Special optical fiber with superstructure and its preparation method and application

Abstract

The application provides a special optical fiber with a superstructure and a preparation method and application thereof. The special optical fiber with a superstructure comprises a core and a cladding layer covering the periphery of the core; the core is a solid single crystal fiber; and the cladding layer structure is a refractive index guiding type photonic crystal superstructure. The application regulates the equivalent refractive index of the cladding layer by designing the superstructure of the cladding layer of the special optical fiber, expands the selection range of the cladding layer material of the optical fiber, effectively regulates the transmission mode, transmission loss and other performances of the special optical fiber, and realizes the low-loss transmission of the special optical fiber. In addition, the application effectively regulates the equivalent refractive index of the cladding layer, and can match the cladding layer structure and material with the core of different materials, and is widely applied.

Description

Technical Field

[0001] This invention relates to the field of special optical fiber technology, and in particular to a special optical fiber with a superstructure, its preparation method, and its application. Background Technology

[0002] The rapid development of industrial technology has created an urgent need for the design and fabrication of specialized optical fibers. In extreme environments such as high temperature, high pressure, strong radiation, strong electromagnetic interference, flammability, explosiveness, and strong corrosion, few sensors can provide accurate and reliable information on temperature, pressure, and operational health. Single-crystal optical fibers, as a type of specialized optical fiber, possess higher melting points and better corrosion resistance. Therefore, using single-crystal optical fibers to replace silica optical fibers for sensing in extreme environments has become a development trend. Single-crystal optical fibers are made by fabricating crystalline materials into fiber-shaped single crystals with diameters ranging from tens of micrometers to one millimeter. They are a combination of bulk crystals and conventional optical fibers, possessing excellent physicochemical properties such as high aspect ratio, large specific surface area, high rare-earth ion doping concentration, low nonlinear gain coefficient, good light transmission, high temperature resistance, and corrosion resistance. The application of single-crystal optical fibers in laser transmission can not only effectively solve the problems of low damage threshold, low thermal conductivity, and severe nonlinear effects in silica fiber lasers, but also overcome the bottlenecks of complex structures and difficulty in achieving high repetition rates in crystal and ceramic disk lasers. In short, single-crystal optical fibers, with their unique advantages, can be used in many fields such as high-power laser transmission and high-temperature sensing.

[0003] Currently, the commonly used fabrication processes for single-crystal optical fibers are the micro-pull-down method and the laser-heated substrate method. However, both of these methods produce bare single-crystal fibers without a cladding structure. Furthermore, the thermal drawing method is not suitable for crystalline materials, as the crystalline material becomes glassy during thermal drawing, resulting in a single-crystal derived fiber. Bare single-crystal fibers are not strictly speaking single-crystal optical fibers; they are easily affected by environmental pollutants, leading to severe attenuation. In addition, the refractive index in air is non-uniform and highly variable, resulting in a significant difference in refractive index between the bare fiber and air.

[0004] Adding cladding to bare monocrystalline fibers enhances their mechanical and thermal properties, forms optical waveguides, and, most importantly, allows for control over transmission modes. Therefore, it is necessary to further add cladding to bare monocrystalline fibers to form monocrystalline optical fibers. The cladding materials for monocrystalline fibers are mainly divided into crystalline materials and glass materials. Crystalline cladding generally employs specific physical or chemical coating processes, including sputtering, femtosecond laser processing, localized etching, liquid phase epitaxy, hydrothermal growth, and molten salt growth. Glass cladding primarily uses the tube tapering method. Compared to crystalline materials, glass materials have the advantage of a wider refractive index adjustment range, meeting the needs of various materials. However, glass materials have lower thermal conductivity and a significantly different coefficient of thermal expansion compared to crystalline materials, which can cause difficulties in later applications of devices.

[0005] Currently, all cladding fabrication processes for single-crystal optical fibers have certain drawbacks. Physical and chemical coating methods suitable for crystalline cladding require sophisticated equipment and are relatively complex. Furthermore, it is difficult to control the refractive index of the cladding during fabrication, and there are significant limitations on the cladding materials. While the tapered sleeve method suitable for glass cladding is relatively simple, the process of heating the cladding to melt it and coat the fiber core presents challenges in thermal management.

[0006] Existing technology discloses a method for preparing the cladding of a single-crystal optical fiber. In this invention, a single-crystal optical fiber is used as a preform material, and a hole is drilled along its central axis to obtain the cladding. Then, a single crystal with an outer diameter roughly equivalent to the central hole diameter of the cladding is inserted into the central hole as the core, forming the preform. Finally, the preform is used as a seed crystal for crystal growth to form a single-crystal optical fiber with both a cladding and core structure. This method utilizes crystal growth to prepare the optical fiber, which makes it difficult to design complex cladding structures and significantly limits the selection of cladding and core materials.

[0007] The prior art also discloses a cladding of sapphire single crystal optical fiber with a refractive index decreasing radially and its preparation method. The invention mainly uses atomic layer deposition technology to deposit two aluminum oxide thin films with different densities (refractive indices) on the surface of sapphire single crystal optical fiber at different deposition temperatures, and then annealing them to obtain a cladding with a refractive index gradually decreasing radially along the optical fiber. This method not only cannot prepare more complex or special cladding structures, but also has high equipment requirements and cannot precisely control the refractive index of the material.

[0008] Existing technologies also disclose a microstructured cladding single-crystal fiber and its preparation method, which uses steps such as tube bundle stacking and heating stretching to prepare the microstructured cladding single-crystal fiber. However, its microstructured cladding material remains silicon-based glass, which cannot meet the requirements of near-infrared laser transmission, and there is a lack of effective data to confirm its ability to suppress higher-order modes of the beam.

[0009] Existing technology also discloses a selenium-tellurium single-crystal composite optical fiber and its preparation method. First, an amorphous selenium-tellurium compound core with a glass cladding is prepared using a drawing method. Then, the fiber core undergoes single-crystalization treatment, that is, the amorphous selenium-tellurium compound core in the composite optical fiber is transformed into a single-crystal selenium-tellurium compound through laser heating. During the single-crystalization process, the selenium-tellurium compound region in the core melts, but the melt temperature is below the cladding glass transition temperature. Therefore, under the constraint of the cladding glass, the selenium-tellurium single-crystalization process can maintain its original geometric shape. However, since high-melting-point crystal materials such as sapphire, yttrium aluminum garnet, and lutetium oxide are difficult to match with cladding materials, this invention method is only applicable to crystal materials with lower melting points.

[0010] Existing technology also discloses a single-crystal optical fiber and its fabrication method. First, multiple tubular glass preforms with matched inner and outer diameters are prepared. Then, the preforms are hot-drawn to obtain a two-layer glass cladding. Finally, a solid single-crystal fiber is inserted into the inner cladding of the glass cladding and then heated and tapered to obtain a single-crystal optical fiber with a glass cladding. However, the single-crystal optical fiber with an air-hole cladding structure prepared by this method is relatively difficult to fabricate because the air holes are prone to collapse during the heating and tapering process, making it difficult to maintain its shape.

[0011] Given the current problems in the fabrication of single-crystal optical fibers, it is necessary to make improvements. Summary of the Invention

[0012] To address the aforementioned issues, this application provides a special optical fiber with a superstructure, its fabrication method, and its applications. By designing a superstructure for the cladding of the special optical fiber, effective control over its transmission modes, transmission loss, and other performance characteristics is achieved, enabling few-mode, low-loss transmission. Furthermore, by optimizing the cladding material composition, the refractive index of the cladding is controlled, thus avoiding the problems associated with introducing air holes into the cladding, such as complex fabrication, easy collapse of the cladding structure, and difficulty in maintaining its shape.

[0013] The specific technical solution of this application is as follows:

[0014] In a first aspect, the present invention provides a special optical fiber with a superstructure, comprising a fiber core and a cladding covering the outer periphery of the fiber core;

[0015] The fiber core is a solid monocrystalline fiber;

[0016] The cladding structure is a refractive index-guided photonic crystal superstructure.

[0017] Preferably, in the special optical fiber, the cladding has a plurality of through holes located along the outer periphery of the fiber core, and the refractive index of the cladding is less than that of the solid single-crystal fiber.

[0018] Preferably, the special optical fiber with superstructure is made of a solid single-crystal fiber made of at least one of metal oxide single crystals, oxyacid salt single crystals and fluoride single crystals, or any of the above single-crystal materials doped with rare earth elements or any of the above single-crystal materials doped with transition metal elements.

[0019] Preferably, in the special optical fiber, the cladding material is a crystal material or a glass material, wherein the crystal material includes any one of oxide single crystal, oxyacid salt single crystal and fluoride single crystal, or any one of the above single crystal materials doped with rare earth elements, or any one of the above single crystal materials doped with transition metal elements.

[0020] The glass material includes at least one of silicate glass, borate glass, phosphate glass, germanate glass, tellurate glass, leadate glass, and lanthanide glass.

[0021] Preferably, the special optical fiber with superstructure has a diameter of 50 μm to 2 mm and a core diameter of 10 μm to 1 mm.

[0022] Preferably, the special optical fiber with superstructure has a cladding material that is a crystalline material, and its preparation method includes any one of atomic layer deposition, magnetron sputtering, dip coating, hydrothermal growth, molten salt growth, and liquid phase epitaxy.

[0023] Preferably, in the special optical fiber with superstructure, the cross-sectional shape of the through hole includes any one of circular, rectangular, square, and star shapes;

[0024] The cross-sectional shape of the special optical fiber includes any one of the following: circular, rectangular, square, or star-shaped.

[0025] Secondly, the present invention also provides a method for fabricating the above-mentioned special optical fiber with a superstructure, comprising the following steps:

[0026] Solid monocrystalline fiber was selected as the fiber core;

[0027] The insulating glass material is thermally drawn to obtain the cladding;

[0028] Solid single-crystal fibers are inserted into the cladding and thermoset to obtain special optical fibers.

[0029] Alternatively, the insulating glass material can be thermally drawn to obtain a capillary glass tube, which is adapted to the through hole and the fiber core.

[0030] Heat seal one end of the capillary glass tube;

[0031] The heat-sealed capillary glass tube is placed inside a hollow glass tube. Under the condition of drawing a negative pressure on the capillary glass tube, the hollow glass tube is hot-drawn to obtain a cladding with through holes and fiber core holes.

[0032] Solid single-crystal fibers are inserted into the core hole and thermoset to obtain special optical fibers.

[0033] Preferably, in the method for fabricating the special optical fiber with a superstructure, the capillary glass tube is either a capillary glass tube with a circular cross-section or a capillary glass tube with an irregular cross-section.

[0034] Thirdly, the present invention also provides an application of the special optical fiber with superstructure described above or the special optical fiber with superstructure prepared by the aforementioned preparation method in fiber lasers.

[0035] The special optical fiber with a superstructure of the present invention has the following advantages over the prior art:

[0036] 1. The special optical fiber with a superstructure of the present invention controls the equivalent refractive index of the cladding by superstructure design, which expands the selection range of cladding materials and enables effective control over the transmission modes and transmission loss of the special optical fiber, achieving few-mode and low-loss transmission. Furthermore, the effective control of the equivalent refractive index of the cladding allows for matching suitable cladding structures and materials to fiber cores of different materials, resulting in wide applications.

[0037] 2. The special optical fiber drawing process with superstructure proposed in this invention is simple and not easily contaminated during the drawing process. It avoids the problems of complicated preparation, easy collapse of cladding structure and difficulty in maintaining shape caused by introducing additional air holes in the cladding.

[0038] 3. The special optical fiber with a superstructure prepared by this invention provides a foundation for research on high-power laser output and high-temperature sensing based on single-crystal optical fibers. The application of single-crystal optical fibers in lasers is expected to break the output limits of existing fiber lasers, enabling a leapfrog increase in the output power of fiber lasers. Furthermore, when applied to sensors, it can operate in extreme environments such as high temperature, high pressure, strong radiation, strong electromagnetic interference, flammability, explosiveness, and strong corrosiveness. Attached Figure Description

[0039] 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 these drawings without creative effort.

[0040] Figure 1 The diagram shows the fiber thermal drawing device provided by the present invention, wherein 11 is a preform clamp, 12 is a pressure control connector, 13 is a preform, 14 is a heating furnace, 15 is a laser diameter gauge, 16 is a traction device, 17 is a cutting device, 18 is the fiber obtained by thermal drawing, and 19 is a winding and take-up device.

[0041] Figure 2 This is a schematic diagram of laser-heated thermosetting provided by the present invention.

[0042] Figure 3 This is a cross-sectional electric field mode distribution diagram of the special optical fiber with glass cladding prepared by the tube thermosetting technique in Embodiment 1 of the present invention.

[0043] Figure 4This is a cross-sectional view of the characteristic optical fiber prepared using the sleeve tapering technique provided in Embodiment 1 of the present invention.

[0044] Figure 5 This is a transmission mode diagram of the special optical fiber with glass cladding prepared by the thermosetting sleeve technology in Embodiment 1 of the present invention.

[0045] Figure 6 This is a cross-sectional electric field mode distribution diagram of the special optical fiber with a 6-hole glass cladding structure prepared by the sleeve tapering technique in Embodiment 2 of the present invention.

[0046] Figure 7 This is a cross-sectional view of the special optical fiber with a 6-hole glass cladding structure prepared by the sleeve tapering technique provided in Embodiment 2 of the present invention.

[0047] Figure 8 This is a transmission mode diagram of the special optical fiber with a 6-hole glass cladding structure prepared by the sleeve tapering technique in Embodiment 2 of the present invention.

[0048] Figure 9 This is a cross-sectional electric field mode distribution diagram of the special optical fiber with a 12-hole glass cladding structure prepared by the sleeve tapering technique in Embodiment 3 of the present invention.

[0049] Figure 10 This is a cross-sectional view of the special optical fiber with a 12-hole glass cladding structure prepared by the sleeve tapering technique provided in Embodiment 3 of the present invention.

[0050] Figure 11 This is a mode transmission diagram of a special optical fiber with a 12-hole glass cladding structure prepared by the sleeve tapering technique in Embodiment 3 of the present invention.

[0051] Figure 12 This is a cross-sectional electric field mode distribution diagram of the special optical fiber with an 18-hole glass cladding structure prepared by the sleeve tapering technique in Embodiment 4 of the present invention.

[0052] Figure 13 This is a cross-sectional view of the special optical fiber with an 18-hole glass cladding structure prepared using the sleeve tapering technique provided in Embodiment 4 of the present invention.

[0053] Figure 14 This is a mode transmission diagram of a special optical fiber with an 18-hole glass cladding structure, prepared by the sleeve tapering technique in Embodiment 4 of the present invention. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. 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.

[0055] To better understand the invention and not to limit its scope, all figures indicating amounts, percentages, and other numerical values ​​used in this application should, in all cases, be understood to be modified by the word "approximately." Therefore, unless specifically stated otherwise, the numerical parameters listed in the specification and appended claims are approximate values ​​and may vary depending on the desired properties being sought. Each numerical parameter should at least be considered as obtained based on reported significant figures and through conventional rounding methods.

[0056] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0057] This invention provides a special optical fiber with a superstructure, comprising a fiber core and a cladding covering the outer periphery of the fiber core;

[0058] The core is a solid monocrystalline fiber;

[0059] The cladding structure is a refractive index-guided photonic crystal superstructure.

[0060] In some embodiments, the cladding structure is a refractive index-guided photonic crystal superstructure. Its specific structural design is as follows: several through holes are opened in the cladding along the outer periphery of the fiber core. The refractive index of the cladding is less than that of the solid single crystal fiber, and its light guiding mechanism is similar to the light guiding mechanism of total internal reflection.

[0061] Specifically, the number of through holes is not limited and can be 2, 3, 4, 5, 6... 12... 18, etc. The through holes are periodically arranged on the outer periphery of the fiber core.

[0062] Specifically, if there are 6 through holes, the 6 through holes are evenly distributed around the outer periphery of the fiber core along the circumferential direction;

[0063] If there are 12 through holes, then 6 through holes are evenly distributed around the outer periphery of the fiber core along the circumference, and the other 6 through holes are evenly distributed around the outer periphery of the circumference where the inner 6 through holes are located.

[0064] If there are 18 through holes, 6 through holes are evenly distributed around the outer periphery of the fiber core along the circumference, and the other 12 through holes are evenly distributed around the outer periphery of the circumference where the 6 through holes are located on the inner side.

[0065] In some embodiments, the material of the solid single-crystal fiber includes at least one of metal oxide single crystals, oxoacid salt single crystals and fluoride single crystals, or any of the above single-crystal materials doped with rare earth elements, or any of the above single-crystal materials doped with transition metal elements.

[0066] Specifically, the doped rare earth ions include Nd 3+ Yb 3+ Tm 3+ Ho 3+ Er 3+ Pr 3+ 、Sm 2+ Doped transition metal ions include Cr 3+ Ti 3+ Ni 2+ Co 2+ wait.

[0067] In some embodiments, the cladding material of the special optical fiber with a superstructure is a crystalline material or a glass material. The crystalline material includes, but is not limited to, any one of metal oxide single crystals, oxyacid salt single crystals, and fluoride single crystals, or rare earth element doping or transition metal element doping of any of the above single crystal materials. The glass material includes, but is not limited to, silicate glass, borate glass, phosphate glass, germanate glass, tellurate glass, leadate glass, lanthanide glass, and hybrid glasses of the above-mentioned glasses.

[0068] In some embodiments, specifically, the cladding of a special optical fiber needs to have a thermal expansion coefficient close to that of a solid single-crystal fiber.

[0069] In some embodiments, the diameter of the special optical fiber is 50 μm to 2 mm; the diameter of the fiber core is 10 μm to 1 mm.

[0070] In some embodiments, the cladding material is a crystalline material, and its preparation method includes any one of atomic layer deposition, magnetron sputtering, dip coating, hydrothermal growth, molten salt growth, and liquid phase epitaxy.

[0071] In some embodiments, the cross-sectional shape of the through hole includes, but is not limited to, any one of a circle, a rectangle, a square, or a star.

[0072] In some embodiments, the cross-sectional shape of the special optical fiber includes, but is not limited to, any one of circular, rectangular, square, or star shapes.

[0073] Based on the same invention, this invention also provides a method for fabricating the above-mentioned special optical fiber with a superstructure, comprising the following steps:

[0074] S1. Select solid monocrystalline fiber as the fiber core;

[0075] S2. The insulating glass material is thermally drawn to obtain the cladding;

[0076] S3. Insert solid single-crystal fibers into the cladding and heat-set them to obtain special optical fibers.

[0077] Specifically, in the above embodiments, the cladding is obtained by thermally drawing the insulating glass material, and a solid single-crystal fiber is inserted into the cladding. Then, the cladding and the fiber core are tightly bonded by thermosetting, while ensuring that the cladding structure does not change. The thermosetting temperature is slightly higher than the melting temperature of the insulating glass material. At this temperature, the insulating glass material will melt, while the solid single-crystal fiber will not change during the thermosetting process. After the insulating glass material melts, it is bonded to the solid single-crystal fiber, thus finally obtaining the special optical fiber. It can be understood that the special optical fiber prepared by this method does not contain a through hole in the cladding.

[0078] In some embodiments, the method for fabricating the above-described special optical fiber with a superstructure includes the following steps:

[0079] S1. Select solid monocrystalline fiber as the fiber core;

[0080] S2. The insulating glass material is hot-drawn to obtain a capillary glass tube, which is matched with the through hole and the fiber core.

[0081] S3. Heat seal one end of the capillary glass tube;

[0082] S4. Place the heat-sealed capillary glass tube inside the hollow glass tube, and heat-draw the hollow glass tube under the condition of drawing a negative pressure on the capillary glass tube to obtain a cladding with through holes and fiber core holes.

[0083] Solid single-crystal fibers are inserted into the core hole and thermoset to obtain special optical fibers.

[0084] Specifically, in the above embodiments, the number of capillary glass tubes is the same as the number of through holes and the number of fiber cores. For example, if there are 6 through holes and 1 fiber core, the hollow glass material is hot-drawn to obtain 7 capillary glass tubes. Then, the 7 capillary glass tubes are arranged in the hollow glass tubes according to the pattern of through holes and fiber cores to obtain a primary preform. Among them, 6 capillary glass tubes are used to form 6 through holes, and the middle capillary glass tube is used to form a fiber core hole for fiber core insertion. Under the condition of negative pressure applied to the capillary glass tubes, the hollow glass tubes are hot-drawn to obtain a cladding with through holes and fiber core holes. Specifically, it is known that hot drawing is performed under a negative pressure of 0.05~0.1kPa to obtain a cladding with through holes and fiber core holes. Then, solid single crystal fibers are inserted into the fiber core holes and thermoset to obtain special optical fibers.

[0085] In some embodiments, the capillary glass tube is a capillary glass tube with a circular cross-section or a capillary glass tube with an irregular cross-section.

[0086] Specifically, the present invention employs Figure 1 The fiber thermal drawing apparatus shown is used to thermally draw a primary preform to obtain a cladding with through holes and core holes; specifically, Figure 1 11 is the preformed bar clamp, 12 is the pressure control connector, 13 is the preformed bar, 14 is the heating furnace, 15 is the laser diameter gauge, 16 is the traction device, 17 is the cutting device, 18 is the fiber obtained by hot drawing (i.e., the cladding), and 19 is the winding and take-up device.

[0087] Specifically, in this invention, a solid single-crystal fiber is inserted into the fiber core hole and thermoset to obtain a special optical fiber, wherein the thermosetting is performed by laser heating. Figure 2 The diagram shows a laser heating process provided by the present invention, wherein 21 is a solid single-crystal fiber, 22 is a glass cladding with a special structure, and 23 is a laser heating process.

[0088] This invention adjusts the equivalent refractive index of the cladding by employing a superstructure design on the cladding of a special fiber core. The cladding material can be selected and controlled over a wide range, ultimately matching parameters such as the refractive index and coefficient of thermal expansion of the cladding with those of the single-crystal fiber core. This allows for effective control over the transmission modes and transmission losses of the special optical fiber. Furthermore, the fabrication process of this invention is simple, reduces the introduction of impurities, and, more importantly, avoids the numerous problems associated with introducing additional air holes into the cladding, such as increased fabrication complexity, easy collapse of the cladding structure, and difficulty in maintaining its shape.

[0089] Based on the same inventive concept, the present invention also provides an application of the above-mentioned special optical fiber with a superstructure or the special optical fiber with a superstructure prepared by the above-mentioned preparation method in fiber lasers.

[0090] The following detailed embodiments further illustrate the special optical fiber with a superstructure and its fabrication method of this application. This section further explains the invention in conjunction with specific embodiments, but should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in the art.

[0091] In the following examples, the refractive index of sapphire single crystal at 1 μm wavelength is 1.76, the refractive index of borosilicate at 1 μm wavelength is 1.52, the refractive index of lutetium oxide single crystal at 2.8 μm wavelength is 1.89, and the refractive index of lanthanide glass at 2.8 μm wavelength is 1.88.

[0092] Example 1

[0093] This application provides a special optical fiber with a conventional core-cladding structure, such as... Figure 4 As shown, it includes a fiber core 21 and a cladding 22 covering the outer periphery of the fiber core 21;

[0094] Specifically, the fabrication method of this special optical fiber includes the following steps:

[0095] S1. Select sapphire single crystal fiber with a diameter of 50μm as the core and borosilicate glass as the cladding material;

[0096] S2. The customized borosilicate glass tube is hot-drawn to obtain a borosilicate glass cladding with an outer diameter of 450μm and an inner diameter of 75μm. The hot-drawing temperature is 760℃, the drawing speed is 480mm / min, the rod feeding speed is 0.5mm / min, and the thickness of the cladding is controllable.

[0097] S3. On the working platform of a digital microscope, a solid sapphire single crystal fiber is inserted into the glass cladding, and then the cladding and the fiber core are tightly bonded by thermosetting, while ensuring that the cladding structure does not change; wherein, the thermosetting temperature is 800℃ and the thermosetting time is 5min.

[0098] Figure 3 The image shows the cross-sectional electric field mode distribution of the glass-clad single-crystal special optical fiber prepared in Example 1 above. For a beam with a wavelength of 1 μm, the transmission loss in the fundamental mode is 1.42 × 10⁻⁶. -13 dB / m. For example... Figure 5 The results show that this special optical fiber can achieve four modes of few-mode transmission, namely LP... 01 Model (fundamental model), LP 11 Model, LP 12 Model, LP 13 The modulus, with corresponding losses of 1.42 × 10⁻⁶. -133.67×10 -12 1.62×10 -11 1.81×10 -8 dB / m, higher-order modes are effectively suppressed.

[0099] Example 2

[0100] This application provides a special single-crystal optical fiber with a 6-hole periodic symmetric structure, such as... Figure 7 As shown, it includes a fiber core 21 and a cladding 22 covering the outer periphery of the fiber core 21. The cladding 22 has 6 through holes 24 located along the outer periphery of the fiber core 21. The 6 through holes 24 are evenly arranged along the circumferential direction on the outer periphery of the fiber core 21.

[0101] The method for preparing the above-mentioned special optical fiber includes the following steps:

[0102] S1. Select sapphire single crystal fiber with a diameter of 50μm as the core and borosilicate glass as the cladding material;

[0103] S2. A capillary glass tube with an outer diameter of 1.3 mm and an inner diameter of 0.66 mm was prepared by hot drawing of a customized borosilicate glass tube. The hot drawing temperature was 760℃. A total of 7 capillary glass tubes were prepared.

[0104] S3. Use a propane flame to heat seal each capillary glass tube at one end. Stack the 7 capillary glass tubes according to the above-mentioned through hole and fiber core arrangement, and then sleeve them with a borosilicate glass tube with an outer diameter of 8 mm and an inner diameter of 4 mm to obtain a primary preform.

[0105] S4. The primary preform is hot-drawn under a negative pressure of 0.1 kPa. By adjusting the hot-drawing process parameters, a glass cladding with a 6-hole structure with an outer diameter of 800 μm, a core hole diameter of 75 μm, and an outer peripheral through hole diameter of 75 μm is obtained.

[0106] S5. Insert a 50μm diameter sapphire single crystal fiber into the core hole of the borosilicate glass cladding, and then melt the cladding onto the single crystal fiber using a heated tapering method, while ensuring that the cladding structure does not change. The heating temperature is 800℃ and the heating time is 5min.

[0107] Figure 6 The image shows the cross-sectional electric field mode distribution of the single-crystal optical fiber with a 6-hole glass cladding prepared in Example 2 above. For a beam with a wavelength of 1 μm, the transmission loss in the fundamental mode is 4.52 × 10⁻⁶. -13 dB / m. For example... Figure 8 The results show that this optical fiber can achieve four modes of few-mode transmission, namely LP... 01 Model (fundamental model), LP 11 Model, LP12 Model, LP 13 The modulus, with corresponding losses of 4.52 × 10⁻⁶. -13 4.57×10 -12 2.34×10 -12 9.65×10 -9 dB / m, higher-order modes are effectively suppressed.

[0108] Example 3

[0109] This application provides a special single-crystal optical fiber with a 12-hole periodic symmetric structure, such as... Figure 10 As shown, it includes a fiber core 21 and a cladding 22 covering the outer periphery of the fiber core 21. The cladding 22 has 12 through holes 24 along the outer periphery of the fiber core 21. Among them, 6 through holes 24 are evenly arranged along the circumferential direction on the outer periphery of the fiber core 21, and the other 6 through holes are evenly arranged along the outer periphery of the circumference where the 6 inner through holes 24 are located.

[0110] The method for preparing the above-mentioned special optical fiber includes the following steps:

[0111] S1. Select sapphire single crystal fiber with a diameter of 50μm as the core and borosilicate glass as the cladding material;

[0112] S2. A capillary glass tube with an outer diameter of 1.55 mm and an inner diameter of 0.78 mm was prepared by hot drawing of a customized borosilicate glass tube. The hot drawing temperature was 760℃. A total of 13 capillary glass tubes were prepared.

[0113] S3. Use a propane flame to heat seal each capillary glass tube at one end. Stack the 13 capillary glass tubes according to the above-mentioned through hole and fiber core arrangement, and then sleeve them with a borosilicate glass tube with an outer diameter of 16 mm and an inner diameter of 8 mm to obtain a primary preform.

[0114] S4. The primary preform is hot-drawn under a negative pressure of 0.1 kPa. By adjusting the hot-drawing process parameters, a glass cladding with a 12-hole structure with an outer diameter of 800 μm, a core hole diameter of 75 μm, and an outer peripheral through hole diameter of 75 μm is obtained.

[0115] S5. Insert a 50μm diameter single crystal fiber into the core hole of the borosilicate glass cladding, and then melt the glass cladding onto the single crystal fiber using a heated tapering method, while ensuring that the cladding structure does not change. The heating temperature is 800℃ and the heating time is 5min.

[0116] Figure 9 The image shows the cross-sectional electric field mode distribution of the single-crystal optical fiber with a 12-hole glass cladding prepared in Example 3 above. For a beam with a wavelength of 1 μm, the transmission loss in the fundamental mode is 2.17 × 10⁻⁶.-13 dB / m. For example... Figure 11 The results show that this optical fiber can achieve four modes of few-mode transmission, namely LP... 01 Model (fundamental model), LP 11 Model, LP 12 Model, LP 13 The modulus, with corresponding losses of 2.17 × 10⁻⁶. -13 2.65×10 -12 5.71×10 -12 5.83×10 -9 dB / m, higher-order modes are effectively suppressed.

[0117] Example 4

[0118] This application provides a special single-crystal optical fiber with an 18-hole periodic symmetric structure, such as... Figure 13 As shown, it includes a fiber core 21 and a cladding 22 covering the outer periphery of the fiber core 21. The cladding 22 has 18 through holes 24 along the outer periphery of the fiber core 21. Among them, 6 through holes 24 are evenly arranged along the circumferential direction on the outer periphery of the fiber core 21, and the other 12 through holes are evenly arranged along the outer periphery of the circumference where the 6 inner through holes are located.

[0119] The method for preparing the above-mentioned special optical fiber includes the following steps:

[0120] S1. Select lutetium oxide single crystal fiber with a diameter of 75μm as the core and lanthanide glass as the cladding material;

[0121] S2. Lanthanide glass capillary tubes with an outer diameter of 1.85 mm and an inner diameter of 0.93 mm were prepared by hot drawing of a customized lanthanide glass tube. The hot drawing temperature was 660℃. A total of 19 capillary glass tubes were prepared.

[0122] S3. Use a butane flame to heat seal each capillary glass tube at one end. Stack 19 lanthanide glass capillary glass tubes according to the above-mentioned through hole and fiber core arrangement. Then, sleeve them with lanthanide glass tubes with an outer diameter of 18 mm and an inner diameter of 9.7 mm to obtain a primary preform. Fix it with high-temperature resistant inorganic adhesive.

[0123] S4. The primary preform is hot-drawn under a negative pressure of 0.1 kPa. By adjusting the hot-drawing process parameters, a glass cladding with an outer diameter of 1200 μm, a central hole diameter of 100 μm, and an outer peripheral hollow hole diameter of 100 μm with an 18-hole structure is obtained.

[0124] S5. Insert a single crystal fiber with a diameter of 75 μm into the core hole of the lanthanide glass cladding. Then, fused the glass cladding onto the single crystal fiber using a heated tapering method, while ensuring that the cladding structure does not change. The heating temperature is 800℃ and the heating time is 5 min.

[0125] Figure 12 The image shows the cross-sectional electric field mode distribution of a single-crystal fiber with an 18-hole glass cladding, fabricated using the sleeve tapering technique. For a beam with a wavelength of 2.8 μm, the transmission loss in the fundamental mode is 1.93 × 10⁻⁶. -12 dB / m. For example... Figure 14 The results show that this optical fiber can achieve four modes of few-mode transmission, namely LP... 01 Model (fundamental model), LP 11 Model, LP 12 Model, LP 13 The modulus, with corresponding losses of 1.93 × 10⁻⁶. -12 1.71×10 -11 1.01×10 -11 1.30×10 -11 dB / m, higher-order modes are effectively suppressed.

[0126] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A special optical fiber with a superstructure, characterized in that, Includes the fiber core and the cladding covering the outer periphery of the fiber core; The cladding has 12 through holes along the outer periphery of the fiber core. Six of the through holes are evenly distributed along the circumference of the fiber core, while the other six through holes are evenly distributed along the outer periphery of the circumference of the six inner through holes. The method for preparing the above-mentioned special optical fiber includes the following steps: S1. Select sapphire single crystal fiber with a diameter of 50μm as the core and borosilicate glass as the cladding material; S2. A capillary glass tube with an outer diameter of 1.55 mm and an inner diameter of 0.78 mm was prepared by hot drawing of a borosilicate glass tube. The hot drawing temperature was 760 ℃. The number of capillary glass tubes prepared was 13. S3. Use a propane flame to heat seal each capillary glass tube at one end. Stack the 13 capillary glass tubes according to the above-mentioned through hole and fiber core arrangement, and then sleeve them with a borosilicate glass tube with an outer diameter of 16 mm and an inner diameter of 8 mm to obtain a primary preform. S4. The primary preform is hot-drawn under a negative pressure of 0.1 kPa. By adjusting the hot-drawing process parameters, a glass cladding with a 12-hole structure with an outer diameter of 800 μm, a core hole diameter of 75 μm, and an outer peripheral through hole diameter of 75 μm is obtained. S5. Insert a single crystal fiber with a diameter of 50 μm into the core hole of the borosilicate glass cladding, and then melt the glass cladding onto the single crystal fiber using a heated tapering method. The heating temperature is 800 ℃ and the heating time is 5 min.

2. The special optical fiber with a superstructure as described in claim 1, characterized in that, The cross-sectional shape of the through hole includes any one of the following: circular, rectangular, square, and star-shaped. The cross-sectional shape of the special optical fiber includes any one of the following: circular, rectangular, square, or star-shaped.

3. The application of a special optical fiber with a superstructure as described in any one of claims 1 to 2 in a fiber laser.

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