Wide-absorptivity bending-resistant optical fiber and optical fiber laser module

Abstract

The invention provides a wide-absorptivity anti-bending optical fiber and an optical fiber laser module, the wide-absorptivity anti-bending optical fiber comprises a fiber core layer, a first cladding layer, a second cladding layer, a third cladding layer and a coating layer which are sequentially arranged from inside to outside in the radial direction, the relative refractive index difference delta n1 of the fiber core layer relative to the first cladding layer is 0.15%-0.45%, and the relative refractive index difference delta n1 of the fiber core layer relative to the third cladding layer is 0.15%-0.45%. The relative refractive index difference delta n2 of the second cladding layer relative to the third cladding layer is 0.06%-0.35%, the relative refractive index difference delta n3 of the fiber core layer relative to the second cladding layer is 0.06%-0.14%, and the relative refractive index difference delta n4 of the third cladding layer relative to the coating layer is greater than 5.6%; according to the wide-absorptivity anti-bending optical fiber provided by the invention, the relative refractive index difference between the layers is meticulously designed, so that the optical fiber can be endowed with wide-range stray light absorption capability and excellent anti-bending performance, and meanwhile, high compatibility and reliability are ensured.

Description

Technical Field

[0001] The present invention relates to the field of gain optical fibers, and in particular to a broad-absorption, bend-resistant optical fiber and an optical fiber laser module. Background Art

[0002] In fiber laser systems, semiconductor lasers with non-wavelength locks of 915nm and 976nm are usually selected as the pump source of the fiber laser to pump the gain fiber. However, the output wavelength of the non-wavelocked 915nm semiconductor laser is usually between 900 and 930nm, and the output wavelength of the non-wavelocked 976nm semiconductor laser is usually between 950 and 1000nm. The absorption of the broad spectrum by the general gain fiber is not stable. When the wavelength of the pump source laser changes, the overall absorption rate of the gain fiber to the pump source will change significantly, and more pump light will not be absorbed. On the one hand, this problem will affect the stability of the fiber laser output power; on the other hand, more residual pump light will be converted into a large amount of waste heat in the back-end devices, which will not only cause great thermal stress on the back-end devices, but also waste a lot of light energy utilization.

[0003] There are gain fibers with high phosphorus doping on the market, which have relatively stable absorption rates for pump light in the 900-1000nm wavelength range. However, high phosphorus doping also results in a higher core numerical aperture. A higher numerical aperture will lead to a lower transverse mode instability threshold and poorer beam quality, which in turn affects the final fiber laser output power and spot processing effect, which is something we do not want to see in laser applications. At the same time, in the field of laser processing, when the optical fiber is bent, the optical signal in the optical fiber core is easily bent outside the core, causing optical signal leakage. Generally speaking, the smaller the bending radius, the more serious the light leakage. A small bending diameter will cause instability and even failure during the optical power transmission process, so anti-bending performance is one of the important indicators for evaluating optical fiber performance. Poor anti-bending performance limits the overall size of the laser, making the current fiber laser larger overall and unable to achieve miniaturization of high-power lasers.

[0004] Therefore, there is an urgent need for a broad absorption bend-resistant optical fiber and an optical fiber laser module to solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a broad absorption and bend-resistant optical fiber and an optical fiber laser module, which are used to solve the technical problems of the prior art gain optical fiber having poor absorption stability over a wide spectrum band and poor bend resistance.

[0006] To solve the above technical problems, the present invention first provides a broad absorption bend-resistant optical fiber, comprising a core layer, a first cladding layer, a second cladding layer, a third cladding layer and a coating layer arranged in order from the inside to the outside along the radial direction; Among them, the relative refractive index difference Δn1 of the core layer relative to the first cladding is 0.15%~0.45%, the relative refractive index difference Δn2 of the second cladding relative to the third cladding is 0.06%~0.35%, the relative refractive index difference Δn3 of the core layer relative to the second cladding is 0.06%~0.14%, and the relative refractive index difference Δn4 of the third cladding relative to the coating layer is greater than 5.6%.

[0007] Preferably, the numerical aperture NA1 of the core layer relative to the first cladding is 0.08~0.14, the numerical aperture NA2 of the second cladding relative to the third cladding is 0.05~0.12, the numerical aperture NA3 of the core layer relative to the second cladding is 0.05~0.075, and the numerical aperture NA4 of the third cladding relative to the coating layer is greater than 0.46.

[0008] Preferably, the diameter of the core layer is 10-30 um, the thickness of the first cladding is 2-10 um, the thickness of the second cladding is 8-50 um, the diameter of the third cladding is 125-1000 um, and the diameter of the coating layer is 235-1400 um.

[0009] Preferably, the refractive index of the core layer is greater than that of the second cladding, the refractive index of the second cladding is greater than that of the first cladding, the refractive index of the third cladding is less than or equal to that of the first cladding, and the refractive index of the coating layer is less than that of the third cladding.

[0010] Preferably, the core layer is made of gain-doped quartz, the second cladding is made of any one of germanium-doped quartz, aluminum-doped quartz and phosphorus-doped quartz, the first cladding and the third cladding are both made of quartz matrix glass, and the coating is made of resin.

[0011] Preferably, the incident wavelength of the broad absorption bend-resistant optical fiber is 1 μm, the material of the core layer is ytterbium-doped aluminum phosphosilicate glass, and the phosphorus doping concentration of the core layer is 8-20 mol%.

[0012] Preferably, the incident wavelength passing through the broad absorption bend-resistant optical fiber is 2 μm, and the material of the core layer is thulium-doped silica glass.

[0013] Preferably, the cross-sections of the core layer, the first cladding layer and the coating layer along the perpendicular radial direction are all circular, and the cross-sections of the second cladding layer and the third cladding layer along the perpendicular radial direction are any one of a circle and a regular polygon.

[0014] Preferably, the broadly absorptive bend-resistant optical fiber is an active optical fiber or a passive optical fiber.

[0015] Correspondingly, the present invention also provides a fiber laser module, comprising a non-wave-locked pump unit, a beam combining unit, a high-reflection grating, a gain fiber, a low-reflection grating, a cladding light stripper, and a laser output head, which are sequentially connected along the transmission direction from the signal input end to the signal output end, wherein the gain fiber is a wide-absorption, bend-resistant fiber.

[0016] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a broad absorption bend-resistant optical fiber and an optical fiber laser module, wherein the broad absorption bend-resistant optical fiber comprises a core layer, a first cladding layer, a second cladding layer, a third cladding layer and a coating layer arranged in sequence from the inside to the outside along the radial direction, wherein the relative refractive index difference Δn1 of the core layer relative to the first cladding layer is 0.15% to 0.45%, the relative refractive index difference Δn2 of the second cladding layer relative to the third cladding layer is 0.06% to 0.35%, the relative refractive index difference Δn3 of the core layer relative to the second cladding layer is 0.06% to 0.14%, and the relative refractive index difference Δn4 of the third cladding layer relative to the coating layer is greater than 5.6%; the present invention provides The wide-absorption, bend-resistant optical fiber achieves multiple performance improvements through the careful design of the relative refractive index differences between each layer: the low relative refractive index difference Δn1 between the core layer and the first cladding can expand the single-mode transmission window, reduce nonlinear effects, and diffuse the light field to enhance bend resistance; the low relative refractive index difference Δn2 between the second and third claddings acts as a mode filter and stress release layer, reducing stress concentration between the claddings; the relative refractive index difference Δn3 between the core layer and the second cladding forms a "refractive index barrier" that inhibits light leakage into the first cladding and reduces bending losses; and the ultra-high relative refractive index difference Δn4 between the third cladding and the coating layer combines the light absorption properties of the coating layer to forcibly absorb leaked light and avoid stray light interference. By carefully designing the relative refractive index differences between each layer, the present invention can endow the optical fiber with wide-range stray light absorption capabilities and excellent bend resistance, while ensuring high compatibility and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the cross-sectional structure and cross-sectional refractive index distribution of a broadly absorptive bend-resistant optical fiber provided in an embodiment of the present invention; Figure 2a to Figure 2d A schematic diagram of the cross-sectional structure of a broad absorption bend-resistant optical fiber provided by another embodiment of the present invention; Figure 3 Schematic diagram of the cross-sectional structure and cross-sectional refractive index distribution of the 14 / 20 / 50 / 250 wide-absorption bend-resistant optical fiber provided in Example 1 of the present invention; Figure 4 This is the absorption spectrum of conventional ytterbium-doped optical fiber; Figure 5 Absorption spectra of the 14 / 20 / 50 / 250 wide-absorption bend-resistant optical fiber provided in Example 1 of the present invention; Figure 6A schematic diagram of the optical path structure of the fiber laser module provided in Example 1 of the present invention; Figure 7 A schematic diagram of the optical path structure of the fiber laser module provided in Example 2 of the present invention; In the attached figure: 1000 - fiber laser module; 100 - broad absorption bend-resistant optical fiber; 10 - core layer; 20 - first cladding; 30 - second cladding; 40 - third cladding; 50 - coating layer; 200 - non-wave-locked pump unit; 201 - non-wave-locked 976nm semiconductor laser; 202 - non-wave-locked 915nm semiconductor laser; 300 - beam combining unit; 400 - high-reflection grating; 500 - low-reflection grating; 600 - cladding light filter; 700 - cladding light filter. DETAILED DESCRIPTION

[0018] The following will be combined with this embodiment to clearly and completely describe the technical solution in this embodiment. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] To address the technical issues of poor absorption stability and bend resistance in existing gain fibers across a wide spectrum, the present invention provides a wide absorption, bend-resisant fiber (WAB) and a fiber laser module to address these issues. This WAB fiber features a wide absorption spectrum in the 900-1000 nm range, ensuring stable absorption in the optical system. This reduces the central wavelength requirement for the pump source, allowing for the use of pump sources with any central wavelength between 900 and 1000 nm or a combination of multiple wavelengths. Furthermore, the gain fiber core has a low effective refractive index, ensuring high beam quality and a high transverse instability threshold. The second cladding design of the WAB fiber provides a composite light spot during laser processing, acting as auxiliary processing light. This reduces metal spatter during processing, controls central penetration depth, and facilitates peripheral preheating. The design of the fiber's bend-resistant depressed layers (first and third claddings) maintains excellent bend resistance, enabling high-power, miniaturized fiber laser modules.

[0020] See also Figure 1 , Figure 1 A schematic diagram of the cross-sectional structure and cross-sectional refractive index distribution of a broad absorption bend-resistant optical fiber 100 provided in an embodiment of the present invention; wherein the broad absorption bend-resistant optical fiber 100 comprises a core layer 10, a first cladding layer 20, a second cladding layer 30, a third cladding layer 40, and a coating layer 50, which are arranged radially from the inside to the outside in sequence; According to the cross-sectional structure of the optical fiber, starting from the axis of the optical fiber core, the layer closest to the axis is defined as the core layer 10, and from the inside to the outside, they are the first cladding 20, the second cladding 30, the third cladding 40, the low refractive index coating layer 50 (such as Figure 1 shown).

[0021] Specifically, the relative refractive index difference of each layer of the broad absorption bend-resistant optical fiber 100 is defined by the following formula (1): ; Among them, n i is the refractive index of the film layer close to the core layer 10, n c is the refractive index of the film layer close to the coating layer 50.

[0022] In the embodiment of the present invention, the relative refractive index difference Δn1 of the core layer 10 relative to the first cladding 20 is 0.15%~0.45%, the relative refractive index difference Δn2 of the second cladding 30 relative to the third cladding 40 is 0.06%~0.35%, the relative refractive index difference Δn3 of the core layer 10 relative to the second cladding 30 is 0.06%~0.14%, and the relative refractive index difference Δn4 of the third cladding 40 relative to the coating layer 50 is greater than 5.6%.

[0023] Specifically, the relative refractive index difference Δn1 between the core layer 10 and the first cladding layer 20 is low, allowing the light field distribution to spread more evenly across the interface between the core layer 10 and the first cladding layer 20. This reduces the optical power density within the core layer 10 and suppresses nonlinear effects (such as self-phase modulation and four-wave mixing), making it suitable for high-power laser or broadband signal transmission. Furthermore, the low Δn1 increases the critical angle for total internal reflection. During bending, light at the core layer 10-first cladding layer 20 interface is less likely to leak beyond the critical angle due to centrifugal forces. The light field diffuses to the first cladding layer 20, where its "buffering effect" shares bending stress, reducing losses caused by mechanical deformation directly experienced by the core layer 10.

[0024] Specifically, the low relative refractive index difference Δn2 forms a gradually varying refractive index transition, allowing a small amount of leaked light to diffuse into the third cladding 40 while suppressing the propagation of higher-order modes in the cladding (higher-order modes require a higher refractive index difference to maintain total internal reflection), thereby reducing energy loss carried by the cladding modes. Furthermore, the low relative refractive index difference Δn2 between the second cladding 30 and the third cladding 40 corresponds to materials with similar refractive indices and a small difference in thermal expansion coefficients, reducing interlayer stress concentration during fiber drawing. This reduces microcracks at the interface during bending or stretching, thereby enhancing the mechanical flexibility of the fiber.

[0025] Specifically, the relationship between the relative refractive index difference Δn1 and the relative refractive index difference Δn3 indicates that the refractive index of the first cladding 20 is lower than that of the second cladding 30, forming a "core → high-refractive-index second cladding 30 → low-refractive-index first cladding 20" structure. The critical angle for total internal reflection of light at the core layer 10-second cladding 30 interface is smaller than that at the core layer 10-first cladding 20 interface, forcing the light field to be preferentially confined within the core layer 10 and the second cladding 30 and preventing light from leaking into the low-refractive-index first cladding 20. Furthermore, the low relative refractive index difference Δn3 between the core layer 10 and the second cladding 30 limits the effective refractive index range of higher-order modes in the core layer 10, expanding the single-mode transmission window and enabling compatibility with wider-band light sources.

[0026] Specifically, a relative refractive index difference Δn4 greater than 5.6% corresponds to a significant refractive index difference. The coating layer 50 is often made of a light-absorbing resin material (such as a carbon black-doped acrylic resin). Light leaking into the third cladding layer 40 is strongly refracted due to the high Δn4, forcing it into the coating layer 50 and being absorbed. This eliminates over 95% of stray light back reflections, preventing signal interference. Furthermore, a high relative refractive index difference Δn4 enhances adhesion to the third cladding layer 40 (through chemical bonding or a roughened interface), improving peel strength.

[0027] The embodiments of the present invention achieve orderly control of the light field from "diffusion constraint → forced constraint → mode screening → stray absorption" through a "low-high-low-high" gradient design of the relative refractive index difference Δn, breaking through the technical bottleneck of "bending resistance will inevitably increase loss" of traditional optical fibers. The bending loss can be reduced by more than 90%, and the stray light suppression efficiency is increased to 95%.

[0028] In the embodiment of the present invention, the numerical aperture NA1 of the core layer 10 relative to the first cladding 20 is 0.08-0.14, the numerical aperture NA2 of the second cladding 30 relative to the third cladding 40 is 0.05-0.12, the numerical aperture NA3 of the core layer 10 relative to the second cladding 30 is 0.05-0.075, and the numerical aperture NA4 of the third cladding 40 relative to the coating layer 50 is greater than 0.46.

[0029] Specifically, the smaller NA1 makes the light field more concentrated in the core. When the optical fiber is bent, the light at the edge of the core layer 10 is not easily separated from the light-guiding area due to centrifugal force, thereby reducing bending losses and meeting the requirements of anti-bending design. The smaller NA2 helps to suppress the transmission of high-order modes in the second cladding 30. Combined with the low NA1 design of the core layer 10, it further optimizes the mode field diameter consistency of the optical fiber and reduces the signal distortion caused by multi-mode transmission. When the optical fiber is bent, the light at the edge of the core layer 10 may leak into the first cladding 20, and the low numerical aperture of NA3 can further block this part of the light from entering the second cladding 30, thereby concentrating the light field on the inner layer structure and reducing the energy loss caused by bending. The higher NA4 can strengthen the total reflection boundary, ensuring that any light entering the third cladding 40 is totally reflected at the interface and cannot leak into the coating layer 50, avoiding energy loss.

[0030] In the embodiment of the present invention, the diameter of the core layer 10 is 10~30um, the thickness of the first cladding 20 is 2~10um, the thickness of the second cladding 30 is 8~50um, the diameter of the third cladding 40 is 125~1000um, and the diameter of the coating layer 50 is 235~1400um.

[0031] Specifically, the diameter of the fiber core layer 10 is 10~30μm, which is compatible with single-mode and multi-mode transmission, and is suitable for long-distance communication and high-power transmission scenarios. The large-diameter fiber core layer 10 can also enhance the bending resistance; the thickness of the first cladding is 202~10μm, which can be used as an optical buffer and stress release layer; the thickness of the second cladding is 308~50μm, which strengthens the light field constraint when thin and provides structural support and thermal management when thick; the diameter of the third cladding is 40125~1000μm, which meets the traditional communication optical fiber standards and meets the large mode field requirements of special optical fibers; the diameter of the coating layer is 50235~1400μm, which is thin enough to meet conventional mechanical protection and thick enough to be suitable for extreme environments, and can also integrate light absorption and heat dissipation functions.

[0032] In the embodiment of the present invention, the refractive index of the core layer 10 is greater than the refractive index of the second cladding 30, the refractive index of the second cladding 30 is greater than the refractive index of the first cladding 20, the refractive index of the third cladding 40 is less than or equal to the refractive index of the first cladding 20, and the refractive index of the coating layer 50 is less than the refractive index of the third cladding 40. Figure 1 shown.

[0033] Specifically, the broadly absorptive, bend-resistant optical fiber 100 achieves enhanced both optical transmission and mechanical properties through a refractive index gradient design (core > second cladding 30 > first cladding 20 ≥ third cladding 40 > coating 50). The high-refractive-index core 10 ensures efficient light confinement and transmission. The refractive index difference between the second cladding 30 and the first cladding 20 forms an optical barrier, reducing bending losses and suppressing light leakage. The low-refractive-index design of the third cladding 40 and coating 50, combined with the light-absorbing properties of the coating 50, forcibly absorbs stray light and improves signal purity. The refractive index matching of each layer reduces interlayer stress and enhances the fiber's mechanical properties, such as bending and tensile strength, making it suitable for a variety of scenarios, including communications, laser processing, and medical treatment, while maintaining both optical stability and environmental adaptability.

[0034] In the embodiment of the present invention, the material of the core layer 10 is gain-doped quartz, the material of the second cladding 30 is any one of germanium-doped quartz, aluminum-doped quartz and phosphorus-doped quartz, the materials of the first cladding 20 and the third cladding 40 are both quartz-based glass, and the material of the coating layer 50 is a resin material.

[0035] Specifically, when the incident wavelength passing through the broad absorption bend-resistant optical fiber 100 is 1 μm, the material of the core layer 10 is ytterbium-doped aluminum phosphosilicate glass, and the phosphorus doping concentration of the core layer 10 is 8~20 mol%; when the incident wavelength passing through the broad absorption bend-resistant optical fiber 100 is 2 μm, the material of the core layer 10 is thulium-doped silicate glass.

[0036] In the embodiment of the present invention, the cross-sections of the core layer 10, the first cladding 20 and the coating layer 50 along the vertical radial direction are all circular, and the cross-sections of the second cladding 30 and the third cladding 40 along the vertical radial direction are either circular or regular polygonal.

[0037] Specifically, in terms of optical performance, the circular core layer 10 and first cladding 20 ensure uniform mode field distribution during optical transmission, reduce scattering loss caused by irregular shapes, and maintain signal transmission stability. The second cladding 30 and third cladding 40 can be circular or regular polygonal. If regular polygons are used, the asymmetric structure can change the reflection path of light in the cladding, suppress cladding mode transmission, reduce stray light interference, and improve signal purity. In terms of mechanical performance, the regular polygonal second cladding 30 and third cladding 40 can increase interlayer friction and contact area, strengthen the bonding between layers, and prevent interlayer misalignment during bending and stretching of the optical fiber. At the same time, the polygonal structure can be tightly stacked during optical fiber cabling, effectively utilizing space and increasing the integration density of the optical cable.

[0038] Specifically, in Figure 1 Middle: The cross sections of the core layer 10 , the first cladding layer 20 , the second cladding layer 30 and the coating layer 50 along the perpendicular radial direction are all circular, and the cross section of the third cladding layer 40 along the perpendicular radial direction is a regular octagon.

[0039] See also Figure 2a to Figure 2d , Figure 2a to Figure 2d Schematic diagram of the cross-sectional structure of a broad absorption bend-resistant optical fiber 100 provided in another embodiment of the present invention; wherein, Figure 2a Middle: The cross-sections of the core layer 10, the first cladding layer 20, the second cladding layer 30, the third cladding layer 40 and the coating layer 50 along the vertical radial direction are all circular; Figure 2b Middle: The cross-sections of the core layer 10, the first cladding layer 20, the third cladding layer 40, and the coating layer 50 along the vertical radial direction are all circular, and the cross-section of the second cladding layer 30 along the vertical radial direction is square; Figure 2c Middle: The cross-sections of the core layer 10, the first cladding layer 20, the third cladding layer 40, and the coating layer 50 along the vertical radial direction are all circular, and the cross-section of the second cladding layer 30 along the vertical radial direction is a regular octagon; Figure 2d Middle: The cross-sections of the core layer 10 , the first cladding layer 20 , and the coating layer 50 along the vertical radial direction are all circular, the cross-section of the second cladding layer 30 along the vertical radial direction is a square, and the cross-section of the third cladding layer 40 along the vertical radial direction is a regular octagon.

[0040] Correspondingly, the present invention also provides a fiber laser module 1000, comprising a non-wave-locked pump unit 200, a beam combining unit 300, a high-reflection grating 400, a gain fiber, a low-reflection grating 500, a cladding light stripper 600 and a laser output head 700, which are sequentially connected along the transmission direction from the signal input end to the signal output end. The gain fiber is a wide-absorption, bend-resistant fiber 100.

[0041] Specifically, the fiber laser module 1000 achieves multi-faceted performance improvements by integrating broad-absorption, bend-resistant gain fiber and high-efficiency optical components: the broad absorption characteristics enable the gain fiber to efficiently couple non-wavelocked pump light, and cooperate with the beam combining unit 300 to improve the light-to-light conversion efficiency; the bend-resistant design allows compact bending of the optical fiber for wiring, adapting to modular integration; the high-reflection grating 400 and the low-reflection grating 500 form a stable resonant cavity, ensuring high-quality output laser beams and narrow linewidth; the cladding light stripper 600 effectively strips off stray light and residual pump light, improving signal purity and optimizing thermal management; the overall modular design is compatible with existing processes and is suitable for industrial processing, medical treatment, scientific research and other scenarios, combining high power, high stability and environmental adaptability. In principle, all fiber structures described herein are within the scope of this invention, including active fibers, passive fibers, tapered fibers, and the like. Optical fibers of various specifications can be produced in large and stable batches using the methods of this invention, and are therefore not limited to the examples provided herein.

[0042] The technical solution of this application is now described in conjunction with specific embodiments.

[0043] Example 1: See also Figure 3 , Figure 3 Schematic diagram of the cross-sectional structure and cross-sectional refractive index distribution of a 14 / 20 / 50 / 250 wide-absorption bend-resistant optical fiber 100 provided in Example 1 of the present invention; wherein the wide-absorption bend-resistant optical fiber 100 includes a core layer 10, a first cladding layer 20, a second cladding layer 30, a third cladding layer 40, and a coating layer 50, which are arranged radially from the inside to the outside. Among them, the relative refractive index difference Δn1 of the core layer 10 relative to the first cladding 20 is 0.15%~0.45%, the relative refractive index difference Δn2 of the second cladding 30 relative to the third cladding 40 is 0.06%~0.35%, the relative refractive index difference Δn3 of the core layer 10 relative to the second cladding 30 is 0.06%~0.14%, and the relative refractive index difference Δn4 of the third cladding 40 relative to the coating layer 50 is greater than 5.6%.

[0044] In this embodiment 1, the specific parameters of the 14 / 20 / 50 / 250 wide-absorption bend-resistant optical fiber 100 are as follows: the core layer 10 is made of ytterbium-doped aluminum phosphosilicate glass, Δn1 = 0.33%, and the core diameter D1 = 14 μm; the first cladding 20 is made of pure quartz, and the diameter of the first cladding 20 is D2 = 24 μm; the second cladding 30 is made of germanium-doped quartz, Δn2 = 0.23%, and the diameter of the second cladding 30 is D3 = 50 μm; the relative refractive index difference between the core layer 10 and the second cladding 30 is Δn3 = 0.096%; the third cladding 40 is made of pure quartz, and the diameter of the third cladding 40 is D4 = 250 μm; and the diameter of the coating layer 50 is D5 = 400 μm.

[0045] See also Figure 4 and Figure 5 , Figure 4 This is the absorption spectrum of conventional ytterbium-doped optical fiber; Figure 5 The absorption spectrum of the 14 / 20 / 50 / 250 wide absorption bend-resistant optical fiber 100 provided in Example 1 of the present invention; wherein, Figure 4 and Figure 5 It can be seen that the absorption value of the 4 / 20 / 50 / 250 wide-absorption bend-resistant fiber 100 in the wavelength range of 900~1000nm is significantly higher than that of conventional ytterbium-doped fiber. The main reason is that the wide-absorption bend-resistant fiber 100 significantly enhances the capture, transmission and absorption capabilities of 900~1000nm pump light through the synergistic effect of the large NA cladding structure, high-concentration gradient doping, bend-resistant design and multi-mode pump compatibility. Conventional ytterbium-doped fiber is limited by structural symmetry, NA value and doping concentration, and has low absorption efficiency.

[0046] See also Figure 6 , Figure 6Schematic diagram of the optical path structure of the fiber laser module 1000 provided in Example 1 of the present invention; wherein, Example 1 of the present invention also provides a fiber laser module 1000 with a single forward oscillation structure, including a non-wavelocked pump unit 200, a beam combining unit 300, a high-reflection grating 400, a gain fiber, a low-reflection grating 500, a cladding light stripper 600 and a laser output head 700 connected in sequence along the transmission direction from the signal input end to the signal output end, and the gain fiber is a wide-absorption, bend-resistant fiber 100.

[0047] Specifically, the non-wave-locked pump unit 200 includes six non-wave-locked 976 nm semiconductor lasers 201 arranged in parallel, and the beam combining unit 300 is a 6*1 pump beam combiner.

[0048] The fiber laser module 1000 provided in Example 1 of the present invention uses a non-wavelocked semiconductor laser with a central wavelength of 976nm as a pump source. Its output central wavelength gradually increases from 960nm to 976nm as the temperature rises. Because the broadly absorptive, bend-resistant fiber 100 has a broad absorption spectrum between 900nm and 1000nm, it is minimally affected by variations in the central wavelength of the pump source. This gives the fiber laser module 1000 advantages such as high power, miniaturization, broad pump absorption, and the ability to output a composite light spot.

[0049] For comparison, a fiber laser module 1000 was fabricated using a conventional 14 / 250 (core diameter 14μm, cladding diameter 250μm) double-clad ytterbium-doped fiber of the same length and bend diameter, and compared with a broad-absorption bend-resistant fiber 100. The test results are shown in Tables 1, 2, and 3 below (optical efficiency = output power of the laser output head 700 / output power of the non-wavelocked pump unit 200 * 100%):

[0050] Table 1 Output light efficiency of broad absorption bend-resistant fiber 100 and common 14 / 250 fiber

[0051] Table 2 Output power of broad absorption bend-resistant fiber 100 and ordinary 14 / 250 fiber

[0052] Table 3 Surface temperature of the cladding light stripper 600 when the broad absorption bend-resistant optical fiber 100 and the ordinary 14 / 250 optical fiber are connected Specifically, as can be seen from Tables 1 and 2, the broad absorption bend-resistant optical fiber 100 of Example 1 has a strong adaptability to the pump source, has a high efficiency in pump light energy utilization, and has stable final output light efficiency and output power compared to ordinary 14 / 250 optical fibers. It has obvious advantages over ordinary 14 / 250 optical fibers.

[0053] As shown in Table 3, conventional 14 / 250 optical fibers in the prior art have unstable absorption rates between 960 and 976 nm. When a non-wavelength-locked 976 nm semiconductor laser is used as a pump source, the gain fiber insufficiently absorbs the pump light when the pump source outputs a central wavelength other than 976 nm. This results in a large amount of residual pump light leaking out and ultimately being filtered out by the cladding stripper 600. This not only results in insufficient pump energy utilization and unstable laser output power, but also generates a large amount of waste heat in the cladding stripper 600, endangering equipment safety. Furthermore, since the pump light passes through the broad-absorption bend-resistant optical fiber 100, the temperature of the cladding stripper 600 is relatively stable, significantly improving the stability of the cladding stripper 600.

[0054] Example 2: Embodiment 2 of the present invention provides a 15 / 20 / 40 / 250 wide absorption bend-resistant optical fiber 100. The 15 / 20 / 40 / 250 wide absorption bend-resistant optical fiber 100 includes a core layer 10, a first cladding layer 20, a second cladding layer 30, a third cladding layer 40, and a coating layer 50, which are sequentially arranged from the inside to the outside along the radial direction. Among them, the relative refractive index difference Δn1 of the core layer 10 relative to the first cladding 20 is 0.15%~0.45%, the relative refractive index difference Δn2 of the second cladding 30 relative to the third cladding 40 is 0.06%~0.35%, the relative refractive index difference Δn3 of the core layer 10 relative to the second cladding 30 is 0.06%~0.14%, and the relative refractive index difference Δn4 of the third cladding 40 relative to the coating layer 50 is greater than 5.6%.

[0055] In this embodiment 2, the specific parameters of the 15 / 20 / 40 / 250 wide-absorption bend-resistant optical fiber 100 are as follows: the core layer 10 is made of ytterbium-doped aluminum phosphosilicate glass, Δn1 = 0.26%, and the core diameter D1 = 15 μm; the first cladding 20 is made of pure quartz, and the diameter D2 of the first cladding 20 is 20 μm; the second cladding 30 is made of germanium-doped quartz, Δn2 = 0.165%, and the diameter D3 of the second cladding 30 is 40 μm; the relative refractive index difference Δn3 between the core layer 10 and the second cladding 30 is 0.096%; the third cladding 40 is made of pure quartz, and the diameter D4 of the third cladding 40 is 250 μm; and the diameter D5 of the coating layer 50 is 400 μm.

[0056] See also Figure 7 , Figure 7Schematic diagram of the optical path structure of the fiber laser module 1000 provided in Example 2 of the present invention; wherein, Example 2 of the present invention also provides a fiber laser module 1000 with a single forward oscillation structure, including a non-wavelocked pump unit 200, a beam combining unit 300, a high-reflection grating 400, a gain fiber, a low-reflection grating 500, a cladding light stripper 600 and a laser output head 700 connected in sequence along the transmission direction from the signal input end to the signal output end, and the gain fiber is a wide-absorption, bend-resistant fiber 100.

[0057] Specifically, the non-wavelocked pump unit 200 includes three non-wavelocked 915 nm semiconductor lasers 202 arranged in parallel, and the beam combining unit 300 is a 3*1 pump beam combiner.

[0058] The fiber laser module 1000 provided in Example 2 of the present invention uses a non-wavelocked semiconductor laser with a central wavelength of 976nm as a pump source. Its output central wavelength gradually increases from 960nm to 976nm as the temperature rises. Because the broadly absorptive, bend-resistant fiber 100 has a broad absorption spectrum between 900nm and 1000nm, it is minimally affected by variations in the central wavelength of the pump source. This gives the fiber laser module 1000 advantages such as high power, miniaturization, broad pump absorption, and the ability to output a composite light spot.

[0059] The minimum allowable bending diameter of common 14 / 250 optical fibers currently available on the market is greater than 10 cm. A bending diameter less than 10 cm will cause the optical waveguide to fail, and a large amount of signal light will leak into the optical fiber cladding and eventually be stripped off by the cladding light stripper 600, resulting in a decrease in laser output power and a large amount of waste heat. Therefore, in order to verify that the wide absorption bend-resistant optical fiber 100 provided in this embodiment 2 has good bend resistance, multiple groups of optical fibers with different minimum bend diameters are coiled and connected to the fiber cladding. Figure 7 The output power of the fiber laser module 1000 was tested to characterize the bend resistance of the broadly absorptive, bend-resistant optical fiber 100 provided in Example 2. Other conditions were maintained consistent during this process to avoid the influence of other factors. For comparison, a fiber laser module 1000 was prepared using a conventional 14 / 250 (core diameter 14μm, cladding diameter 250μm) double-clad ytterbium-doped fiber of the same length and bend diameter, and compared with the broadly absorptive, bend-resistant optical fiber 100 of Example 2. The test results are shown in Table 4 below:

[0060] Table 4 Output power of wide absorption bend-resistant fiber 100 and ordinary 14 / 250 fiber at different bend diameters As shown in Table 4, the output power of the broad-absorption bend-resistant optical fiber 100 provided in Example 2 remains constant at different minimum bend diameters, while the output power of the conventional 14 / 250 double-clad ytterbium-doped optical fiber gradually decreases as the minimum bend diameter gradually decreases. This indicates that the broad-absorption bend-resistant optical fiber 100 provided in Example 2 has better bend resistance than the conventional 14 / 250 double-clad ytterbium-doped optical fiber and has obvious advantages over the conventional 14 / 250 double-clad ytterbium-doped optical fiber.

[0061] In the prior art, ordinary large-mode-area double-clad ytterbium-doped optical fibers do not have good anti-bending properties, and the applicable bending range is usually greater than 10 cm. High-power fiber lasers cannot be miniaturized. Once the gain fiber or the matching passive fiber is bent slightly, waveguide failure will occur, resulting in a reduction in the laser output power. The wide-absorption, bend-resistant optical fiber 100 provided by the present invention has good anti-bending properties, which enables high-power fiber lasers to be miniaturized. One of its applications is as a gain medium for high-power ytterbium-doped fiber lasers. In this application, the wide-absorption, bend-resistant optical fiber 100 provided by the present invention has a minimum bending diameter of as low as 5 cm, which effectively solves the problem of large size of high-power fiber lasers currently on the market.

[0062] The present invention provides a broadly absorptive, bend-resistant optical fiber 100 that can be mass-produced. This fiber exhibits stable fiber absorptivity between 900 and 1000 nm and excellent bend resistance. This fiber aims to address the intertwined constraints of broad spectrum absorption, low numerical aperture, high lateral instability threshold, and excellent bend resistance in related fiber laser technologies.

[0063] Thanks to the structural design of the broadly absorptive, bend-resistant optical fiber 100, whose core effective refractive index is the relative refractive index difference between the core layer 10 and the second cladding 30, the broadly absorptive, bend-resistant optical fiber 100 ensures a low effective numerical aperture, a large mode field area, and a high lateral instability threshold. When the broadly absorptive, bend-resistant optical fiber 100 bends, the presence of the first cladding 20 effectively confines the fundamental mode in the core layer 10 under slight bending conditions, preventing leakage and power loss.

[0064] Different from the prior art, the broad absorption bend-resistant optical fiber 100 provided by the present invention has the following advantages: (1) The broad absorption bend-resistant optical fiber 100 of the present invention has a broad absorption spectrum, which allows it to be pumped using any pump source between 900 and 1000 nm without generating a large amount of excess pump light in laser applications, thereby improving the energy utilization rate of the fiber pump light. Semiconductor lasers with a variety of central wavelengths can be used as pump sources, which reduces the requirements for the central wavelength and stability of the pump source, and reduces the requirements for environmental use, further saving costs.

[0065] (2) The broadly absorptive, bend-resistant optical fiber 100 of the present invention has a low core effective refractive index, enabling a large mode field diameter, a high lateral instability threshold, and good beam quality output. Furthermore, due to the design of the optical fiber structure, it exhibits excellent bend resistance, resolving the mutual constraints of large mode field diameter, high lateral instability threshold, and miniaturized bending. This allows the optical fiber to be further bent without affecting its performance, thus offering the advantage of miniaturization of high-power lasers.

[0066] (3) The broad absorption bend-resistant optical fiber 100 of the present invention can output a composite light spot when used for laser processing, forming an auxiliary processing light, which can reduce metal processing spatter, control the center melting depth, and preheat the periphery.

[0067] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For any details not described in individual embodiments, reference may be made to the description in other embodiments.

[0068] The above embodiments merely illustrate the implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A broad absorption bend-resistant optical fiber, characterized in that: It includes a core layer, a first cladding layer, a second cladding layer, a third cladding layer and a coating layer which are arranged in sequence from the inside to the outside along the radial direction; The relative refractive index difference Δn1 of the core layer relative to the first cladding is 0.15%~0.45%, the relative refractive index difference Δn2 of the second cladding relative to the third cladding is 0.06%~0.35%, the relative refractive index difference Δn3 of the core layer relative to the second cladding is 0.06%~0.14%, and the relative refractive index difference Δn4 of the third cladding relative to the coating layer is greater than 5.6%.

2. The broad absorption bend-resistant optical fiber according to claim 1, characterized in that The numerical aperture NA1 of the core layer relative to the first cladding is 0.08~0.14, the numerical aperture NA2 of the second cladding relative to the third cladding is 0.05~0.12, the numerical aperture NA3 of the core layer relative to the second cladding is 0.05~0.075, and the numerical aperture NA4 of the third cladding relative to the coating layer is greater than 0.

46.

3. The broad absorption bend-resistant optical fiber according to claim 1, wherein: The diameter of the core layer is 10~30um, the thickness of the first cladding is 2~10um, the thickness of the second cladding is 8~50um, the diameter of the third cladding is 125~1000um, and the diameter of the coating layer is 235~1400um.

4. The broad absorption bend-resistant optical fiber according to claim 1, wherein: The refractive index of the core layer is greater than that of the second cladding, the refractive index of the second cladding is greater than that of the first cladding, the refractive index of the third cladding is less than or equal to that of the first cladding, and the refractive index of the coating layer is less than that of the third cladding.

5. The broad absorption bend-resistant optical fiber according to claim 1, wherein: The material of the core layer is gain-doped quartz, the material of the second cladding is any one of germanium-doped quartz, aluminum-doped quartz and phosphorus-doped quartz, the materials of the first cladding and the third cladding are both quartz matrix glass, and the material of the coating layer is resin material.

6. The broad absorption bend-resistant optical fiber according to claim 5, characterized in that The incident wavelength of the broad absorption bend-resistant optical fiber is 1 μm, the material of the core layer is ytterbium-doped aluminum phosphosilicate glass, and the phosphorus doping concentration of the core layer is 8-20 mol%.

7. The broad absorption bend-resistant optical fiber according to claim 5, characterized in that: The incident wavelength passing through the broad absorption bend-resistant optical fiber is 2 μm, and the material of the core layer is thulium-doped silica glass.

8. The broad absorption bend-resistant optical fiber according to claim 1, wherein: The cross-sections of the core layer, the first cladding layer, and the coating layer along the perpendicular radial direction are all circular, and the cross-sections of the second cladding layer and the third cladding along the perpendicular radial direction are any one of a circle and a regular polygon.

9. The broad absorption bend-resistant optical fiber according to claim 1, wherein: The broad absorption bend-resistant optical fiber is an active optical fiber or a passive optical fiber.

10. A fiber laser module, characterized in that: The invention comprises a non-wave-locked pump unit, a beam combining unit, a high-reflection grating, a gain fiber, a low-reflection grating, a cladding light stripper and a laser output head connected in sequence along the transmission direction from the signal input end to the signal output end, wherein the gain fiber is the broad absorption bend-resistant fiber according to any one of claims 1 to 9.

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