High-birefringence polarization-maintaining single-mode hollow-core anti-resonance optical fiber

Abstract

A high-birefringence polarization-maintaining single-mode hollow-core anti-resonance optical fiber comprises an optical fiber outer cladding and an air fiber core, a first closed cavity and a second closed cavity are formed in the slow axis direction, a third closed cavity and a fourth closed cavity are formed in the fast axis direction, and the radial section of each closed cavity is in a sector shape with the diameter being Ds; the distance between the first closed cavity and the second closed cavity is Dc, and the distance between the third closed cavity and the fourth closed cavity is Dc; the radial section of the pipe wall of the middle layer of the first closed cavity and the fourth closed cavity is in a sector shape with the diameter being Das1, the radial section of the pipe wall of the middle layer of the second closed cavity and the third closed cavity is in a sector shape with the diameter being Das2, and Das1 is not equal to Das2. Through the design of the double-thickness mixed silicon dioxide / silicon tube wall, the optical fiber has high birefringence for keeping a polarization state; and meanwhile, by nesting a non-double rotational symmetric nesting structure, the loss of two polarization fundamental modes is greatly reduced, the transmission of a high-order mode is inhibited, and the single-mode transmission in a broadband range is realized.

Description

Technical Field

[0001] The invention relates to the technical field of optical fibers, and in particular to a high-birefringence polarization-maintaining single-mode hollow-core anti-resonance optical fiber. Background Art

[0002] Polarization-maintaining fiber (PMF) can effectively prevent two orthogonal polarization states from coupling with each other during long-distance transmission, and therefore plays a vital role in many fields.

[0003] In 2007, Couny et al. proposed hollow core antiresonant fiber (HC-ARF, also known as suppressed coupling HCF). HC-ARF has shown many advantages, such as wide transmission bandwidth, high damage threshold, pure spatial mode, low backscattering and ultra-low loss. However, it is still a very challenging task to realize polarization-maintaining hollow core antiresonant fiber with high birefringence.

[0004] In order to promote the application of HC-ARF in the field of polarization maintenance, in 2015, Ding Wei et al. proposed a method to introduce high birefringence in HC-ARF. By adjusting the wall thickness in the orthogonal direction, a high birefringence of about 10 -4 In 2022, Hong Yifeng and others successfully manufactured the first polarization-maintaining HC-ARF using a double-thickness semicircular tube, achieving a 9.1×10 -5 However, the polarization-maintaining capability of HC-ARF fiber cannot reach the level of traditional polarization-maintaining fiber.

[0005] The prior application CN118795591A discloses a low-loss polarization-maintaining hollow-core antiresonant optical fiber. Through the double-thickness thin-wall design and the simple fiber nested cladding tube design, the optical fiber has a polarization-maintaining birefringence, and the average birefringence in the C-band and L-band range exceeds 3×10 -5 , reducing the transmission loss of the two polarization modes. However, the polarization-maintaining effect of this patent still fails to fully meet actual needs, and does not consider the transmission suppression of higher-order modes, which has significant defects in single-mode transmission. This is mainly reflected in the fact that although its structure helps to reduce losses, it still needs to be improved in maintaining high birefringence and single-mode transmission.

[0006] In summary, although HC-ARF has made some progress in the field of polarization maintenance, there are still many challenges and shortcomings. In particular, how to ensure the single-mode transmission performance of the optical fiber while achieving high birefringence polarization maintenance characteristics has become a key issue that needs to be solved urgently.

[0007] Therefore, developing a polarization-maintaining HC-ARF that has both high birefringence and single-mode transmission is of great significance for promoting the development of optical fiber communications and related fields. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention discloses a polarization-maintaining single-mode hollow-core antiresonant optical fiber with high birefringence. The structure of the optical fiber includes an optical fiber outer cladding arranged in sequence from the outside to the inside, a plurality of closed cavities with the same structure, and an air core. Each closed cavity is composed of the following parts: an outermost layer of mixed silica / silicon tube wall, whose radial cross-section is a fan-shaped or circular shape of the first diameter; a second layer of silica tube wall, whose radial cross-section is a fan-shaped or circular shape, and whose diameter is the second diameter or the third diameter; and an innermost layer of silica wall, whose radial cross-section is a circle of the fourth diameter, surrounding an internal space. This structure can keep the birefringence of the HC-ARF optical fiber within a bandwidth range of 145nm and maintain a bandwidth greater than 3.2×10 -4 At the same time, in the communication band, the limiting losses of the two orthogonal polarization fundamental modes are both less than 1dB / m, and the high-order mode extinction ratio reaches 222, which can achieve low-loss quasi-single-mode transmission.

[0009] The technical solution of the present invention is as follows:

[0010] A high birefringence polarization-maintaining single-mode hollow core antiresonant optical fiber, comprising an optical fiber outer cladding and an air core, characterized in that:

[0011] Between the outer cladding of the optical fiber and the air core, a first closed cavity and a second closed cavity are provided along the slow axis direction, and a third closed cavity and a fourth closed cavity are provided along the fast axis direction. The radial cross section of each closed cavity is a diameter D s The first closed cavity and the second closed cavity have a spacing of D, and the spacing between the third closed cavity and the fourth closed cavity has a spacing of D. c Each of the enclosed cavities includes, from outside to inside, an outermost tube wall, an intermediate tube wall and an innermost tube wall, the outermost tube wall material is a mixture of silicon dioxide and silicon, the intermediate tube wall material is silicon dioxide, and the innermost tube wall material is silicon dioxide;

[0012] Preferably, the thickness of the outermost tube wall of the first closed cavity and the second closed cavity is t1+t3, and the distance from the outermost tube wall to the outer cladding of the optical fiber is S1; the thickness of the outermost tube wall of the third closed cavity and the fourth closed cavity is t2+t3, and the distance from the outermost tube wall to the outer cladding of the optical fiber is S2, wherein t1 is the thickness of the silica tube wall in the outermost tube wall of the first closed cavity and the second closed cavity, t2 is the thickness of the silica tube wall in the outermost tube wall of the third closed cavity and the fourth closed cavity, t3 is the thickness of the silicon tube in the outermost tube wall, and t1≠t2;

[0013] Preferably, the thickness of the intermediate layer wall of the first closed cavity, the second closed cavity, the third closed cavity and the fourth closed cavity is t4, and the radial cross section of the intermediate layer wall of the first closed cavity and the fourth closed cavity is a diameter D as1The radial cross section of the intermediate layer of the second closed cavity and the third closed cavity is a sector-shaped, and the diameter D as2 The fan shape, and D as1 ≠D as2 ;

[0014] Preferably, the thickness of the innermost tube wall of the first closed cavity, the second closed cavity, the third closed cavity and the fourth closed cavity is t4, and the radial cross section of the innermost tube wall is a diameter D ac circle.

[0015] Preferably, the distance from the outermost tube wall to the middle tube wall of the first closed cavity and the fourth closed cavity is Z1, and the distance from the outermost tube wall to the middle tube wall of the second closed cavity and the third closed cavity is Z2; to meet the optical fiber single-mode transmission conditions, the two take different values, that is, Z1≠Z2.

[0016] Preferably, the distance from the outermost tube wall to the middle tube wall of the first closed cavity and the fourth closed cavity is Z1 and the sector diameter D as1 Satisfaction: D as1 =D as -Z1; the distance from the outermost wall of the second closed cavity and the third closed cavity to the middle wall is Z2 and the fan diameter D as2 Satisfy D as2 =D as -Z2.

[0018] Preferably, the silicon layer thickness t3 is in the range of 0.02-0.04 μm, and t4 complies with the anti-resonance waveguide vibration waveguide condition:

[0019]

[0020] Wherein, λ is the C-band operating wavelength, n1 represents the refractive index of silicon dioxide, n0 represents the refractive index of air, m is a positive integer, and the value range of m is 1, 2, ... When λ = 1.15um, m = 2, t4 = 1.15μm can be obtained.

[0021] Preferably, the high birefringence polarization-maintaining single-mode hollow-core antiresonant optical fiber is characterized in that t1 and t2 respectively follow the resonant waveguide condition in two stopbands adjacent to the passband where the working wavelength is located:

[0022]

[0023] When λ=1.55um, the wavelength ranges of the two adjacent stopbands are 1.445-1.480um and 1.787–1.820um, the t1 value range is 1.38-1.42um, and the t2 value range is 0.93-0.95um.

[0024] Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

[0025] 1. The present invention introduces a double-thickness mixed silica / silicon tube wall in the orthogonal direction to destroy the degeneracy of the cladding mode. In the 145nm broadband (1.510μm to 1.655μm), the fiber structure can stably maintain more than 3.2×10 -4 High birefringence value.

[0026] 2. This paper uses a non-double rotationally symmetric nested tube structure to confine most of the light energy in the air core, effectively avoiding the high loss problem caused by the absorption of the matrix material in traditional solid core optical fibers. Since the absorption of light by air is almost zero, this structure can greatly reduce the material absorption loss during transmission and also suppress light leakage. Within the 95nm bandwidth range, the limiting loss of the two orthogonal polarization fundamental modes is less than 1dB / m, and at 1.554μm, the limiting loss of the y-polarization fundamental mode is only 0.004dB / m.

[0027] 3. The design of the closed cavity achieves the suppression of high-order modes by finely controlling its shape and size. The fiber structure achieves a high-order mode extinction ratio of 222 at 1.55μm and maintains good stability within an 80nm bandwidth (1.526μm to 1.606μm), ensuring the realization of pure single-mode transmission.

[0028] 4. The hollow-core antiresonant optical fiber of the present invention effectively maintains the polarization state of the light wave during transmission through a carefully designed optical fiber structure and closed cavity arrangement. This polarization-maintaining performance is crucial for application scenarios that require high-precision polarization control (such as coherent optical fiber communications, optical fiber gyroscopes, etc.). Polarization-maintaining optical fiber can reduce polarization crosstalk and polarization mode dispersion of optical signals during transmission, thereby improving the overall performance of the system.

[0029] 5. The low loss characteristic means that the attenuation of the optical signal in the optical fiber is reduced, thereby improving the transmission efficiency of the optical signal. This makes the optical fiber particularly suitable for application scenarios that require long-distance transmission, such as optical fiber communications, optical fiber sensing and other fields. In high-power laser transmission applications, the low loss characteristic also helps to reduce laser damage and wavelength conversion effects, and improve the stability and reliability of laser transmission.

[0030] 6. The optical fiber structure of the present invention has certain flexibility and scalability. By adjusting the number, shape and size of the closed cavity and other parameters, the performance of the optical fiber can be further optimized to meet the needs of different application scenarios. This flexibility is also reflected in the preparation process of the optical fiber. Through advanced microstructure processing technology, mass production and customized design of optical fibers can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the cross-sectional structure of a low-loss polarization-maintaining single-mode hollow-core anti-resonant optical fiber according to a preferred embodiment of the present invention;

[0032] Figure 2 is a curve showing the variation of phase birefringence with wavelength in a hollow core antiresonant optical fiber according to a preferred embodiment of the present invention;

[0033] Figure 3 This is a curve showing how the limiting loss in the hollow-core antiresonant optical fiber varies with wavelength in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0035] The above scheme is further described below in conjunction with specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0036] Embodiment 1:

[0037] In this embodiment, if Figure 1 As shown, between the optical fiber outer cladding 9 and the air core 8, a first closed cavity 1 and a second closed cavity 2 are provided along the slow axis direction, and a third closed cavity 3 and a fourth closed cavity 4 are provided along the fast axis direction, the radial cross-section of each closed cavity is a fan-shaped with a diameter Ds, and the spacing between the first closed cavity and the second closed cavity, and the spacing between the third closed cavity and the fourth closed cavity are both Dc; each of the closed cavities includes, from the outside to the inside, an outermost tube wall, an intermediate tube wall and an innermost tube wall, the outermost tube wall material is a mixture of silica and silicon, the intermediate tube wall material is silica, and the innermost tube wall material is silica; each of the closed cavities includes, from the outside to the inside, an outermost tube wall, an intermediate tube wall and an innermost tube wall, the outermost tube wall material is a mixture of silica and silicon, the intermediate tube wall material is silica, and the innermost tube wall material is silica;

[0038] The thickness of the outermost tube wall of the first closed cavity and the second closed cavity is t1+t3, and the distance from the outermost tube wall to the outer cladding 9 of the optical fiber is S1. The thickness of the outermost tube wall of the third closed cavity and the fourth closed cavity is t2+t3, and the distance from the outermost tube wall to the outer cladding 9 of the optical fiber is S2, wherein t1 is the thickness of the silica tube wall in the outermost tube wall of the first closed cavity and the second closed cavity, t2 is the thickness of the silica tube wall in the outermost tube wall of the third closed cavity and the fourth closed cavity, t3 is the thickness of the silicon tube in the outermost tube wall, and t1≠t2;

[0039] The thickness of the intermediate layer tube wall of the first closed cavity, the second closed cavity, the third closed cavity and the fourth closed cavity is t4, and the radial section of the intermediate layer tube wall 5 of the first closed cavity and the fourth closed cavity is a diameter D as1 The radial cross section of the intermediate layer tube wall 6 of the second closed cavity and the third closed cavity is a diameter D as2 The fan shape, and D as1 ≠D as2 ;

[0040] The thickness of the innermost tube wall 7 of the first closed cavity, the second closed cavity, the third closed cavity and the fourth closed cavity is t4, and the radial cross section of the innermost tube wall is a diameter D ac circle.

[0041] See also Figure 1 , its structural parameters are as follows: D c =20μm, t1=1.41μm, t2=0.93μm ， t3=0.03μm, t4=1.15μm, S1=24μm, S2=24.48μm, D s =36μm,D as1 =28μm, D as2 =34μm ， Z1=8μm,Z2=2μm,D ac =12μm.

[0042] Preferably, the silicon layer thickness t3 is in the range of 0.02 to 0.04 μm, and t4 complies with the anti-resonance waveguide vibration waveguide condition:

[0043]

[0044] Where λ is the C-band operating wavelength, n1 is the refractive index of silicon dioxide, n0 is the refractive index of air, m is a positive integer, and the value range of m is 1, 2, .... When λ = 1.15um and m = 2, t4 = 1.15μm

[0045] Preferably, t1 and t2 follow the resonant waveguide conditions in two stopbands adjacent to the passband where the operating wavelength is located:

[0046]

[0047] When λ=1.55um, the wavelength ranges of the two adjacent stopbands are 1.445-1.480um and 1.787-1.820um, the value range of t1 is 1.38-1.42um, and the value range of t2 is 0.93-0.95um.

[0048] See also Figure 2 , which is Figure 1 The performance data of the structure, the hollow core antiresonant fiber achieves birefringence by introducing the outermost hybrid silica / silicon tube wall of different thicknesses in the orthogonal direction around the core, so that the air core mode and the surface mode of the hybrid silica / silicon tube have polarization-dependent effects, which is called "anti-crossing effect". In the 145nm broadband (1.510μm to 1.655μm), the fiber structure can stably maintain more than 3.2×10 -4 The birefringence value

[0049] Figure 3 It is a curve of the limiting loss changing with wavelength in the birefringent hollow core antiresonant optical fiber in the embodiment of the present invention. In the simulation results: According to the multi-layer guiding model, the thickness of the circular nested tubes and the air layer between the half tubes meet their antiresonance conditions, which can significantly reduce the limiting loss. At the same time, by adjusting the distance between the half tubes, the high-order mode is coupled with the mode in the tube, which increases the loss of the high-order mode. Within the 95nm bandwidth range, the limiting losses of the two orthogonal polarization fundamental modes are both less than 1dB / m, and at 1.554μm, the limiting loss of the y-polarization fundamental mode is only 0.004dB / m. At 1.55μm, the high-order mode extinction ratio of this optical fiber structure reaches 222, and maintains good stability within the 80nm bandwidth (1.526μm to 1.606μm), ensuring the realization of pure single-mode transmission.

[0050] The above describes the embodiments of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be equivalent replacement methods. As long as they meet the purpose of the invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the protection scope of the present invention.

Claims

1. A high birefringence polarization-maintaining single-mode hollow core antiresonant optical fiber, comprising an optical fiber outer cladding and an air core, characterized in that: Between the outer cladding of the optical fiber and the air core, a first closed cavity and a second closed cavity are provided along the slow axis direction, and a third closed cavity and a fourth closed cavity are provided along the fast axis direction. The radial cross section of each closed cavity is a diameter D s The fan-shaped, and the distance between the first closed cavity and the second closed cavity, and the distance between the third closed cavity and the fourth closed cavity are both D c ; Each of the closed cavities comprises, from outside to inside, an outermost tube wall, an intermediate tube wall and an innermost tube wall, wherein the outermost tube wall material is a mixture of silicon dioxide and silicon, the intermediate tube wall material is silicon dioxide, and the innermost tube wall material is silicon dioxide; The thickness of the outermost tube wall of the first closed cavity and the second closed cavity is t1+t3, and the distance from the outermost tube wall to the outer cladding of the optical fiber is S1. The thickness of the outermost tube wall of the third closed cavity and the fourth closed cavity is t2+t3, and the distance from the outermost tube wall to the outer cladding of the optical fiber is S2, wherein t1 is the thickness of the silica tube wall in the outermost tube wall of the first closed cavity and the second closed cavity, t2 is the thickness of the silica tube wall in the outermost tube wall of the third closed cavity and the fourth closed cavity, t3 is the thickness of the silicon tube in the outermost tube wall, and t1≠t2; The thickness of the intermediate layer wall of the first closed cavity, the second closed cavity, the third closed cavity and the fourth closed cavity is t4, and the radial section of the intermediate layer wall of the first closed cavity and the fourth closed cavity is a diameter D as1 The radial cross section of the intermediate layer of the second closed cavity and the third closed cavity is a sector-shaped, and the diameter D as2 The fan shape, and D as1 ≠D as2 ; The thickness of the innermost tube wall of the first closed cavity, the second closed cavity, the third closed cavity and the fourth closed cavity is t4, and the radial cross section of the innermost tube wall is a diameter D ac circle.

2. The high birefringence polarization-maintaining single-mode hollow-core antiresonant optical fiber according to claim 1, characterized in that: The distances from the outermost tube wall to the middle tube wall of the first and fourth closed cavities are both Z1, and the distances from the outermost tube wall to the middle tube wall of the second and third closed cavities are both Z2; and Z1≠Z2.

3. The high birefringence polarization-maintaining single-mode hollow-core antiresonant optical fiber according to claim 1, characterized in that: The distance Z1 from the outermost tube wall to the middle tube wall of the first closed cavity and the fourth closed cavity, and the sector diameter D as1 Satisfaction: D as1 =D as -Z1; the distance Z2 from the outermost wall of the second closed cavity and the third closed cavity to the intermediate wall, and the sector diameter D as2 Satisfy D as2 =D as -Z2.

4. The high birefringence polarization-maintaining single-mode hollow-core antiresonant optical fiber according to claim 1, characterized in that: The silicon layer thickness t3 ranges from 0.02 to 0.04 μm, and t4 follows the anti-resonance waveguide vibration waveguide condition: Wherein, λ is the C-band operating wavelength, n1 represents the refractive index of silicon dioxide, n0 represents the refractive index of air, m is a positive integer, and the value range of m is 1, 2, ...

5. The high birefringence polarization-maintaining single-mode hollow-core antiresonant optical fiber according to claim 4, characterized in that: When λ=1.15um, m=2, we can get t4=1.15μm.

6. The high birefringence polarization-maintaining single-mode hollow-core antiresonant optical fiber according to claim 1, characterized in that: t1 and t2 follow the resonant waveguide conditions in the two stopbands adjacent to the passband where the operating wavelength is located:

7. The high birefringence polarization-maintaining single-mode hollow-core antiresonant optical fiber according to claim 6, characterized in that: When λ=1.55um, the wavelength ranges of the two adjacent stopbands are 1.445-1.480um and 1.787-1.820um, the value range of t1 is 1.38-1.42um, and the value range of t2 is 0.93-0.95um.

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