Single-crystal fiber cladding and its preparation method

Abstract

To address common bottlenecks in current single-crystal fiber cladding fabrication processes, such as weak interfacial bonding, insufficient element diffusion, thermal stress concentration, and poor material universality, this invention aims to provide a single-crystal fiber cladding and its fabrication method. Through a secondary tapering and collapse process, atomic-level tight bonding between the single-crystal fiber core and the fluorine-doped quartz glass tube is achieved. By adjusting the collapse temperature and collapse rate, elemental gradient diffusion transition layers of varying thicknesses can be formed, enabling deep elemental interdiffusion and smoothing out abrupt changes in refractive index. This solves problems such as easy peeling and poor mechanical properties of single-crystal fiber cladding, providing a universal cladding solution for high-power single-crystal fiber lasers and single-crystal fiber sensors in extreme environments.

Description

Technical Field

[0001] This invention mainly relates to the field of optical fiber device fabrication technology, and in particular to a single-crystal optical fiber cladding and its fabrication method. Background Technology

[0002] Single-crystal optical fibers, used as gain media in high-power lasers, suffer from drawbacks such as high surface scattering loss, strong environmental sensitivity, and susceptibility to mechanical damage due to their unclad structure, severely limiting their applications. To address these limitations, researchers have developed various cladding fabrication techniques to provide optical waveguide confinement and match the coefficient of thermal expansion. These techniques mainly include the following:

[0003] Co-stretching laser heating base method: By simultaneously stretching a single crystal source rod covered with a ceramic sleeve, the uniformity of the cladding thickness and the optimization of thermal expansion differences are achieved.

[0004] Laser micromachining: This method uses Bessel beam segmented focusing technology to directly inscribe microstructures on the surface of optical fibers to solve the problem of process complexity.

[0005] Femtosecond laser internal etching: Utilizing the adjustable diameter of the annular laser spot, the refractive index of a single-crystal fiber can be controlled without length limitations.

[0006] Additive manufacturing: It combines the advantages of design flexibility and structural density by depositing cladding material layer by layer through a 3D printing head;

[0007] Melt-filling crystallization method: Based on capillary action, rare earth-doped melts are directionally crystallized within the perforated single-crystal cladding, significantly improving optical quality;

[0008] Micro-pull-down one-step growth method: Based on the solute segregation effect and the difference in electronic polarizability, the core-cladding structure is directly grown;

[0009] Tube stacking method: forming a microstructure cladding by assembling, heating, and stretching;

[0010] MCVD deposition method: Bragg structure cladding is constructed by alternating deposition of high / low refractive index materials.

[0011] These existing technologies collectively constitute the core technology system for the current fabrication of single-crystal fiber cladding. Despite significant progress in existing single-crystal fiber cladding technology, the following core shortcomings still exist:

[0012] The co-stretching laser heating base method results in insufficient high-temperature contact time between the ceramic sleeve and the single-crystal optical fiber, leading to an element interdiffusion depth of only 0.2μm-0.8μm and an interfacial shear strength of less than 20MPa.

[0013] While laser micromachining improves surface precision, etching microstructures disrupts crystal integrity and causes additional scattering losses. );

[0014] Melt-filling crystallization is limited by capillary force, resulting in a coating thickness uniformity deviation of >10%, and it is difficult to control the refractive index of fluorine doping.

[0015] Micro-pull-down one-step growth method due to material segregation coefficient and electronic polarizability Its stringent matching requirements make it unsuitable for mainstream YAG systems.

[0016] However, the tube stacking method and the MCVD deposition method suffer from the mismatch in thermal expansion at the multi-material interface (the CTE difference between quartz and YAG is significant). At high temperatures, interfacial stresses exceeding 100 MPa are generated, leading to a significant increase in the risk of cladding cracking. Summary of the Invention

[0017] To address the common bottlenecks in the aforementioned single-crystal fiber cladding fabrication processes, such as weak interfacial bonding, insufficient element diffusion, thermal stress concentration, and poor material universality, this invention aims to provide a single-crystal fiber cladding and its fabrication method. This invention achieves atomic-level tight bonding between the single-crystal fiber core and the fluorine-doped quartz glass tube through an innovative secondary tapering and collapse process. By adjusting the collapse temperature and collapse rate, elemental gradient diffusion transition layers of varying thicknesses can be formed, achieving deep elemental interdiffusion and smoothing abrupt changes in refractive index. This provides a universal cladding solution for high-power single-crystal fiber lasers and single-crystal fiber sensors operating in extreme environments.

[0018] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0019] This invention provides a method for preparing the cladding of a single-crystal optical fiber, comprising the following steps:

[0020] Prepare monocrystalline fiber cores and glass tubes. The monocrystalline fiber core is a 1at% Yb:YAG fiber core, and the glass tube is a fluorine-doped quartz glass tube.

[0021] The single-crystal fiber core and glass tube are cleaned.

[0022] A glass tube is pre-tapered to obtain a pre-tapered glass tube, which has a waist region and a first tapered end and a second tapered end distributed at both ends of the waist region.

[0023] The monocrystalline fiber core is inserted from the first tapered end of the pre-stretched tapered glass tube until it is aligned with the critical surface of the waist and the end of the second tapered section of the pre-stretched tapered glass tube. The port of the first tapered end of the pre-stretched tapered glass tube is sealed with UV-curing adhesive. Then, the UV-curing adhesive is cured by UV lamp until the assembly of the monocrystalline fiber core and the pre-stretched tapered glass tube is completed, resulting in a composite of the monocrystalline fiber core and the pre-stretched tapered glass tube.

[0024] The composite undergoes a secondary tapering and collapse process: Under an argon protective atmosphere, a uniform thermal field is applied to the composite. A vacuum pump connected to the second tapered end continuously evacuates air, and a tapering machine stretches the composite axially, causing the diameter of the glass tube's waist region to continuously decrease until it completely adheres to the single-crystal fiber core. The glass tube uniformly collapses onto the surface of the single-crystal fiber core. At high temperatures, the fluorine-doped quartz glass tube reacts with the YAG crystals in the single-crystal fiber core, promoting… , Directional diffusion from the single-crystal fiber core to the cladding in fluorinated quartz glass tubes , Driven by the concentration gradient, the material diffuses backward into the single-crystal core, forming a uniform structure with a certain thickness. Interdiffusion gradient layers ultimately form a structure consisting of a Yb:YAG core, ... A three-layer gradient structure consisting of an interdiffusion gradient layer and a fluorine-doped quartz cladding was used to complete the fabrication of the single-crystal optical fiber cladding.

[0025] Preferably, a uniform thermal field of 1850±20°C is applied to the composite by heating with a graphite electrode under an argon protective atmosphere.

[0026] Preferably, when the tapering machine stretches the assembly along the axial direction, the tapering speed gradually increases from 0, and the diameter of the glass tube waist area continuously decreases until it is completely attached to the single crystal fiber core. After that, the tapering speed remains stable. When the glass tube collapses evenly onto the surface of the single crystal fiber core, the tapering stops, and the vacuum pump stops pumping air.

[0027] Preferably, the cleaning process for the single-crystal fiber core and glass tube includes: placing the Yb:YAG fiber core and glass tube in a container filled with alcohol and ultrasonically cleaning them using an ultrasonic cleaner; then transferring them to a deionized aqueous solution containing a surfactant and immersing them for 7 hours; subsequently, rinsing the single-crystal fiber core and glass tube repeatedly with deionized water; finally, performing a final cleaning of the single-crystal fiber core and glass tube with ultrapure water; and finally placing the cleaned Yb:YAG fiber core and glass tube in a vacuum drying oven for drying.

[0028] Furthermore, the present invention provides a single-crystal fiber cladding, which is prepared using the above-described single-crystal fiber cladding preparation method.

[0029] In the cladding of single-crystal optical fibers Interdiffusion graded layers play a crucial role in fiber laser applications. Interdiffusion gradient layers are formed at high temperatures through... , and , The bidirectional interdiffusion of elements forms an interfacial structure with a continuous transition in chemical composition. This not only significantly improves the interfacial bonding quality of the core and cladding and effectively suppresses interfacial scattering, but also reduces light transmission loss by forming a smooth, gradually changing refractive index distribution. Simultaneously, The interdiffusion gradient layer improves the matching of the thermal expansion coefficients of the core and cladding, thereby enhancing the thermal stability and laser damage threshold of the device. The moderate refractive index difference and gradient distribution of the interdiffused graded layer provide good waveguide confinement, contributing to higher beam quality and laser efficiency. Furthermore, and The introduction of rare earth elements provides a suitable dissolution environment for rare earth ions, facilitating the achievement of high-concentration, uniform rare earth doping, thereby improving the gain efficiency of optical fibers and the laser output power. These characteristics enable... Interdiffusion graded layers have become an effective technical approach to improve the performance of high-power fiber lasers.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] This invention provides a method for preparing single-crystal fiber cladding, which significantly solves the problems of difficult fabrication and poor mechanical properties of ultra-fine single-crystal fiber cladding structures. In a high-temperature environment, a fluorine-doped quartz glass tube reacts with the YAG crystal in the single-crystal fiber, causing elemental interdiffusion to form a uniform, graded-varying layer. The thickness of this layer can be adjusted by controlling the secondary tapering collapse temperature and rate. Interdiffusion graded layer (achieved by controlling the temperature and rate of secondary tapered collapse) (Thickness control of interdiffusion gradient layer) to enable and Through chemical bonding ( Clusters enhance the interface shear strength, effectively solving the interface peeling problem.

[0032] Interdiffusion graded layers can effectively reduce interface defects and scattering losses caused by core-cladding material mismatch. The result is a smooth refractive index gradient distribution, which can reduce light scattering and thus is expected to reduce the transmission loss of optical fibers. The moderate refractive index difference and gradient distribution formed by the interdiffusion graded layer can provide good waveguide confinement capability, control the laser transmission mode, and help to obtain higher beam quality (such as near-diffraction-limited output) and improve laser efficiency.

[0033] Preferably, the fluorine doping concentration in the fluorine-doped quartz glass tube is 5.0 wt%, and the 5 wt% fluorine doping results in a thermal expansion coefficient of fluorine-doped quartz cladding of [value missing]. The coefficient of thermal expansion of Yb:YAG fiber core The matching accuracy reached 96.3% (calculated as follows: By combining the gradient cooling process after secondary tapering and collapse to control thermal stress, the thermal load capacity of single-crystal optical fibers can be improved and the risk of cladding cracking can be eliminated.

[0034] Meanwhile, experiments have confirmed that the uniformity of the cladding diameter (fluctuation <0.2%) and concentricity deviation (<1μm) of the fabricated single-crystal fiber cladding can reduce the excitation of higher-order modes, thus significantly reducing the number of modes in the single-crystal fiber. The interdiffusion layer forms a smooth and gradual change in refractive index, achieving wide-range waveguide confinement, providing core support for achieving near-diffraction-limited output (beam divergence angle <0.8mrad) in high-power lasers above 2kW using single-crystal fiber. Furthermore, simplified processes shorten the production cycle and reduce energy consumption, achieving multiple breakthroughs in high strength, low loss, high thermal stability, and high yield, meeting the demands of industrial-grade mass production. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of a clad single-crystal optical fiber in one embodiment;

[0037] Figure 2 This is a schematic diagram of the assembled Yb:YAG fiber core and glass tube in one embodiment;

[0038] Figure 3 These are microscope and SEM images of the cross-section of a clad single-crystal fiber prepared in one embodiment. Figure 3 (a) is a microscope image of the cross-section of a clad single-crystal fiber. Figure 3 (b) is Figure 3 (a) SEM photos of the area selected in the box;

[0039] Figure 4 This is a diameter fluctuation diagram of a clad single-crystal fiber prepared in one embodiment;

[0040] Figure 5 The radial elemental distribution map of the prepared clad single-crystal fiber obtained by EPMA testing is shown below. Figure 5 (a) is a microscopic image of the cross-section of the prepared clad single-crystal fiber, where the positions marked a, b, c, d, and e represent radial positions of 0 μm, 180 μm, 192 μm, 205 μm, and 250 μm, respectively. Figure 5 (b) is a radial elemental distribution diagram of the optical fiber obtained by EPMA testing;

[0041] Figure 6 The image shows the EDS mapping of the prepared clad single-crystal fiber, where... Figure 6 (a) is a scanning electron microscope (SEM) image of the test area. Figure 6 (b) is a distribution map of all elements within the test area. Figure 6 (c) is a distribution map of the Y element within the test area. Figure 6 (d) is a distribution map of Al elements within the test area. Figure 6 (e) is a distribution map of Si elements in the test area. Figure 6 (f) is a distribution map of element F within the test area. Figure 6 (g) is a distribution map of Yb elements within the test area. Figure 6 (h) is a distribution map of O elements within the test area;

[0042] Figure 7 The refractive index distribution of the prepared clad single-crystal fiber is shown in the figure.

[0043] Numbering on the map:

[0044] 1. Yb: YAG fiber core, 2. 3. Interdiffusion gradient layer; 4. Fluorine-doped quartz cladding; 5. Single crystal fiber core; 6. Pre-stretched tapered glass tube; 7. Waist region; 8. First tapered end; 9. Second tapered end; 10. UV-curable adhesive; 11. Critical surface between the waist region and the end of the second tapered region. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] To address key issues such as weak interfacial bonding, insufficient element diffusion, and thermal stress concentration in single-crystal fiber cladding, a method for preparing single-crystal fiber cladding is provided. A single-crystal fiber core (Yb:YAG core with a diameter of 400±5μm) prepared by laser heating substrate method is inserted into a pre-stretched tapered fluorine-doped quartz glass tube (Heraeus TNUF, fluorine doping concentration of 5wt%, refractive index...). The initial inner diameter (ID) / outer diameter (OD) of the fluorinated quartz glass tube was 800 μm / 1100 μm. After pre-tapering, the inner diameter (ID) / outer diameter (OD) of the fluorinated quartz glass tube was 450 μm / 620 μm. Tapering and collapse were then performed under argon protection at 1850±20℃. By precisely controlling the collapse temperature and collapse rate, the process was accelerated... , Elements diffuse directionally from the Yb:YAG core to the cladding, forming a layer approximately 13 μm thick. Interdiffusion gradient layers are used to ultimately construct a three-layer gradient structure (such as...). Figure 1 As shown): Yb:YAG fiber core (refractive index) → Interdiffusion graded layer (refractive index) → Fluorine-doped quartz cladding (refractive index n=1.444) achieves simultaneous optimization of optical performance and mechanical strength.

[0047] like Figure 1 As shown, the prepared clad single-crystal fiber has a three-layer graded structure, consisting of a Yb:YAG core 1, a Yb:YAG core 2, and a Yb:YAG core 3. Interdiffusion gradient layer 2, fluorine-doped quartz cladding layer 3.

[0048] In one embodiment, a method for preparing a single-crystal fiber cladding is provided, comprising the following steps:

[0049] Prepare single crystal fiber core 4 and glass tube. The single crystal fiber core is 1at% Yb:YAG fiber core, and the glass tube is fluorine-doped quartz glass tube.

[0050] The single-crystal fiber core 4 and the glass tube were cleaned.

[0051] Reference Figure 2 The glass tube is pre-tapered to obtain a pre-tapered glass tube 5. The pre-tapered glass tube 5 has a waist region 501 and a first tapered end 502 and a second tapered end 503 distributed at both ends of the waist region 501.

[0052] The single crystal fiber core 4 is inserted into the first tapered end 502 of the pre-stretched tapered glass tube 5 until the critical surface A of the waist region and the end of the second tapered region of the pre-stretched tapered glass tube 5 is aligned. The port of the first tapered end 502 of the pre-stretched tapered glass tube 5 is sealed with UV-curing adhesive 6. Then, the UV-curing adhesive is cured by UV lamp until the assembly of the single crystal fiber core and the pre-stretched tapered glass tube is completed, resulting in a composite of the single crystal fiber core and the pre-stretched tapered glass tube.

[0053] The composite material undergoes a secondary tapering collapse, with the collapse direction from the first tapered end to the second tapered end. A vacuum pump connected to the second tapered end evacuates air before collapse to aid in the subsequent bonding between the glass tube and the single-crystal fiber core. Under an argon protective atmosphere, a uniform thermal field of 1850±20℃ is applied to the composite material via graphite electrodes. The vacuum pump connected to the second tapered end continuously evacuates air. A tapering machine stretches the composite material axially, gradually increasing the tapering speed from 0. The diameter of the glass tube's waist region continuously decreases until it is completely bonded to the single-crystal fiber core, after which the tapering speed remains stable. Tapering stops when the glass tube uniformly collapses onto the surface of the single-crystal fiber core, and the vacuum pump stops evacuating air. Under high-temperature conditions, the fluorine-doped quartz glass tube reacts with the YAG crystals in the single-crystal fiber core, promoting… , Directional diffusion from the single-crystal fiber core to the cladding, while in the fluorinated quartz glass tube , Driven by the concentration gradient, the material diffuses backward into the single-crystal core, forming a bidirectional interdiffusion mechanism, thereby creating a uniform structure with a certain thickness. Interdiffusion gradient layers ultimately form a Yb:YAG fiber core from the inside out. The three-layer gradient structure of the interdiffusion gradient layer and the fluorine-doped quartz cladding completes the fabrication of the single-crystal optical fiber cladding.

[0054] The element interdiffusion mechanism of this invention is achieved through the following synergistic effect: under a high temperature environment of 1850±20℃ (close to the critical point of YAG lattice loosening), the interdiffusion of elements in the YAG lattice... A migration energy exceeding 1.5 eV is achieved for diffusion into the cladding, while simultaneously, in the fluorine-doped quartz glass tube... Driven by the concentration gradient, back-diffusion occurs towards the fiber core, forming a bidirectional interdiffusion flow; a diffusion time window is provided by precisely controlling the tapering speed, and... Eliminating the air gap under vacuum conditions reduces the diffusion barrier, ultimately promoting The multi-layered system interlocks in the interface area to form a certain thickness. Interdiffusion gradient layer.

[0055] In one specific embodiment, the single-crystal fiber cladding is prepared using the single-crystal fiber cladding preparation method provided by the present invention, specifically including the following steps:

[0056] (1) Material pretreatment:

[0057] Preparation of single-crystal fiber cores and glass tubes: The single-crystal fiber cores used were 1at% Yb:YAG fiber cores with a diameter of 400±3μm, prepared by laser heating pedestal method. The glass tubes used were commercially available Heraeus TNU fluorine-doped quartz glass tubes (fluorine doping concentration of 5.0wt%, initial inner / outer diameter of 800μm / 1100μm, and refractive index of the glass tubes). ).

[0058] Before fabricating the single-crystal fiber cladding, the Yb:YAG fiber core and glass tube need to be cleaned. The specific steps are as follows: First, the Yb:YAG fiber core and glass tube are placed in a container filled with alcohol and ultrasonically cleaned for 20 minutes using an ultrasonic cleaner. Then, they are transferred to a deionized water solution containing surfactants and soaked for 7 hours. Subsequently, they are repeatedly rinsed with deionized water to remove residual surfactants and other impurities. Finally, a final rinse is performed using ultrapure water to ensure the cleaning effect. After completing the above cleaning process, the Yb:YAG fiber core and glass tube are placed in a vacuum drying oven to dry them, removing surface moisture and ensuring they are completely dry, thus preparing them for the subsequent single-crystal fiber cladding fabrication process.

[0059] (2) Pre-tapering treatment of glass tube:

[0060] The Heraeus TNU fluorine-doped quartz glass tube was pre-tapered using an MT-180 high-precision fiber optic tapering machine. The specific process was as follows: the glass tube was passed through the graphite electrode of the tapering machine and clamped between two displacement stages. The tapering speed was controlled by the speed difference Δv between the two displacement stages. Under an argon protective atmosphere (oxygen content <10ppm), a uniform thermal field of 1850±20℃ was applied to the fluorine-doped quartz glass tube through heating via the graphite electrode, stretching the glass tube axially. The speed difference Δv between the two displacement stages gradually increased from 0, and the inner and outer diameters of the fluorine-doped quartz glass tube gradually decreased proportionally, forming a tapered region. When the inner diameter of the glass tube decreased from the initial 800μm to 450±5μm, the current speed difference Δv between the two displacement stages was kept constant (i.e., the increase in the speed difference Δv between the two displacement stages was stopped), and the fluorine-doped quartz glass tube continued to be stretched to form a waist region. Subsequently, the velocity difference Δv between the two displacement stages is gradually reduced, and the inner and outer diameters of the fluorine-doped quartz glass tube gradually increase, forming another tapered region. After tapering, the tube is slowly cooled to room temperature at a rate of 10℃ / s to avoid the generation of thermal stress cracks. After the glass tube is pre-tapered, a pre-tapered glass tube is obtained, which has a waist region and a first tapered end and a second tapered end distributed at both ends of the waist region.

[0061] (3) The pre-tapered glass tube is assembled and positioned with the Yb:YAG fiber core;

[0062] In a Class 100 cleanroom environment, perform precision assembly of the Yb:YAG fiber core and the pre-tapered glass tube (e.g.) Figure 2As shown in the diagram, the specific process is as follows: First, the Yb:YAG fiber core is inserted into the first conical section of the pre-stretched tapered glass tube. An optical microscopy system (200× optical magnification, 0.5μm CCD resolution) is used to perform two-dimensional imaging of the Yb:YAG fiber core and the glass tube. The position of the Yb:YAG fiber core is adjusted using a piezoelectric ceramic micro-motion platform to ensure that the waist region of the Yb:YAG fiber core inserted into the pre-stretched tapered glass tube is aligned with the critical surface A at the end of the second conical section. Then, UV-curable adhesive is used to seal the port at the first conical section of the pre-stretched tapered glass tube, facilitating air extraction at the second conical section during the subsequent collapse process. After assembly, non-destructive testing is performed using X-ray micro-CT (2μm resolution) to confirm that the concentricity deviation between the Yb:YAG fiber core and the pre-stretched tapered glass tube is <0.8μm. Then, the UV-curable adhesive is irradiated and cured with a UV lamp until the assembly of the single-crystal fiber core and the pre-stretched tapered glass tube is completed, resulting in a composite of the Yb:YAG fiber core and the pre-stretched tapered glass tube.

[0063] (4) Perform secondary tapering and collapse on the combination of Yb:YAG fiber core and pre-tapered glass tube;

[0064] The Yb:YAG fiber core and pre-tapered glass tube were subjected to a secondary tapering collapse, with the collapse direction from the first tapered region end to the second tapered region end. A vacuum pump connected to the second tapered region end was used to evacuate air before collapse to assist in the subsequent bonding between the glass tube and the single-crystal fiber core. Under an argon protective atmosphere (oxygen content <10ppm), a uniform thermal field of 1850±20℃ was applied to the composite through graphite electrode heating. The vacuum pump connected to the second tapered region end continuously evacuated air. A tapering machine stretched the composite axially, gradually increasing the tapering speed from 0, until the diameter of the glass tube's waist region continuously decreased until it was completely bonded to the Yb:YAG fiber core. The tapering speed then remained stable. Tapering was stopped when the glass tube uniformly collapsed onto the surface of the Yb:YAG fiber core, and the vacuum pump stopped evacuating air. Under high-temperature conditions, the fluorinated quartz glass tube reacted with the YAG crystals in the Yb:YAG fiber core, promoting… , Directional diffusion from the Yb:YAG core to the cladding, while fluorine-doped quartz glass tubes... , Driven by the concentration gradient, the material diffuses backward into the Yb:YAG core, forming a bidirectional interdiffusion mechanism, thereby creating a uniform matrix with a certain thickness. Interdiffusion graded layer. This ultimately forms a Yb:YAG fiber core from the inside out. The three-layer graded structure of the interdiffusion graded layer and the fluorine-doped quartz cladding completes the fabrication of the single-crystal optical fiber cladding.

[0065] After optical-grade precision polishing, the end face of the clad single-crystal fiber clearly exhibits a three-layer structure under both an optical microscope (Nikon ECLIPSEL V100D) and a scanning electron microscope (SEM, manufacturer: TESCAN (Czech Republic), instrument model: MIRA4 LMH). Figure 3 As shown, Figure 3 Microscopic and SEM images of the prepared clad single-crystal fiber cross-section are shown. Figure 3 (a) is a microscope image of the cross-section of a clad single-crystal fiber. Figure 3 (b) is Figure 3 (a) SEM image of the area selected in the box. The fabricated clad single-crystal fiber includes a central Yb:YAG core (diameter 380±1μm). Interdiffusion graded layer (thickness 13±0.5μm) and fluorine-doped quartz cladding (outer diameter 512±1μm), wherein The interface between the interdiffusion gradient layer and the fluorine-doped quartz cladding exhibits a gradual fusion characteristic, with no microcracks or bubble defects.

[0066] The 7cm clad single-crystal optical fiber was scanned using the 3SAE Combination Manufacturing System (CMS). Figure 4 As shown, Figure 4 The diameter fluctuation diagram of the prepared clad single-crystal fiber shows that the diameter fluctuation range is 511.4 μm-513.2 μm (mean 512.38 μm, standard deviation...). This confirms that the cladding uniformity meets industrial-grade standards. / mean <0.06%).

[0067] The prepared clad single-crystal optical fiber was subjected to line-scan quantitative analysis using electron probe microanalysis (EPMA, instrument model: Shimadzu EPMA-1720T, Japan) to reveal the interdiffusion behavior of elements. The test results are as follows: Figure 5 As shown in Table 1. Figure 5 The radial elemental distribution map of the prepared clad single-crystal fiber obtained by EPMA testing is shown below. Figure 5 (a) is a microscopic image of the cross-section of the prepared clad single-crystal fiber, where the positions marked a, b, c, d, and e represent radial positions of 0 μm, 180 μm, 192 μm, 205 μm, and 250 μm, respectively. Figure 5(b) shows the radial elemental distribution of the optical fiber obtained by EPMA testing. From the core center (0 μm) to the cladding (250 μm), Y (16.65→15.59→9.64→0 at%) and Al (26.75→25.87→15.35→0.02 at%) decrease exponentially, while Si (0→18.73→34.53 at%) and F (0→0.61→3.12 at%) increase in opposite directions. The Yb concentration is stable at 0.11-0.14 at% (change rate <20%). The interface region (192 μm) shows an abnormal F depletion (0.61 at% vs. 3.12 at% in the cladding). Figure 6 The EDS (One Max 50) surface scanning mapping results are consistent, showing that the Al / Y element diffusion front and the Si / F anti-diffusion form a 13μm wide interlocking region. Figure 6 The image shows the EDS mapping of the prepared clad single-crystal fiber, where... Figure 6 (a) is a scanning electron microscope (SEM) image of the test area. Figure 6 (b) is a distribution map of all elements within the test area. Figure 6 (c) is a distribution map of the Y element within the test area. Figure 6 (d) shows the distribution of Al elements within the test area. Figure 6 (e) is a distribution map of Si elements in the test area. Figure 6 (f) is a distribution map of element F within the test area. Figure 6 (g) is a distribution map of Yb elements within the test area. Figure 6 (h) is a distribution map of O elements in the test area.

[0068]

[0069] The refractive index distribution of the fabricated optical fiber was measured using the M-line method (RIP-100, test wavelength 632 nm), and the results are as follows: Figure 7 As shown, Figure 7This image shows the refractive index distribution of the fabricated clad single-crystal fiber. The test results show that the refractive index of the fiber cross-section exhibits a gradual distribution, with a high refractive index at the core and a low refractive index at the edges. Near the core, the refractive index change is relatively gradual, with a slower decrease from the center to the edge; however, the rate of refractive index decrease accelerates when the diameter exceeds approximately 200 μm. The maximum refractive index at the core is 1.6363, gradually decreasing from the center to the edge, reaching a minimum of 1.438 at a diameter of approximately 387.1 μm. It then gradually increases, rising again to 1.443 at approximately 399 μm, and fluctuates within the range of 0.002 between a diameter of 400 μm and the fiber edge. This test method is based on interference fringe analysis, with a test wavelength of 632 nm. The interference fringes contain information such as the incident light wavelength and the phase difference of the light along the interference path. The changes in the interference fringes caused by the tested fiber reflect the changes in its material refractive index and the total phase change along the light path. Given the wavelength of the test light, the refractive index gradient difference along the path of the light can be calculated by numerical analysis of the interference fringes. Since the refractive index difference between crystalline and glass materials is relatively large (>0.3), while this test method is generally applicable to materials with a small refractive index difference (<0.002), the test results can only serve as a qualitative reference for the refractive index distribution trend and are not suitable for quantitative characterization.

[0070] Matters not covered in this invention are common knowledge.

[0071] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing the cladding of a single-crystal optical fiber, characterized in that, Includes the following steps: Prepare monocrystalline fiber cores and glass tubes. The monocrystalline fiber core is a 1at% Yb:YAG fiber core, and the glass tube is a fluorine-doped quartz glass tube. The single-crystal fiber core and glass tube are cleaned. A glass tube is pre-tapered to obtain a pre-tapered glass tube, which has a waist region and a first tapered end and a second tapered end distributed at both ends of the waist region. The monocrystalline fiber core is inserted from the first tapered end of the pre-stretched tapered glass tube until it is aligned with the critical surface of the waist and the end of the second tapered section of the pre-stretched tapered glass tube. The port of the first tapered end of the pre-stretched tapered glass tube is sealed with UV-curing adhesive. Then, the UV-curing adhesive is cured by UV lamp until the assembly of the monocrystalline fiber core and the pre-stretched tapered glass tube is completed, resulting in a composite of the monocrystalline fiber core and the pre-stretched tapered glass tube. The composite undergoes a secondary tapering and collapse process: Under an argon protective atmosphere, a uniform thermal field is applied to the composite. A vacuum pump connected to the second tapered end continuously evacuates air, and a tapering machine stretches the composite axially, causing the diameter of the glass tube's waist region to continuously decrease until it completely adheres to the single-crystal fiber core. The glass tube uniformly collapses onto the surface of the single-crystal fiber core. At high temperatures, the fluorine-doped quartz glass tube reacts with the YAG crystals in the single-crystal fiber core, promoting… , Directional diffusion from the single-crystal fiber core to the cladding in fluorinated quartz glass tubes , Driven by the concentration gradient, the material diffuses backward into the single-crystal core, forming a uniform structure with a certain thickness. Interdiffusion gradient layers ultimately form a structure consisting of a Yb:YAG core, ... A three-layer gradient structure consisting of an interdiffusion gradient layer and a fluorine-doped quartz cladding was used to complete the fabrication of the single-crystal optical fiber cladding.

2. The method for preparing single-crystal fiber cladding according to claim 1, characterized in that, The fluorine doping concentration in the fluorine-doped quartz glass tube is 5.0 wt%.

3. The method for preparing single-crystal fiber cladding according to claim 1, characterized in that, A uniform thermal field of 1850±20℃ was applied to the conjugate by heating with a graphite electrode under an argon protective atmosphere.

4. The method for preparing single-crystal fiber cladding according to claim 1, characterized in that, When the tapering machine stretches the assembly along the axial direction, the tapering speed gradually increases from 0. The diameter of the waist area of ​​the glass tube continuously decreases until it is completely attached to the single crystal fiber core. After that, the tapering speed remains stable. When the glass tube collapses evenly on the surface of the single crystal fiber core, the tapering stops and the vacuum pump stops pumping air.

5. The method for preparing single-crystal fiber cladding according to any one of claims 1 to 4, characterized in that, The cleaning process for the single-crystal fiber core and glass tube includes: placing the Yb:YAG fiber core and glass tube in a container filled with alcohol and ultrasonically cleaning them using an ultrasonic cleaner; then transferring them to a deionized aqueous solution containing surfactant and immersing them for 7 hours; subsequently, rinsing the single-crystal fiber core and glass tube repeatedly with deionized water; finally, performing a final cleaning of the single-crystal fiber core and glass tube with ultrapure water; and finally, placing the cleaned Yb:YAG fiber core and glass tube in a vacuum drying oven for drying.

6. A single-crystal optical fiber cladding, characterized in that, The single-crystal fiber cladding is prepared using the single-crystal fiber cladding preparation method as described in claim 1.

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