A single-mode hollow counter resonant optical fiber for transmitting high power laser light

Abstract

The application relates to a single-mode hollow anti-resonant optical fiber for transmitting high-power laser, which comprises, from outside to inside, a cladding and a core, the cladding comprises an outer cladding and an inner cladding, the inner cladding comprises a plurality of anti-resonant layer units, each of the anti-resonant layer units comprises a first anti-resonant layer, a second anti-resonant layer and a thin wall, the first anti-resonant layer and the second anti-resonant layer are tangent at a region close to the outer cladding, the tangent point is cut off, and the thin wall is connected, and the end of the thin wall is connected with the outer cladding. Compared with the prior art, the application has the advantages of low fundamental mode transmission loss, high single-mode performance, wide spectral bandwidth, high damage threshold and low nonlinear coefficient.

Description

Technical Field

[0001] This invention relates to an anti-resonant optical fiber, and more particularly to a single-mode hollow-core anti-resonant optical fiber for transmitting high-power lasers. Background Technology

[0002] High-power lasers refer to lasers ranging from kilowatts to megawatts, widely used in industrial fields such as laser cutting, laser marking, and laser grinding, as well as in military applications. High-power single-mode lasers, in particular, excel in industrial applications, especially in cutting, welding, and marking. Their high-quality laser beams enable precise and efficient material processing, improving the efficiency and quality of industrial production. For example, in metal cutting, high-power single-mode lasers offer high-precision and high-speed processing; in laser welding, their precision and flexibility have led to their widespread use in the automotive, aerospace, and electronics industries.

[0003] Solid fiber optic cables have some inherent drawbacks when transmitting high-power single-mode lasers. During high-power laser transmission, the fiber may be damaged due to excessive laser power, leading to a decrease in transmission performance or fiber breakage. Furthermore, the transmission distance is limited due to factors such as fiber loss and dispersion. Hollow fiber optic cables can effectively solve these problems.

[0004] Hollow-core antiresonant fiber is an important research direction in fiber optics. Through its specific microstructure design, light can be confined within the fiber core, reducing the overlap between the light field and the quartz region. Compared to traditional solid-core fiber, hollow-core fiber overcomes intrinsic losses due to material properties and scattering, and in principle can achieve ultra-low-loss optical transmission. Furthermore, it possesses advantages such as low delay, low dispersion, low nonlinearity, high optical damage threshold, interference resistance, and high flexibility in being filled with liquids or gases. It has broad application prospects in high-power pulsed laser transmission, ultrafast optics, and nonlinear optics, driving the rapid development of fiber optics.

[0005] By designing and optimizing the microstructure within the cladding of hollow antiresonant optical fibers, confining losses can be reduced. Furthermore, due to their simple cladding structure, the internal structure and specific dimensions of hollow antiresonant optical fibers can be flexibly designed to meet the requirements of a particular transmission wavelength and application.

[0006] Hollow-core optical fiber has seen rapid development due to its excellent properties such as low delay, low loss, low dispersion, and high damage threshold. Although the loss of hollow-core antiresonant fiber has been reduced to 0.08 dB / km, its ability to maintain single-mode transmission is not significant.

[0007] A search revealed that Chinese Patent Publication No. CN119247539A discloses a high single-mode, low-loss hollow-core anti-resonant optical fiber, specifically comprising an outer cladding and an inner cladding. The inner cladding is composed of nested structural units arranged circumferentially along and connected to the inner wall of the outer cladding. The central cavity enclosed by the inner cladding forms the fiber core. Each nested structural unit includes two layers of nested glass tubes with different radii: an outer nested glass tube and an inner nested glass tube. However, this existing patent suffers from problems such as high loss.

[0008] Therefore, how to design a hollow antiresonant fiber that maintains single-mode characteristics while keeping low loss, so as to realize the transmission of high-power single-mode lasers, has become a technical problem that needs to be solved. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a single-mode hollow-core anti-resonant optical fiber with low fundamental mode transmission loss, wide spectral bandwidth, high damage threshold, good single-mode characteristics, and low nonlinearity for transmitting high-power lasers.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] According to one aspect of the present invention, a single-mode hollow-core anti-resonant optical fiber for transmitting high-power laser is provided, comprising a cladding and a core arranged sequentially from the outside to the inside. The cladding includes an outer cladding and an inner cladding. The inner cladding includes a plurality of anti-resonant layer units. Each anti-resonant layer unit includes a first anti-resonant layer, a second anti-resonant layer, and a thin wall. The first anti-resonant layer and the second anti-resonant layer are tangent to each other in a region near the outer cladding. The tangent point is cut off and connected by a thin wall. The end of the thin wall is connected to the outer cladding.

[0012] As a preferred technical solution, the anti-resonance layer unit is provided with five units, and the spacing between adjacent anti-resonance layer units is equal.

[0013] As a preferred technical solution, the cut width 'a' at the removal point of the first and second anti-resonance layers is 7.5-8.5 μm.

[0014] As a preferred technical solution, the length L of the thin wall is 3.5-4.5 μm.

[0015] As a preferred technical solution, the thickness t of the first anti-resonant layer, the second anti-resonant layer, and the thin wall is consistent, and t satisfies the condition with respect to the transmission wavelength.

[0016]

[0017] Where n is the refractive index of the silica glass, λ is the transmission wavelength, and m is a positive integer.

[0018] As a preferred technical solution, the thickness t is 0.75-0.85μm.

[0019] As a preferred technical solution, the second anti-resonance layer is nested within the first anti-resonance layer.

[0020] As a preferred technical solution, the diameter c of the first anti-resonant layer is 16-17 μm, and the diameter b of the second anti-resonant layer is 7.8-8.5 μm.

[0021] As a preferred technical solution, the diameter d of the outer cladding layer is 110-150 μm.

[0022] As a preferred technical solution, the core radius r is 13.5-14.5μm.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1) The present invention removes the connection point between the first anti-resonant layer and the second anti-resonant layer, and uses a thin wall to support each unit anti-resonant layer. Removing the connection point can further reduce the confining loss and make it easier for higher-order modes to leak, so that the optical fiber maintains good single-mode characteristics; and the optical fiber structure is simple and easy to process and manufacture.

[0025] 2) The hollow-core anti-resonant fiber of this invention can achieve low-loss transmission of high-power lasers. In the transmission wavelength range of 1010-1130nm, the total loss of the fundamental mode is less than 0.4dB / km, the total loss of the higher-order modes is greater than 560dB / km, and the suppression ratio of the higher-order modes is greater than 2000. The 1010-1130nm band includes the wavelengths of 1064nm and 1080nm commonly used in existing industries for high-power lasers. Therefore, the hollow-core fiber of this invention has great application prospects in the industrial field.

[0026] 3) The total fundamental mode loss of the hollow-core antiresonant fiber of this invention is 0.25 dB / km and 0.24 dB / km at 1064 nm and 1080 nm, respectively. The higher-order mode suppression ratios are 2391 and 2645, respectively. Therefore, the hollow-core antiresonant fiber of this invention can transmit laser light at wavelengths of 1064 nm and 1080 nm with low loss and can maintain good single-mode characteristics.

[0027] 4) The hollow-core anti-resonant fiber of the present invention has excellent tuning characteristics. By further optimizing its structure, the loss can be further reduced and the single-mode characteristics can be improved. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the cross-sectional structure of the optical fiber in an embodiment of the present invention.

[0029] Figure 2This is a diagram showing the fundamental mode electric field distribution in an embodiment of the present invention.

[0030] Figure 3 This is a diagram showing the electric field distribution of a higher-order mode in an embodiment of the present invention.

[0031] Figure 4 This is a graph showing the variation of fundamental mode loss with transmission wavelength in an embodiment of the present invention.

[0032] Figure 5 This is a graph showing the variation of higher-order mode loss with transmission wavelength in an embodiment of the present invention.

[0033] Figure 6 This is a graph showing the variation of the higher-order mode rejection ratio with the transmission wavelength in an embodiment of the present invention.

[0034] Figure 7 This is a graph showing the variation of the nonlinear coefficient with the transmission wavelength in an embodiment of the present invention.

[0035] 1 is the outer cladding layer, 2 is the second anti-resonant layer, 3 is the first anti-resonant layer, 4 is the fiber core, and 5 is the thin wall. Detailed Implementation

[0036] The technical solutions of the embodiments of the present 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 the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0037] Example

[0038] like Figure 1 As shown, a single-mode hollow-core anti-resonant optical fiber for transmitting high-power lasers includes a high-refractive-index cladding and a low-refractive-index core 4 arranged sequentially from the outside to the inside. The cladding includes an outer cladding 1 and an inner cladding, with the outer cladding covering the inner cladding and the core. The material is silica glass with a refractive index of n.

[0039] The inner cladding layer includes multiple anti-resonance layer units, each of which includes a first anti-resonance layer 3, a second anti-resonance layer 2, and a thin wall 5. The wall thickness of the anti-resonance layer is t, and the material is silicon dioxide glass with a refractive index of n.

[0040] The diameter of the first anti-resonant layer 3 of the hollow anti-resonant optical fiber is c, and the diameter of the second anti-resonant layer 2 is b. The second anti-resonant layer 2 is nested inside the first anti-resonant layer 3. The first anti-resonant layer 3 and the second anti-resonant layer 2 are tangent to each other in the region near the outer cladding layer 1. The tangent point is cut off and connected by a thin wall 5. The end of the thin wall 5 is connected to the outer cladding layer 1 to support the anti-resonant layer.

[0041] The above design method can further reduce the limiting loss of the fundamental mode while increasing the leakage loss of higher-order modes, maintaining good single-mode characteristics. Theoretical simulations show that in the 1010-1130nm band, the loss of the fundamental mode is as low as 0.4dB / km, the loss of higher-order modes is higher than 560dB / km, the suppression ratio of higher-order modes is higher than 2000, and it exhibits a very low nonlinear coefficient.

[0042] The anti-resonance layer unit is provided in five units, and the spacing between adjacent anti-resonance layer units is equal.

[0043] The thickness t of the first anti-resonant layer 3, the second anti-resonant layer 2, and the thin wall 5 is consistent, and t satisfies the condition with respect to the transmission wavelength.

[0044]

[0045] Where n is the refractive index of the silica glass, λ is the transmission wavelength, m is a positive integer, and in this invention, m is 2, and t is 0.75–0.85 μm.

[0046] like Figure 1 As shown, the cut width 'a' of the first anti-resonant layer 3 and the second anti-resonant layer 2 is 7.5-8.5 μm. The length L of the thin wall 5 is 3.5-4.5 μm. The thickness 't' is 0.75-0.85 μm. The diameter c of the first anti-resonant layer 3 is 16-17 μm, and the diameter b of the second anti-resonant layer 2 is 7.8-8.5 μm. The diameter 'd' of the outer cladding layer 1 is 110-150 μm. The radius r of the fiber core 4 is 13.5-14.5 μm.

[0047] The specific fabrication process of the inner cladding layer in this embodiment is as follows: First, the second anti-resonant layer 2 is nested inside the first anti-resonant layer 3, and the second anti-resonant layer 2 and the first anti-resonant layer 3 are tangent in the region near the outer cladding layer 1; then the connection point between the first anti-resonant layer 3 and the second anti-resonant layer 2 is cut off.

[0048] The matrix material of the hollow-core antiresonant optical fiber is silica glass with a refractive index n of 1.4517-1.448. The core of the hollow-core antiresonant optical fiber is air with a refractive index of 1.

[0049] In the hollow anti-resonant optical fiber, the electric field distribution of the fundamental mode is as follows: Figure 2 As shown, the electric field of the fundamental mode is confined within the fiber core, resulting in very low transmission loss. The electric field distribution of higher-order modes is as follows: Figure 3 As shown, it can be seen that a portion of the electric field of the higher-order mode is leaked through the first anti-resonant layer, causing the higher-order mode to be leaked out.

[0050] In the hollow-core anti-resonant optical fiber, the loss of the fundamental mode changes with the transmission wavelength as follows: Figure 4 As shown, the confinement loss is very low in the anti-resonant window; the main factor affecting the total loss is surface scattering loss; the loss of higher-order modes varies with the transmission wavelength as follows: Figure 5 As shown in the figure, it can be seen that the total loss of higher-order modes is mainly the limiting loss, with the minimum total loss being 560 dB / km; the higher-order mode rejection ratio varies with the transmission wavelength as follows: Figure 6 As shown, it can be seen that the higher-order mode suppression ratio is greater than 2000 in the wavelength range of 1010-1130nm.

[0051] In the hollow anti-resonant optical fiber, the nonlinear coefficient changes with the transmission wavelength as follows: Figure 7 As shown, within the transmission wavelength range, the nonlinear coefficient decreases with increasing wavelength. Within the range of 1010-1130nm, the nonlinear coefficient is less than 0.00055, making it suitable for the transmission of high-power lasers.

[0052] In summary, the single-mode hollow-core antiresonant fiber described in this invention, which can be used to transmit high-power lasers, exhibits a total fundamental mode transmission loss of less than 0.4 dB / km and a total higher-order mode transmission loss of more than 560 dB / km in the 1010-1130 nm wavelength range, with a higher-order mode suppression ratio greater than 2000. Therefore, it can achieve low-loss transmission while maintaining excellent single-mode characteristics. The transmission wavelength of 1010-1130 nm includes the commonly used laser wavelengths of 1064 nm and 1080 nm in industrial processing. Theoretical calculations show that the nonlinear coefficient is very small; therefore, the single-mode hollow-core antiresonant fiber described in this invention can be used to transmit high-power lasers.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A single-mode hollow-core anti-resonant optical fiber for transmitting high-power lasers, comprising a cladding and a core (4) arranged sequentially from the outside to the inside, wherein the cladding comprises an outer cladding (1) and an inner cladding, and the inner cladding comprises a plurality of anti-resonant layer units, characterized in that, Each of the anti-resonance layer units includes a first anti-resonance layer (3), a second anti-resonance layer (2), and a thin wall (5). The first anti-resonance layer (3) and the second anti-resonance layer (2) are tangent to each other in the region near the outer cladding layer (1). The tangent point is cut off and connected by the thin wall (5). The end of the thin wall (5) is connected to the outer cladding layer (1). There are five anti-resonance layer units, and the spacing between adjacent anti-resonance layer units is equal. The length L of the thin wall (5) is 3.5-4.5 μm. In the transmission wavelength range of 1010-1130 nm, the total loss of the fundamental mode is less than 0.4 dB / km, the total loss of the higher-order mode is greater than 560 dB / km, and the suppression ratio of the higher-order mode is greater than 2000.

2. The single-mode hollow-core antiresonant optical fiber for transmitting high-power lasers according to claim 1, characterized in that, The cut width a of the first anti-resonance layer (3) and the second anti-resonance layer (2) is 7.5-8.5μm.

3. The single-mode hollow-core anti-resonant optical fiber for transmitting high-power lasers according to claim 1, characterized in that, The thickness t of the first anti-resonant layer (3), the second anti-resonant layer (2), and the thin wall (5) is consistent, and t satisfies the condition with respect to the transmission wavelength. Where n is the refractive index of silica glass, λ is the transmission wavelength, and m is a positive integer.

4. The single-mode hollow-core anti-resonant optical fiber for transmitting high-power lasers according to claim 3, characterized in that, The thickness t is 0.75-0.85 μm.

5. The single-mode hollow-core anti-resonant optical fiber for transmitting high-power lasers according to claim 1, characterized in that, The second anti-resonant layer (2) is nested within the first anti-resonant layer (3).

6. A single-mode hollow-core anti-resonant optical fiber for transmitting high-power laser according to claim 1 or 5, characterized in that, The diameter c of the first anti-resonant layer (3) is 16-17 μm, and the diameter b of the second anti-resonant layer (2) is 7.8-8.5 μm.

7. The single-mode hollow-core anti-resonant optical fiber for transmitting high-power lasers according to claim 1, characterized in that, The diameter d of the outer cladding layer (1) is 110-150 μm.

8. The single-mode hollow-core anti-resonant optical fiber for transmitting high-power lasers according to claim 1, characterized in that, The core (4) has a radius r of 13.5-14.5 μm.

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