Multi-core optical fiber manufacturing method, multi-core optical fiber, and fiber oscillator

Abstract

The application provides a multi-core optical fiber preparation method, a multi-core optical fiber and an optical fiber oscillator. The method comprises the following steps: preparing an inner quartz tube and performing grinding processing; performing core layer deposition on the inner quartz tube after the grinding processing, doping rare earth ions in a loose layer formed in the core layer deposition, and removing a gap between the inner quartz tube and the core layer by heating the inner quartz tube with the deposited core layer, so as to sinter a single-core preform rod; preparing an outer quartz tube, placing N single-core preform rods in the outer quartz tube in parallel to perform sleeve assembly, filling a gap between the single-core preform rods by using a solid quartz rod, and controlling the interval between the cores of adjacent single-core preform rods, so as to obtain a multi-core preform; and placing the multi-core preform in a drawing tower to perform drawing and coating, so as to obtain a multi-core optical fiber. The application can ensure the independent transmission of optical signals of each core in the multi-core optical fiber, and is beneficial to improving the TMI threshold of the whole optical fiber.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber technology, and in particular to a method for preparing multi-core optical fibers, multi-core optical fibers, and optical fiber oscillators. Background Technology

[0002] Over the past two decades, thanks to cladding pumping technology and improved pump brightness, fiber lasers have continuously increased the average output power of solid-state lasers while maintaining diffraction-limited beam quality. However, power increases in fiber lasers have gradually encountered some physical bottlenecks, partly due to nonlinear effects caused by excessively concentrated power density. Furthermore, because the thermal conductivity of fiber materials is approximately one-tenth that of crystal materials used in common solid-state lasers, heat accumulation at high power operation leads to a series of problems that further limit power growth. For fiber lasers requiring high stability and high beam quality, thermally induced mode distortion / instability (TMI) is a major challenge that urgently needs to be addressed. While nonlinear effects can be mitigated by increasing the mode area, increasing the mode area inevitably makes higher-order modes easier to excite, resulting in a lower TMI threshold. Therefore, these two power constraints are directly contradictory. Currently, the potential for further power increases in single-core fiber is limited, with the highest output power stagnating in the tens of kilowatts range.

[0003] Multi-core optical fibers with multiple cores bundled in parallel are considered promising for further improving the signal transmission power of single-fiber output. Multi-core fibers have significant potential applications in power enhancement. For example, using multi-core fibers, coherently synthesized multiple independent amplifiers can be bundled and concentrated into a single multi-core fiber sharing a common pump. This can largely overcome the spatial separation and system complexity drawbacks of traditional coherent synthesis schemes, expanding the application scenarios of coherent synthesis methods. However, traditional coupled-core multi-core fibers, due to their small core spacing, are prone to crosstalk and supermode, resulting in a lower TMI threshold. Therefore, designing and fabricating uncoupled multi-core fibers can significantly extend the upper limit of single-fiber output power. Similar to single-core fibers, variable core area technology is beneficial for generating high-power and high-pulse-energy lasers in multi-core fibers. The design of tapered fibers can significantly increase the laser mode field area and available doping volume, improving the energy extractable per unit fiber length and maintaining near-ideal beam quality while reducing nonlinear effects. However, simply applying the ordinary tapered fiber drawing process to multi-core fibers to produce common tapered multi-core fibers results in an angle between the transmitted light in each core and the fiber axis due to the tapered angle between each core and the fiber axis. This causes the beams in each core to diverge, as shown in the attached figure. Figure 1 The image shown is a cross-sectional view of a typical tapered multi-core optical fiber. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a method for preparing multi-core optical fibers, a multi-core optical fiber, and an optical fiber oscillator.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for fabricating multi-core optical fibers includes the following steps:

[0007] (1) Prepare the inner quartz tube and perform grinding;

[0008] Let N be the number of fiber cores in the multi-core optical fiber to be processed, where N is greater than or equal to 2;

[0009] Prepare N inner quartz tubes, and perform acid washing and grinding on each inner quartz tube to ensure that the dimensions and shapes of each inner quartz tube are the same after processing.

[0010] (2) Core layer deposition is performed on the inner quartz tube after grinding and processing. Rare earth ions are doped into the loose layer formed by core layer deposition. The gap between the inner quartz tube and the core layer is removed by heating the inner quartz tube with core layer deposition and sintering the rod to obtain a single core preform.

[0011] (3) Prepare the outer quartz tube and bundle the N single-core preforms from the outer quartz tube sleeve;

[0012] The outer quartz tube is acid-washed and ground to make the inner wall of the outer quartz tube into a square with rounded corners. N single-core preforms are then bundled together and placed parallel inside the outer quartz tube. The N single-core preforms are arranged in an array in the inner cavity of the outer quartz tube. The outer wall of the single-core preforms is in close contact with the inner wall of the outer quartz tube. At the same time, solid quartz rods are used to fill the gaps between the single-core preforms, and the spacing d between the cores of adjacent single-core preforms is controlled to obtain a multi-core preform.

[0013] (5) The multi-core preform is placed into the drawing tower for drawing and coating to obtain multi-core optical fiber.

[0014] Furthermore, in step (3), N single-core preforms are arranged in a square, rectangular or circular array in the inner cavity of the outer quartz tube.

[0015] Furthermore, in step (2), the doped rare earth ions are one or more of ytterbium, erbium, cerium, thulium, and holmium.

[0016] Further, in step (2), the inner quartz tube after grinding is deposited with a core layer by vapor deposition, plasma chemical vapor deposition, or chemical vapor deposition, and a loose core layer is deposited.

[0017] Furthermore, in step (1), the outer wall of the inner quartz tube after processing is circular, and the inner wall of the inner quartz tube is ground and processed into a frustum shape with the diameter gradually increasing from one end to the other end.

[0018] Furthermore, in step (3), the spacing d between adjacent single-core preforms is 1.5 to 2 times the core diameter.

[0019] Further, in step (4), the lower end of the multi-core preform is heated and melted using the heating device in the drawing tower, and the bare optical fiber is gradually pulled out from one end of the multi-core preform downwards. The wire diameter measuring device measures the wire diameter of the pulled bare optical fiber and controls the drawing speed of the traction disc. The coating and curing device coats the resin material onto the bare optical fiber to form a finished fiber. The winding device winds the finished fiber into an optical fiber disc.

[0020] On the other hand, the present invention provides a multi-core optical fiber prepared by the multi-core optical fiber preparation method described above.

[0021] On the other hand, the present invention provides an optical fiber oscillator, which uses a multi-core optical fiber prepared by the multi-core optical fiber preparation method described above as a multi-core gain optical fiber.

[0022] This invention provides a method for fabricating multi-core optical fibers, to solve the following problems: Figure 1 The conventional tapered multi-core optical fiber shown has an angle problem in its inter-core optical transmission.

[0023] Furthermore, by controlling the spacing between fiber cores between adjacent single-core preforms, the present invention can ensure the independent transmission of optical signals in each core of the fabricated multi-core optical fiber, which is beneficial to improving the overall TMI threshold of the optical fiber.

[0024] Furthermore, the present invention processes the inner quartz tube, and the outer wall of the processed inner quartz tube is circular. The inner wall of the inner quartz tube is ground and processed into a frustum, saddle, or biconical shape with the diameter gradually changing from one end to the other. This ensures that the core-to-cladding ratio of the fabricated multi-core optical fiber is designed to be gradually changing, which is beneficial to balancing mode instability and nonlinear effects. By increasing the mode field area at the large end of the fiber core, nonlinear effects are suppressed, while the small end maintains good beam quality laser injection, which is beneficial to improving the TMI threshold.

[0025] Furthermore, since the outer wall of the inner quartz tube after processing is circular, and the inner wall of the inner quartz tube is ground into a frustum shape with the diameter gradually increasing from one end to the other, the single-core preform itself is designed with a tapered core. In step (4), it is not necessary to control the feeding and drawing speed to obtain tapered optical fiber. In the drawing process of step (4), uniform drawing speed can be maintained, and multi-core optical fiber with a gradually changing core-cladding ratio can also be obtained.

[0026] Furthermore, compared with conventional tapered / spindle-shaped multi-core optical fibers with a constant core-to-cladding ratio, the multi-core optical fiber designed in this invention has parallel cores, enabling parallel emission of laser light from each core. Attached Figure Description

[0027] 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.

[0028] Figure 1 This is a cross-sectional view of a typical tapered multi-core optical fiber.

[0029] Figure 2 A flowchart illustrating a method for fabricating a multi-core optical fiber according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the structure of the processed inner quartz tube in one embodiment of the present invention, wherein (a) is a transverse cross-sectional view; and (b) is a longitudinal cross-sectional view.

[0031] Figure 4 This is a schematic diagram of a sintered rod with a core layer deposited in an inner quartz tube according to an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the outer quartz tube after grinding according to an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of a bundled sleeve according to an embodiment of the present invention;

[0034] Figure 7 This is a longitudinal and transverse cross-sectional view of a multi-core optical fiber with a graded core-to-cladding ratio prepared according to an embodiment of the present invention.

[0035] Figure 8 This is a cross-sectional view of a multi-core optical fiber with a gradually varying core-to-cladding ratio (n×n) obtained by changing the number of cores in a bundle according to an embodiment of the present invention.

[0036] Figure 9 A diagram illustrating the relationship between core-to-core distance and coupling coefficient in the multi-core optical fiber spacing design of embodiments of the present invention;

[0037] Figure 10 This is a schematic diagram of the structure of an optical fiber oscillator according to an embodiment of the present invention;

[0038] Figure 11 This is a schematic cross-sectional view of a multi-core gain optical fiber according to an embodiment of the present invention;

[0039] Figure 12This is a cross-sectional view of the pump reflector etched in an optical fiber oscillator according to an embodiment of the present invention;

[0040] Figure 13 This is a schematic diagram of the structure of a multi-core gain optical fiber used in one embodiment of the present invention;

[0041] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Specific implementation methods

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the spirit of the disclosed content will be clearly explained below with reference to the accompanying drawings and detailed description. Any person skilled in the art, after understanding the embodiments of the present invention, can make changes and modifications based on the techniques taught in the present invention without departing from the spirit and scope of the present invention. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0043] Reference Figure 2 A flowchart of a multi-core optical fiber fabrication method provided in an embodiment of the present invention includes the following steps:

[0044] (1) Prepare the inner quartz tube and perform grinding;

[0045] Let N be the number of fiber cores in the multi-core optical fiber to be processed, where N is greater than or equal to 2;

[0046] Prepare N inner quartz tubes 2-2, and perform acid washing and grinding on each inner quartz tube to ensure that the dimensions and shapes of the inner quartz tubes are the same after processing. Figure 3 This is a schematic diagram of the structure of the processed inner quartz tube in one embodiment of the present invention, where (a) is a transverse cross-sectional view; (b) is a longitudinal cross-sectional view. The outer wall of the processed inner quartz tube 2-2 is circular, and the inner wall 2-3 of the inner quartz tube is ground and processed into a frustum shape with the diameter gradually increasing from one end to the other. Furthermore, it can be understood that the present invention is not limited to grinding and processing the inner wall 2-3 of the inner quartz tube into a frustum shape with the diameter gradually changing from one end to the other; it can also grind and process the inner wall 2-3 of the inner quartz tube into a saddle shape or a double cone shape with the diameter gradually changing from one end to the other.

[0047] (2) Core layer deposition is performed on the ground inner quartz tube 2-2. Rare earth ions are doped into the loose layer formed by core layer deposition. The gap between the inner quartz tube and the core layer is removed by heating the inner quartz tube with the deposited core layer. The rod is then sintered and shrunk to obtain a single-core preform 4-1. Figure 4 The diagram shown is a schematic of the sintering of the core layer of the inner quartz tube into a shrink rod.

[0048] (3) Prepare the outer quartz tube 3-1 and bundle the N single-core preforms 4-1 from the outer quartz tube sleeve;

[0049] The outer quartz tube 3-1 is acid-washed and ground, so that the inner wall 3-2 of the outer quartz tube is ground into a square with rounded corners, such as... Figure 5 As shown.

[0050] like Figure 6 As shown, N single-core preforms 4-1 are placed parallel to each other inside the outer quartz tube for bundling, ensuring that the cores of the resulting multi-core optical fiber are parallel to each other. The N single-core preforms 4-1 are arranged in an array within the inner cavity of the outer quartz tube, with the outer wall of the outer single-core preforms in close contact with the inner wall of the outer quartz tube. Solid quartz rods 6-1 are used to fill the gaps between the single-core preforms 4-1, and the spacing d between the cores of adjacent single-core preforms is controlled, thus obtaining the multi-core preform 5-1.

[0051] (4) The multi-core preform 5-1 is placed into the drawing tower for drawing and coating to obtain multi-core optical fiber.

[0052] In step (4), the lower end of the multi-core preform is heated and melted using the heating device in the drawing tower. The bare optical fiber is gradually pulled out from one end of the multi-core preform downwards. The wire diameter measuring device measures the wire diameter of the pulled bare optical fiber and controls the drawing speed of the traction disc. The coating and curing device coats the resin material onto the bare optical fiber to form a finished fiber. The winding device winds the finished fiber into an optical fiber disc.

[0053] In step (1) of the above embodiment, the outer wall of the inner quartz tube after processing is circular, and the inner wall of the inner quartz tube is ground into a frustum shape with the diameter gradually increasing from one end to the other. This makes the single-core preform itself have a tapered core design. In step (4), it is not necessary to obtain tapered optical fiber by controlling the feeding and drawing speed. During the drawing process in step (4), uniform drawing speed can be maintained, and multi-core optical fiber with a gradually increasing core-to-cladding ratio can also be obtained. Refer to Figure 7 This is a longitudinal and transverse cross-sectional view of a multi-core fiber with a tapered core-to-cladding ratio prepared according to an embodiment of the present invention. This ensures that the core-to-cladding ratio of the prepared multi-core fiber is designed to be tapered, which is beneficial to balancing mode instability and nonlinear effects. The nonlinear effect is suppressed by increasing the mode field area at the large end of the fiber core, while the small end maintains good laser injection beam quality, which is beneficial to improving the TMI threshold.

[0054] In a preferred embodiment, in step (3), N single-core preforms are arranged in an array of various shapes, such as square, rectangular, or circular, within the inner cavity of the outer quartz tube. (Refer to...) Figure 8 , Figure 8 This is a cross-sectional view of a multi-core optical fiber with a gradually varying core-to-packing ratio (n×n) obtained by changing the number of cores in a bundle according to an embodiment of the present invention.

[0055] In a preferred embodiment, in step (2), the doped rare earth ions are one or more of ytterbium, erbium, cerium, thulium, and holmium.

[0056] As a preferred embodiment, in step (2), various existing deposition methods such as vapor deposition, plasma chemical vapor deposition, or chemical vapor deposition are used to deposit the core layer of the ground inner quartz tube, and a loose core layer is deposited.

[0057] Specifically, the spacing *d* between adjacent single-core preforms needs to be controlled. The core-to-core spacing cannot be too small, as this will lead to optical coupling between cores; conversely, the spacing cannot be too large, as this will reduce the compactness of the multi-core fiber and decrease the power scaling potential of a single fiber. (See attached...) Figure 9 The simulation showed that when the core diameter was 20 μm, the coupling between cores varied with the core-core spacing. The simulation results showed that when the core-core spacing d was more than 1.5 times the core diameter, the cores would not be significantly coupled due to the relatively large coupling coefficient, thus exciting the supermode. Therefore, step (3) requires controlling the size of the solid quartz rod and adjusting the spacing d between adjacent single-core preforms to 1.5 to 2 times the core diameter.

[0058] One embodiment of the present invention provides an optical fiber oscillator, using a multi-core fiber prepared by the multi-core fiber preparation method described above as the multi-core gain fiber. Further, a graded core-to-cladding ratio multi-core fiber is used as the multi-core gain fiber. The graded core-to-cladding ratio multi-core gain fiber reduces the effective length and weakens nonlinear effects while maintaining a large core-to-cladding ratio, thereby mitigating mode instability effects. By designing the core-to-core spacing, the multi-core fiber is designed as a non-coupled type, effectively maintaining the TMI threshold of each core. Furthermore, compared with conventional tapered / spindle-shaped multi-core fibers with a constant core-to-cladding ratio, its greater advantage lies in the parallelism between the cores, ensuring parallel laser output from each core.

[0059] Reference Figure 10 In one embodiment, a multi-core fiber optic oscillator is provided, including a pump source 1, a signal pump power combiner 3, a multi-core high-reflectivity grating array 4, a multi-core gain fiber 5, and a multi-core low-reflectivity grating array 6.

[0060] The pump power combiner 3 is a signal fiber-free pump power combiner, and one end of the pump power combiner has multiple pump arms.

[0061] There are multiple pump sources 1, each pump source 1 is connected to a corresponding pump arm on the pump power combiner 3, and each pump arm is engraved with a first high-reflectivity grating 2 for reflecting the signal light transmitted in the pump arm, which can prevent the signal light with excessive power from damaging the pump source.

[0062] The other end of the pump power combiner 3 is connected to the input end of the multi-core gain fiber 5. The multi-core gain fiber 5 has two or more fiber cores. Each fiber core near the input end of the multi-core gain fiber 5 is provided with a second high-reflection grating, forming a multi-core high-reflection grating array 4. Each fiber core near the output end of the multi-core gain fiber 5 is provided with a low-reflection grating, forming a multi-core low-reflection grating array 6.

[0063] A pump reflector 7 is inscribed on the cladding of the multi-core gain fiber 5 between the multi-core low-reflection grating array 6 and the output end of the multi-core gain fiber 5, which can further improve the pump absorption rate and change the longitudinal distribution of gain.

[0064] High-reflectivity grating arrays enable multiple fiber core laser oscillation transmission, ensuring multi-path laser gain and improving output efficiency; low-reflectivity grating arrays enable multiple fiber core laser wavelength selection, controlling laser linewidth and laser output, among other functions.

[0065] Without loss of generality, the pump source 1 may be a semiconductor pump source, preferably a wavelength-stable semiconductor laser.

[0066] Reference Figure 11 Firstly, the multi-core gain fiber 5 in this embodiment includes a core 501 and a cladding, employing a double-cladding structure, including an inner cladding 502 and an outer cladding 503. Multiple cores 501 are arranged in an array, with each core 501 parallel to the others, and each core 501 has a circular cross-section. All cores 501 of the multi-core gain fiber 5 are encased in the inner cladding 502. Adjacent cores 501 are spaced apart by inner cladding material filling the spaces. This spatial separation of the cores increases the mode field area while maintaining the TMI threshold of each core, thereby increasing the single-fiber power several times over. Furthermore, the cores 501 in the inner cladding 502 are arranged in an array, and the thickness of the inner cladding 502 spacing between adjacent cores 501 is equal. The outer contour of the cross-section of the inner cladding 502 is a rounded square. This arrangement prevents pump light from spiraling and failing to enter the core.

[0067] In the above embodiments, the cores of the multi-core gain fiber are parallel to each other. Furthermore, the cores at different length positions in the multi-core gain fiber have equal diameters, and the spacing between the cores is greater than twice the core diameter. (Refer to...) Figure 13In one embodiment, a multi-core gain fiber is used. At the input end, all cores have equal diameters, and the spacing between cores is greater than twice the current core diameter. Similarly, at the middle position, all cores have equal diameters, and the spacing between cores is greater than twice the current core diameter. At the output end, all cores have equal diameters, and the spacing between cores is greater than twice the current core diameter. However, the diameters of the cores at the input end and the output end are smaller than those at the middle position. This overcomes the drawback of traditional multi-core gain fibers, which are prone to crosstalk due to insufficient spacing between cores, resulting in a lower mode instability threshold.

[0068] In the above embodiments, the multi-core high-reflectivity grating array 4 and the multi-core low-reflectivity grating array 6 are inscribed by covering all fiber cores to ensure that the performance of all gratings remains consistent.

[0069] The multi-core gain fiber described in the above embodiments is a doped fiber, that is, each core of the multi-core gain fiber is a doped core. The doping ions include, but are not limited to, one or more of ytterbium, erbium, cerium, thulium, and holmium. The doping distribution of the doping ions can be one of step type, center type, or gain-cut type doping.

[0070] The arrangement of all cores in the multi-core gain fiber is not limited, including but not limited to a square, rectangular or circular array arrangement.

[0071] Reference Figure 10In a preferred embodiment of the multi-core fiber oscillator, the multi-core gain fiber is a graded core-to-cladding ratio multi-core gain fiber. At the input end of the multi-core gain fiber, the diameters of all cores are equal, and the spacing between cores is greater than twice the diameter of the core at the current position. At the middle position of the multi-core gain fiber, the diameters of all cores are equal, and the spacing between cores is greater than twice the diameter of the core at the current position. At the output end of the multi-core gain fiber, the diameters of all cores are equal, and the spacing between cores is greater than twice the diameter of the core at the current position. However, the diameters of all cores at the input end of the multi-core gain fiber are smaller than those at the middle position, and the diameters of all cores at the output end are also smaller than those at the middle position. From the input end to the middle position, the diameter of each core gradually increases, and the core-to-cladding ratio gradually increases; from the middle position to the output end, the diameter of each core gradually decreases, and the core-to-cladding ratio gradually decreases. Multi-core gain fiber employing a graded core-to-cladding ratio can reduce the effective length, weaken nonlinear effects, and maintain a large core-to-cladding ratio, thereby alleviating mode instability effects. Compared with conventional tapered / spindle-shaped multi-core gain fiber with a constant core-to-cladding ratio, its greater advantage lies in the parallelism between the individual cores, resulting in parallel laser output.

[0072] In the above embodiments, low-reflection gratings and high-reflection gratings are respectively etched on each core of the multi-core gain fiber near both ends. That is, Bragg gratings (FBGs) are respectively etched on multiple cores of a multi-core gain fiber to form a resonant cavity. By separating each core in the multi-core gain fiber in space, the mode field area is increased while the TMI threshold of each core is maintained, thereby increasing the power of a single fiber by a factor of two.

[0073] The above embodiments increase the mode field area and reduce the overall effective length while reducing the core-to-packet ratio, which can better alleviate the mode instability effect and has good power improvement potential. They have important application prospects in high-power fiber lasers.

[0074] Figure 10 In the embodiment shown, the multi-core fiber oscillator employs a forward-pumped structure. The design of the pump power combiner without a signal fiber reduces the fabrication difficulty of the combiner and makes it easier to couple the pump power into the gain fiber. Its working principle is as follows:

[0075] A semiconductor pump source, acting as pump source 1, outputs pump laser light. After passing through a first high-reflectivity grating 2 etched on the pump arm, it is coupled through a pump power combiner 3 and a multi-core high-reflectivity grating array 4 into a graded-ratio multi-core gain fiber 5. Multiple doped cores of the graded-ratio multi-core gain fiber 5 generate spontaneous emission after being pumped. During the oscillation and propagation of the spontaneously emitted laser light within the individual cavities of each core, wavelength selection is achieved by a multi-core low-reflectivity grating array 6. Simultaneously, multiple resonant cavities are formed with the multi-core high-reflectivity grating array 4. After multiple oscillations, each core stably outputs laser light. A pump reflector 7 etched on the inner cladding of the multi-core gain fiber reflects residual pump light, improving pump absorption. The first high-reflectivity grating 2 etched on the pump arm reflects signal backlight, preventing signal light from damaging or interfering with the pump source.

[0076] In this invention, a pump reflector 7 is etched onto the cladding of the multi-core gain fiber 5 between the multi-core low-reflection grating array 6 and the output end of the multi-core gain fiber 5. (Refer to...) Figure 12 In one embodiment, the pump reflector 7 is an inner cladding between adjacent cores of the multi-core gain fiber 5, which is etched between the output end of the multi-core low-reflection grating array 6 and the multi-core gain fiber 5. That is, adjacent cores are separated by an inner cladding, and the pump reflector 7 is etched on the inner cladding between adjacent cores. The pump reflector is a high-reflection grating with a reflection wavelength of the pump wavelength, and is etched only in the inner cladding region.

[0077] Matters not covered in this invention are common knowledge.

[0078] 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.

[0079] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An optical fiber oscillator, characterized in that, Multi-core fiber is used as multi-core gain fiber. The multi-core gain fiber is a core-to-cladding ratio graded multi-core gain fiber. The diameter of each fiber core at the input end of the multi-core gain fiber is equal, and the spacing between the fiber cores is greater than twice the diameter of the fiber core at the current position. In a multi-core gain fiber, the diameters of the cores at the middle position are equal, and the spacing between the cores must be greater than twice the diameter of the core at the current position. At the output end of a multi-core gain fiber, the diameters of each core are equal, and the spacing between the cores must be greater than twice the diameter of the core at the current position. The diameter of each core at the input end of the multi-core gain fiber is smaller than the diameter of each core at the middle position of the multi-core gain fiber, and the diameter of each core at the output end of the multi-core gain fiber is smaller than the diameter of each core at the middle position of the multi-core gain fiber. From the input end of the multi-core gain fiber to the middle position of the multi-core gain fiber, the diameter of each core gradually increases, and the core-to-cladding ratio gradually increases; from the middle position of the multi-core gain fiber to the output end of the multi-core gain fiber, the diameter of each core gradually decreases, and the core-to-cladding ratio gradually decreases. The cores of a multi-core optical fiber are parallel to each other, and the lasers output from each core are emitted in parallel. The multi-core optical fiber is fabricated by the following method: (1) Prepare the inner quartz tube and perform grinding; Let the number of cores in the multi-core optical fiber to be processed be... N , N Greater than or equal to 2; Prepare N The inner quartz tubes are acid-washed and ground to make the dimensions and shapes of the inner quartz tubes the same after processing. The outer wall of the inner quartz tubes is circular after processing, and the inner wall of the inner quartz tubes is ground into a double cone shape. (2) Core layer deposition is performed on the inner quartz tube after grinding and processing. Rare earth ions are doped into the loose layer formed by core layer deposition. The gap between the inner quartz tube and the core layer is removed by heating the inner quartz tube with core layer deposition and sintering the rod to obtain a single core preform. (3) Prepare the outer quartz tube and... N The single-core preform is bundled from an outer quartz tube sleeve; The outer quartz tube is acid-washed and ground to grind the inner wall of the outer quartz tube into a square with rounded corners. N Single-core preforms are inserted parallel to each other into the outer quartz tube for bundling. N The single-core preforms are arranged in an array within the inner cavity of the outer quartz tube. The outer wall of the outermost single-core preform is in close contact with the inner wall of the outer quartz tube. Solid quartz rods are used to fill the gaps between the single-core preforms, and the spacing between the cores of adjacent single-core preforms is controlled. d This results in multi-core prefabricated components; (4) The multi-core preform is placed into the drawing tower for drawing and coating to obtain multi-core optical fiber.

2. The fiber optic oscillator according to claim 1, characterized in that, In step (3), N The single-core preforms are arranged in a square pattern in the inner cavity of the outer quartz tube.

3. The fiber optic oscillator according to claim 1, characterized in that, In step (3), N The single-core preforms are arranged in a rectangular pattern in the inner cavity of the outer quartz tube.

4. The fiber optic oscillator according to claim 1, characterized in that, In step (3), N The single-core preforms are arranged in a circular array in the inner cavity of the outer quartz tube.

5. The fiber optic oscillator according to claim 1, characterized in that, In step (2), the doped rare earth ions are one or more of ytterbium, erbium, cerium, thulium, and holmium.

6. The fiber optic oscillator according to claim 1, characterized in that, In step (2), the core layer of the polished inner quartz tube is deposited by vapor deposition to form a loose core layer.

7. The fiber optic oscillator according to claim 1, characterized in that, In step (2), the core layer of the polished inner quartz tube is deposited using plasma chemical vapor deposition to deposit a loose core layer.

8. The fiber optic oscillator according to claim 1, characterized in that, In step (2), chemical vapor deposition is used to deposit a core layer on the ground inner quartz tube to form a loose core layer.

9. The fiber optic oscillator according to any one of claims 1 to 8, characterized in that, In step (4), the lower end of the multi-core preform is heated and melted using the heating device in the drawing tower. The bare optical fiber is gradually pulled out from one end of the multi-core preform downwards. The wire diameter measuring device measures the wire diameter of the pulled bare optical fiber and controls the drawing speed of the traction disc. The coating and curing device coats the resin material onto the bare optical fiber to form a finished fiber. The winding device winds the finished fiber into an optical fiber disc.

10. The fiber optic oscillator according to claim 1, characterized in that, It features a pump source, a pump power combiner, a multi-core high-reflectivity grating array, a multi-core gain fiber, and a multi-core low-reflectivity grating array; The pump power combiner is a signal fiber-free pump power combiner, and one end of the pump power combiner has multiple pump arms. There are multiple pump sources, each pump source is connected to a corresponding pump arm on the pump power combiner, and each pump arm is engraved with a first high-reflectivity grating for reflecting the signal light transmitted in the pump arm. The other end of the pump power combiner is connected to the input end of a multi-core gain fiber. The multi-core gain fiber has two or more fiber cores. Each fiber core near the input end of the multi-core gain fiber is provided with a second high-reflection grating, forming a multi-core high-reflection grating array. Each fiber core near the output end of the multi-core gain fiber is provided with a low-reflection grating, forming a multi-core low-reflection grating array. A pump reflector is inscribed on the cladding of the multi-core gain fiber between the multi-core low-reflection grating array and the output end of the multi-core gain fiber.

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