A large-mode-field dual-channel polarization-maintaining optical fiber

Abstract

This invention relates to a large-mode-field dual-channel polarization-suppressed optical fiber. This fiber has a solid-core anti-resonant structure. The outer cladding of the fiber contains 2n cladding rings and two or more sets of cladding rectangles. The core fills the space between the outer cladding and the cladding rings and rectangles. The two or more sets of cladding rectangles are positioned on any straight line passing through the center of the fiber cross-section, and are symmetrical. The 2n cladding rings are evenly distributed on both sides of the line containing the cladding rectangles. The distance d1 between adjacent cladding rings is equal, and the minimum distance between a cladding ring and a cladding rectangle is d2, where d2 > d1. The cladding rings and rectangles form an anti-resonant cladding, and the refractive index of the cladding rings and rectangles is greater than that of the core. This invention solves the technical problems of limited mode field area, fundamental mode transmission limitations, and limited functionality in existing technologies.

Description

Technical Field

[0001] This invention relates to the fields of optics and laser technology, specifically to the fields of microstructured optical fibers and polarized optical fibers, and particularly to a large-mode-field dual-channel polarization-suppressing optical fiber. Background Technology

[0002] With technological advancements, antiresonant fiber has become a cutting-edge field in microstructure fiber research. Antiresonant fiber technology is primarily used in laser transmission and sensing, and compared to traditional fiber technology, it features lower transmission loss, higher quality, and a larger transmission mode field.

[0003] Unlike traditional optical fibers that rely on total internal reflection for light guidance, antiresonant optical fibers rely on the antiresonance effect. This also means that antiresonant optical fibers are not limited to hollow-core or liquid-core fibers, but can also be used in solid-core fibers. These fibers have very broad application prospects in high-quality optical communication, laser technology, and sensing technology.

[0004] With the development of laser technology, the demand for large mode area optical fibers is increasing. Currently, large mode area optical fibers mostly adopt photonic crystal fiber technology, but the mode area is limited (usually less than 500 μm). 2 Furthermore, its fundamental mode transmission and single function (difficult to combine large mode field and polarization suppression functions) make it difficult to meet the ever-increasing technical demands. Summary of the Invention

[0005] Purpose of the invention:

[0006] This invention provides a large mode field dual-channel polarization suppression optical fiber, which aims to solve the technical problems of limited mode field area, fundamental mode transmission, and single function in the existing technology.

[0007] Technical solution:

[0008] The first method of this invention proposes a large-mode-field dual-channel polarization suppression fiber. This large-mode-field dual-channel polarization suppression fiber has a solid-core anti-resonant structure. The outer cladding of the fiber contains 2n cladding rings (n > 2) and two or more sets of cladding rectangles. The fiber core fills the space between the outer cladding and the cladding rings and rectangles. The two or more sets of cladding rectangles are arranged on any straight line passing through the center of the fiber cross-section and are symmetrical. The 2n cladding rings are evenly distributed on both sides of the straight line containing the cladding rectangles. The distance d1 between adjacent cladding rings is equal, and the minimum distance between the cladding ring and the cladding rectangle is d2, where d2 > d1. The cladding rings and rectangles form an anti-resonant cladding, and the refractive index of the cladding rings and rectangles is greater than the refractive index of the fiber core.

[0009] Furthermore, the cladding ring can be a single cladding ring or an anti-resonance hole structure formed by an inner cladding ring and an outer cladding ring. When the cladding ring is an anti-resonance hole structure formed by an inner cladding ring and an outer cladding ring, the inner cladding ring and the outer cladding ring are concentrically arranged.

[0010] Furthermore, when the cladding rectangles are set to two groups, each group of cladding rectangles can contain 1-5 layers of rectangular structures, and the 1-5 layers of rectangular structures are set in parallel.

[0011] Furthermore, the formula for calculating the cladding ring thickness is as follows:

[0012]

[0013] In the formula, t m λ is the thickness of the cladding ring at this resonance order, λ is the resonant wavelength, m is the resonance order, n1 is the refractive index of the cladding, and n0 is the refractive index of the fiber material.

[0014] Furthermore, the arrangement of the cladding rectangles is consistent with the polarization direction of the suppression mode field.

[0015] Furthermore, the thickness of the cladding rectangle is less than 0.8 μm.

[0016] Furthermore, the refractive index of the cladding ring and the cladding rectangle is greater than the refractive index of the fiber core, and the difference in refractive index is at least 0.02.

[0017] Furthermore, the material of the fiber core can produce an anti-resonance effect, and is one of rare earth-doped glass, sulfide glass, or telluride glass.

[0018] Furthermore, the outer cladding layer contains six cladding rings.

[0019] The second method of this invention proposes an application of a large-mode-field dual-channel polarization-suppressed fiber in laser transmission to achieve large-mode-field laser transmission.

[0020] Beneficial effects:

[0021] The present invention discloses a large-mode-area dual-channel polarization-suppressing optical fiber. Its working principle is as follows: When the core refractive index is less than that of the cladding ring and the cladding rectangle, the fiber can guide light through an anti-resonance effect. In this case, large-mode-area light guiding can be achieved, and with appropriate cladding ring gaps, a significant suppression effect on higher-order modes can be achieved. Furthermore, the rectangular structure of the cladding rectangle resonates with the mode field polarization, thereby generating mode field suppression. This significantly increases the loss of undesirable mode fields, thus providing polarization suppression and controlling the light guiding channel.

[0022] This invention solves the technical problems of limited mode field area, fundamental mode transmission, and single function in the prior art. The large mode field polarization suppression fiber of this invention can be designed with different working bands and different suppression ratios by using different materials and structures. Compared with traditional large mode field fibers, this large mode field polarization suppression fiber has a larger transmission mode field and can simultaneously achieve polarization suppression and higher-order mode suppression in specific bands, which is of great significance for the development of optical components. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the cross-section of a large-mode-field dual-channel polarization suppression fiber made of SiO2 and doped glass, as provided in Embodiment 1 of the present invention.

[0024] Figure 2 This is the wavelength-higher-order mode loss curve of the large-mode-field dual-channel polarization suppression fiber in Embodiment 1 of the present invention;

[0025] Figure 3 This is a rendering of Embodiment 1 of the present invention;

[0026] Figure 4 This is a schematic diagram of the cross-section of a large-mode-field dual-channel polarization suppression fiber made of SiO2 and doped glass, as provided in Embodiment 2 of the present invention.

[0027] Figure 5 This is the wavelength-higher-order mode loss relationship curve of the large-mode-field dual-channel polarization-suppressed fiber in Embodiment 2 of the present invention.

[0028] Figure 6 This is a rendering of Embodiment 2 of the present invention;

[0029] Figure 7 This is a schematic diagram of the cross-section of a large-mode-field dual-channel polarization suppression optical fiber provided in Comparative Example 1 of the present invention, consisting of SiO2 and doped glass.

[0030] Figure 8 The wavelength-higher-order mode loss curve of the large-mode-field dual-channel polarization-suppressing fiber in Comparative Example 1 of this invention is shown.

[0031] The image is labeled as follows:

[0032] 1. Outer cladding, 2. Cladding ring, 21. Individual cladding ring, 22. Inner cladding ring, 23. Outer cladding ring, 3. Cladding rectangle, 4. Core. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be described below with reference to the accompanying drawings. Obviously, these embodiments are only a part of the embodiments of this invention, and not all of them. The embodiments of this invention described and shown in the accompanying drawings can generally be arranged and designed according to different requirements.

[0034] The development of anti-resonant fiber technology provides theoretical support for the design and development of novel large-mode-field and polarization-controlled fibers. Anti-resonant fibers rely on leakage modes in the anti-resonance effect for light guidance. This invention achieves large-mode-field transmission by designing a special fiber structure and utilizing the anti-resonance effect. Furthermore, it utilizes the difference in resonance effects between the leakage mode and the special structure to suppress polarization and higher-order modes, thereby realizing dual-channel polarization suppression for large-mode-field applications. This technology is of great significance for the application of anti-resonant fibers and the development of laser technology.

[0035] This invention provides a large-mode-field dual-channel polarization-suppressed optical fiber, such as... Figure 1 As shown in Figure 3, this large-mode-field dual-channel polarization suppression fiber is a solid-core single-layer anti-resonant structure. Specifically, the solid fiber contains a cladding tube. The outer cladding 1 of the fiber is provided with 2n (n>2) cladding rings 2 and two or more sets of cladding rectangles 3. The space between the outer cladding and the cladding rings 2 and cladding rectangles 3 is filled with fiber core 4. The two or more sets of cladding rectangles 3 are arranged on any straight line passing through the center of the fiber cross-section, and the two or more sets of cladding rectangles 3 are symmetrical with respect to the center of the fiber cross-section. The 2n cladding rings 2 are symmetrically distributed on both sides of the straight line where the cladding rectangles 3 are located. The distance d1 between adjacent cladding rings 2 is equal, and the minimum distance between the cladding ring 2 and the cladding rectangle 3 is d2, where d2>d1. The cladding rings 2 and cladding rectangles 3 form an anti-resonant cladding, and the refractive index of the cladding rings 2 and cladding rectangles 3 is greater than the refractive index of the fiber core 4. Preferred n=3, meaning the number of cladding rings 2 is preferably 6. Fewer than 6 rings cannot achieve an anti-resonant structure, and 8 or more may generate high-order mode field interference. Using 8 or more rings is not highly recommended.

[0036] The cladding ring 2 is a single cladding ring 21 or an anti-resonance hole structure formed by an inner cladding ring 22 and an outer cladding ring 23. When the cladding ring 2 is an anti-resonance hole structure formed by an inner cladding ring 22 and an outer cladding ring 23, the inner cladding ring 22 and the outer cladding ring 23 are concentrically arranged.

[0037] When the cladding rectangles 3 are set in two groups, each group of cladding rectangles 3 can contain 1-5 layers of structure, and the 1-5 layers of structure are arranged in parallel. The cladding rectangles 3 control the channel, polarization suppression, and mode field suppression through the resonance effect. The cladding rings 2 are arranged relatively uniformly with the cladding rectangles 3 as the central axis. The cladding rings 2 and the cladding rectangles 3 together form an anti-resonant cladding.

[0038] The cladding ring 2 and cladding rectangle 3 are preferably made of materials with high refractive indices. The refractive index relationship between the materials of the cladding ring 2 and cladding rectangle 3 and the core 4 is that the cladding refractive index > the core refractive index, and the difference between the refractive indices of the cladding ring 2 and cladding rectangle 3 and the core 4 is at least 0.02. The difference only needs to be greater than zero; any difference will produce a phenomenon, but if it is too small, the phenomenon will not be obvious. Therefore, this application limits it to at least >0.02. For example, the cladding ring can be made of doped silica with a refractive index of 1.48, while other materials of the optical fiber can be undoped silica with a refractive index of 1.45.

[0039] Furthermore, the relationship between the cladding tube thickness and the refractive index of the material can be set according to the operating wavelength. The specific settings are as follows:

[0040]

[0041] t m The thickness of the cladding ring at this resonance order is in micrometers, λ is the resonant wavelength in units of 1, m is the resonance order, n1 is the refractive index of the cladding, and n0 is the refractive index of the optical fiber material.

[0042] The thickness of the cladding ring 2 is preferably the thickness at the first-order resonance. The thickness of the cladding ring 2 should be the thickness at the non-resonant frequency.

[0043] The thin-layer ring thickness calculated using this formula at this resonance order can ensure that the working band and the resonant band of the optical fiber do not overlap.

[0044] Furthermore, the cladding rectangle 3 should be aligned with the polarization direction of the suppressed mode field, meaning the rectangle suppresses mode fields in the same direction as itself. It is recommended that the thickness of the cladding rectangle 3 be less than the thickness at first-order resonance to reduce the possibility of additional resonance interference.

[0045] Furthermore, the core 4 of the large-mode-field dual-channel polarization-suppression fiber can be made of a material capable of producing an anti-resonance effect, preferably one of rare-earth-doped glass, sulfide glass, or telluride glass. When the core 4 is made of one of sulfide glass or telluride glass, mid-infrared laser transmission is achieved through large-mode-field polarization-suppression fiber.

[0046] This invention utilizes the anti-resonant fiber guiding principle to design and improve traditional large-mode-field optical fibers. This enables the fiber to simultaneously achieve fundamental mode large-mode-field guiding, higher-order mode suppression, and polarization suppression within a specific wavelength band, exhibiting strong guiding performance and a high suppression ratio, making it applicable to laser technology. The operating spectrum of the large-mode-field dual-channel polarization-suppression fiber can be adjusted by the cladding thickness (cladding ring 2 and cladding rectangle 3), cladding material (cladding ring 2 and cladding rectangle 3), and core material. The polarization suppression capability of the large-mode-field dual-channel polarization-suppression fiber can be adjusted by the rectangular shape (length, width, number, and position) and number of layers of the cladding rectangle 3.

[0047] A large-mode-field polarization-suppressed fiber is used for laser transmission. It can realize large-mode-field transmission of laser and simultaneously achieve polarization suppression and high-order mode suppression functions.

[0048] For ease of explanation, the effects of light wavelength and temperature on the refractive index of the optical fiber material are ignored in the embodiments.

[0049] Example 1

[0050] A large-mode-field dual-channel polarization-suppressing fiber, its cross-sectional schematic diagram is shown below. Figure 1 The large mode field and polarization control fiber described in this embodiment includes an outer cladding 1, which contains 6 cladding rings 2 and 2 cladding rectangles 3. The cladding material is germanium-doped glass with a refractive index of 1.48. The remaining part is the fiber core 4, which is made of undoped quartz with a refractive index of 1.45.

[0051] The outer diameter of the optical fiber is 187 μm. The cladding rectangle 3 is located at 0° and 180° of the optical fiber cross section. The three pairs of cladding rings 2 are located at ±40°, ±90° and ±140°. The outer diameter of the cladding ring 2 is 21 μm and the thickness of the cladding ring is 1.74 μm. The distance of the cladding rectangle 3 from the center point of the optical fiber is 25 μm. The length of the rectangle is 45 μm and the thickness is 0.5 μm.

[0052] Simulation analysis was performed on this embodiment, and its waveband, transmission mode field, and mode loss with other mode fields are as follows: Figure 2 and 3 As shown, in the 1455-1480nm and 1505nm-1535nm bands, the transmission mode loss is at least 20dB lower than other mode losses, and the mode area is not less than 2000um. 2 However, its suppression of longitudinal polarization is not significant.

[0053] Example 2

[0054] A large-mode-field dual-channel polarization-suppressing fiber, its cross-sectional schematic diagram is shown below. Figure 4 The large mode field and polarization control fiber described in this embodiment includes an outer cladding 1, comprising 6 sets of cladding rings 2 and 2 sets of cladding rectangles 3. The cladding material is germanium-doped glass with a refractive index of 1.48. The remaining part is the fiber core 4, which is made of undoped quartz with a refractive index of 1.45.

[0055] The outer diameter of the optical fiber is 207 μm. Cladding rectangles 3 are located at 0° and 180° positions on the fiber cross-section. Each group of cladding rectangles 3 contains three rectangles, each 45 μm long and 0.5 μm wide, with a spacing of 5 μm between the rectangles. Six groups of cladding rings are located at ±40°, ±90°, and ±140° positions. The outer diameter of the outer cladding ring 23 is 21 μm, the outer diameter of the inner cladding ring 22 is 13 μm, and the cladding ring thickness is 1.74 μm. Each group of cladding rectangles 3 consists of three rectangles, with the middle rectangle 25 μm from the center of the fiber. Each cladding rectangle 3 has a length of 45 μm and a width of 0.5 μm.

[0056] Simulation analysis was performed on this embodiment, and its waveband, polarization direction, and higher-order mode loss are as follows: Figure 5 and 6 As shown, a rectangular group at the horizontal position of the optical fiber generates a resonance effect that modulates the fiber's performance, producing different effects under different sizes and arrangements. Figure 6 The longitudinal mode field was suppressed, achieving dual-path large mode field polarization-suppressed transmission. Achieved polarization suppression of greater than 2000µm. 2 The mode field guiding provides dual-path polarization suppression greater than 20dB. In the 1558-1566nm band, the transverse polarization loss is at least 40dB lower than that of longitudinal polarization and other modes.

[0057] Comparative Example 1

[0058] A cross-sectional schematic diagram of a large-mode-field polarization-suppressing fiber is shown below. Figure 7 The large mode field and polarization control fiber described in this embodiment includes an outer cladding, comprising eight cladding rings 2 and one rectangle 3. The cladding material is germanium-doped glass with a refractive index of 1.48, and the remaining fiber material 4 is undoped quartz with a refractive index of 1.45.

[0059] The outer diameter of the optical fiber is 240 μm. The cladding rectangle 3 is located at 0° and 180° of the fiber cross-section. The three pairs of cladding rings 2 are located at ±40°, ±90° and ±140°. The outer diameter of the cladding ring 2 is 22 μm and the thickness is 1.74 μm. The rectangle is located horizontally in the fiber core, with a length of 188 μm and a width of 0.5 μm.

[0060] In this case, compared to Example 1, the fiber outer diameter and cladding tube 2 thickness are the same, but the cladding tube 2 is replaced with 8 groups, and the two groups of cladding rectangles 3 are replaced with single rectangles. The comparison results of second-order mode suppression and fundamental mode (first-order mode) in this design are as follows: Figure 8 As shown, the difference between the higher-order mode and the lower-order mode is small, and its higher-order mode suppression capability is significantly lower than that of Example 1 and Example 2.

[0061] Comparative Example 2

[0062] Among Newport's existing polarization-maintaining fiber products, the one with the largest mode field diameter is F-PM1550nm, with a single-core mode field diameter of only 10-11µm, meaning the mode field area is only about 95µm. 2 It is much smaller than the 2000 μm in Examples 1 and 2. 2 Model field transmission area.

Claims

1. A large-mode-field dual-channel polarization-suppressing optical fiber, characterized in that, The large-mode-field dual-channel polarization suppression fiber is a solid-core anti-resonant structure. The outer cladding (1) of the fiber is provided with 2n cladding rings (2) and two or two sets of cladding rectangles (3), where n>2. The fiber core (4) is filled between the outer cladding and the cladding rings (2) and cladding rectangles (3). The two or two sets of cladding rectangles (3) are set on any straight line passing through the center of the fiber cross section, and the two or two sets of cladding rectangles (3) are symmetrical. The 2n cladding rings (2) are evenly distributed on both sides of the straight line where the cladding rectangles (3) are located. The distance d1 between adjacent cladding rings (2) is equal. The minimum distance between the cladding rings (2) and the cladding rectangles (3) is d2, where d2>d1. The cladding rings (2) and cladding rectangles (3) form an anti-resonant cladding. The refractive index of the cladding rings (2) and cladding rectangles (3) is greater than the refractive index of the fiber core (4).

2. The large-mode-field dual-channel polarization-suppressing optical fiber according to claim 1, characterized in that, The cladding ring (2) is a single cladding ring (21) or an anti-resonance hole structure formed by an inner cladding ring (22) and an outer cladding ring (23). When the cladding ring (2) is an anti-resonance hole structure formed by an inner cladding ring (22) and an outer cladding ring (23), the inner cladding ring (22) and the outer cladding ring (23) are concentrically arranged.

3. The large-mode-field dual-channel polarization-suppressing optical fiber according to claim 1, characterized in that, When the cladding rectangle (3) is set to two groups, each group of cladding rectangle (3) can contain 1-5 layers of rectangular structure, and the 1-5 layers of rectangular structure are set in parallel.

4. The large-mode-field dual-channel polarization-suppressing optical fiber according to claim 1, characterized in that, The formula for calculating the thickness of the cladding ring (2) is as follows: ； In the formula, m The resonance order is... t m Let λ be the thickness of the cladding ring at this resonance order, and λ be the resonant wavelength. n 1 represents the refractive index of the cladding. n 0 represents the refractive index of the optical fiber material.

5. The large-mode-field dual-channel polarization-suppressing optical fiber according to claim 1, characterized in that, The arrangement of the cladding rectangle (3) is consistent with the polarization direction of the suppression mode field.

6. The large-mode-field dual-channel polarization-suppressing optical fiber according to claim 1, characterized in that, The thickness of the cladding rectangle (3) is less than 0.8 μm.

7. The large-mode-field dual-channel polarization-suppressing optical fiber according to claim 1, characterized in that, The refractive index of the cladding ring (2) and the cladding rectangle (3) is greater than that of the core (4), and the difference in refractive index is at least 0.

02.

8. The large-mode-field dual-channel polarization-suppressing optical fiber according to claim 1, characterized in that, The material of the fiber core (4) can produce an anti-resonance effect and is one of rare earth doped glass, sulfide glass, or telluride glass.

9. The large-mode-field dual-channel polarization-suppressing optical fiber according to claim 1, characterized in that, The outer cladding layer (1) contains six cladding rings (2).

10. An application of the large-mode-field dual-channel polarization-suppressed fiber as described in any one of claims 1-9 in realizing large-mode-field laser transmission.

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