Photonic lantern for dual-ring fiber laser and its fabrication method

Abstract

This invention provides a photonic lantern for a dual-ring fiber laser and its fabrication method, belonging to the field of optical communication. The photonic lantern includes: a fiber array, a transition region, and a few-mode port connected sequentially. The fiber array consists of a predetermined number of 980nm single-mode fibers with cladding and two 1550nm few-mode fibers with cladding placed inside a quartz capillary tube, stretched to a predetermined length using a thermal tapering method, maintaining its shape after stretching. The transition region is the portion whose shape changes after tapering, and the few-mode port is the port portion whose shape changes after tapering. This photonic lantern can achieve a 980 / 1550nm dual-ring design, i.e., selective switching of the 980nm wavelength mode, mode preservation of the 1550nm wavelength mode, and low-loss closed-loop transmission. It can be used to construct a fiber dual-ring laser cavity, providing an effective device for generating multiple 1550nm high-order mode lasers. Adding it to a dual-ring fiber laser enables direct oscillation and controllable output of multiple 1550nm high-order transverse mode lasers.

Description

Technical Field

[0001] This invention relates to the field of optical communication, and more particularly to a photonic lantern for a dual-ring fiber laser and a method for its fabrication. Background Technology

[0002] The generation and related applications of higher-order transverse-mode lasers in optical fibers are currently cutting-edge topics in the field of optics. In fiber optic communication technology, higher-order modes can serve as new degrees of freedom to expand communication channels, break through the upper limit of single-mode transmission capacity, and achieve high-bandwidth, high-capacity information transmission. In optical imaging, beams in higher-order modes can overcome the diffraction limit, improving the resolution of microscopic imaging. Furthermore, higher-order mode lasers also demonstrate significant value in many fields such as optical tweezers, laser micromachining, and high-dimensional quantum entanglement.

[0003] For dual-ring fiber lasers, the generation of higher-order transverse modes in the fiber is currently mainly achieved through mode-changing devices. However, due to the limitations of the existing fiber mode-changing devices in terms of structure and performance, only the first few higher-order transverse modes can be generated, resulting in a very limited number of controllable transverse modes. Therefore, how to generate multiple higher-order transverse modes simply and efficiently in the fiber is a problem that needs to be solved in the application of dual-ring lasers. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a photonic lantern for a dual-ring fiber laser and a method for its fabrication.

[0005] This invention provides a photonic lantern for a dual-ring fiber laser, comprising: a fiber array, a transition region, and a few-mode port connected in sequence; the fiber array consists of a predetermined number of 980nm single-mode fibers with cladding and two 1550nm few-mode fibers with cladding placed inside a quartz capillary tube, and the portion whose shape remains unchanged after being adiabatically tapered to a predetermined stretch length according to a predetermined stretch ratio; the transition region is the portion whose shape changes after tapering, and the few-mode port is the port portion whose shape changes after tapering; wherein, the stretch ratio is determined according to the normalized frequency of the few-mode fibers, so that the few-mode port generates a linearly polarized LP mode, and the predetermined number corresponds to the number of modes used in the photonic lantern application.

[0006] According to the present invention, a photonic lantern for a dual-ring fiber laser is provided, wherein the preset quantity includes 3, 6, 10 and 15.

[0007] According to the present invention, a photonic lantern for a dual-ring fiber laser is provided, wherein the fiber arrangement before tapering is as follows: the few-mode fiber is symmetrical about the center, and the outer periphery of the overall array of the few-mode fiber and the single-mode fiber is arranged in a regular polygonal pattern, and the adjacent single-mode fibers are arranged at equal intervals.

[0008] According to the present invention, a photonic lantern for a dual-ring fiber laser is provided, wherein the LP modes are respectively LP 01 Pattern, LP 11a and LP 11b In this mode, the preset quantity is 3, and the fiber arrangement before tapering is as follows: one single-mode fiber is located in the center, the remaining fibers are arranged in a regular quadrilateral, two few-mode fibers are located on the diagonal of the quadrilateral, and adjacent single-mode fibers are arranged at equal intervals.

[0009] According to the present invention, a photonic lantern for a dual-ring fiber laser is provided, wherein the core and cladding refractive indices of the 980nm single-mode fiber are 1.45 and 1.444, respectively; the core and cladding tube refractive indices of the 1550nm few-mode fiber are 1.4669 and 1.444, respectively; and the refractive index of the quartz capillary is 1.438.

[0010] According to the present invention, a photonic lantern for a dual-ring fiber laser has a core and cladding size of 6 μm and 125 μm for the 980 nm single-mode fiber at the center, a core and cladding size of 4 μm and 125 μm for the two 980 nm single-mode fibers in the ring, and a core and cladding size of 15 μm and 125 μm for the 1550 nm few-mode fiber.

[0011] According to the present invention, a photonic lantern for a dual-ring fiber laser is provided, wherein the quartz capillary has an inner diameter of 400 μm and an outer diameter of 415 μm.

[0012] This invention also provides a method for fabricating a photonic lantern device for a dual-ring fiber laser, comprising: placing a predetermined number of 980nm single-mode fibers with cladding and two 1550nm few-mode fibers with cladding inside a quartz capillary; performing adiabatic tapering of the quartz capillary containing the fibers to a predetermined stretch length according to a predetermined stretching ratio; wherein, the stretching ratio is determined based on the normalized frequency of the few-mode fibers, so that the few-mode port generates an LP mode, the few-mode port being the port portion whose shape changes after tapering, and the predetermined number corresponding to the number of modes used in the photonic lantern application.

[0013] According to the present invention, a method for fabricating a photonic lantern for a dual-ring fiber laser is provided, wherein the fiber arrangement before tapering is as follows: the few-mode fiber is symmetrical about the center, and the outer periphery of the overall array of the few-mode fiber and the single-mode fiber is arranged in a regular polygonal pattern, with adjacent single-mode fibers arranged at equal intervals.

[0014] According to the present invention, a method for fabricating a photonic lantern for a dual-ring fiber laser is provided, wherein the LP modes are respectively LP 01 Pattern, LP 11a and LP 11bIn this mode, the preset quantity is 3, and the fiber arrangement before tapering is as follows: one single-mode fiber is located in the center, the remaining fibers are arranged in a regular quadrilateral, two few-mode fibers are located on the diagonal of the quadrilateral, and adjacent single-mode fibers are arranged at equal intervals.

[0015] This invention also provides a dual-ring fiber laser, comprising: a 980nm laser and a photonic lantern of the dual-ring fiber laser described above; the 980nm laser is connected to each 980nm single-mode fiber of the photonic lantern, and pump light injected from different 980nm single-mode fibers passes through the photonic lantern to achieve selective excitation of the fundamental mode to a higher-order linearly polarized mode; the two 1550nm few-mode fibers of the photonic lantern are respectively connected to a few-port ring to form a dual-ring laser cavity, and a few-mode erbium-doped fiber is inserted into the dual-ring laser cavity as a gain fiber to convert the wavelength of operation within the cavity to 1550nm.

[0016] The photonic lantern and its fabrication method for a dual-ring fiber laser provided by this invention can achieve a 980 / 1550nm dual-ring structure, namely, selective switching of the 980nm wavelength mode, mode maintenance of the 1550nm wavelength mode, and low-loss closed-loop transmission. It can be used to construct a full multimode (few-mode) fiber dual-ring laser cavity, providing an effective device for generating multiple 1550nm high-order mode lasers. When added to a dual-ring fiber laser, it can realize the direct oscillation and controllable output of multiple 1550nm high-order transverse mode lasers. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the photonic lantern structure for a dual-ring fiber laser provided by the present invention;

[0019] Figure 2 This is a schematic diagram of the few-mode port cross-section of the 3+2 photonic lantern for a dual-ring fiber laser provided by the present invention;

[0020] Figure 3 This is a schematic diagram of the effective refractive index change of the mode corresponding to the 980nm wavelength provided by the present invention;

[0021] Figure 4 This is a schematic diagram of the simulation results of the mode field evolution of the novel 3+2 photonic lantern with 980nm wavelength laser transmission under different taper ratios provided by the present invention.

[0022] Figure 5 This is a schematic diagram of the few-mode end face of the novel 3+2 photonic lantern with 1550nm laser transmission provided by the present invention;

[0023] Figure 6 This is a schematic diagram showing the variation of the effective refractive index of the 1550nm mode with the tapering ratio provided by the present invention;

[0024] Figure 7 This is a schematic diagram of the simulation results of the mode field evolution of the novel 3+2 photonic lantern with 1550nm laser transmission under different taper ratios provided by the present invention.

[0025] Figure 8 This is a schematic diagram of the process for fabricating a photonic lantern for a dual-ring fiber laser provided by the present invention.

[0026] Figure 9 This is a schematic diagram of the dual-ring fiber laser provided by the present invention;

[0027] Explanation of reference numerals in the attached figures: 1. Fiber array; 2. Transition zone; 3. Few-mode port; 1-1. 980nm single-mode fiber; 1-2. 1550nm few-mode fiber; 101 (102, 103). 980nm single-mode fiber; 200 (201). 1550nm few-mode fiber. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] To address the issue of the limited number of transverse modes in dual-ring fiber lasers, this invention proposes a self-matching photonic lantern device and its fabrication method. For 980nm lasers, it can selectively excite multiple higher-order transverse modes, exhibiting mode selection characteristics. For 1550nm lasers, it enables closed-loop transmission of multiple higher-order transverse modes, demonstrating self-cavity characteristics. These 980 / 1550nm dual-band multiplexing characteristics make the self-matching photonic lantern particularly suitable for constructing all-few-mode fiber ring cavity lasers, enabling the generation and flexible switching of multiple higher-order transverse modes at 1550nm.

[0030] Based on this novel n+2 photonic lantern device, a dual-ring fiber laser can generate high-order transverse-mode lasers, possessing three major advantages: 980 / 1550nm dual-band multiplexing, 980nm wavelength mode selection, and 1550nm wavelength few-mode fiber self-forming cavity. Ultimately, it achieves direct oscillation and controllable output of multiple 1550nm high-order transverse-mode lasers within a fully few-mode fiber dual-ring cavity. This invention offers significant advantages such as a large number of output transverse-mode lasers, high mode conversion efficiency, low transmission loss, and independence from wavelength division multiplexing devices.

[0031] The following combination Figures 1-9 The present invention describes a photonic lantern for a dual-ring fiber laser and a method for its fabrication. Figure 1 This is a schematic diagram of the photonic lantern structure of the dual-ring fiber laser provided by the present invention, as shown below. Figure 1 As shown, the photonic lantern of the dual-ring fiber laser provided by the present invention includes: a fiber array 1, a transition region 2, and a few-mode port 3 connected in sequence; the fiber array 1 consists of a predetermined number of 980nm single-mode fibers 1-1 with cladding and two 1550nm few-mode fibers 1-2 with cladding placed in a quartz capillary tube, and the portion whose shape remains unchanged after being adiabatically tapered to a predetermined stretch length according to a predetermined stretch ratio; the transition region 2 is the portion whose shape changes after tapering, and the few-mode port 3 is the port portion whose shape changes after tapering; wherein, the stretch ratio is determined according to the normalized frequency of the few-mode fibers, so that the few-mode port 3 generates a linearly polarized LP mode, and the predetermined number corresponds to the number of modes used in the photonic lantern.

[0032] The tapering ratio is the ratio of the diameter of the coupling region section after tapering to the diameter of the section before tapering, and the tapering length is the increase in length after tapering. The tapering ratio is closely related to the normalized frequency of the few-mode port of the photonic lantern, and ultimately determines the mode of the few-mode port. The preset tapering ratio and preset tapering length can be obtained through simulation results, such as the beam propagation method and finite element analysis method, or through experiments.

[0033] During the adiabatic tapering process, the fiber array gradually fuses into a single unit. The 980nm single-mode core and the 1550nm few-mode core gradually thin until they finally lose their ability to confine light. The original cladding in the fiber array becomes the new core, and the external low-refractive-index quartz sleeve becomes the new cladding. When the fiber is stretched to a certain tapering length according to the preset tapering ratio, tapering stops, ultimately forming a new few-mode waveguide, namely few-mode port 3. Its parameters are similar to those of the 1550nm few-mode fiber, supporting mode-closed-loop low-loss transmission.

[0034] The photonic lantern of the dual-ring fiber laser of the present invention can realize a 980 / 1550nm dual-ring structure, that is, selective switching of 980nm wavelength mode, 1550nm wavelength mode maintenance, and low-loss closed-loop transmission. It can be used to construct a full multimode (few-mode) fiber dual-ring laser cavity, providing an effective device for generating multiple 1550nm high-order mode lasers. Adding it to a dual-ring fiber laser can realize the direct oscillation and controllable output of multiple 1550nm high-order transverse mode lasers.

[0035] In one embodiment, the preset number n of 980nm single-mode optical fiber includes 3, 6, 10, and 15.

[0036] In one embodiment, the fiber arrangement before tapering is as follows: the few-mode fiber is symmetrical about the center, and the outer periphery of the overall array of the few-mode fiber and the single-mode fiber is arranged in a regular polygonal pattern, with adjacent single-mode fibers arranged at equal intervals.

[0037] Considering that the structure of higher-order transverse modes is symmetrical, the fiber array in this embodiment is arranged with equal spacing on the periphery and in the form of a regular polygon, which makes the generation of higher-order modes better. Furthermore, the few-mode fibers are arranged in a centrally symmetrical manner. Under the above conditions, the coupling efficiency of the few-mode fibers is improved by arranging adjacent single-mode fibers with equal spacing.

[0038] In one embodiment, the LP modes are respectively LP 01 Pattern, LP 11a and LP 11b In this mode, the preset quantity is 3, and the fiber arrangement before tapering is as follows: one single-mode fiber is located in the center, the remaining fibers are arranged in a regular quadrilateral, two few-mode fibers are located on the diagonal of the quadrilateral, and adjacent single-mode fibers are arranged at equal intervals.

[0039] The following explanation uses the new 3+2 photon lantern as an example. A schematic diagram of the new 3+2 photon lantern is shown below. Figure 1 As shown. The few-mode port can selectively excite three linear polarization modes: LP01, LP11a, and LP11b. The corresponding 980nm single-mode fiber cluster contains 3 single-mode fibers, which correspond to... Figure 1 The numbers 100, 101, and 102 in the figure represent this. Correspondingly, 1550nm few-mode fiber can be selected from three-mode fiber, corresponding to 200 and 201 in the figure.

[0040] Based on the relationship between the fiber geometry arrangement in a photonic lantern and its influence on mode conversion, for a photonic lantern supporting the propagation and conversion of LPmn modes (where m is the radial order of the mode field and n is the angular order of the mode field), the fiber array should be arranged in a pattern of m concentric circles. The number of fibers on each circle should be N = 2n.max +1, thus enabling selective excitation of modes in the photonic lantern. When the photonic lantern supports modes LP01, LP11a, and LP11b, m = 1, n max =1, N=3, the three 980nm single-mode optical fibers should be distributed on a circular ring.

[0041] In this embodiment of the invention, to incorporate the mode field evolution of the few-mode fiber, and considering that the three-mode fiber used to transmit 1550nm laser light is also part of the novel 3+2 photonic lantern but does not inject a 980nm beam, the five fibers can be arranged as described in the above embodiment. Specifically, in this embodiment, one single-mode fiber is located at the center, and the remaining fibers form a regular quadrilateral. Naturally, due to the central symmetry of the few-mode fiber, it is located on the diagonal of the quadrilateral, and the two outer single-mode fibers are naturally located on the other diagonal, while ensuring equal spacing between adjacent single-mode fibers to support the functional requirement of the novel 3+2 photonic lantern for 980 / 1550nm dual-band mode multiplexing.

[0042] In one embodiment, the core and cladding refractive indices of the 980nm single-mode fiber are 1.45 and 1.444, respectively, and the core and cladding refractive indices of the 1550nm few-mode fiber are 1.4669 and 1.444, respectively.

[0043] In one embodiment, the core and cladding dimensions of the central 980nm single-mode fiber are 6μm and 125μm, respectively; the core and cladding dimensions of the two 980nm single-mode fibers in the ring are 4μm and 125μm, respectively; and the core and cladding dimensions of the 1550nm few-mode fiber are 15μm and 125μm, respectively.

[0044] In one embodiment, the quartz capillary has a refractive index of 1.438, an inner diameter of 400 μm, and an outer diameter of 415 μm.

[0045] Furthermore, in this invention, the core and cladding refractive indices of the three 980nm single-mode fibers in the novel 3+2 photonic lantern are designed to be 1.45 and 1.444, respectively. The core and cladding dimensions of two of the 980nm single-mode fibers are designed to be 4μm and 125μm, respectively, which allows for better selective excitation of the LP. 11a and LP 11b The other 980nm single-mode fiber has a core and cladding size designed to be 6μm and 125μm, respectively, to excite the LP. 01 The core and cladding refractive indices of the 1550nm trimode fiber are designed to be 1.4669 and 1.444, respectively, and the core and refractive index dimensions are designed to be 15μm and 125μm, respectively.

[0046] It should be noted that the above-mentioned fiber and cladding dimensions are not conventional choices in the field, but rather size parameters with better coupling effect set to better match the arrangement of 3 single-mode fibers and 2 few-mode fibers in the above embodiment.

[0047] With the cladding of all five optical fibers being 125 μm, the inner diameter of the outermost low-refractive-index quartz capillary is approximately 400 μm, its outer diameter is designed to be 415 μm, and its refractive index is designed to be 1.438.

[0048] In one embodiment, the stretching ratio is 0.1.

[0049] Based on the above parameters, the simulation settings of the new 3+2 photonic lantern were carried out to simulate the light field evolution process of 980nm light wave inside the new 3+2 photonic lantern. Figure 2 This is a schematic diagram of the few-mode port cross-section of the 3+2 photonic lantern for a dual-ring fiber laser provided by the present invention. The bright portions represent the cores of 980nm single-mode fibers 100, 101, and 102. Cores 100 and 101 have the same size (4μm) and correspond to the excitation of LP... 11a With LP 11b The mode, with a 102 core (6μm), corresponds to the excitation of LP. 01 model. Figure 3 In the process, when the taper ratio reaches 0.1, the fundamental mode in the original 100, 101, and 102 single-mode fibers excites corresponding LPs at the few-mode port. 01 LP 11a With LP 11b The mode enables selective excitation of the 980nm band mode. Figure 4 Simulation results of mode field evolution for a novel 3+2 photonic lantern with 980nm laser transmission under different taper ratios.

[0050] Based on the above parameters, a simulation was performed on the novel 3+2 photonic lantern to simulate the evolution of the light field of 1550nm light wave inside the novel 3+2 photonic lantern. Figure 5 This is a schematic diagram of the few-mode end cross-section of the novel 3+2 photonic lantern. The highlighted part is the 1550nm few-mode fiber core after tapering. Figure 6 The effective refractive index of the 1550nm mode varies with the taper ratio. When the taper reaches 0.1, the 1550nm three-mode fiber can stably transmit LP. 01 and LP 11 Pattern. As the taper ratio decreases, LP 11 The mode first leaks into the cladding. When the taper ratio is below 0.05, the fiber core can no longer guide mode transmission, and the cladding of the fiber array becomes the new "fiber core," guiding stable mode transmission. Figure 7 In the process, when the taper ratio reaches 0.05, the LP injected into the original 1550nm trimode fiber...01 LP 11a With LP 11b The mode can achieve matching with the initial mode field at the few-mode port. That is, the 1550nm mode can maintain its mode shape through the new 3+2 photonic lantern, and can achieve low-loss closed-loop transmission when connected with few-mode fiber.

[0051] The novel 3+2 photonic lantern solves the single-mode and few-mode incompatibility problem inherent in conventional photonic lanterns used to construct fiber lasers. The few-mode fiber added to the fiber array can be matched with the few-mode port formed by the tapered fiber, achieving dual closed-loop transmission of the 1550nm mode. Furthermore, the novel 3+2 photonic lantern possesses 980 / 1550nm dual-band mode multiplexing characteristics, eliminating the reliance on wavelength division multiplexing (WDM) devices when used to construct fiber lasers. The novel 3+2 photonic lantern is used to construct a fully few-mode fiber dual-ring cavity laser, generating high-order mode laser light in the 1550nm band.

[0052] The novel n+2 photonic lantern of this invention achieves 980 / 1550nm dual-band mode multiplexing, making it suitable for constructing fiber lasers and eliminating reliance on wavelength division multiplexers. Furthermore, the matching characteristics between the input 1550nm few-mode fiber and the output (multimode) few-mode port of the novel n+2 photonic lantern can be used to construct a fully few-mode fiber dual-ring laser cavity, enabling direct oscillation and output of multiple high-order mode lasers within this cavity. A single device can generate high-order modes at two wavelengths. This invention's method for generating high-order transverse modes based on a dual-ring fiber laser is highly practical, inexpensive to manufacture, simple to use, and boasts a mode conversion efficiency far exceeding other fiber laser systems. Moreover, the novel n+2 photonic lantern allows for low-loss insertion into laser systems, making it suitable for large-scale deployment and generating significant economic value.

[0053] A novel n+2 photonic lantern was constructed by adding two few-mode fibers to the fiber array of the photonic lantern, which can serve the generation of multiple high-order transverse modes at 1550nm. The novel n+2 photonic lantern can achieve dual-band mode multiplexing of 980 / 1550nm. The 980nm pump light input through different single-mode fibers can be selectively converted into the corresponding high-order transverse modes, and the self-cavity characteristics of the few-mode fibers enable low-loss closed-loop transmission of the 1550nm high-order transverse modes.

[0054] This invention enriches the types and functions of photonic lanterns. With further research into photonic lantern devices and continuous improvement of manufacturing methods, the novel n+2 photonic lantern can serve the generation of 1550nm high-order transverse mode lasers, achieving the output of dozens or even hundreds of transverse modes.

[0055] By precisely controlling the parameters and arrangement of the fiber array and the taper ratio of the novel n+2 photonic lantern, efficient switching between 980 / 1550nm dual-band modes in the transition region is achieved. The few-mode fiber port formed by the few-mode fiber and the taper can perform low-loss closed-loop transmission of multiple high-order transverse modes.

[0056] A novel n+2 photonic lantern was used to construct a fully few-mode fiber dual-ring cavity laser for generating high-order transverse-mode lasers at 1550nm. This effectively simplifies the laser structure and reduces reliance on other few-mode fiber devices. Crucially, the novel n+2 photonic lantern developed in this project exhibits strong scalability, enabling the generation and conversion of multiple high-order modes, thus laying a key technological foundation for the efficient generation and flexible control of high-order transverse-mode lasers.

[0057] The following describes the method for fabricating a photonic lantern for a dual-ring fiber laser provided by the present invention. The method for fabricating a photonic lantern for a dual-ring fiber laser described below can be referred to in correspondence with the method for fabricating a photonic lantern for a dual-ring fiber laser described above.

[0058] Figure 8 This is a flowchart illustrating the method for fabricating a photonic lantern for a dual-ring fiber laser provided by the present invention, as shown below. Figure 8 As shown, the present invention provides a method for fabricating a photonic lantern for a dual-ring fiber laser, comprising:

[0059] 801. Place a predetermined number of 980nm single-mode optical fibers with cladding and two 1550nm few-mode optical fibers with cladding inside a quartz capillary.

[0060] 802. Perform thermal tapering of the quartz capillary tube with built-in optical fiber to the preset stretch length according to the preset stretch ratio.

[0061] The stretching ratio is determined based on the normalized frequency of the few-mode fiber, so that the few-mode port generates LP mode. The few-mode port is the port portion whose shape is changed after tapering. The preset number corresponds to the number of modes used in the photonic lantern application.

[0062] In one embodiment, the fiber arrangement before tapering is as follows: the few-mode fiber is symmetrical about the center, and the outer periphery of the overall array of the few-mode fiber and the single-mode fiber is arranged in a regular polygonal pattern, with adjacent single-mode fibers arranged at equal intervals.

[0063] In one embodiment, the LP modes are respectively LP 01 Pattern, LP 11a and LP 11bIn this mode, the preset quantity is 3, and the fiber arrangement before tapering is as follows: one single-mode fiber is located in the center, the remaining fibers are arranged in a regular quadrilateral, two few-mode fibers are located on the diagonal of the quadrilateral, and adjacent single-mode fibers are arranged at equal intervals.

[0064] The method embodiments provided in this invention are for implementing the above-described device embodiments. For specific processes and details, please refer to the above-described device embodiments, which will not be repeated here.

[0065] The method for fabricating a photonic lantern for a dual-ring fiber laser provided in this embodiment of the invention has the same implementation principle and technical effect as the aforementioned embodiment of a photonic lantern for a dual-ring fiber laser. For the sake of brevity, any parts not mentioned in the embodiment of the method for fabricating a photonic lantern for a dual-ring fiber laser can be referred to the corresponding content in the aforementioned embodiment of a photonic lantern for a dual-ring fiber laser.

[0066] Figure 9 This is a schematic diagram of the structure of the dual-ring fiber laser provided by the present invention, as shown below. Figure 9 As shown, the dual-ring fiber laser includes: a 980nm laser and a photonic lantern of the dual-ring fiber laser described in any of the above embodiments; the 980nm laser is connected to each 980nm single-mode fiber of the photonic lantern, and the pump light injected by different 980nm single-mode fibers passes through the photonic lantern to achieve selective excitation of the fundamental mode to a higher-order linearly polarized mode; the two 1550nm few-mode fibers of the photonic lantern are respectively connected to a few-port ring to form a dual-ring laser cavity, and a few-mode erbium-doped fiber is inserted into the dual-ring laser cavity as a gain fiber to convert the wavelength of operation in the cavity to 1550nm.

[0067] like Figure 9 As shown, the 980nm single-mode fiber bundle of the novel 3+2 photonic lantern is connected to a 980nm laser via an optical switch. Pump light injected from different 980nm single-mode fibers passes through the novel photonic lantern, achieving selective excitation of the fundamental mode to higher-order linearly polarized modes. The 1550nm tri-mode fiber of the novel photonic lantern is connected to the few-mode port via a beam splitter to form a dual-ring laser cavity. A few-mode erbium-doped fiber is introduced into the ring cavity as a gain fiber, converting the wavelength operating within the cavity to 1550nm, allowing the 1550nm higher-order transverse mode to oscillate within the dual-ring cavity. Additionally, an isolator is introduced into the system to ensure unidirectional light transmission; a polarization controller is introduced to adjust the polarization state of the mode field and generate a vector beam. The wavelength and spectral characteristics of the output laser are measured using a spectrometer, and the light field distribution of the output laser is observed using a 1550nm CCD.

[0068] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photonic lantern for a dual-ring fiber laser, characterized in that, include: The fiber array, transition zone, and few-mode port are connected in sequence. The fiber array consists of a predetermined number of 980nm single-mode fibers with cladding and two 1550nm few-mode fibers with cladding placed inside a quartz capillary tube, and the portion whose shape remains unchanged after being thermally tapered to a predetermined stretch length according to a predetermined stretch ratio. The transition zone is the part whose shape changes after tapering, and the less-formed port is the port part whose shape changes after tapering; The stretching ratio is determined based on the normalized frequency of the few-mode fiber so that the few-mode port generates a linearly polarized LP mode, and the preset number corresponds to the number of modes used in the photonic lantern application. The fiber arrangement before tapering is as follows: the few-mode fiber is symmetrical about the center, and the outer periphery of the overall array of the few-mode fiber and the single-mode fiber is arranged in a regular polygon, with adjacent single-mode fibers arranged at equal intervals.

2. The photonic lantern for a dual-ring fiber laser according to claim 1, characterized in that, The preset quantities include 3, 6, 10, and 15.

3. The photonic lantern for a dual-ring fiber laser according to claim 1, characterized in that, The LP modes are respectively LP 01 Pattern, LP 11a and LP 11b In this mode, the preset quantity is 3, and the fiber arrangement before tapering is as follows: One single-mode fiber is located in the center, the remaining fibers are arranged in a regular quadrilateral, two few-mode fibers are located on the diagonal of the quadrilateral, and adjacent single-mode fibers are arranged at equal intervals.

4. The photonic lantern for a dual-ring fiber laser according to claim 3, characterized in that, The core and cladding refractive indices of the 980nm single-mode fiber are 1.45 and 1.444, respectively, and the core and cladding refractive indices of the 1550nm few-mode fiber are 1.4669 and 1.444, respectively.

5. The photonic lantern for a dual-ring fiber laser according to claim 3, characterized in that, The core and cladding dimensions of the 980nm single-mode fiber at the center are 6μm and 125μm, respectively. The core and cladding dimensions of the two 980nm single-mode fibers in the ring are 4μm and 125μm, respectively. The core and cladding dimensions of the 1550nm few-mode fiber are 15μm and 125μm, respectively.

6. The photonic lantern for a dual-ring fiber laser according to claim 3, characterized in that, The quartz capillary has a refractive index of 1.438, an inner diameter of 400 μm, and an outer diameter of 415 μm.

7. A method for fabricating a photonic lantern for a dual-ring fiber laser, characterized in that, include: A predetermined number of 980nm single-mode fibers with cladding and two 1550nm few-mode fibers with cladding are placed inside a quartz capillary. The quartz capillary tube with built-in optical fiber is thermally tapered to the preset stretch length according to the preset stretch ratio. The stretching ratio is determined based on the normalized frequency of the few-mode fiber to enable the few-mode port to generate LP mode. The few-mode port is the port portion whose shape changes after tapering. The preset number corresponds to the number of modes applied by the photonic lantern. The fiber arrangement before tapering is as follows: the few-mode fiber is symmetrical about the center, and the outer periphery of the overall array of the few-mode fiber and the single-mode fiber is arranged in a regular polygon, with adjacent single-mode fibers arranged at equal intervals.

8. A dual-ring fiber laser, characterized in that, include: A 980nm laser and a photonic lantern of the dual-ring fiber laser according to any one of claims 1-6; The 980nm laser is connected to each 980nm single-mode fiber of the photonic lantern. Pump light injected by different 980nm single-mode fibers passes through the photonic lantern to achieve selective excitation of the fundamental mode to higher-order linearly polarized modes. The two 1550nm few-mode fibers of the photonic lantern are respectively connected to the few-port ring to form a dual-ring laser cavity. The few-mode erbium-doped fiber is inserted into the dual-ring laser cavity as a gain fiber, so that the wavelength of operation inside the cavity is converted to 1550nm.

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