A wide-absorption anti-bending optical fiber and an optical fiber laser module

Abstract

The application provides a wide-absorption bending-resistant optical fiber and an optical fiber laser module, the wide-absorption bending-resistant optical fiber comprises, from inside to outside along a radial direction, a core layer, a first cladding layer, a second cladding layer, a third cladding layer and a coating layer, wherein a relative refractive index difference Δn1 of the core layer relative to the first cladding layer is 0.15% to 0.45%, a relative refractive index difference Δn2 of the second cladding layer relative to the third cladding layer is 0.06% to 0.35%, a relative refractive index difference Δn3 of the core layer relative to the second cladding layer is 0.06% to 0.14%, and a relative refractive index difference Δn4 of the third cladding layer relative to the coating layer is greater than 5.6%. The wide-absorption bending-resistant optical fiber can be endowed with a wide-range stray light absorption capacity and excellent bending resistance through careful design of the relative refractive index difference between layers, and meanwhile, high compatibility and reliability are ensured.

Description

Technical Field

[0001] This invention relates to the field of gain fiber, and more particularly to a wide-absorption, bend-resistant fiber and a fiber laser module. Background Technology

[0002] In fiber laser systems, unlocked wavelength 915nm and 976nm semiconductor lasers are typically used as pump sources to pump the gain fiber. However, the output wavelength of an unlocked 915nm semiconductor laser is usually between 900 and 930nm, and that of an unlocked 976nm semiconductor laser is usually between 950 and 1000nm. Since the absorption of gain fiber across a wide spectrum is generally unstable, when the wavelength of the pump source laser changes, the overall absorption rate of the gain fiber to the pump source changes significantly, resulting in a large amount of pump light not being absorbed. This problem affects the stability of the fiber laser's output power; furthermore, the excess pump light is converted into a large amount of waste heat in downstream devices, causing significant thermal stress and wasting considerable optical energy.

[0003] Highly phosphorus-doped gain fibers exist on the market, exhibiting relatively stable absorption of pump light in the 900-1000nm wavelength range. However, high phosphorus doping also results in a higher numerical aperture (NAP) in the fiber core. A higher NAP leads to a lower transverse mode instability threshold and poorer beam quality, consequently affecting the final output power and beam processing performance of the fiber laser—a desirable outcome in laser applications. Furthermore, in laser processing, when the fiber is bent, the optical signal within the fiber core is easily spun out, causing signal leakage. Generally, the smaller the bending radius, the more severe the leakage. A small bending diameter can lead to instability and even failure during optical power transmission. Therefore, bending resistance is a crucial indicator for evaluating fiber performance. Poor bending resistance limits the overall size of the laser, resulting in a relatively large overall size for current fiber lasers and hindering the miniaturization of high-power lasers.

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

[0005] The purpose of this invention is to provide a wide-absorption, bend-resistant optical fiber and a fiber laser module to solve the technical problems of poor absorption stability and poor bend resistance of existing gain optical fibers across a wide spectrum.

[0006] To solve the above-mentioned technical problems, the present invention first provides a wide absorption bending-resistant optical fiber, comprising a core layer, a first cladding layer, a second cladding layer, a third cladding layer and a coating layer arranged radially from the inside to the outside; Among them, the relative refractive index difference Δn1 between the core layer and the first cladding layer is 0.15%~0.45%, the relative refractive index difference Δn2 between the second cladding layer and the third cladding layer is 0.06%~0.35%, the relative refractive index difference Δn3 between the core layer and the second cladding layer is 0.06%~0.14%, and the relative refractive index difference Δn4 between the third cladding layer and the coating layer is >5.6%.

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

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

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

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

[0011] Preferably, the incident wavelength of the wide-absorption, bend-resistant optical fiber is 1 μm, the core layer is made of ytterbium aluminum phosphide silicon glass, and the phosphorus doping concentration of the core layer is 8~20 mol.

[0012] Preferably, the incident wavelength of the wide-absorption, bend-resistant optical fiber is 2 μm, and the core layer is made of thulium-doped silicon glass.

[0013] Preferably, the cross-sections of the core layer, the first cladding layer, and the coating layer along the vertical radial direction are all circular, and the cross-sections of the second cladding layer and the third cladding layer along the vertical radial direction are either circular or regular polygonal.

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

[0015] Accordingly, the present invention also provides a fiber laser module, comprising a non-locked pump unit, a beam combiner unit, a high-reflection grating, a gain fiber, a low-reflection grating, a cladding 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 this invention are as follows: Unlike existing technologies, this invention provides a wide-absorption, bend-resistant optical fiber and a fiber laser module. The wide-absorption, bend-resistant optical fiber includes a core layer, a first cladding layer, a second cladding layer, a third cladding layer, and a coating layer arranged radially from the inside out. The relative refractive index difference Δn1 between the core layer and the first cladding layer is 0.15%~0.45%, the relative refractive index difference Δn2 between the second cladding layer and the third cladding layer is 0.06%~0.35%, the relative refractive index difference Δn3 between the core layer and the second cladding layer is 0.06%~0.14%, and the relative refractive index difference Δn4 between the third cladding layer and the coating layer is >5.6%. This invention provides... This invention achieves multiple performance enhancements through carefully designed relative refractive index differences between layers: the low relative refractive index difference Δn1 between the core layer and the first cladding expands the single-mode transmission window, reduces nonlinear effects, and enhances light field diffusion and bending resistance; the low relative refractive index difference Δn2 between the second and third claddings acts as a mode filter and stress relief layer, reducing stress concentration between claddings; the relative refractive index difference Δn3 between the core layer and the second cladding forms a "refractive index barrier," suppressing light leakage to the first cladding and reducing bending loss; and the ultra-high relative refractive index difference Δn4 between the third cladding and the coating layer, combined with the light absorption characteristics of the coating layer, forcibly absorbs leaked light, avoiding stray light interference. This invention, through careful design of the relative refractive index differences between layers, endows the optical fiber with a wide range of stray light absorption capabilities and excellent bending resistance, while ensuring high compatibility and reliability. Attached Figure Description

[0017] Figure 1 A schematic diagram of the cross-sectional structure and refractive index distribution of a wide-absorption, bend-resistant optical fiber provided in an embodiment of the present invention; Figures 2a-2d A schematic diagram of the cross-sectional structure of a wide-absorption, bend-resistant optical fiber provided in other different embodiments of the present invention; Figure 3 A schematic diagram of the cross-sectional structure and refractive index distribution of the 14 / 20 / 50 / 250 wide absorbent bend-resistant optical fiber provided in Embodiment 1 of the present invention; Figure 4 This is the absorption spectrum of a conventional ytterbium-doped optical fiber. Figure 5 Absorption spectrum of the 14 / 20 / 50 / 250 wide absorbent bend-resistant optical fiber provided in Embodiment 1 of the present invention; Figure 6This is a schematic diagram of the optical path structure of the fiber laser module provided in Embodiment 1 of the present invention; Figure 7 This is a schematic diagram of the optical path structure of the fiber laser module provided in Embodiment 2 of the present invention; In the attached diagram: 1000 – Fiber laser module; 100 – Wide-absorption, bend-resistant fiber; 10 – Core layer; 20 – First cladding; 30 – Second cladding; 40 – Third cladding; 50 – Coating layer; 200 – Unlocked pump unit; 201 – Unlocked 976nm semiconductor laser; 202 – Unlocked 915nm semiconductor laser; 300 – Beam combiner; 400 – High-reflection grating; 500 – Low-reflection grating; 600 – Cladding optical filter; 700 – Cladding optical filter. Detailed Implementation

[0018] The technical solutions in this embodiment will be clearly and completely described below with reference to this embodiment. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] To address the technical problems of poor absorption stability and inadequate bending resistance in existing gain fibers across a wide spectral band, this invention provides a Wide Absorptivity Bent-resisant Fiber (WAB) and a fiber laser module to solve these issues. This WAB possesses a wide absorption spectrum in the 900–1000 nm range, ensuring stable absorption in the optical path system. It reduces the requirement for the center wavelength of the pump source, allowing for the use of any center wavelength pump source within the 900–1000 nm range or a combination of multiple wavelength pump sources. Simultaneously, the gain fiber core has a low effective refractive index, ensuring high beam quality and a high lateral instability threshold output. The design of the second cladding in the WAB enables the output of a composite beam during laser processing, forming an auxiliary processing beam that reduces metal spatter, controls center melt depth, and facilitates peripheral preheating. The bending-resistant recessed layers (first and third claddings) maintain the fiber's excellent bending resistance, enabling the fiber laser module to achieve high power miniaturization.

[0020] Please see Figure 1 , Figure 1 A schematic diagram of the cross-sectional structure and refractive index distribution of the wide absorption bend-resistant optical fiber 100 provided in an embodiment 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 arranged sequentially from the inside to the outside along the radial direction; Based on the cross-sectional structure of the optical fiber, starting from the fiber core axis and according to the change in transverse refractive index, the layer closest to the axis is defined as the core layer 10. From the inside out, they are the first cladding layer 20, the second cladding layer 30, the third cladding layer 40, and the low refractive index coating layer 50 (e.g., ...). Figure 1 (As shown).

[0021] Specifically, the relative refractive index difference of each layer of the wide-absorption bend-resistant fiber 100 is defined by the following formula (1): ; Where, n i n is the refractive index of the film layer on the side closest to the fiber core layer 10. c The refractive index is the film layer on the side closest to the coating layer 50.

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

[0023] Specifically, the lower relative refractive index difference Δn1 between the core layer 10 and the first cladding layer 20 results in a more uniform light field distribution extending to 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 lasers or broadband signal transmission. Simultaneously, the lower Δn1 increases the critical angle for total internal reflection, making it less prone to light leakage from the interface between the core layer 10 and the first cladding layer 20 due to centrifugal force during bending. The light field diffuses to the first cladding layer 20, utilizing its "buffering effect" to share the bending stress and reduce losses caused by the mechanical deformation directly borne by the core layer 10.

[0024] Specifically, the low relative refractive index difference Δn2 creates a gradually changing refractive index transition, allowing a small amount of leaked light to diffuse into the third cladding 40, but suppressing the transmission of higher-order modes in the cladding (higher-order modes require a higher refractive index difference to maintain total internal reflection), thus reducing energy loss carried by the cladding modes. Simultaneously, 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 small differences in their coefficients of thermal expansion, reducing interlayer stress concentration during fiber drawing. When bent or stretched, microcracks are less likely to form at the interface, improving the mechanical flexibility of the optical fiber.

[0025] Specifically, since the relative refractive index difference Δn1 > relative refractive index difference Δn3, it can be deduced that the refractive index of the first cladding layer 20 is lower than that of the second cladding layer 30, forming a structure of "core → high-refractive-index second cladding layer 30 → low-refractive-index first cladding layer 20". The critical angle for total internal reflection at the interface between the core layer 10 and the second cladding layer 30 is smaller than that at the interface between the core layer 10 and the first cladding layer 20, forcing the light field to be preferentially confined within the core layer 10 and the second cladding layer 30, preventing light leakage to the low-refractive-index first cladding layer 20. At the same time, the low relative refractive index difference Δn3 between the core layer 10 and the second cladding layer 30 limits the effective refractive index range of higher-order modes in the core layer 10, expanding the single-mode transmission window and making it compatible with a wider range of light sources.

[0026] Specifically, a relative refractive index difference Δn4 > 5.6% corresponds to a significant refractive index difference, and the coating layer 50 is often made of a light-absorbing resin material (such as acrylic resin doped with carbon black). Light leaking into the third cladding layer 40 is strongly refracted due to the high Δn4 and forced into the coating layer 50 to be absorbed, which can eliminate more than 95% of stray light back reflection and avoid interference signals. At the same time, the high relative refractive index difference Δn4 can enhance the adhesion to the third cladding layer 40 (achieved through chemical bonding or a rough interface) and improve the peel strength.

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

[0028] In this embodiment of the invention, the numerical pore size NA1 of the core layer 10 relative to the first cladding layer 20 is 0.08~0.14, the numerical pore size NA2 of the second cladding layer 30 relative to the third cladding layer 40 is 0.05~0.12, the numerical pore size NA3 of the core layer 10 relative to the second cladding layer 30 is 0.05~0.075, and the numerical pore size NA4 of the third cladding layer 40 relative to the coating layer 50 is >0.46.

[0029] Specifically, a smaller NA1 concentrates the light field in the fiber core. When the fiber bends, light at the edge of the core layer 10 is less likely to escape the light-guiding area due to centrifugal force, thus reducing bending loss and meeting the requirements of bending resistance design. A smaller NA2 helps suppress the transmission of higher-order modes in the second cladding 30. Combined with the low NA1 design of the core layer 10, this further optimizes the mode field diameter uniformity of the fiber and reduces signal distortion caused by multimode transmission. When the fiber bends, light at the edge of the core layer 10 may leak into the first cladding 20. The low numerical aperture of NA3 can further block this light from entering the second cladding 30, thereby concentrating the light field in the inner structure and reducing energy loss caused by bending. A higher NA4 strengthens the total internal reflection boundary, ensuring that any light entering the third cladding 40 undergoes total internal reflection at the interface and cannot leak into the coating layer 50, thus avoiding energy loss.

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

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

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

[0033] Specifically, the wide-absorption, bend-resistant fiber 100 achieves a dual improvement in optical transmission performance and mechanical properties through a refractive index gradient design (core > second cladding 30 > first cladding 20 ≥ third cladding 40 > coating layer 50). The high-refractive-index core layer 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 loss and suppressing light leakage; the low-refractive-index design of the third cladding 40 and the coating layer 50, combined with the light absorption characteristics of the coating layer 50, forcibly absorbs stray light and improves signal purity; the refractive index matching of each layer reduces interlayer stress and enhances the fiber's bending and tensile mechanical properties, making it suitable for multiple scenarios such as communication, laser processing, and medical applications, while taking into account both optical stability and environmental adaptability.

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

[0035] Specifically, when the incident wavelength of the wide-absorption bend-resistant optical fiber 100 is 1 μm, the core layer 10 is made of ytterbium aluminum phosphide silicon glass, and the phosphorus doping concentration of the core layer 10 is 8~20 mol%; when the incident wavelength of the wide-absorption bend-resistant optical fiber 100 is 2 μm, the core layer 10 is made of thulium silicon glass.

[0036] In this embodiment of the invention, 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, and the cross-sections of the second cladding layer 30 and the third cladding layer 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 the first cladding layer 20 ensure uniform mode field distribution during light transmission, reduce scattering loss caused by irregular shapes, and maintain signal transmission stability. The second cladding layer 30 and the third cladding layer 40 can be circular or regular polygonal. If regular polygons are used, the reflection path of light in the cladding can be changed through the asymmetric structure, suppressing cladding mode transmission, reducing stray light interference, and improving signal purity. In terms of mechanical performance, the regular polygonal second cladding layer 30 and the third cladding layer 40 can increase interlayer friction and contact area, enhance the bonding force between layers, and make the fiber less prone to interlayer misalignment during bending and stretching. At the same time, the polygonal structure can be tightly stacked during fiber cabling, effectively utilizing space and increasing the integration density of the optical cable.

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

[0039] Please see Figures 2a-2d , Figures 2a-2d This is a schematic diagram of the cross-sectional structure of the wide-absorption, bend-resistant optical fiber 100 provided in other different embodiments of the present invention; wherein, Figure 2a In the middle: the cross-section of the fiber 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 is circular; Figure 2b In the middle: the cross-sections of the fiber 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 In the middle: the cross-sections of the fiber 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 In the middle: the cross-sections of the fiber 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 square, and the cross-section of the third cladding layer 40 along the vertical radial direction is regular octagonal.

[0040] Accordingly, the present invention also provides a fiber laser module 1000, comprising a non-locked pump unit 200, a beam combiner 300, a high-reflectivity grating 400, a gain fiber, a low-reflectivity grating 500, a cladding stripper 600, and a laser output head 700 connected sequentially 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 100.

[0041] Specifically, the fiber laser module 1000 achieves multifaceted performance improvements by integrating a wide-absorption, bend-resistant gain fiber and high-efficiency optical components: the wide absorption characteristics enable the gain fiber to efficiently couple unlocked pump light, and the beam combiner 300 enhances the light-to-light conversion efficiency; the bend-resistant design allows for compact, curved fiber cabling, adapting to modular integration; the high-reflectivity grating 400 and the low-reflectivity grating 500 form a stable resonant cavity, ensuring high output laser beam quality and narrow linewidth; the cladding stripper 600 effectively removes stray light and residual pump light, improving signal purity and optimizing thermal management; the overall modular design is compatible with existing processes, suitable for industrial processing, medical, and scientific research scenarios, and combines high power, high stability, and environmental adaptability. In principle, all optical fiber structures described in this invention fall within the scope of protection of this invention, including active optical fibers, passive optical fibers, tapered optical fibers, etc. Optical fibers of various specifications can be stably produced in batches using the method of this invention, therefore the invention is not limited to the examples exemplified herein.

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

[0043] Example 1: Please see Figure 3 , Figure 3 A schematic diagram of the cross-sectional structure and refractive index distribution of the 14 / 20 / 50 / 250 wide-absorption bend-resistant optical fiber 100 provided in Embodiment 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 arranged sequentially from the inside to the outside along the radial direction; The relative refractive index difference Δn1 between the core layer 10 and the first cladding layer 20 is 0.15%~0.45%, the relative refractive index difference Δn2 between the second cladding layer 30 and the third cladding layer 40 is 0.06%~0.35%, the relative refractive index difference Δn3 between the core layer 10 and the second cladding layer 30 is 0.06%~0.14%, and the relative refractive index difference Δn4 between the third cladding layer 40 and the coating layer 50 is >5.6%.

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

[0045] Please see Figure 4 and Figure 5 , Figure 4 This is the absorption spectrum of a conventional ytterbium-doped optical fiber. Figure 5 The absorption spectrum of the 14 / 20 / 50 / 250 wide absorbent bend-resistant optical fiber 100 provided in Embodiment 1 of the present invention; wherein, by Figure 4 and Figure 5 It can be seen that the 4 / 20 / 50 / 250 wide-absorption bend-resistant fiber 100 has a significantly higher absorption value in the 900~1000nm wavelength range than 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 pump light in the 900~1000nm range through the synergistic effect of large NA cladding structure, high concentration gradient doping, bend-resistant design and multimode pump compatibility. In contrast, conventional ytterbium-doped fiber has a lower absorption efficiency due to its structural symmetry, NA value and doping concentration.

[0046] Please see Figure 6 , Figure 6This is a schematic diagram of the optical path structure of the fiber laser module 1000 provided in Embodiment 1 of the present invention; wherein, Embodiment 1 of the present invention also provides a fiber laser module 1000 with a single positive oscillation structure, including a non-locked wave pump unit 200, a beam combiner unit 300, a high-reflection grating 400, a gain fiber, a low-reflection grating 500, a cladding stripper 600, and a laser output head 700 connected sequentially 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 100.

[0047] Specifically, the non-locked wave pumping unit 200 includes six non-locked wave 976nm 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 Embodiment 1 of this invention uses a non-wavelocked semiconductor laser with a center wavelength of 976 nm as the pump source. Its output center wavelength gradually increases from 960 nm to 976 nm as the temperature rises. Because the wide-absorption, bend-resistant fiber 100 has a wide absorption spectrum in the 900 nm to 1000 nm range, it is minimally affected by changes in the pump source center wavelength. This results in the fiber laser module 1000 possessing advantages such as high power miniaturization, wide pump absorption, and the ability to output composite beams.

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

[0050] Table 1. Optical efficiency of output light from wide-absorption, bend-resistant fiber 100 and ordinary 14 / 250 fiber.

[0051] Table 2 Output Power of Wide Absorption Bending-Insensitive Fiber 100 and Ordinary 14 / 250 Fiber

[0052] Table 3. Surface temperature of cladding stripper 600 when using wide-absorption, bend-resistant fiber 100 and ordinary 14 / 250 fiber optic connections. Specifically, as shown in Tables 1 and 2, the wide-absorption, bend-resistant fiber 100 of this embodiment 1 has a strong adaptability to pump sources compared with ordinary double-clad ytterbium-doped fiber, has a high efficiency in pump light energy utilization, and the final output light has stable optical efficiency and output power, which is significantly superior to ordinary 14 / 250 fiber.

[0053] As shown in Table 3, the ordinary 14 / 250 fiber in the prior art has unstable absorption in the 960~976nm range. When using a non-locked wavelength 976nm semiconductor laser as a pump source, the gain fiber does not fully absorb the pump light when the center wavelength of the pump source output is not 976nm, resulting in a large amount of residual pump light leakage. This residual pump light is eventually filtered out by the cladding stripper 600. On the one hand, this leads to insufficient pump energy utilization and unstable laser output power; on the other hand, the large amount of residual pump light generates a lot of waste heat in the cladding stripper 600, endangering equipment safety. Meanwhile, because less residual pump light is generated after the pump light passes through the wide-absorption, bend-resistant fiber 100, the temperature of the cladding stripper 600 is more stable. Using the wide-absorption, bend-resistant fiber 100 has a significant advantage in improving the device stability of the cladding stripper 600.

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

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

[0056] Please see Figure 7 , Figure 7This is a schematic diagram of the optical path structure of the fiber laser module 1000 provided in Embodiment 2 of the present invention; wherein, Embodiment 2 of the present invention also provides a fiber laser module 1000 with a single positive oscillation structure, including a non-locked wave pump unit 200, a beam combiner unit 300, a high-reflection grating 400, a gain fiber, a low-reflection grating 500, a cladding stripper 600, and a laser output head 700 connected sequentially 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 100.

[0057] Specifically, the non-wave-locked pump unit 200 includes three non-wave-locked 915nm 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 Embodiment 2 of the present invention uses a non-wavelocked semiconductor laser with a center wavelength of 976 nm as the pump source, and its output center wavelength gradually increases from 960 nm to 976 nm as the temperature rises. Since the wide-absorption, bend-resistant fiber 100 has a wide absorption spectrum in the range of 900 nm to 1000 nm, it is minimally affected by changes in the center wavelength of the pump source. As a result, the fiber laser module 1000 has advantages such as high power miniaturization, wide pump absorption, and the ability to output composite beams.

[0059] Currently, the minimum allowable bending diameter of commercially available ordinary 14 / 250 optical fibers is >10cm. A bending diameter smaller than 10cm will cause optical waveguide failure, resulting in significant signal light leakage into the fiber cladding, which is eventually stripped by the cladding stripper 600. This leads to reduced laser output power and the generation of substantial waste heat. Therefore, to verify the excellent bending resistance of the wide-absorption, bend-resistant optical fiber 100 provided in Embodiment 2, multiple sets of optical fibers with different minimum bending diameters were coiled and connected to... Figure 7 The output power of the fiber laser module 1000 was tested to characterize the bending resistance of the wide-absorption, bend-resistant fiber 100 provided in Example 2. During this process, other conditions were kept consistent to avoid the influence of other factors. For comparison, a fiber laser module 1000 fabricated using ordinary 14 / 250 (core diameter 14 μm, cladding diameter 250 μm) double-clad ytterbium-doped fiber of the same length and bending diameter was compared with the wide-absorption, bend-resistant 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 bending diameters. As shown in Table 4, the output power of the wide-absorption bend-resistant fiber 100 provided in Example 2 remains unchanged under different minimum bending diameters, while the output power of the ordinary 14 / 250 double-clad ytterbium-doped fiber gradually decreases as the minimum bending diameter gradually decreases. This indicates that the wide-absorption bend-resistant fiber 100 provided in Example 2 has better bend resistance than the ordinary 14 / 250 double-clad ytterbium-doped fiber and has a significant advantage over the ordinary 14 / 250 double-clad ytterbium-doped fiber.

[0061] In existing technologies, conventional large-mode-field double-clad ytterbium-doped fibers do not possess good bending resistance, and the applicable bending depth is typically greater than 10 cm. High-power fiber lasers cannot be miniaturized; if the gain fiber or matching passive fiber experiences even a small bend, waveguide failure will occur, leading to a reduction in laser output power. The wide-absorption, bend-resistant fiber 100 provided by this invention exhibits excellent bending resistance, enabling the miniaturization of high-power fiber lasers. One application is as a gain medium for high-power ytterbium-doped fiber lasers. In this application, the minimum bending diameter of the wide-absorption, bend-resistant fiber 100 provided by this invention can be as low as 5 cm, effectively solving the problem of the large size of currently available high-power fiber lasers.

[0062] This invention provides a wide-absorption, bend-resistant optical fiber 100 capable of mass production. This fiber 100 exhibits a stable absorption rate in the 900-1000 nm range and excellent bend resistance. This fiber aims to address the mutually restrictive issues in related fiber laser technologies, such as wide-spectrum absorption, low numerical aperture, high lateral instability threshold, and good bend resistance.

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

[0064] Unlike existing technologies, the wide-absorption, bend-resistant optical fiber 100 provided by this invention has the following advantages: (1) The wide-absorption, bend-resistant fiber 100 of the present invention has a wide absorption spectrum, which allows for pumping with any pump source of 900~1000nm in laser applications without generating a large amount of residual pump light, thereby improving the energy utilization rate of fiber pump light. Multiple semiconductor lasers with different center wavelengths can be used as pump sources, reducing the requirements for the center wavelength and stability of the pump source, lowering environmental requirements, and further saving on usage costs.

[0065] (2) The wide-absorption bend-resistant fiber 100 of the present invention has a low core effective refractive index, which enables large mode field diameter, high lateral instability threshold and good beam quality output. Furthermore, due to the design of the fiber structure, it has good bend resistance, which solves the problem of mutual constraints between large mode field diameter, high lateral instability threshold and miniaturized bending, allowing the fiber to bend even less without affecting its performance, and has the advantage of miniaturization of high-power lasers.

[0066] (3) When the wide absorption bend-resistant optical fiber 100 of the present invention is used for laser processing, it can output a composite light spot to form an auxiliary processing light, which can reduce metal processing spatter, control the central melting depth, and preheat the periphery.

[0067] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

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

Claims

1. A wide-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 arranged radially from the inside to the outside; Wherein, the relative refractive index difference Δn1 between the core layer and the first cladding layer is 0.15%~0.45%, the relative refractive index difference Δn2 between the second cladding layer and the third cladding layer is 0.06%~0.35%, the relative refractive index difference Δn3 between the core layer and the second cladding layer is 0.06%~0.14%, and the relative refractive index difference Δn4 between the third cladding layer and the coating layer is >5.6%.

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

46.

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

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

5. The wide-absorption, bend-resistant optical fiber according to claim 1, characterized in that, The core layer is made of gain-doped quartz, the second cladding layer is made of any one of germanium-doped quartz, aluminum-doped quartz, and phosphorus-doped quartz, the first cladding layer and the third cladding layer are both made of quartz matrix glass, and the coating layer is made of resin.

6. The wide-absorption, bend-resistant optical fiber according to claim 5, characterized in that, The incident wavelength of the wide-absorption, bend-resistant optical fiber is 1 μm, and the core layer is made of ytterbium aluminum phosphide silicon glass with a phosphorus doping concentration of 8~20 mol.

7. The wide-absorption, bend-resistant optical fiber according to claim 5, characterized in that, The incident wavelength of the wide-absorption, bend-resistant optical fiber is 2 μm, and the core layer is made of thulium-doped silicon glass.

8. The wide-absorption, bend-resistant optical fiber according to claim 1, characterized in that, The cross-sections of the fiber core layer, the first cladding layer, and the coating layer along the vertical radial direction are all circular, and the cross-sections of the second cladding layer and the third cladding layer along the vertical radial direction are either circular or regular polygonal.

9. The wide-absorption, bend-resistant optical fiber according to claim 1, characterized in that, The wide-absorption, bend-resistant optical fiber can be an active or passive optical fiber.

10. A fiber laser module, characterized in that, The device includes a non-locked wave pump unit, a beam combiner unit, a high-reflection grating, a gain fiber, a low-reflection grating, a cladding stripper, and a laser output head, which are connected sequentially along the transmission direction from the signal input end to the signal output end. The gain fiber is a wide-absorption, bend-resistant fiber as described in any one of claims 1 to 9.

Images