L: 10cm; Coupling structure: Coaxial alignment is used (offset = 0 µm).

[0028] Test results: When the input VCSEL laser beam (@980nm) is applied, the stepped profile of the fiber cannot be activated within 10cm because only low-order modes are excited. Output spot uniformity: 22%, indicating uneven energy field distribution.

[0029] Example 2: Fiber profile: The relative refractive index difference Δn3.1 of the first step layer is -0.60%, and the width is 2.5 µm; the relative refractive index difference Δn3.2 of the second step layer is -0.80%, and the width is 2.5 µm; fiber length L: 20 cm; coupling structure: the radial offset Offset = 12 µm.

[0030] Test results: Input VCSEL Gaussian laser beam (@ 850nm), output spot uniformity: 91% (flat-top distribution).

[0031] Example 3: Fiber profile: The relative refractive index difference Δn3.1 of the first step layer is -0.50%, and the width is 3.5 µm; the relative refractive index difference Δn3.2 of the second step layer is -0.70%, and the width is 3.5 µm; fiber length L: 5 cm; coupling structure: the radial offset Offset = 8 µm.

[0032] Test results: Input LD Gaussian laser beam (@ 905nm); Output spot uniformity: 82% (flat-top distribution).

[0033] Comparative Analysis of Examples: A comparison between Example 1 and the comparative example shows that, with identical fiber cross-sections and lengths, the fundamental difference in homogenization effect (22% vs 88%) arises solely from the different coupling structures (coaxial vs. offset). This demonstrates that the "controlled offset" coupling structure of this invention (…) Figure 2 This is the essential invention for activating and achieving short-distance (centimeter-level) homogenization.

Claims

1. A fiber-optic beam homogenizer, comprising a frame, a laser source mounted at one end of the frame, and a multimode fiber mounted at the other end of the frame corresponding to the laser source, wherein the laser source emits a laser beam, and the multimode fiber receives the laser beam, characterized in that... The relative refractive index difference profile inside the recessed inner cladding of the multimode fiber has a two-step decreasing shape, and the centerline of the laser beam is aligned with and parallel to the center of the end face of the multimode fiber by a radial offset.

2. The fiber-optic spot homogenizer according to claim 1, characterized in that... The radial offset is 5µm to 15µm.

3. The fiber-optic spot homogenizer according to claim 1 or 2, characterized in that... The multimode fiber includes a core and a cladding. The cladding is divided into a recessed inner cladding and an outer cladding from the inside out. The relative refractive index difference on the inner side of the recessed inner cladding decreases in two steps, including a first step layer and a second step layer. The relative refractive index difference Δn3.1 of the first step layer is -0.5% to -0.6%, and the radial thickness on one side is 2µm to 4µm. The relative refractive index difference Δn3.2 of the second step layer is -0.7% to -0.8%, and the radial thickness on one side is 2µm to 4µm.

4. The fiber-optic spot homogenizer according to claim 3, characterized in that... The core layer comprises a main core layer and an auxiliary core layer covering it. The main core layer has a radius of 21.0~26.0 μm, and its refractive index profile exhibits a graded refractive index distribution with a refractive index distribution index α of 1.80~2.

20. The maximum relative refractive index difference Δn1 of the main core layer is 0.5%~0.6%, and the minimum relative refractive index difference is 0. The auxiliary core layer has a radius of 35~40 μm, and its refractive index profile is a diagonal line extending from the main core layer. The edge of the layer extends downwards at an angle A of 50º to 85º with the horizontal axis. The minimum relative refractive index difference Δn2 of the auxiliary core layer is -0.30% to -0.40%. The core layer is successively covered by a recessed inner cladding layer and an outer cladding layer. The radius of the recessed inner cladding layer is 90 to 100 μm, and the relative refractive index difference Δn3 is -0.9% to -1.1%. The outer cladding layer is a pure silica glass layer with a radius of 62.5 μm.

5. The fiber-optic spot homogenizer according to claim 4, characterized in that... The angle A between the refractive index profile of the auxiliary core layer and the horizontal axis is 55º~80º.

6. The fiber-optic spot homogenizer according to claim 4, characterized in that... The core layer is a fluorine- and germanium-doped silica glass layer, and the recessed inner cladding is a fluorine-doped silica glass layer.

7. The fiber-optic spot homogenizer according to claim 4, characterized in that... The multimode fiber has an effective mode bandwidth of ≥2000MHz·km at a wavelength of 850nm.

8. The fiber-optic spot homogenizer according to claim 4, characterized in that... The multimode fiber has an effective mode bandwidth of ≥1500MHz·km at a wavelength of 980nm.

9. The fiber-optic spot homogenizer according to claim 3, characterized in that... The length L of the multimode optical fiber is 5cm to 50cm.

10. The fiber-optic spot homogenizer according to claim 1 or 2, characterized in that... At the other end of the rack, a ferrule for fixing the optical fiber is provided at the multimode fiber mounting location. The center line of the ferrule hole is aligned with the center line of the laser beam and offset by a radial offset.

11. The fiber-optic spot homogenizer according to claim 10, characterized in that... The multimode fiber end is inserted into the ferrule and fixed in the ferrule by adhesive bonding.

12. The fiber-optic beam homogenizer according to claim 10, characterized in that... The laser source is a laser emitter, which is mounted on a support at one end of the frame. The support is a fine-tuning support, equipped with left-right fine-tuning and up-down fine-tuning.

13. The fiber-optic spot homogenizer according to claim 10, characterized in that... The ferrule is mounted on the ferrule holder at the other end of the frame. The ferrule holder is a fine-tuning ferrule holder, which is equipped with left and right fine-tuning devices and up and down fine-tuning devices.

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