A high birefringence polarization-maintaining single-mode hollow-core antiresonant optical fiber

Abstract

A high birefringence polarization maintaining single-mode hollow core antiresonant optical fiber, comprising an optical fiber outer cladding and an air core, with a first closed cavity and a second closed cavity along the slow axis direction, and a third closed cavity and a fourth closed cavity along the fast axis direction, wherein the radial cross section of each closed cavity is a diameter D s The first closed cavity and the second closed cavity are spaced apart by a distance D between them, and the third closed cavity and the fourth closed cavity are spaced apart by a distance D between them. c The radial cross section of the wall between the first closed cavity and the fourth closed cavity is the diameter D as1 The radial cross section of the pipe wall between the second closed cavity and the third closed cavity is the diameter D as2 The fan shape, and D as1 ≠D as2 The present invention uses a double-thickness hybrid silica / silicon tube wall design to enable the optical fiber to have high birefringence that maintains the polarization state; at the same time, by nesting a non-double rotationally symmetric nested structure, the loss of the two polarization fundamental modes is greatly reduced, and the transmission of high-order modes is suppressed, achieving single-mode transmission within a broadband range.

Description

Technical Field

[0001] The present 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 into HC-ARF. By adjusting the wall thickness in the orthogonal direction, they successfully achieved a 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 fibers cannot reach the level of traditional polarization-maintaining fibers.

[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. The average birefringence in the C-band and L-band range exceeds 3×10 -5 , reducing transmission loss in both polarization modes. However, the patent's polarization-maintaining effect still fails to fully meet practical needs and fails to consider transmission suppression of higher-order modes, resulting in significant drawbacks in single-mode transmission. This is primarily due to the fact that while its structure helps reduce losses, it still needs to be improved in maintaining high birefringence and single-mode transmission.

[0006] In summary, despite the progress made in polarization-maintaining HC-ARF, many challenges and shortcomings remain. In particular, ensuring single-mode transmission performance while achieving high birefringence and polarization-maintaining properties remains a key issue that needs to be addressed.

[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 response to the shortcomings of the existing technology, 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, multiple 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 / silica tube wall, whose radial cross-section is a fan-shaped or circular with a first diameter; a second layer of silica tube wall, whose radial cross-section is a fan-shaped or circular with a second diameter or a third diameter; and an innermost layer of silica wall, whose radial cross-section is a circle with a fourth diameter, enclosing an internal space. This structure can maintain the birefringence of the HC-ARF optical fiber within a bandwidth of 145nm and maintain a birefringence greater than 3.2×10 -4 At the same time, in the communication band, the limiting loss of the two orthogonal polarization fundamental modes is 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 solutions of the present invention are 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 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 enclosed cavities comprises, from the outside to the inside, an outermost tube wall, an intermediate tube wall, and an innermost tube wall. The outermost tube wall is made of a mixture of silicon dioxide and silicon, the intermediate tube wall is made of silicon dioxide, and the innermost tube wall is made of silicon dioxide.

[0012] Preferably, the thickness of the outermost tube wall of the first and second closed cavities 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 and fourth closed cavities 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 and second closed cavities, t2 is the thickness of the silica tube wall in the outermost tube wall of the third and fourth closed cavities, 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 diameter D as1The radial cross section of the wall between the second closed cavity and the third closed cavity is a sector-shaped, and the diameter D as2 sector, 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; in order to meet the conditions of optical fiber single-mode transmission, the two take different values, that is, Z1≠Z2.

[0016] Preferably, the distance from the outermost wall to the middle wall of the first closed cavity and the fourth closed cavity is Z1 and the sector diameter D as1 Satisfied: 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 sector diameter D as2 Satisfy D as2 =D as -Z2

[0017] Preferably, the thickness t3 of the silicon layer ranges from 0.02 to 0.04 μm, and t4 complies with the anti-resonant waveguide vibration waveguide condition:

[0018]

[0019] Where λ is the C-band operating wavelength, n1 is the refractive index of silicon dioxide, n0 is the refractive index of air, and m is a positive integer ranging from 1, 2, .... When λ = 1.15 μm and m = 2, we get t4 = 1.15 μm.

[0020] 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 operating wavelength is located:

[0021]

[0022] 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.

[0023] Compared with the prior art, the present invention has the following obvious outstanding substantial features and significant advantages:

[0024] 1. The present invention introduces a double-layer 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.

[0025] 2. This paper utilizes a non-double rotationally symmetric nested tube structure to confine most of the optical energy to the air core, effectively avoiding the high losses caused by matrix material absorption in traditional solid-core optical fibers. Because air absorbs almost no light, this structure significantly reduces material absorption losses during transmission while also suppressing light leakage. Within a 95nm bandwidth, the confinement losses of the two orthogonal polarization fundamental modes are both less than 1dB / m, and at 1.554μm, the confinement loss of the y-polarization fundamental mode is only 0.004dB / m.

[0026] 3. The closed cavity design achieves suppression of higher-order modes by finely controlling its shape and size. This fiber structure achieves a high-order mode extinction ratio of 222 at 1.55μm and maintains excellent stability within an 80nm bandwidth (1.526μm to 1.606μm), ensuring pure single-mode transmission.

[0027] 4. The hollow-core antiresonant fiber of this invention effectively maintains the polarization state of light waves during transmission through its carefully designed fiber structure and closed cavity arrangement. This polarization-maintaining performance is crucial for applications requiring high-precision polarization control, such as coherent fiber communications and fiber optic gyroscopes. Polarization-maintaining fiber can reduce polarization crosstalk and polarization mode dispersion during optical signal transmission, improving overall system performance.

[0028] 5. Low loss means that the attenuation of optical signals in the optical fiber is reduced, thereby improving the transmission efficiency of optical signals. This makes the optical fiber particularly suitable for applications requiring long-distance transmission, such as optical fiber communications and optical fiber sensing. In high-power laser transmission applications, low loss also helps reduce laser damage and wavelength conversion effects, improving the stability and reliability of laser transmission.

[0029] 6. The optical fiber structure of this invention offers a degree of flexibility and scalability. By adjusting parameters such as the number, shape, and size of the enclosed cavities, the optical fiber's performance can be further optimized to meet the needs of different application scenarios. This flexibility is also reflected in the optical fiber fabrication process. Advanced microstructural processing techniques enable mass production and customized design of optical fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This 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;

[0031] Figure 2 is a curve showing the change of phase birefringence with wavelength in a hollow-core antiresonant optical fiber according to a preferred embodiment of the present invention;

[0032] 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

[0033] The following describes the specific embodiments of the present invention 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 detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0034] The above solution is further described below with reference to specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0035] Example 1:

[0036] 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 sector with a diameter Ds, and the spacing between the first closed cavity and the second closed cavity, as well as 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 wall, an intermediate wall, and an innermost wall. The outermost wall material is a mixture of silica and silicon, the intermediate wall material is silica, and the innermost wall material is silica. Each of the closed cavities includes, from the outside to the inside, an outermost wall, an intermediate wall, and an innermost wall. The outermost wall material is a mixture of silica and silicon, the intermediate wall material is silica, and the innermost wall material is silica.

[0037] The thickness of the outermost tube wall of the first and second closed cavities 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 and fourth closed cavities 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 and second closed cavities, t2 is the thickness of the silica tube wall in the outermost tube wall of the third and fourth closed cavities, t3 is the thickness of the silicon tube in the outermost tube wall, and t1≠t2;

[0038] The thickness of the intermediate layer tube wall of the four first closed cavities, the second closed cavities, the third closed cavities and the fourth closed cavities is t4, and the radial cross section of the intermediate layer tube wall 5 of the first closed cavities and the fourth closed cavities is the diameter D as1 The radial cross section of the intermediate layer pipe wall 6 of the second closed cavity and the third closed cavity is a diameter D as2 sector, and D as1 ≠D as2 ;

[0039] 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.

[0040] 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.

[0041] Preferably, the thickness t3 of the silicon layer ranges from 0.02 to 0.04 μm, and t4 complies with the anti-resonant waveguide vibration waveguide condition:

[0042]

[0043] Where λ is the C-band operating wavelength, n1 represents the refractive index of silicon dioxide, n0 represents the refractive index of air, and m is a positive integer whose value range is 1, 2, .... When λ = 1.15 μm and m = 2, we can get t4 = 1.15 μm

[0044] Preferably, t1 and t2 respectively follow the resonant waveguide condition in two stopbands adjacent to the passband where the operating wavelength is located:

[0045]

[0046] 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.

[0047] See also Figure 2 , which is Figure 1 The performance data of the structure shows that the birefringence of the hollow-core antiresonant fiber depends on the introduction of the outermost hybrid silica / silica tube wall with different thicknesses in orthogonal directions around the core, so that the air core mode and the surface mode of the hybrid silica / silica tube undergo polarization-dependent interaction, which is called the "anti-crossing effect." Within a broadband of 145nm (1.510μm to 1.655μm), the fiber structure can stably maintain a birefringence of more than 3.2×10 -4 The birefringence value

[0048] Figure 3 This is a curve showing how the limiting loss in the birefringent hollow-core antiresonant optical fiber in the embodiment of the present invention changes with wavelength. 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 both 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, thereby increasing the loss of the high-order mode. Within the 95nm bandwidth, 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.

[0049] 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 principles of the technical solution of the present invention should be equivalent replacement methods. As long as they comply with the purpose of the invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the scope of protection 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 first closed cavity and the second closed cavity are spaced apart from each other, and the third closed cavity and the fourth closed cavity are spaced apart from each other. c ; Each of the closed cavities comprises, from the outside to the inside, an outermost tube wall, an intermediate tube wall, and an innermost tube wall, wherein the outermost tube wall is made of a mixture of silicon dioxide and silicon, the intermediate tube wall is made of silicon dioxide, and the innermost tube wall is made of silicon dioxide; The thickness of the outermost tube wall of the first and second closed cavities 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 and fourth closed cavities 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 and second closed cavities, t2 is the thickness of the silica tube wall in the outermost tube wall of the third and fourth closed cavities, 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 cross section of the intermediate layer wall of the first closed cavity and the fourth closed cavity is the diameter D as1 The radial cross section of the wall between the second closed cavity and the third closed cavity is a sector-shaped, and the diameter D as2 sector, 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 distance from the outermost wall to the middle wall of the first and fourth closed cavities is Z1, and the distance from the outermost wall to the middle wall of the second and third closed cavities is 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 between the outermost wall of the first closed cavity and the fourth closed cavity and the middle wall of the cavity, and the sector diameter D as1 Satisfied: 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 complies with the anti-resonant 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, and 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, 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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