A large mode area active optical fiber that is easy to manufacture

Abstract

This invention discloses a large-mode-field active optical fiber that is easy to fabricate. The optical fiber includes an active core region and a cladding region. The active core region is doped with luminescent rare-earth ions. The cladding region includes an inner cladding region and an outer cladding region. The inner cladding region is composed of a passive background material region and double-layered nested capillaries of thickness satisfying the anti-resonance condition, distributed around the active core region. The double-layered nested capillaries include an inner capillary and an outer capillary. The distance between the outer wall of the inner capillary and the inner wall of the outer capillary satisfies the LP value of the active core region. 11 The resonance condition of the mode; the outer cladding region surrounds the inner cladding region, confining the pump light to the inner cladding region and the core region for transmission. This invention, while increasing the refractive index difference between the core region and the background region and facilitating fiber fabrication, effectively suppresses the degradation of laser mode characteristics caused by thermally induced refractive index changes in the active core region under high power conditions.

Description

Technical Field

[0001] This invention relates to the field of high-power laser fibers, and more particularly to a large-mode-field active optical fiber that is easy to fabricate. Background Technology

[0002] In recent years, high-power fiber lasers have been widely used in industrial manufacturing due to their all-electric drive, high efficiency, and flexible transmission capabilities. However, with the manufacturing industry moving towards intelligent and high-end development, the comprehensive improvement of fiber laser performance has become increasingly urgent. Maintaining high beam quality while increasing output power is crucial for achieving high-efficiency and high-quality industrial processing. Currently, the power level of fiber lasers based on single-fiber structures is often increased by increasing the size of the fiber core. However, the large fiber core diameter and limited numerical aperture cause large-mode-field fibers to operate in few-mode or multi-mode states, making it difficult to simultaneously achieve high output power and high beam quality. Analysis of the output characteristics of high-power fiber lasers indicates that the key to solving this problem lies in developing high-performance laser fibers that can increase the fiber mode field while maintaining single-mode operation. To this end, all-solid-state photonic bandgap fibers, chiral-coupled core fibers, partially doped fibers, and variable core diameter fibers have been proposed and researched and developed. However, these fiber structures still face challenges such as complex fabrication processes and difficulty in controlling single-mode operation at high power.

[0003] Solid-core antiresonant fiber, as a novel type of solid-core microstructure fiber, boasts a simple structure and flexible design. By designing the parameters of the antiresonant unit, large-mode-field single-mode laser transmission can be achieved. Active fibers formed by doping the core region of antiresonant fibers with rare-earth ions can be used to generate and amplify high-power single-mode lasers. However, current rare-earth-doped solid-core antiresonant fibers all require a sufficiently small refractive index difference between the rare-earth-doped core region and the background region (5 × 10⁻⁶). -5 ~5×10 -4 Quantity [1,2] This ensures that the fundamental mode light is effectively controlled within the fiber core region. While this design can be implemented in actual fiber fabrication, the refractive index difference remains quite extreme, far lower than the refractive index difference of the glass material in commercial core-clad optical fibers (1×10⁻⁶). -3 The sheer volume of optical fibers (on the order of magnitude) poses a significant challenge to the mass production of optical fibers. Therefore, there is an urgent need to reduce the refractive index requirements of optical fiber materials through innovative fiber structure design, providing a feasible technical solution for the practical fabrication of active solid-core antiresonant optical fibers.

[0004] References:

[0005] [1]Zhang X, Gao S, Wang Y, Ding W, Wang P. Design of large mode areaall-solid anti-resonant fiber for high-power lasers. High Power Laser Science and Engineering. 2021, 9:e23.

[0006] [2]Fu S, Xu H, Tian H, Sheng Q, Xia W, Z Lu, Yao Z, Shi W, and Yao J, Large-mode-area Nd-doped anti-resonant phosphate fiber for high-power single-mode 900 nm laser generation. Optics Express. 2024, 32, 36240-3625. Summary of the Invention

[0007] This invention provides an easily fabricated large-mode-field active optical fiber. To address the bottleneck issue of low refractive index difference between the core and background materials in active solid-core antiresonant optical fibers, which imposes extremely stringent requirements on glass fabrication processes, this invention proposes an active solid-core antiresonant optical fiber with a double-layer nested antiresonant unit structure. This double-layer nested antiresonant unit enhances the confinement capability of the active core's fundamental mode, increasing the range of refractive index difference between the core and background regions. Simultaneously, by designing the distance between the double-layered antiresonant units, a large-mode-field (LP) optical fiber is achieved in the core region. 11 The high confinement loss of the mode allows for the acquisition of large-mode-field single-mode fibers that are easy to fabricate in practice, as detailed below:

[0008] A large-mode-field active optical fiber that is easy to fabricate, the optical fiber comprising: an active core region and a cladding region;

[0009] The active core region is doped with luminescent rare earth ions; the cladding region includes an inner cladding region and an outer cladding region, wherein the inner cladding region is composed of a passive background material region and a double-layered nested capillary distributed around the active core region, satisfying the anti-resonance condition thickness;

[0010] The double-layer nested capillary includes an inner capillary and an outer capillary. The distance between the outer wall of the inner capillary and the inner wall of the outer capillary satisfies the active core region LP. 11 The resonance condition of the mode;

[0011] The outer cladding region surrounds the inner cladding region, confining the pump light to the inner cladding region and the fiber core region for transmission.

[0012] The active fiber core region and the inner cladding region have the same glass matrix.

[0013] At the signal light wavelength, the refractive index of the inner and outer capillaries is greater than the refractive index of the background material in the inner cladding region, which is greater than the refractive index of the active fiber core region.

[0014] At the pump light wavelength, the refractive index of the outer cladding region is less than the refractive index of the passive background material region;

[0015] The refractive index of the inner capillary is the same as that of the outer capillary.

[0016] Among them, the refractive index of the fundamental mode effective mode, which is determined by the refractive index and diameter of the passive background material region in the inner capillary, is less than the refractive index of the fundamental mode effective mode in the active fiber core region.

[0017] The number of the double-layered nested capillaries is determined by the following formula:

[0018]

[0019] Where t is the capillary thickness, d c d is the diameter of the active fiber core region. cl d is the inner diameter of the inner capillary, and d is the distance between the outer wall of the inner capillary and the inner wall of the outer capillary.

[0020] The beneficial effects of the technical solution provided by this invention are:

[0021] 1. The present invention proposes a large-mode-field active optical fiber that is easy to fabricate. It adopts a double-layer nested anti-resonant unit structure to enhance the confinement capability of the fundamental mode in the fiber core region. This ensures that the large-mode-field optical fiber can maintain the low-loss transmission characteristics of the fundamental mode even when the refractive index difference between the fiber core region and the background region is increased. This provides a technical solution for the high-quality and mass production of optical fibers.

[0022] 2. This invention proposes a large-mode-field active optical fiber that is easy to fabricate. The core LP (Large Mode Field) is achieved by optimizing the distance between the double-layer nested anti-resonant unit structure. 11 The efficient coupling between the mode and the cladding region ensures that the optical fiber can still operate in single mode even with a large mode field area;

[0023] 3. The present invention proposes a large-mode-field active optical fiber that is easy to fabricate. It adopts a double-layer nested anti-resonant unit structure, which increases the refractive index difference between the core region and the background region and facilitates the fabrication of the optical fiber. At the same time, it effectively suppresses the degradation of laser mode characteristics caused by thermal refractive index changes in the active core region under high power conditions, and provides strong support for the generation and amplification of high-power, high-beam-quality lasers. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the cross-sectional structure of a large-mode-field active optical fiber that is easy to fabricate;

[0025] Figure 2 For a core fundamental mode LP of an easily fabricated large-mode-field active optical fiber 01 Model and LP 11 The distribution diagram of the model's field.

[0026] The attached diagram lists the components represented by each number as follows:

[0027] 1: Active fiber core area; 2: Passive background material area;

[0028] 3: Inner capillary; 4: Outer capillary;

[0029] 5: Outer layer area. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0031] Example 1

[0032] A type of large-mode-field active optical fiber that is easy to fabricate, see [link to relevant documentation]. Figure 1 and Figure 2 The active optical fiber includes: an active core region 1 and a cladding region;

[0033] The active core region 1 is doped with luminescent rare earth ions. The cladding region includes an inner cladding region and an outer cladding region. The inner cladding region consists of a passive background material region 2 and a double-layered nested capillary distributed around the active core region 1, which satisfies the anti-resonance condition.

[0034] The distance between the outer wall of the inner capillary 3 and the inner wall of the outer capillary 4 satisfies the active core region LP. 11 The mode's resonance condition; the outer cladding region 5 surrounds the inner cladding region, confining the pump light to the inner cladding region and the fiber core region for transmission.

[0035] Furthermore, the active core region 1 and the inner cladding region have the same glass matrix, but different compositions and refractive indices. Specifically, at the signal light wavelength, the refractive indices of the inner capillary 3 and outer capillary 4 are greater than the refractive index of the background material in the inner cladding region, which in turn is greater than the refractive index of the active core region 1. At the pump light wavelength, the refractive index of the outer cladding region 5 is less than the refractive index of the passive background material region 2. The refractive indices of the inner capillary 3 and outer capillary 4 are the same.

[0036] Furthermore, the refractive index of the fundamental mode effective mode, determined by the refractive index and diameter of the passive background material region 2 within the inner capillary 3, is less than the refractive index of the fundamental mode effective mode of the active core region 1.

[0037] Furthermore, the number of double-layered nested capillaries (i.e., inner capillary 3 and outer capillary 4) within the inner cladding region is determined by the following formula:

[0038]

[0039] Where t is the capillary thickness, d c d is the diameter of the active fiber core region. cl d is the inner diameter of the inner capillary 3, and d is the distance between the outer wall of the inner capillary 3 and the inner wall of the outer capillary 4.

[0040] Example 2

[0041] A large-mode-field active optical fiber that is easy to fabricate; see schematic diagram of its cross-sectional structure. Figure 1 The active optical fiber includes an active core region 1 and a cladding region. The active core region 1 is doped with ytterbium ions to generate 1-micron wavelength lasers. The cladding region includes an inner cladding region and an outer cladding region 5. The inner cladding region consists of a passive background material region 2 and inner capillaries 3 and outer capillaries 4, which are distributed around the active core region 1 and meet the anti-resonance condition. The inner capillaries 3 and outer capillaries 4 are concentrically nested to form a double-nested anti-resonance unit structure.

[0042] Active fiber core region 1, with a diameter of d c =40 μm, the material refractive index is 1.4885; passive background material region 2 is distributed around active core region 1, the material refractive index is 1.49; inner capillary 3 and outer capillary 4 both have a thickness of t=1.3 μm, which is the second-order anti-resonance thickness at a wavelength of 1080 nm, and the refractive index of inner capillary 3 and outer capillary 4 is 1.61; the inner diameter of inner capillary 3 is d cl =8 μm, the distance between the outer wall of the inner capillary 3 and the inner wall of the outer capillary 4 is d=7.3 μm, which satisfies the LP of the active core region. 11The resonant conditions of the mode; the refractive index of the material of the outer cladding region 5 is 1.38 and its thickness is 10 μm. Composite materials such as acrylic resin and polyimide can be selected; the number of double-layer nested capillaries is 7, which are uniformly surrounded around the active core region 1 (i.e., the core).

[0043] Figure 2 For optical fiber at 1080 nm LP 01 With LP 11 Mode field distribution diagram of the mode. This fiber LP 01 The mode-limiting loss is 0.84 dB / m, LP 11 Mode coupling occurs between the outer wall of the inner capillary 3 and the inner wall of the outer capillary 4, resulting in increased confinement loss of 194.4 dB / m, thereby enabling low-loss single-mode transmission at 1080 nm in an optical fiber with a core diameter of up to 40 μm.

[0044] In summary, the large-mode-field active optical fiber proposed in this invention, which is easy to fabricate, can still achieve a fundamental mode loss of less than 1 dB / m with a core diameter of up to 40 μm, even when the refractive index difference between the active core material and the background material reaches 0.0015. 11 With a mode loss of 194.4 dB / m, it ensures low-loss single-mode transmission of 1080 nm laser, providing a feasible technical path for high-quality fabrication of large-mode-field active solid-core anti-resonant fiber, and has important application value in the field of high-power fiber laser technology.

[0045] The large-mode-field active fiber design proposed in this embodiment of the invention is not limited to the materials and fiber structure parameters selected in this embodiment; different materials and structure parameters can be used to meet specific application requirements. By adjusting the fiber structure parameters and selecting different materials, the active fiber proposed in this embodiment of the invention can realize high-power single-mode generation and amplification of lasers in other wavelength bands.

[0046] Unless otherwise specified, the model numbers of the various devices in this embodiment of the invention are not limited, and any device that can perform the above functions is acceptable.

[0047] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A large-mode-field active optical fiber that is easy to fabricate, characterized in that, The optical fiber includes: an active core region and a cladding region; The active core region is doped with luminescent rare earth ions; the cladding region includes an inner cladding region and an outer cladding region, wherein the inner cladding region is composed of a passive background material region and a double-layered nested capillary distributed around the active core region, satisfying the anti-resonance condition thickness; The double-layer nested capillary includes an inner capillary and an outer capillary. The distance between the outer wall of the inner capillary and the inner wall of the outer capillary satisfies the active core region LP. 11 The resonance condition of the mode; The outer cladding region surrounds the inner cladding region, confining the pump light to the inner cladding region and the fiber core region for transmission. The active fiber core region and the inner cladding region have the same glass matrix; At the signal light wavelength, the refractive index of the inner and outer capillaries is greater than the refractive index of the background material in the inner cladding region, which is greater than the refractive index of the active fiber core region. At the pump light wavelength, the refractive index of the outer cladding region is less than the refractive index of the passive background material region; The refractive index of the fundamental mode, determined by the refractive index and diameter of the passive background material region within the inner capillary, is less than the refractive index of the fundamental mode in the active core region.

2. The large-mode-field active optical fiber that is easy to fabricate according to claim 1, characterized in that, The refractive index of the inner capillary is the same as that of the outer capillary.

3. The large-mode-field active optical fiber that is easy to fabricate according to claim 1, characterized in that, The number of the double-layered nested capillaries is determined by the following formula: ； Where t is the capillary thickness, d c d is the diameter of the active fiber core region. cl d is the inner diameter of the inner capillary, and d is the distance between the outer wall of the inner capillary and the inner wall of the outer capillary.

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