Broadband ultralow-loss all-solid-state anti-resonance single-mode fiber based on coaxial double-clad tube unit

Abstract

The invention discloses a broadband ultra-low loss all-solid-state anti-resonance single-mode optical fiber based on a coaxial double-clad tube unit. The optical fiber adopts an all-solid-state composite glass structure and comprises a fiber core, a coaxial nested double-cladding tube unit array and an outer cladding sleeve from inside to outside. The coaxial nested double-clad tube unit array is composed of six coaxial double-clad tube units which are uniformly and symmetrically arranged around the fiber core, and each unit is composed of two dielectric tubes which are coaxially nested and have a large dielectric tube and a small dielectric tube. The cladding tube unit and the outer cladding sleeve are made of high-refractive-index N-lASF9 glass, and the background material between the fiber core and the unit is made of pure silicon dioxide. Through cooperation of the specific combination of high and low refractive index materials and a unique coaxial double-tube geometric structure, a strong anti-resonance effect is generated in a target wave band, so that a light field is efficiently constrained in a low refractive index fiber core for transmission. According to the invention, the optical fiber realizes extremely high mode field constraint capability and extremely wide single-mode bandwidth in a short-wave infrared band.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and in particular to a broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit. Background Technology

[0002] High-power fiber lasers are widely used in industrial manufacturing, medical surgery, lidar, space communication, and defense; however, increasing the power of fiber lasers faces serious challenges. Nonlinear effects and mode instability are the two core bottlenecks restricting further breakthroughs in their performance. Generally, increasing the fiber mode field area is an effective method to suppress nonlinear effects, but large mode field fibers are prone to introducing multimode transmission, which in turn induces mode instability at high power, leading to beam quality degradation. To balance large mode field and stable single-mode transmission, various special fiber structures have been proposed.

[0003] In recent years, hollow antiresonant fibers have attracted attention due to their wide bandwidth, low loss, and high mode purity. They can effectively suppress higher-order modes through the resonant coupling mechanism of the cladding capillary. However, their air-hole structure is easily deformable, the fabrication process is complex, their bending resistance is poor, and it is difficult to achieve rare-earth doping gain, which limits their integrated application in all-fiber high-power laser systems.

[0004] Meanwhile, research on all-solid-state solid antiresonant single-mode fibers has also made a series of advances, but their overall performance still faces significant limitations. While existing all-solid-state solid antiresonant fibers have achieved large mode field areas and certain high-order mode suppression capabilities, they generally suffer from high transmission loss and limited single-mode bandwidth. Especially in the 1.55 μm communication band, high-performance large-mode-field single-mode fibers remain a subject of limited research.

[0005] Existing solutions struggle to achieve synergistic optimization among mode area, single-mode bandwidth, and loss control, hindering the development of fiber lasers towards higher power and more stable operation. Therefore, there is an urgent need for a novel fiber structure capable of simultaneously achieving large mode area, broadband single-mode operation, and ultra-low loss in the communication band, in order to drive substantial progress in high-power fiber laser technology. Summary of the Invention

[0006] The purpose of this invention is to provide a broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on coaxial double-clad tube units, so as to solve the performance problem that current high-power optical fiber systems cannot simultaneously achieve large mode area, ultra-low loss and broadband single-mode transmission, while reducing manufacturing process requirements.

[0007] A broadband ultra-low loss all-solid-state antiresonant single-mode optical fiber based on coaxial double-clad tube units, comprising:

[0008] Fiber core;

[0009] The fiber core is surrounded by a ring of coaxial double-clad tube unit arrays and is covered by an outer cladding tube;

[0010] The coaxial double-clad tube unit, through the anti-resonance reflection mechanism formed by its inner and outer tube walls, simultaneously satisfies the following within a continuous broadband range exceeding 700 nm:

[0011] Fundamental mode loss ≤10 -9 dB / m, higher-order mode extinction ratio ≥10 4 Model area ≥ 600 μm 2 .

[0012] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0013] This invention creatively combines a "coaxial double-clad tube" structure with special glass materials, achieving both ultra-low loss and stable single-mode transmission capabilities in an all-solid-state optical fiber over an ultra-wideband range. The key to achieving ultra-low loss in optical fiber lies in the "double anti-resonant reflection" mechanism. In each cladding unit, the inner and outer cladding tubes, made of N-1ASF9 glass, act like two closely spaced highly reflective mirrors. When light propagates through the central pure silica core and attempts to leak outward, it encounters these two mirrors sequentially. By precisely designing the thickness and radius ratio of the two tubes, they generate strong light reflections at different but adjacent wavelengths. These two reflection effects seamlessly connect spectrally, thus jointly constructing an almost insurmountable barrier over an extremely wide wavelength range, suppressing light leakage loss to an astonishing 10%. -10 dB / m level.

[0014] The key to achieving broadband single-mode transmission lies in the structure's powerful "mode-selective attenuation" capability. The fundamental mode light is tightly confined to the fiber core, allowing it to pass through with low loss. However, the light fields of higher-order modes extend further into the cladding region. When these higher-order modes encounter the complex structure of the N-1ASF9 glass tube, they experience strong scattering and leakage. Through ingenious design, the loss of all higher-order modes is designed to be 10 times higher than that of the fundamental mode across a wide wavelength range. 4 More than twice as many light particles are efficiently filtered out. This ensures that the optical fiber can only transmit a single fundamental mode light within this wide spectral window.

[0015] In summary, this invention, by precisely combining a unique "coaxial dual-tube" structure with special glass materials, successfully solves the long-standing technical challenge of simultaneously achieving broadband, low loss, and single-mode operation, providing a novel high-performance optical fiber solution for future ultra-high-speed optical communication and high-power laser systems. Furthermore, the proposed optical fiber structure is simple, the fabrication process is feasible, and it is easy to implement in engineering applications. Attached Figure Description

[0016] Figure 1This is a schematic cross-sectional view of the broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit disclosed in an embodiment of the present invention.

[0017] Figure 2 for Figure 1 The publicly disclosed transmission loss curves of the fiber fundamental mode LP01 and the higher-order mode LP11, as well as the extinction ratio variation curves of the higher-order mode (k=0.6).

[0018] Figure 3 for Figure 1 The publicly disclosed transmission loss curves of the fiber fundamental mode LP01 and the higher-order mode LP11, as well as the extinction ratio variation curves of the higher-order mode (k=0.78).

[0019] Figure 4 for Figure 1 A publicly disclosed optical fiber, showing the structure of the fiber when its inner cladding tube moves radially.

[0020] Figure 5 for Figure 1 The publicly disclosed transmission loss of the fundamental mode LP01 and the higher-order mode LP11, as well as the change curve of the higher-order mode extinction ratio, are shown in the following data (k=0.6) when the optical fiber moves radially in the inner cladding tube. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Figure 1 This is a cross-sectional view of a broadband ultra-low loss all-solid-state anti-resonant single-mode fiber based on coaxial double-clad tube units. The fiber adopts an all-solid-state composite glass structure, including: fiber core 1, coaxial nested double-clad tube unit array, and outer cladding tube 4. Each cladding tube unit consists of two coaxial nested dielectric tubes, one large and one small, namely inner cladding tube 2 and outer cladding tube 3.

[0023] In a preferred example, the fiber optic cladding tube and the coaxial nested double cladding tube unit array are made of high refractive index N-1ASF9 glass, while other areas are made of pure silicon dioxide.

[0024] In a preferred example, the fiber core diameter D is 40.0 μm; the ratio of the outer diameter of the inner and outer cladding tubes of the coaxial circular dielectric tube is k = 0.6 or 0.78, and the tube thickness is t = 1.07 μm;

[0025] In a preferred example, the spacing between the two cladding tube units of the optical fiber is g = 1.3 μm;

[0026] In a preferred example, in the fiber-coaxial double-clad tube unit, the inner cladding tube can move radially, and the moving distance L ranges from -6μm to 6μm;

[0027] In a preferred example, the thickness of the outer sheath tube is set to be no less than 15 μm.

[0028] This optical fiber employs an anti-resonant cladding structure composed of coaxial double-clad tube units. By precisely designing the radius ratio and thickness of the dielectric tubes, it achieves efficient suppression of fundamental mode transmission loss and precise control of transmission loss for different higher-order modes. Simultaneously, it achieves large mode area, ultra-low loss, and broadband single-mode transmission performance. Furthermore, the proposed fiber structure is simple, the fabrication process is feasible, and it is easy to implement in engineering applications.

[0029] The working principle of this optical fiber will be explained below.

[0030] The working principle of the optical fiber of this invention is based on its unique coaxial double-clad tube structure. In each cladding unit, the inner and outer cladding tubes made of high refractive index N-1ASF9 glass, together with the pure silicon dioxide background, form an anti-resonant optical waveguide.

[0031] The core of achieving ultra-low loss is the dual anti-resonance effect. When light propagates in the fiber core, the inner and outer glass tubes act like two continuous optical barriers, designed to strongly reflect light attempting to leak at different but adjacent wavelengths. These two reflective layers work together across a wide spectral range to tightly confine the light to the fiber core, thereby reducing leakage loss to extremely low levels.

[0032] Achieving broadband single-mode operation relies on "mode-selective loss." The optical field of the fundamental mode is concentrated at the core, protected by double barriers, resulting in minimal loss. However, the optical fields of higher-order modes diffuse to the cladding edges, where they experience strong scattering and leakage when encountering the complex double-layer glass tube structure. Through precise design, the loss of all higher-order modes is increased by 10% compared to the fundamental mode across a wide wavelength range. 4 More than twice as many, thus being efficiently filtered out, ensuring that the optical fiber transmits only a single fundamental mode.

[0033] In short, this design achieves both wide-spectrum leak prevention and high-order mode filtration through a single structure, thus combining ultra-low loss and broadband single-mode performance.

[0034] The ratio between the fundamental mode loss of an optical fiber and the minimum loss of the cut-off higher-order modes (higher-order mode extinction ratio) is an important performance parameter for evaluating the single-mode characteristics of the optical fiber. When the ratio is greater than 100, it indicates that the optical fiber has single-mode characteristics, and the larger the ratio, the better the single-polarization single-mode characteristics.

[0035] The following is a description of a specific embodiment:

[0036] like Figure 2 As shown, the structural parameters of the optical fiber are assumed to be D=40.0 μm, k=0.6 μm, g=1.3 μm, t1=1.07 μm, and L=0 μm, i.e., the inner and outer cladding tubes are coaxially nested. In the wavelength ranges of 1163 nm to 1906 nm, 1918 nm to 1930 nm, and 1971 nm to 1982 nm, the ratio of the loss-limiting LP01 mode (fundamental mode) to the LP11 mode (higher-order mode with the lowest loss) is greater than 100. When the wavelength is 1174 nm, the higher-order mode extinction ratio reaches its maximum, reaching 76960.44; when the wavelength is 1440 nm, the loss of the LP01 mode reaches its minimum, as low as 3.27 × 10⁻⁶. -10 dB / m; when D=40.0 μm, k=0.6 μm, g=1.3 μm, t1=1.07 μm, L=0 μm, and the wavelength is 1550 nm, the mode area is 689 μm. 2 When D = 100.0 μm, the mode field area is 4299 μm. 2 This indicates that the optical fiber simultaneously possesses excellent large mode area, low loss, and wideband single-mode characteristics, with a maximum single-mode bandwidth of 743nm.

[0037] like Figure 3 As shown, the structural parameters of the optical fiber are assumed to be D=40.0 μm, k=0.78 μm, g=1.3 μm, t1=1.07 μm, and L=0 μm (i.e., the inner and outer cladding tubes remain coaxial). In the wavelength range of 1170 nm to 1980 nm, the ratio of the LP01 mode to the LP11 mode confinement loss of the optical fiber is greater than 100; when the wavelength is 1690 nm, the higher-order mode extinction ratio reaches its maximum of 6.05 × 10⁻⁶. 7 This indicates that the fiber exhibits excellent single-mode characteristics, with a maximum single-mode bandwidth of 810 nm. The loss of the LP01 mode reaches its lowest point at a wavelength of 1470 nm, as low as 3.17 × 10⁻⁶. -9 The loss of LP11 mode remains in the high-loss region (greater than 0.01 dB / m) within the single-mode wavelength range, indicating that the fiber maintains excellent broadband single-mode characteristics while exhibiting good low-loss characteristics.

[0038] Figure 4 The diagram shows the structure of the optical fiber when the inner cladding tube in the cladding tube array moves radially. With the axis of the coaxial cladding tube as the origin, L is a positive movement when the inner cladding circle moves radially outward and a negative movement when the inner cladding circle moves radially inward. In this case, the structural parameters of the optical fiber are set as D=40.0 μm, k=0.6 μm, g=1.3 μm, t1=1.07 μm, and the working wavelength is 1550 nm.

[0039] like Figure 5 As shown, in Figure 4 Based on the fiber structure shown, when L varies from -6 μm to 6 μm, the fiber can still maintain excellent low-loss broadband single-mode characteristics, indicating that the inner cladding circle of the fiber has good manufacturing tolerance.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on coaxial double-clad tube units, characterized in that, include: Fiber core; The fiber core is surrounded by a ring of coaxial double-clad tube unit arrays and is covered by an outer cladding tube; The coaxial double-clad tube unit, through the anti-resonance reflection mechanism formed by its inner and outer tube walls, simultaneously satisfies the following within a continuous broadband range exceeding 700 nm: Fundamental mode loss ≤10 -9 dB / m, higher-order mode extinction ratio ≥10 4 Model area ≥ 600 μm 2 .

2. The broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to claim 1, characterized in that, The coaxial double-clad tube unit is composed of inner and outer dielectric tubes nested coaxially, and the inner and outer dielectric tubes together form an anti-resonance reflection structure.

3. The broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to claim 2, characterized in that, The coaxial double-clad tube unit and the outer cladding sleeve are made of N-1ASF9 glass, while other areas are made of pure silicon dioxide.

4. A broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to any one of claims 1 to 3, characterized in that, The ratio k of the outer radius R2 of the inner medium tube to the outer radius R1 of the outer medium tube in the coaxial double-clad tube unit is 0.6 or 0.

78.

5. A broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to claim 4, characterized in that, The wall thickness t of both the inner and outer media tubes is 1.07 μm.

6. A broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to claim 4, characterized in that, The spacing g between two adjacent coaxial double-clad tube units is 1.3 μm.

7. A broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to claim 4, characterized in that, The inner dielectric tube can move radially relative to the outer dielectric tube, with a moving distance L ranging from -6 μm to +6 μm, while maintaining low loss and single-mode performance within this range.

8. A broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to claim 1, characterized in that, The wall thickness of the outer sheath is not less than 15 μm.

9. A broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to claim 1, characterized in that, There are a total of 6 coaxial double-clad tube units, forming the coaxial double-clad tube unit array, and each unit has the same structure.

10. A broadband ultra-low loss all-solid-state anti-resonant single-mode optical fiber based on a coaxial double-clad tube unit according to claim 1, characterized in that, The core diameter D is 40 μm.

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