Rare earth doped antiresonant hollow core fiber

Abstract

The present application relates to the field of optical fiber technology, and in particular to a rare earth-doped antiresonant hollow core optical fiber. The rare earth-doped antiresonant hollow core optical fiber comprises a cladding and a plurality of antiresonant tubes, wherein the cladding comprises a first refraction tube and a rare earth-doped tube sleeved on the first refraction tube; each antiresonant tube is sequentially arranged on the inner wall of the first refraction tube at intervals, and each antiresonant tube together forms a core region, which is used to transmit laser; the rare earth-doped tube is used to amplify the laser, and the first refraction tube is used to couple the amplified laser into the core region. The rare earth-doped antiresonant hollow core optical fiber provided by the present application can achieve laser gain and reduce the possibility of mode instability during laser transmission.

Description

Technical Field

[0001] The present application relates to the field of optical fiber technology, and in particular to a rare-earth-doped anti-resonant hollow-core optical fiber. Background Art

[0002] Fiber lasers are lasers that use rare-earth-doped optical fibers as gain media. They have been widely used in industrial manufacturing, medical and other fields due to their high electro-optical conversion efficiency, good beam quality and small size.

[0003] In the prior art, rare earth-doped optical fiber is usually prepared by doping one or more rare earth elements into a high-purity silica matrix to form a rare earth layer. Laser gain can be achieved through the gain mechanism caused by the doped rare earth elements, and the amplified laser is transmitted in the rare earth layer.

[0004] However, the laser will cause the rare earth layer to heat up, making the rare earth layer density uneven, thus producing a mode instability effect. Summary of the invention

[0005] The present application provides a rare earth-doped antiresonant hollow core optical fiber, which can achieve laser gain and reduce the possibility of mode instability during laser transmission.

[0006] The rare-earth-doped anti-resonant hollow-core optical fiber provided in the present application comprises a cladding and a plurality of anti-resonant tubes, wherein the cladding comprises a first refractive tube and a rare-earth-doped tube sleeved on the first refractive tube.

[0007] The anti-resonance tubes are sequentially arranged at intervals on the inner wall of the first refraction tube, and the anti-resonance tubes together form a core area, which is used for transmitting laser light.

[0008] The rare earth-doped tube is used for amplifying laser light, and the first refraction tube is used for coupling the amplified laser light into the fiber core region.

[0009] In a possible implementation, in the rare earth-doped antiresonant hollow core optical fiber provided by the present application, the axial direction of each antiresonant tube is parallel to the axial direction of the first refractive tube, and the antiresonant tubes are uniformly spaced in sequence around the circumference of the first refractive tube.

[0010] In a possible implementation, in the rare-earth-doped antiresonant hollow-core optical fiber provided by the present application, the first refractive tube is a germanium-doped tube.

[0011] In a possible implementation, in the rare-earth-doped antiresonant hollow-core optical fiber provided by the present application, the content of germanium in the germanium-doped tube decreases from the outside to the inside of the germanium-doped tube.

[0012] In a possible implementation, the rare-earth-doped antiresonant hollow-core optical fiber provided by the present application has a number of antiresonant tubes greater than or equal to 4 and less than or equal to 16.

[0013] In a possible implementation, the rare earth-doped antiresonant hollow core optical fiber provided in the present application, the cladding further includes a second refractive tube and a coating layer, the second refractive tube is sleeved on the rare earth-doped tube, and the coating layer is arranged on the outer surface of the second refractive tube.

[0014] A pure quartz layer is arranged between the rare earth-doped tube and the second refractive tube, and the second refractive tube and the pure quartz layer are used for reflecting pump light.

[0015] In a possible implementation, in the rare-earth-doped antiresonant hollow-core optical fiber provided by the present application, the second refractive tube is a fluorine-doped quartz tube.

[0016] In a possible implementation, in the rare-earth-doped antiresonant hollow-core optical fiber provided by the present application, the outer wall of the fluorine-doped quartz tube is polygonal.

[0017] In a possible implementation, the rare earth-doped antiresonant hollow core optical fiber provided by the present application has a coating layer including a first coating layer and a second coating layer, and the first coating layer is located on a side of the second coating layer close to the second refractive tube.

[0018] In a possible implementation, in the rare earth-doped antiresonant hollow core optical fiber provided by the present application, the first coating is a fluorine-doped acrylic resin layer, and the second coating is an acrylic resin layer.

[0019] The rare earth-doped antiresonant hollow core optical fiber provided by the present application is provided with a cladding and a plurality of antiresonant tubes, wherein the cladding includes a first refraction tube and a rare earth-doped tube sleeved on the first refraction tube. The antiresonant tubes are sequentially arranged on the inner wall of the first refraction tube at intervals, and the antiresonant tubes together enclose a core region, which is used to transmit lasers. Since the core region is filled with air, the core region can reduce nonlinear effects and ensure the stability of laser transmission. The rare earth-doped tube is used to amplify the laser and can achieve laser gain. The first refraction tube is used to couple the amplified laser into the core region so that the laser propagates in the core region and avoids the laser propagating on the rare earth-doped tube, thereby reducing the possibility of unstable propagation mode. Therefore, the rare earth-doped antiresonant hollow core optical fiber provided by the present application can achieve laser gain and reduce the possibility of mode instability during laser transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 A schematic diagram of the structure of a rare earth-doped antiresonant hollow core optical fiber provided in an embodiment of the present application;

[0022] Figure 2 A schematic diagram of the refractive index of a rare earth-doped antiresonant hollow core optical fiber provided in an embodiment of the present application;

[0023] Figure 3 Transmission loss spectrum of the ytterbium-doped antiresonant hollow-core optical fiber provided in the embodiment of the present application;

[0024] Figure 4 Transmission loss spectrum of the erbium-doped antiresonant hollow-core optical fiber provided in the embodiment of the present application;

[0025] Figure 5 This is a transmission loss spectrum of the thulium-doped antiresonant hollow-core optical fiber provided in an embodiment of the present application.

[0026] Description of reference numerals:

[0027] 100-cladding; 110-first refraction tube; 120-rare earth-doped tube; 130-pure quartz layer; 140-second refraction tube; 150-coating layer; 151-first coating layer; 152-second coating layer;

[0028] 200-anti-resonance tube;

[0029] 300-fiber core area.

[0030] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0031] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the present application and are not intended to limit the scope of protection of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0032] Secondly, it should be noted that in the description of this application, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, or it can be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0033] Then, it should be noted that, in the description of the present application, the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0034] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0035] As shown in the background technology, in the prior art, rare earth-doped optical fiber is usually formed by doping one or more rare earth elements into a high-purity silica matrix to form a rare earth layer. Laser gain can be achieved through the gain mechanism caused by the doped rare earth elements, and the laser after gain is transmitted in the rare earth layer. However, the laser will cause the rare earth layer to heat up, making the rare earth layer density uneven, thereby generating a mode instability effect.

[0036] Based on this, the rare earth-doped antiresonant hollow core optical fiber provided by the present application is provided with a cladding and a plurality of antiresonant tubes, wherein the cladding includes a first refraction tube and a rare earth-doped tube sleeved on the first refraction tube. The antiresonant tubes are sequentially arranged on the inner wall of the first refraction tube at intervals, and the antiresonant tubes together enclose a core region, which is used to transmit lasers. Since the core region is air, the core region can reduce nonlinear effects and ensure the stability of laser transmission. The rare earth-doped tube is used to amplify the laser and can achieve laser gain. The first refraction tube is used to couple the amplified laser into the core region so that the laser propagates in the core region and avoids the laser propagating on the rare earth-doped tube, thereby reducing the possibility of unstable propagation mode. Therefore, the rare earth-doped antiresonant hollow core optical fiber provided by the present application can achieve laser gain and reduce the possibility of mode instability during laser transmission.

[0037] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described in more detail below in conjunction with the drawings in the preferred embodiments of the present application. In the drawings, the same or similar reference numerals throughout represent the same or similar parts or parts with the same or similar functions. The described embodiments are part of the embodiments of the present application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limitations on the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0038] Reference Figure 1 As shown, the rare-earth-doped antiresonant hollow-core optical fiber provided in the present application includes a cladding 100 and a plurality of antiresonant 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 .

[0039] The anti-resonance tubes 200 are sequentially arranged at intervals on the inner wall of the first refraction tube 110 , and the anti-resonance tubes 200 together form a core region 300 , which is used to transmit laser light.

[0040] The rare earth-doped tube 120 is used to amplify laser light, and the first refraction tube 110 is used to couple the amplified laser light into the fiber core region 300 .

[0041] It should be noted that the antiresonance tube 200 is made of pure quartz, and the antiresonance tube 200 can be a circular tube structure or a nested circular tube structure. The inscribed circle of the antiresonance tube 200 defines the core area 300, and the space inside the core area 300 and the antiresonance tube 200 is air. Compared with the traditional solid core optical fiber that transmits optical signals through glass or other materials, glass or other materials will inevitably cause light loss and easily produce nonlinear effects. Since the absorption and scattering losses of air are much lower than those of materials such as glass, the core area 300 of the present application is air, which can reduce light loss and increase signal transmission speed. In high-power optical transmission, nonlinear effects (such as self-phase modulation, cross-phase modulation, and four-wave mixing, etc.) will affect the signal quality. The nonlinear coefficient of air is much lower than that of materials such as glass. Therefore, the air core area 300 can reduce these nonlinear effects, ensure the stability of laser transmission, and improve signal quality.

[0042] It should also be noted that the material of the rare earth-doped tube 120 is rare earth-doped quartz material. Rare earth elements have a specific energy level structure. Rare earth ions can be excited by optical pumping (usually using a laser diode) to be in a high energy state. When signal light passes through, the rare earth ions in the high energy state will release energy, thereby amplifying the signal light and achieving laser gain. Since the rare earth doping amount is stable and controllable and the doping area is large, high light conversion efficiency and high cladding 100 absorption performance can be achieved.

[0043] By arranging the first refraction tube 110 in the rare earth-doped tube 120, the first refraction tube 110 can realize the grazing coupling of the laser from the side of the cladding 100, so that the laser propagates in the core region 300, and avoids the laser propagating on the rare earth-doped tube 120, thereby reducing the possibility of unstable propagation mode. Therefore, the rare earth-doped antiresonant hollow core optical fiber provided in the present application realizes the functions of laser gain and laser transmission, and the output laser will not form photoinduced heating to the rare earth-doped tube 120, thereby achieving high-power laser output without the problem of mode instability.

[0044] It should also be noted that when the rare earth-doped antiresonant hollow core fiber provided in the present application is applied to a laser, the front and rear sections are connected to high and low reflective gratings to form laser output. However, the pump light cannot meet the antiresonance condition and leaks into the cladding 100 of the optical fiber, and can be filtered out from the cladding 100 during subsequent output.

[0045] In some embodiments, reference Figure 1 As shown, the axial direction of each anti-resonance tube 200 is parallel to the axial direction of the first refraction tube 110 , and the anti-resonance tubes 200 are evenly spaced in sequence around the circumference of the first refraction tube 110 .

[0046] It can be understood that the uniform spacing of the anti-resonance tubes 200 can reduce the loss of laser light during transmission, thereby improving the transmission efficiency of the rare-earth-doped anti-resonance hollow-core optical fiber.

[0047] The evenly spaced anti-resonance tubes 200 also help stabilize the transmission mode in the optical fiber, further reducing the possibility of mode instability.

[0048] In some embodiments, reference Figure 1 As shown, the first refraction tube 110 is a germanium-doped tube.

[0049] The first refraction tube 110 is a germanium-doped tube. In specific implementation, germanium-doped quartz material can be deposited on the inner wall of a pure quartz substrate tube, and then the pure quartz substrate tube is cut and polished to a thickness equal to that of the pure quartz substrate tube. After polishing, only the sediment remains, and the preparation of the germanium-doped tube is completed.

[0050] It should be noted that the germanium-doped quartz material, that is, quartz doped with germanium, can increase the refractive index of the first refraction tube 110 to couple the laser into the fiber core region 300 for propagation.

[0051] In some embodiments, reference Figure 1 As shown, the content of germanium in the germanium-doped tube decreases from the outside to the inside of the germanium-doped tube.

[0052] Specifically, the content of germanium element decreases from the outside to the inside of the germanium-doped tube, so that the refractive index of the first refractive tube 110 gradually decreases from the outside to the inside, that is, the first refractive tube 110 is a gradient 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.

[0053] It should be noted that when the germanium-doped quartz material is deposited on the inner wall of the pure quartz substrate tube, the germanium content in the germanium-doped quartz material can be gradually reduced to achieve a sequential reduction in the content of the germanium element in the germanium-doped tube.

[0054] It should also be noted that both the outer wall and the inner wall of the first refraction tube 110 may be circular.

[0055] In some embodiments, the rare earth-doped tube 120 contains rare earth elements, and the total concentration of the rare earth elements is 300 ppm to 5000 ppm.

[0056] It is understandable that the rare earth-doped tube 120 contains rare earth elements, which can achieve the effect of light amplification and laser gain in the optical fiber. In specific implementation, the rare earth-doped tube 120 can be rare earth elements such as ytterbium, erbium, thulium and holmium, or other rare earth elements, and the embodiments of the present application do not impose too many restrictions on this.

[0057] It should be noted that both the outer wall and the inner wall of the rare earth-doped tube 120 can be circular.

[0058] In a specific implementation, the concentration of the rare earth element may be determined according to the type of the rare earth element, so that the rare earth-doped tube 120 can achieve the effect of laser gain.

[0059] In some embodiments, reference Figure 1 As shown, the number of the anti-resonance tubes 200 is greater than or equal to 4 and less than or equal to 16.

[0060] It can be understood that, through the anti-resonance effect, the tube wall of the anti-resonance tube 200 can reflect light of a specific wavelength, limiting the transmission of the laser in the core region 300. The number of anti-resonance tubes 200 is between 4 and 16, which can provide a better limiting effect, reduce the leakage of laser to the cladding 100, thereby reducing the transmission loss, the transmission effect of the optical fiber is better, and it can ensure that the optical fiber is easy to manufacture.

[0061] Specifically, the anti-resonance tubes 200 may be attached to the inner wall of the first refraction tube 110 at uniform intervals, and the anti-resonance tubes 200 do not contact each other.

[0062] In some embodiments, reference Figure 1 As shown, the cladding 100 further includes a second refractive tube 140 and a coating layer 150 . 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 .

[0063] A pure quartz layer 130 is disposed between the rare-earth-doped tube 120 and the second refractive tube 140 . The second refractive tube 140 and the pure quartz layer 130 are used to reflect pump light.

[0064] A second refraction tube 140 is disposed 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 refraction tube 140, thereby reducing the reflection of high-power density pump light at the interface between the fragile coating layer 150 and the second refraction tube 140, avoiding the impact of high-power density energy on the coating layer 150, and thus improving the stability and reliability of optical fiber transmission.

[0065] In some embodiments, reference Figure 1 As shown, the second refraction tube 140 is a fluorine-doped quartz tube.

[0066] It can be understood that the second refractive tube 140 is a fluorine-doped quartz tube, that is, the material of the second refractive tube 140 is fluorine-doped quartz material, and the refractive index of the fluorine-doped quartz tube is lower than that of the pure quartz tube, so that the fluorine-doped quartz tube can form a more effective beam limiting structure, so that most of the pump light is reflected at the interface between the pure quartz layer 130 and the second refractive tube 140.

[0067] In some embodiments, reference Figure 1 As shown, the outer wall of the fluorine-doped quartz tube is polygonal.

[0068] The outer wall of the fluorine-doped quartz tube is polygonal, that is, the outer wall of the fluorine-doped quartz tube has multiple edges. For example, the outer wall of the fluorine-doped quartz tube can have 5 to 10 edges, and the embodiment of the present application does not impose too many restrictions on this. It can be understood that the polygon can enhance the reflection effect and further limit the pump light from being reflected at the interface between the pure quartz layer 130 and the second refractive tube 140.

[0069] It should be noted that the inner wall of the fluorine-doped quartz tube may be circular.

[0070] In some embodiments, reference Figure 1 As shown, the coating layer 150 includes a first coating layer 151 and a second coating layer 152 , and the first coating layer 151 is located on a side of the second coating layer 152 close to the second refractive tube 140 .

[0071] It can be understood that the double-layer coating of the first coating 151 and the second coating 152 can enhance the mechanical strength and durability of the optical fiber.

[0072] In some embodiments, reference Figure 1 As shown, the first coating layer 151 is a fluorine-doped acrylic resin layer, and the second coating layer 152 is an acrylic resin layer.

[0073] Specifically, the first coating 151 is a fluorine-doped acrylic resin layer, which has good chemical corrosion resistance, can effectively protect the optical fiber from corrosion by chemical substances, and improve the service life of the optical fiber in harsh environments. In addition, the fluorine-doped acrylic resin layer also has good moisture resistance, which can prevent moisture from penetrating into the interior of the optical fiber and protect the optical properties of the optical fiber. The second coating 152 is an acrylic resin layer, which has good UV resistance, can protect the optical fiber from damage by ultraviolet radiation, and extend the service life of the optical fiber.

[0074] In some embodiments, the diameter of the core region 300 may be 10-120 μm, the ratio of the outer diameter of the antiresonance tube 200 to the diameter of the core region 300 may be 0.3-1.2, and the ratio of the inner diameter of the antiresonance tube 200 to the radius of the core region 300 may be 0.1-1. The wall thickness of the antiresonance tube 200 may range from 0.1 to 3 μm, and the specific value of the wall thickness is determined by the following method:

[0075] The wall thickness satisfies the anti-resonance condition of the laser When t 1 is the anti-resonance wall thickness, λ 1 is the excitation light wavelength, m 1 is the anti-resonance layer order, m 1 =1,2,3…(generally not greater than 5), n is the refractive index of the antiresonance ring.

[0076] The wall thickness meets the resonance condition of the pump light When t 2 is the resonant wall thickness, λ 2 is the pump light wavelength, m 2 is the resonant layer order, m 2 =1,2,3… (usually not more than 5), n is the refractive index of the antiresonant ring. 1 and m 2 Value (m 1 and m 2 are not necessarily equal), when t 1 and t 2 When the difference is the smallest, m 1 The wall thickness t determined by the value 1 is the wall thickness of the anti-resonance tube 200 .

[0077] The relationship between the refractive index n and the thickness r at different radial thicknesses from the outside to the inside of the first refractive tube 111 can be described by the following relationship: Among them, n 0 is the refractive index of the outermost layer of the first refractive tube 110 , a is the thickness of the first refractive 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 refractive tube 110 .

[0078] It should be noted that the outermost refractive index of the first refractive tube 110 is not lower than the refractive index of the rare earth-doped tube 120, and the relative difference can be 0-0.004. The refractive index difference between the rare earth-doped tube 120 and pure quartz can be 0.0001-0.01. The refractive index of the second refractive 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 (fluorine-doped 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.

[0079] In some embodiments, the inner diameter of the first refractive tube 110 can be 30~215μm, the outer diameter of the first refractive tube 110 is 37~260μm, the outer diameter of the rare earth-doped tube 120 is 55~375μm, the outer diameter of the pure quartz layer 130 is 65~465μm, the distance between the two opposite sides of the second refractive tube 140 is 70~490μm, the outer diameter of the first coating 151 is 85~590μm, and the outer diameter of the second coating 152 is 95~645μm.

[0080] 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.

[0081] The method for preparing the rare earth-doped antiresonant hollow core optical fiber provided in the present application comprises:

[0082] S101 , preparing a rare earth-doped tube 120 and a first refractive tube 110 .

[0083] Specifically, to prepare the rare earth-doped tube 120 , a pure quartz substrate tube can be installed on the MCVD equipment, and then the rare earth-doped quartz material can be deposited on the inner wall of the pure quartz substrate tube using a “liquid phase method” or a “gas phase method”, so that the deposited rare earth-doped quartz material forms the rare earth-doped tube 120 .

[0084] It should be noted that the MCVD method is an improved chemical vapor deposition method, and the MCVD equipment is a complete set of equipment for manufacturing optical fiber preform rods using the MCVD process. The MCVD method and MCVD equipment are technologies well known to those skilled in the art and will not be described in detail.

[0085] When the cladding 100 includes the second refractive tube 140, it is necessary to prepare the second refractive tube 140. Specifically, another pure quartz substrate tube can be installed on the PCVD equipment, and a proper amount of silicon tetrachloride, oxygen and fluoride gas (any one or more of hexafluoroethane, sulfur hexafluoride, and carbon tetrafluoride) are introduced into the pure quartz substrate tube to form a deep fluorine-doped layer on the inner wall of the pure quartz substrate tube, and the deep fluorine-doped layer is the second refractive tube 140.

[0086] It should be noted that the PCVD method is a plasma chemical vapor deposition method, and the PCVD equipment is a plasma chemical vapor deposition device. The PCVD method and PCVD equipment are technologies well known to those skilled in the art and will not be described in detail.

[0087] The second refractive tube 140 is sleeved on 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 gas burner. During melting and shrinking, the gap between the rare earth-doped tube 120 and the second refractive tube 140 is evacuated to ensure that the two are tightly fused. After the rare earth-doped tube 120 and the second refractive tube 140 are melted and shrunk, the outer surfaces thereof are polished 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.

[0088] Specifically, the first refraction tube 110 is prepared by installing a pure quartz substrate tube on a PCVD device, and depositing a germanium-doped quartz material on the inner wall of the pure quartz substrate tube, wherein the cross-sectional diagram of the refractive index of the germanium-doped quartz material is a parabola.

[0089] The pure quartz substrate tube on which the germanium-doped quartz material is deposited is cut and polished on the outer cylindrical grinding window. The polishing thickness is the thickness of the pure quartz substrate 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.

[0090] 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 .

[0091] S102, preparing an anti-resonance tube 200, and assembling the anti-resonance tube 200 and the first refraction tube 110 to obtain a primary preform.

[0092] Specifically, the drawn capillary (ie, the anti-resonance tube 200 ) and the first refraction tube 110 are assembled by stacking to form a nested capillary structure, and then welded by oxyhydrogen flame, graphite furnace or other heat sources on a glass lathe to obtain a primary preform.

[0093] It should be noted that the technique of drawing a capillary is well known to those skilled in the art and will not be described in detail.

[0094] S103, drawing the primary preform into a hollow core optical fiber intermediate.

[0095] Specifically, the primary preform is drawn in a graphite drawing furnace to form an intermediate, and the intermediate with stable size and structure is used for assembling the secondary preform.

[0096] S104, inserting the hollow core optical fiber intermediate into the rare earth doped tube 120, and applying negative pressure to the gap between the hollow core optical fiber intermediate and the rare earth doped tube 120 to obtain a secondary preform.

[0097] Specifically, the hollow-core optical fiber intermediate is inserted into the rare-earth-doped sleeve and assembled with the inflation mold to ensure that the gap between the hollow-core optical fiber intermediate and the rare-earth-doped sleeve can be evacuated with negative pressure to obtain a secondary preform.

[0098] It should be noted that the core region 300 of the hollow-core optical fiber intermediate, the inner tube and the outer tube of the nested capillary can be inflated independently, and the gap between the inflated tube and the secondary preform is fully sealed by applying temperature-resistant glue.

[0099] S105, drawing the secondary preform into a rare earth-doped antiresonant hollow core optical fiber.

[0100] Specifically, the assembled secondary preform is placed on a drawing tower for drawing, negative pressure is drawn between the hollow-core optical fiber intermediate and the rare-earth-doped sleeve, and the size and wall thickness of the tubular element are controlled by adjusting the three-level independent inflation pressure values ​​of the hollow-core optical fiber core region 300, the inner tube and the outer tube of the nested capillary to form a nested anti-resonant ring tube structure. Then, through the coating and curing device, the inner coating layer 150 is a fluorine-doped acrylic resin and the outer coating layer 150 is a conventional acrylic resin, and a rare-earth-doped anti-resonant hollow-core optical fiber is drawn.

[0101] It should be noted that the rare earth-doped antiresonant hollow-core optical fiber and its preparation method provided in the present application, the antiresonant tube 200 of the hollow-core optical fiber is prepared by a stacking method of a pure quartz tube, the rare earth-doped tube 120 is realized by the MCVD method, and the second refractive tube 140 is realized by the PCVD method. The preparation process is simple and mature, and lower transmission loss can be achieved. No special processing is required, and the preparation cost is low.

[0102] In some embodiments, reference Figure 1As shown, in the ytterbium-doped antiresonant hollow-core optical fiber prepared according to the above-mentioned method for preparing rare-earth-doped antiresonant hollow-core optical fiber, the antiresonant tube 200 is a five-nested circular ring structure, the cross-section of the outer wall of the second refractive tube 140 is a regular octagon, the diameter of the core region 300 is 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 of the first refractive tube 110 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 the 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.

[0103] Reference Figure 2 As shown, the concentration of ytterbium element in the rare earth-doped tube 120 is 2000ppm, 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 consistent with 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 pure quartz.

[0104] After testing, refer to Figure 3 As shown in the figure, the transmission loss of the Yb-doped antiresonant hollow core fiber at the transmission light wavelength of 1064nm is 0.75dB / km, while the pump light wavelength of 915nm is completely in the resonance band, indicating that good excitation light transmission can be achieved while suppressing pump light transmission. According to the laser output test, the light-to-light conversion efficiency is 68%, the 915nm cladding 100 absorption is 4.3dB / m, and the transmission achieves no thermally induced mode instability at high power of 10kW, and there is no obvious photo-darkening phenomenon after aging for 400h.

[0105] In some embodiments, reference Figure 1 As shown, in the erbium-doped antiresonant hollow-core optical fiber prepared according to the method for preparing the rare-earth-doped antiresonant hollow-core optical fiber, the antiresonant tube 200 is a structure of five nested circular rings, the cross section of the outer wall of the second refractive tube 140 is a regular octagon, the diameter of the core region 300 is 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 of the first refractive tube 110 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 the 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.

[0106] Reference Figure 2As shown, the concentration of erbium element in the rare earth-doped tube 120 is 2500ppm, 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 consistent with 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 pure quartz.

[0107] After testing, such as Figure 4 As shown in the figure, the transmission loss of the erbium-doped antiresonant hollow core fiber at the transmission light wavelength of 1530nm is 0.39dB / km, while the pump light wavelength of 980nm is completely in the resonance band, indicating that good excitation light transmission can be achieved while suppressing pump light transmission. According to the laser output test, the light-to-light conversion efficiency is 40%, the 980nm cladding 100 absorption is 10.5dB / m, and 30mW laser output is achieved.

[0108] In some embodiments, reference Figure 1 As shown, the thulium-doped antiresonant hollow-core optical fiber prepared according to the above-mentioned method for preparing rare-earth-doped antiresonant hollow-core optical fiber, the antiresonant tube 200 is a structure of 5 nested circular rings, the cross-section of the outer wall of the second refractive tube 140 is a regular octagon, the diameter of the core region 300 is 40μm, the outer ring diameter of the antiresonant tube 200 is 49μm, the inner ring diameter is 25μm, and the wall thickness is 0.76μm. The inner diameter of the first refractive tube 110 is 158μm, the outer diameter of the first refractive tube 110 is 185μm, the outer diameter of the rare-earth-doped tube 120 is 240μm, the outer diameter of the pure quartz layer 130 is 275μm, the distance between the two opposite sides of the second refractive tube 140 is 295μm, the outer diameter of the first coating 151 is 340μm, and the outer layer diameter of the second coating 152 is 380μm.

[0109] Reference Figure 2 As shown, the concentration of thulium element 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 consistent with 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 pure quartz.

[0110] After testing, refer to Figure 5 As shown in the figure, the transmission loss of the thulium-doped antiresonant hollow core fiber at the transmission light wavelength of 1950nm is 0.88dB / km, while the pump light wavelength of 793nm is completely in the resonance band, indicating that good excitation light transmission can be achieved while suppressing pump light transmission. According to the laser output test, the light-to-light conversion efficiency is 60%, the 793nm cladding 100 absorption is 15.7dB / m, and there is no thermally induced mode instability at 1000W power output, and there is no obvious photo-darkening phenomenon after aging for 400h.

[0111] It can be understood by those skilled in the art that the rare earth-doped antiresonant hollow core optical fiber provided by the present application is provided with a cladding 100 and a plurality of antiresonant tubes 200, wherein the cladding 100 includes a first refraction tube 110 and a rare earth-doped tube 120 sleeved on the first refraction tube 110. Each antiresonant tube 200 is sequentially arranged on the inner wall of the first refraction tube 110 at intervals, and each antiresonant tube 200 together encloses a core region 300, and the core region 300 is used to transmit laser light. Since the core region 300 is air, the core region 300 can reduce nonlinear effects and ensure the stability of laser transmission. The rare earth-doped tube 120 is used to amplify laser light and can achieve laser gain. The first refraction tube 110 is used to couple the amplified laser light into the core region 300, so that the laser light propagates in the core region 300, and the laser light is prevented from propagating on the rare earth-doped tube 120, thereby reducing the possibility of unstable propagation mode. Therefore, the rare earth-doped antiresonant hollow core optical fiber provided by the present application can achieve laser gain and reduce the possibility of mode instability during laser transmission.

[0112] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0113] It should be understood that the various numerical numbers involved in the embodiments of the present application are only used for the convenience of description and are not used to limit the scope of the embodiments of the present application.

[0114] So far, the technical solutions of the present application have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present 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 fall within the protection scope of the present application.

Claims

1. A rare earth doped antiresonant hollow core optical fiber, characterized in that: It comprises a cladding (100) and a plurality of anti-resonance tubes (200), wherein the cladding (100) comprises a first refraction tube (110) and a rare earth-doped tube (120) sleeved on the first refraction tube (110); The anti-resonance tubes (200) are sequentially arranged at intervals on the inner wall of the first refraction tube (110), and the anti-resonance tubes (200) together form a core region (300), and the core region (300) is used to transmit laser light; The rare earth-doped tube (120) is used to amplify the laser, and the first refraction tube (110) is used to couple the amplified laser into the fiber core region (300); The cladding (100) further comprises 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 arranged on the outer surface of the second refractive tube (140); A pure quartz layer (130) is provided between the rare-earth-doped tube (120) and the second refractive tube (140), and the second refractive tube (140) and the pure quartz layer (130) are used to reflect pump light.

2. The rare earth doped antiresonant hollow core optical fiber according to claim 1, characterized in that: The axial direction of each of the anti-resonance tubes (200) is parallel to the axial direction of the first refraction tube (110), and the anti-resonance tubes (200) are arranged in sequence at even intervals around the circumference of the first refraction tube (110).

3. The rare earth doped antiresonant hollow core optical fiber according to claim 1, characterized in that: The first refraction tube (110) is a germanium-doped tube.

4. The rare earth doped antiresonant hollow core optical fiber according to claim 3, characterized in that: The content of the germanium element in the germanium-doped tube decreases from the outer side to the inner side of the germanium-doped tube.

5. The rare earth doped antiresonant hollow core optical fiber according to any one of claims 1 to 4, characterized in that: The number of the anti-resonance tubes (200) is greater than or equal to 4 and less than or equal to 16.

6. The rare earth doped antiresonant hollow core optical fiber according to any one of claims 1 to 4, characterized in that: The second refraction tube (140) is a fluorine-doped quartz tube.

7. The rare earth doped antiresonant hollow core optical fiber according to claim 6, characterized in that: The outer wall of the fluorine-doped quartz tube is polygonal.

8. The rare earth doped antiresonant hollow core optical fiber according to any one of claims 1 to 4, characterized in that: The coating layer (150) comprises a first coating layer (151) and a second coating layer (152), wherein the first coating layer (151) is located on a side of the second coating layer (152) close to the second refractive tube (140).

9. The rare earth doped antiresonant hollow core optical fiber according to claim 8, characterized in that: The first coating (151) is a fluorine-doped acrylic resin layer, and the second coating (152) is an acrylic resin layer.

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