Rare earth-doped Anti-resonant hollow-core optical fiber
By designing rare-earth-doped anti-resonant hollow fiber and utilizing the air core region and anti-resonant tube structure, the mode instability problem caused by the heating of the rare-earth layer was solved, and laser gain and stable transmission were achieved.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ZHONGTIAN TECH ADVANCED MATERIALS CO LTD
- Filing Date
- 2025-07-25
- Publication Date
- 2026-06-04
AI Technical Summary
In existing rare-earth-doped optical fibers, the rare-earth layer heats up during laser transmission, leading to uneven density and resulting in mode instability.
A rare-earth-doped anti-resonant hollow fiber structure is adopted. By setting the cladding and multiple anti-resonant tubes, the fiber core region is filled with air. The rare-earth-doped tubes amplify the laser, and the laser is coupled into the fiber core region for propagation through the first refraction tube, thus avoiding the propagation of the laser on the rare-earth-doped tubes.
This improved laser gain and reduced the possibility of mode instability during laser transmission, thereby enhancing the stability and signal quality of laser transmission.
Smart Images
Figure CN2025110543_04062026_PF_FP_ABST
Abstract
Description
Rare earth-doped anti-resonant hollow fiber
[0001] This application claims priority to Chinese Patent Application No. 202411719427.7, filed on November 28, 2024, entitled “Rare-earth-doped anti-resonant hollow optical fiber”, the entire contents of which are incorporated herein by reference. Technical Field
[0002] This application relates to the field of optical fiber technology, and in particular to a rare-earth-doped anti-resonant hollow optical fiber. Background Technology
[0003] Fiber lasers are lasers that use rare-earth-doped optical fibers as the gain medium. Due to their advantages such as high electro-optical conversion efficiency, good beam quality, and small size, they have been widely used in industrial manufacturing and medical fields.
[0004] In existing technologies, rare earth-doped optical fibers are typically formed by doping one or more rare earth elements into a high-purity silica matrix to create a rare earth layer. The gain mechanism caused by the doped rare earth elements can achieve laser gain, and the amplified laser is transmitted within the rare earth layer.
[0005] However, lasers cause the rare earth layer to heat up, resulting in uneven density of the rare earth layer and thus producing mode instability effects. Summary of the Invention
[0006] This application provides a rare-earth-doped anti-resonant hollow fiber that can achieve laser gain and reduce the possibility of mode instability during laser transmission.
[0007] The rare-earth-doped anti-resonant hollow optical fiber provided in this application includes a cladding and multiple anti-resonant tubes. The cladding includes a first refractive tube and a rare-earth-doped tube sleeved on the first refractive tube.
[0008] Each anti-resonant tube is arranged sequentially at intervals on the inner wall of the first refractive tube, and the anti-resonant tubes together form the fiber core region, which is used to transmit laser light.
[0009] The rare-earth-doped tube is used to amplify the laser, and the first refractive tube is used to couple the amplified laser into the fiber core region.
[0010] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application has each anti-resonant tube having its axial direction parallel to that of the first refractive tube, and the tubes are arranged at uniform intervals around the circumference of the first refractive tube.
[0011] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application has a germanium-doped tube as the first refractive tube.
[0012] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application has a germanium content that decreases sequentially from the outer to the inner side of the germanium-doped tube.
[0013] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application has a number of anti-resonant tubes greater than or equal to 4 and less than or equal to 16.
[0014] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application further includes a second refractive tube and a coating layer in its cladding. The second refractive tube is sleeved on the rare-earth-doped tube, and the coating layer is disposed on the outer surface of the second refractive tube.
[0015] A pure quartz layer is placed between the rare earth-doped tube and the second refracting tube. The second refracting tube and the pure quartz layer are used to reflect the pump light.
[0016] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application has a fluorine-doped quartz tube as the second refractive tube.
[0017] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application has a polygonal outer wall of a fluorine-doped quartz tube.
[0018] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application has a coating layer comprising a first coating layer and a second coating layer, wherein the first coating layer is located on the side of the second coating layer closer to the second refractive tube.
[0019] In one possible implementation, the rare-earth-doped anti-resonant hollow optical fiber provided in this application has a first coating of fluorine-doped acrylic resin and a second coating of acrylic resin.
[0020] The rare-earth-doped antiresonant hollow fiber provided in this application comprises a cladding and multiple antiresonant tubes. The cladding includes a first refractive tube and a rare-earth-doped tube sleeved on the first refractive tube. The antiresonant tubes are sequentially and spaced apart on the inner wall of the first refractive tube, collectively forming a core region for laser transmission. Since the core region is filled with air, it reduces nonlinear effects and ensures the stability of laser transmission. The rare-earth-doped tubes amplify the laser, achieving laser gain. The first refractive tube couples the amplified laser into the core region, allowing the laser to propagate within the core region and preventing propagation along the rare-earth-doped tubes, thereby reducing the possibility of propagation mode instability. Therefore, the rare-earth-doped antiresonant hollow fiber provided in this application can achieve laser gain and reduce the possibility of mode instability during laser transmission. Attached Figure Description
[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0022] Figure 1 is a schematic diagram of the structure of the rare earth-doped anti-resonant hollow optical fiber provided in the embodiment of this application;
[0023] Figure 2 is a schematic diagram of the refractive index of the rare earth-doped anti-resonant hollow optical fiber provided in the embodiments of this application;
[0024] Figure 3 is a transmission loss spectrum of the ytterbium-doped anti-resonant hollow optical fiber provided in the embodiment of this application;
[0025] Figure 4 is a transmission loss spectrum of the erbium-doped anti-resonant hollow optical fiber provided in the embodiment of this application;
[0026] Figure 5 shows the transmission loss spectrum of the thulium-doped anti-resonant hollow optical fiber provided in the embodiment of this application.
[0027] Explanation of reference numerals in the attached figures: 100-cladding; 110-first refractive tube; 120-rare earth doped tube; 130-pure quartz layer; 140-second refractive tube; 150-coating layer; 151-first coating layer; 152-second coating layer; 200-anti-resonant tube; 300-fiber core region.
[0028] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation
[0029] First, those skilled in the art should understand that these embodiments are merely for explaining the technical principles of this application and are not intended to limit the scope of protection of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.
[0030] Secondly, it should be noted that, in the description of this application, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.
[0031] Furthermore, it should be noted that in the description of this application, the terms "upper," "lower," "front," "back," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.
[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.
[0033] As shown in the background section, in existing technologies, rare-earth-doped optical fibers typically involve doping a high-purity silica matrix with one or more rare-earth elements to form a rare-earth layer. Laser gain is achieved through the gain mechanism induced by the doped rare-earth elements, and the amplified laser beam propagates within the rare-earth layer. However, the laser beam causes the rare-earth layer to heat up, resulting in uneven density and thus mode instability.
[0034] Based on this, the rare-earth-doped antiresonant hollow-core optical fiber provided in this application, by setting a cladding and multiple antiresonant tubes, includes a first refractive tube and a rare-earth-doped tube sleeved on the first refractive tube. The antiresonant tubes are sequentially and spaced apart on the inner wall of the first refractive tube, and together they form the fiber core region, which is used to transmit laser light. Since the fiber core region is filled with air, it can reduce nonlinear effects and ensure the stability of laser transmission. The rare-earth-doped tubes are used to amplify the laser light, achieving laser gain. The first refractive tubes are used to couple the amplified laser light into the fiber core region, allowing the laser to propagate within the fiber core region and preventing it from propagating on the rare-earth-doped tubes, thereby reducing the possibility of propagation mode instability. Therefore, the rare-earth-doped antiresonant hollow-core optical fiber provided in this application can achieve laser gain and reduce the possibility of mode instability during laser transmission.
[0035] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The described embodiments are some, but not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.
[0036] Referring to FIG1, the rare earth-doped anti-resonant hollow optical fiber provided in this application includes a cladding 100 and a plurality of anti-resonant tubes 200. The cladding 100 includes a first refractive tube 110 and a rare earth-doped tube 120 sleeved on the first refractive tube 110.
[0037] Each anti-resonant tube 200 is arranged sequentially at intervals on the inner wall of the first refractive tube 110, and the anti-resonant tubes 200 together form the core region 300, which is used to transmit laser light.
[0038] The rare earth-doped tube 120 is used to amplify the laser, and the first refracting tube 110 is used to couple the amplified laser into the fiber core region 300.
[0039] It should be noted that the antiresonator 200 is made of pure quartz. The antiresonator 200 can be a circular tube structure or a nested circular tube structure. The inscribed circle of the antiresonator 200 defines the core region 300. Both the core region 300 and the space inside the antiresonator 200 are filled with air. Compared to traditional solid-core optical fibers that transmit optical signals through glass or other materials, where glass or other materials inevitably cause optical loss and are prone to nonlinear effects, the absorption and scattering losses of air are much lower than those of glass and other materials. Therefore, the core region 300 of this application is made of air, which can reduce optical loss and improve signal transmission speed. In high-power optical transmission, nonlinear effects (such as self-phase modulation, cross-phase modulation, and four-wave mixing) affect signal quality. The nonlinear coefficient of air is much lower than that of glass and other materials; therefore, an air-filled core region 300 can reduce these nonlinear effects, ensure the stability of laser transmission, and improve signal quality.
[0040] It should also be noted that the rare-earth-doped tube 120 is made of rare-earth-doped quartz. Rare-earth elements have specific energy level structures, which can be excited by optical pumping (usually using laser diodes) to bring rare-earth ions to a high energy level. When signal light passes through, the rare-earth ions in the high energy level release energy, thereby amplifying the signal light and achieving laser gain. Because the amount of rare-earth doping is stable and controllable, and the doping area is large, high light conversion efficiency and high cladding absorption performance can be achieved.
[0041] By incorporating a first refractive tube 110 within the rare-earth-doped tube 120, the first refractive tube 110 enables grazing-in coupling of the laser from the side of the cladding 100, allowing the laser to propagate within the core region 300 and preventing propagation along the rare-earth-doped tube 120, thereby reducing the possibility of propagation mode instability. Therefore, the rare-earth-doped antiresonant hollow-core fiber provided in this application achieves both laser gain and laser transmission functions, and the output laser does not cause photothermal heating of the rare-earth-doped tube 120, thus achieving high-power laser output while minimizing mode instability issues.
[0042] It should also be noted that when the rare-earth-doped anti-resonant hollow fiber provided in this application is applied to a laser, high- and low-reflection gratings can be connected at the front and rear ends to form laser output. However, the pump light, which cannot meet the anti-resonance condition, leaks into the cladding 100 of the fiber, which can be filtered out from the cladding 100 during subsequent output.
[0043] In some embodiments, as shown in FIG1, the axial direction of each anti-resonant tube 200 is parallel to the axial direction of the first refractive tube 110, and they are arranged at uniform intervals around the circumference of the first refractive tube 110.
[0044] Understandably, the uniform spacing of the anti-resonant tubes 200 can reduce laser loss during transmission, thereby improving the transmission efficiency of rare-earth-doped anti-resonant hollow optical fibers.
[0045] The uniformly spaced antiresonant tubes 200 also help stabilize the transmission mode in the optical fiber, further reducing the possibility of mode instability.
[0046] In some embodiments, as shown in FIG1, the first refractive tube 110 is a germanium-doped tube.
[0047] The first refractive tube 110 is a germanium-doped tube. In practice, germanium-doped quartz material can be deposited on the inner wall of a pure quartz base tube, and then the pure quartz base tube can be cut and polished to a thickness equal to that of the pure quartz base tube. After polishing, only the deposit remains, thus completing the preparation of the germanium-doped tube.
[0048] It should be noted that germanium-doped quartz, that is, adding germanium to quartz, can increase the refractive index of the first refracting tube 110, so as to couple the laser into the core region 300 for propagation.
[0049] In some embodiments, as shown in FIG1, the germanium content in the germanium-doped tube decreases sequentially from the outer side to the inner side of the germanium-doped tube.
[0050] Specifically, the germanium content decreases sequentially from the outside to the inside of the germanium-doped tube, thereby gradually reducing the refractive index of the first refractive tube 110 from the outside to the inside. That is, the first refractive tube 110 is a graded refractive index tube, so that the laser can be coupled from the side of the cladding 100, thereby further optimizing the coupling and transmission characteristics of the laser.
[0051] It should be noted that when depositing germanium-doped quartz material on the inner wall of a pure quartz tube, the germanium content in the germanium-doped quartz material can be gradually reduced to achieve a sequential decrease in the germanium content in the germanium-doped tube.
[0052] It should also be noted that both the outer and inner walls of the first refracting tube 110 can be circular.
[0053] In some embodiments, the rare earth-doped tube 120 contains rare earth elements, and the total concentration of rare earth elements is 300 ppm to 5000 ppm.
[0054] It is understandable that the rare earth-doped tube 120 contains rare earth elements, which can achieve optical amplification and laser gain in optical fibers. In specific implementations, the rare earth-doped tube 120 can be made of rare earth elements such as ytterbium, erbium, thulium, and holmium, or other rare earth elements. This application does not impose too many restrictions on this.
[0055] It should be noted that both the outer and inner walls of the rare earth-doped pipe 120 can be circular.
[0056] In practical implementation, the concentration of rare earth elements can be determined according to the type of rare earth element, so that the rare earth-doped tube 120 can achieve the effect of laser gain.
[0057] In some embodiments, as shown in FIG1, the number of anti-resonant transistors 200 is greater than or equal to 4 and less than or equal to 16.
[0058] Understandably, through the anti-resonance effect, the wall of the anti-resonant tube 200 can reflect light of a specific wavelength, limiting the transmission of laser light within the fiber core region 300. The number of anti-resonant tubes 200, ranging from 4 to 16, can provide a good confinement effect, reducing laser leakage into the cladding 100, thereby reducing transmission loss, resulting in better fiber transmission performance, and ensuring ease of fiber manufacturing.
[0059] Specifically, each anti-resonant tube 200 can be attached to the inner wall of the first refractive tube 110 at equal intervals, and each anti-resonant tube 200 does not contact each other.
[0060] In some embodiments, as shown in FIG1, the cladding 100 further includes a second refractive tube 140 and a coating layer 150, wherein the second refractive tube 140 is sleeved on the rare earth-doped tube 120 and the coating layer 150 is disposed on the outer surface of the second refractive tube 140.
[0061] A pure quartz layer 130 is disposed between the rare earth-doped tube 120 and the second refracting tube 140. The second refracting tube 140 and the pure quartz layer 130 are used to reflect pump light.
[0062] A second refractive tube 140 is provided on the outer surface of the pure quartz layer 130 so that most of the pump light is reflected at the interface between the pure quartz layer 130 and the second refractive tube 140, reducing the reflection of high power density pump light at the interface between the fragile coating layer 150 and the second refractive tube 140, avoiding the impact of high power density energy on the coating layer 150, thereby improving the stability and reliability of optical fiber transmission.
[0063] In some embodiments, as shown in FIG1, the second refracting tube 140 is a fluorine-doped quartz tube.
[0064] Understandably, the second refracting tube 140 is a fluorine-doped quartz tube, meaning that the material of the second refracting tube 140 is fluorine-doped quartz. The refractive index of the fluorine-doped quartz tube is lower than that of the pure quartz tube, so the fluorine-doped quartz tube can form a more effective beam confinement structure, so that most of the pump light is reflected at the interface between the pure quartz layer 130 and the second refracting tube 140.
[0065] In some embodiments, as shown in FIG1, the outer wall of the fluorine-doped quartz tube is polygonal.
[0066] The outer wall of the fluorine-doped quartz tube is polygonal, meaning it has multiple sides. For example, the outer wall of the fluorine-doped quartz tube can have 5 to 10 sides, but this embodiment does not impose excessive limitations on this. It is understood that the polygonal shape can enhance the reflection effect and further limit the reflection of pump light at the interface between the pure quartz layer 130 and the second refracting tube 140.
[0067] It should be noted that the inner wall of a fluorine-doped quartz tube can be circular.
[0068] In some embodiments, as shown in FIG1, the coating layer 150 includes a first coating layer 151 and a second coating layer 152, wherein the first coating layer 151 is located on the side of the second coating layer 152 near the second refractive tube 140.
[0069] Understandably, the double coating of the first coating 151 and the second coating 152 can enhance the mechanical strength and durability of the optical fiber.
[0070] In some embodiments, as shown in FIG1, the first coating 151 is a fluorinated acrylic resin layer and the second coating 152 is an acrylic resin layer.
[0071] Specifically, the first coating 151 is a fluorinated acrylic resin layer, which has good chemical corrosion resistance and can effectively protect the optical fiber from chemical corrosion, improving its service life in harsh environments. Furthermore, the fluorinated acrylic resin layer also has good moisture-proof properties, preventing moisture from penetrating the optical fiber and protecting its optical performance. The second coating 152 is an acrylic resin layer, which has good UV resistance and can protect the optical fiber from UV radiation damage, extending its service life.
[0072] In some embodiments, the diameter of the core region 300 can be 10–120 μm, the ratio of the outer diameter of the anti-resonant tube 200 to the diameter of the core region 300 is 0.3–1.2, and the ratio of the inner diameter of the anti-resonant tube 200 to the radius of the core region 300 can be 0.1–1. The wall thickness of the anti-resonant tube 200 can range from 0.1 to 3 μm, and the specific value of the wall thickness is determined by the following method:
[0073] The wall thickness satisfies the anti-resonance condition of the laser. When t1 is the anti-resonant wall thickness, λ1 is the excitation wavelength, m1 is the order of the anti-resonant layer, m1 = 1, 2, 3... (generally not greater than 5), and n is the refractive index of the anti-resonant ring.
[0074] The wall thickness satisfies the resonance condition of the pump light. When t2 is the resonant wall thickness, λ2 is the pump light wavelength, m2 is the resonant layer order, m2 = 1, 2, 3… (generally not greater than 5), and n is the refractive index of the anti-resonant ring. Values of m1 and m2 are taken within the integer range of 1 to 5 (m1 and m2 are not necessarily equal). When the difference between t1 and t2 is minimized, the wall thickness t1 determined by the value of m1 at this point is the wall thickness of the anti-resonant tube 200.
[0075] The relationship between the refractive index n and thickness r at different radial thicknesses from the outside to the inside of the first refracting tube 110 can be described by the following formula: Where n0 is the refractive index of the outermost layer of the first refracting tube 110, a is the thickness of the first refracting tube 110 from the inside to the outside, and Δ is the difference between the refractive index of the outermost layer and the refractive index of the innermost layer of the first refracting tube 110.
[0076] It should be noted that the refractive index of the outermost part of the first refracting tube 110 is not lower than the refractive index of the rare earth-doped tube 120, and the relative difference can be 0 to 0.004. The refractive index difference between the rare earth-doped tube 120 and pure quartz can be 0.0001 to 0.01. The refractive index of the second refracting tube 140 is lower than the refractive index of the pure quartz layer 130, and the relative difference is not less than 0.014. The refractive index of the first coating 151 (fluorinated acrylic resin layer) is lower than the refractive index of the pure quartz layer 130, and the relative difference is not less than 0.08.
[0077] In some embodiments, the inner diameter of the first refractive tube 110 can be 30–215 μm, the outer diameter of the first refractive tube 110 can be 37–260 μm, the outer diameter of the rare earth-doped tube 120 can be 55–375 μm, the outer diameter of the pure quartz layer 130 can be 65–465 μm, the distance between the two opposite sides of the second refractive tube 140 can be 70–490 μm, the outer diameter of the first coating 151 can be 85–590 μm, and the outer diameter of the second coating 152 can be 95–645 μm.
[0078] It should be noted that the thickness of the first refractive tube 110 is not less than 10 μm, the thickness of the rare earth-doped tube 120 is not less than 20 μm, the thickness from the outer wall of the second refractive tube 140 to the pure quartz layer 130 is not less than 5 μm, the thickness between the first coating 151 and the outer wall of the second refractive tube 140 is not less than 20 μm, and the thickness of the second coating 152 is not less than 15 μm.
[0079] The method for fabricating rare-earth-doped anti-resonant hollow optical fiber provided in this application includes:
[0080] S101. Prepare rare earth-doped tube 120 and first refractive tube 110.
[0081] Specifically, to prepare the rare earth-doped tube 120, a pure quartz base tube can be installed on an MCVD device, and then the rare earth-doped quartz material can be deposited on the inner wall of the pure quartz base tube using a "liquid phase method" or a "gas phase method", thereby forming the rare earth-doped tube 120 from the deposited rare earth-doped quartz material.
[0082] It should be noted that MCVD is a modified chemical vapor deposition method, and MCVD equipment is a complete set of equipment for manufacturing optical fiber preforms using the MCVD process. MCVD and MCVD equipment are technologies well known to those skilled in the art, and will not be described in detail here.
[0083] When the cladding 100 includes the second refractive tube 140, the second refractive tube 140 needs to be prepared. Specifically, another pure quartz base tube can be installed on the PCVD equipment, and an appropriate amount of silicon tetrachloride, oxygen, and fluoride gas (any one or more of hexafluoroethane, sulfur hexafluoride, and carbon tetrafluoride) can be introduced into the pure quartz base tube to form a deeply fluorinated layer on the inner wall of the pure quartz base tube. This deeply fluorinated layer is the second refractive tube 140.
[0084] It should be noted that PCVD is plasma chemical vapor deposition, and PCVD equipment is plasma chemical vapor deposition equipment. PCVD and PCVD equipment are technologies well known to those skilled in the art, and will not be described in detail here.
[0085] The second refractive tube 140 is fitted onto the rare-earth-doped tube 120 and installed on a glass lathe for melting and shrinking. The melting and shrinking heating method includes one of a graphite heating furnace, an induction heating furnace, and a ring-shaped gas torch. During melting and shrinking, a vacuum is drawn into the gap between the rare-earth-doped tube 120 and the second refractive tube 140 to ensure that the two are tightly fused together. After the rare-earth-doped tube 120 and the second refractive tube 140 are melted and shrunk, their outer surfaces are ground into regular polygons to form a rare-earth-doped sleeve. The pure quartz base tube located between the rare-earth-doped tube 120 and the second refractive tube 140 forms a pure quartz layer 130.
[0086] Specifically, a first refractive tube 110 is prepared by mounting a pure quartz base tube on a PCVD device and depositing germanium-doped quartz material on the inner wall of the pure quartz base tube. The cross-sectional view of the refractive index of the germanium-doped quartz material is parabolic.
[0087] The pure quartz tube with germanium-doped quartz material deposited is cut and polished on the outer cylindrical grinding window. The polishing thickness is the same as that of the pure quartz tube. The surface roughness after polishing does not exceed Ra0.4. The germanium-doped quartz material left after polishing is the first refractive tube 110.
[0088] It should be noted that the refractive index of the outer wall of the first refractive tube 110 is greater than or equal to the refractive index of the rare earth-doped tube 120.
[0089] S102. Prepare the anti-resonant tube 200 and assemble the anti-resonant tube 200 with the first refractive tube 110 to obtain the primary preform.
[0090] Specifically, the drawn capillary tube (i.e., anti-resonance tube 200) and the first refractive tube 110 are assembled by stacking to form a nested capillary structure, and then welded on a glass lathe using an oxyhydrogen flame, a graphite furnace or other heat source to obtain a primary preform.
[0091] It should be noted that capillary drawing is a technique well-known to those skilled in the art, and will not be described in detail here.
[0092] S103. The primary preform is drawn into a hollow optical fiber intermediate.
[0093] Specifically, the primary preform is drawn into an intermediate body in a graphite drawing furnace, and a section of the intermediate body with stable size and structure is selected for the assembly of the secondary preform.
[0094] S104. Insert the hollow fiber intermediate into the rare earth-doped tube 120, and apply negative pressure to the gap between the hollow fiber intermediate and the rare earth-doped tube 120 to obtain the secondary preform.
[0095] Specifically, the hollow fiber intermediate is inserted into the rare earth-doped sleeve and assembled with the gas-filled mold to ensure that the gap between the hollow fiber intermediate and the rare earth-doped sleeve can be evacuated to obtain the secondary preform.
[0096] It should be noted that the core region 300 of the hollow fiber intermediate, the inner tube and the outer tube of the nested capillary can be independently inflated, and the gap between the inflation tube and the secondary preform is fully sealed by applying heat-resistant adhesive.
[0097] S105. The secondary preform is drawn into a rare-earth-doped anti-resonant hollow optical fiber.
[0098] Specifically, the secondary preform is placed on a drawing tower for drawing. A negative pressure is applied between the hollow fiber intermediate and the rare-earth-doped sleeve. The size and wall thickness of the tubular element are controlled by adjusting the three independent inflation pressures of the hollow fiber core region 300, the inner tube, and the outer tube of the nested capillary, forming a nested anti-resonant loop structure. Then, through a coating and curing device, the inner coating layer 150 is made of fluorine-doped acrylic resin, and the outer coating layer 150 is made of conventional acrylic resin, resulting in the rare-earth-doped anti-resonant hollow fiber.
[0099] It should be noted that the rare-earth-doped anti-resonant hollow optical fiber and its preparation method provided in this application are prepared by stacking pure quartz tubes for the anti-resonant tube 200, by MCVD method for the rare-earth-doped tube 120, and by PCVD method for the second refraction tube 140. The preparation process is simple and mature, can achieve low transmission loss, requires no special processing, and has low preparation cost.
[0100] In some embodiments, referring to FIG1, the ytterbium-doped antiresonant hollow fiber prepared according to the above-described method for preparing rare-earth-doped antiresonant hollow fiber has an antiresonant tube 200 consisting of five nested circular rings. The outer wall of the second refractive tube 140 has a regular octagonal cross-section. The core region 300 has a diameter of 30 μm. The outer ring diameter of the antiresonant tube 200 is 33 μm, the inner ring diameter is 16 μm, and the wall thickness is 0.44 μm. The inner diameter of the first refractive tube 110 is 92.6 μm, the outer diameter is 115 μm, the outer diameter of the rare-earth-doped tube 120 is 168 μm, the outer diameter of the pure quartz layer 130 is 206 μm, the distance between two opposite sides of the second refractive tube 140 is 220 μm, the outer diameter of the first coating 151 is 262 μm, and the outer diameter of the second coating 152 is 295 μm.
[0101] Referring to Figure 2, the concentration of ytterbium in the rare earth-doped tube 120 is 2000 ppm, and the refractive index difference relative to the pure quartz layer 130 is 0.0020. The refractive index of the outer wall of the first refractive tube 110 is the same as that of the rare earth-doped tube 120. The refractive index of the second refractive tube 140 is 0.015 lower than that of the pure quartz layer 130, and the refractive index of the first coating 151 is 0.084 lower than that of the pure quartz.
[0102] As shown in Figure 3, the ytterbium-doped antiresonant hollow-core fiber exhibits a transmission loss of 0.75 dB / km at a wavelength of 1064 nm for the transmitted light, while the pump light at 915 nm is entirely within the resonant band. This indicates that it can achieve good excitation light transmission while suppressing pump light transmission. Laser output testing revealed an optical-to-optical conversion efficiency of 68%, a 915 nm cladding 100 absorption of 4.3 dB / m, and high-power transmission at 10 kW without thermally induced mode instability. Furthermore, no significant darkening was observed after 400 hours of aging.
[0103] In some embodiments, referring to FIG1, the erbium-doped antiresonant hollow fiber prepared according to the above-described method for preparing rare-earth-doped antiresonant hollow fiber has an antiresonant tube 200 consisting of five nested circular rings. The outer wall of the second refractive tube 140 has a regular octagonal cross-section. The core region 300 has a diameter of 30 μm. The outer ring diameter of the antiresonant tube 200 is 33 μm, the inner ring diameter is 31.5 μm, and the wall thickness is 0.48 μm. The inner diameter of the first refractive tube 110 is 92.8 μm, the outer diameter is 120 μm, the outer diameter of the rare-earth-doped tube 120 is 185 μm, the outer diameter of the pure quartz layer 130 is 228 μm, the distance between two opposite sides of the second refractive tube 140 is 250 μm, the outer diameter of the first coating 151 is 300 μm, and the outer diameter of the second coating 152 is 340 μm.
[0104] Referring to Figure 2, the erbium concentration in the rare earth-doped tube 120 is 2500 ppm, and the refractive index difference relative to the pure quartz layer 130 is 0.0050. The refractive index of the outer wall of the first refractive tube 110 is the same as that of the rare earth-doped tube 120. The refractive index of the second refractive tube 140 is 0.015 lower than that of the pure quartz layer 130, and the refractive index of the first coating 151 is 0.084 lower than that of the pure quartz.
[0105] As shown in Figure 4, the erbium-doped antiresonant hollow-core fiber exhibits a transmission loss of 0.39 dB / km at a wavelength of 1530 nm for the transmitted light, while the pump light at 980 nm is entirely within the resonant band. This indicates that good excitation light transmission can be achieved while suppressing pump light transmission. Laser output testing revealed an optical-to-optical conversion efficiency of 40%, a 100% absorption rate in the 980 nm cladding layer, and a 30 mW laser output.
[0106] In some embodiments, referring to FIG1, the thulium-doped antiresonant hollow fiber prepared according to the above-described method for preparing rare-earth-doped antiresonant hollow fiber has an antiresonant tube 200 consisting of five nested circular rings. The outer wall of the second refractive tube 140 has a regular octagonal cross-section. The core region 300 has a diameter of 40 μm. The outer ring diameter of the antiresonant tube 200 is 49 μm, the inner ring diameter is 25 μm, and the wall thickness is 0.76 μm. The inner diameter of the first refractive tube 110 is 158 μm, the outer diameter of the first refractive tube 110 is 185 μm, the outer diameter of the rare-earth-doped tube 120 is 240 μm, the outer diameter of the pure quartz layer 130 is 275 μm, the distance between two opposite sides of the second refractive tube 140 is 295 μm, the outer diameter of the first coating 151 is 340 μm, and the outer diameter of the second coating 152 is 380 μm.
[0107] Referring to Figure 2, the concentration of thulium in the rare earth-doped tube 120 is 3000 ppm, and the refractive index difference relative to the pure quartz layer 130 is 0.015. The refractive index of the outer wall of the first refractive tube 110 is the same as that of the rare earth-doped tube 120. The refractive index of the second refractive tube 140 is 0.015 lower than that of the pure quartz layer 130, and the refractive index of the first coating 151 is 0.084 lower than that of the pure quartz.
[0108] As shown in Figure 5, the thulium-doped antiresonant hollow-core fiber exhibits a transmission loss of 0.88 dB / km at a wavelength of 1950 nm for the transmitted light, while the pump light at 793 nm remains entirely within the resonant band. This indicates that it can achieve good excitation light transmission while suppressing pump light transmission. Laser output testing revealed an optical-to-optical conversion efficiency of 60%, a 100% absorption rate at 793 nm cladding, and no thermally induced mode instability at 1000 W power output. Furthermore, no significant darkening was observed after 400 hours of aging.
[0109] Those skilled in the art will understand that the rare-earth-doped anti-resonant hollow fiber provided in this application, by setting a cladding 100 and multiple anti-resonant tubes 200, includes a first refractive tube 110 and a rare-earth-doped tube 120 sleeved on the first refractive tube 110. Each anti-resonant tube 200 is sequentially and spaced apart on the inner wall of the first refractive tube 110, and together they form a core region 300, which is used to transmit laser light. Since the core region 300 is filled with air, it can reduce nonlinear effects and ensure the stability of laser transmission. The rare-earth-doped tube 120 is used to amplify the laser light, increasing laser gain. The first refractive tube 110 couples the amplified laser light into the core region 300, allowing the laser to propagate within the core region 300 and preventing it from propagating on the rare-earth-doped tube 120, thereby reducing the possibility of propagation mode instability. Therefore, the rare-earth-doped anti-resonant hollow fiber provided in this application can achieve laser gain and reduce the possibility of mode instability during laser transmission.
[0110] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0111] It is understood that the various numerical designations used in the embodiments of this application are merely for descriptive convenience and are not intended to limit the scope of the embodiments of this application.
[0112] The technical solutions of this application have been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of this application is obviously not limited to these specific embodiments. Without departing from the principles of this application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of this application.
Claims
1. A rare-earth-doped anti-resonant hollow optical fiber, characterized in that, It includes a cladding (100) and a plurality of anti-resonance tubes (200), wherein the cladding (100) includes a first refractive tube (110) and a rare earth-doped tube (120) sleeved on the first refractive tube (110); Each of the anti-resonant tubes (200) is arranged sequentially at intervals on the inner wall of the first refractive tube (110), and each of the anti-resonant tubes (200) together forms a core region (300), which is used to transmit laser light; The rare earth-doped tube (120) is used to amplify the laser, and the first refractive tube (110) is used to couple the amplified laser into the fiber core region (300).
2. The rare-earth-doped anti-resonant hollow optical fiber according to claim 1, characterized in that, The axial direction of each of the anti-resonant tubes (200) is parallel to the axial direction of the first refractive tube (110), and they are arranged at uniform intervals around the circumference of the first refractive tube (110).
3. The rare-earth-doped anti-resonant hollow optical fiber according to claim 1, characterized in that, The first refractive tube (110) is a germanium-doped tube.
4. The rare-earth-doped anti-resonant hollow optical fiber according to claim 3, characterized in that, The germanium content in the germanium-doped tube decreases sequentially from the outer side to the inner side of the tube.
5. The rare-earth-doped anti-resonant hollow optical fiber according to any one of claims 1 to 4, characterized in that, The number of anti-resonant tubes (200) is greater than or equal to 4 and less than or equal to 16.
6. The rare-earth-doped anti-resonant hollow optical fiber according to any one of claims 1 to 4, characterized in that, The cladding (100) further includes a second refractive tube (140) and a coating layer (150), wherein the second refractive tube (140) is sleeved on the rare earth-doped tube (120), and the coating layer (150) is disposed on the outer surface of the second refractive tube (140); A pure quartz layer (130) is disposed between the rare earth-doped tube (120) and the second refracting tube (140), and the second refracting tube (140) and the pure quartz layer (130) are used to reflect pump light.
7. The rare-earth-doped anti-resonant hollow optical fiber according to claim 6, characterized in that, The second refracting tube (140) is a fluorine-doped quartz tube.
8. The rare-earth-doped anti-resonant hollow optical fiber according to claim 7, characterized in that, The outer wall of the fluorine-doped quartz tube is polygonal.
9. The rare-earth-doped anti-resonant hollow optical fiber according to claim 6, characterized in that, The coating layer (150) includes a first coating layer (151) and a second coating layer (152), wherein the first coating layer (151) is located on the side of the second coating layer (152) near the second refractive tube (140).
10. The rare-earth-doped anti-resonant hollow optical fiber according to claim 9, characterized in that, The first coating (151) is a fluorinated acrylic resin layer, and the second coating (152) is an acrylic resin layer.