A reverse-harmonic hollow-core optical fiber with polarization-maintaining performance

Abstract

This invention provides an anti-resonant hollow-core optical fiber with polarization-maintaining performance, relating to the field of special optical fiber design and manufacturing technology. It includes four anti-resonant units uniformly attached to the inner surface of the cladding, collectively surrounding and forming a hollow core region. Each anti-resonant unit includes multiple anti-resonant sub-units arranged radially, wherein the wall thickness of each anti-resonant sub-unit closest to the cladding corresponds to the anti-resonant thickness of the operating wavelength band of the anti-resonant hollow-core optical fiber. Two non-adjacent anti-resonant units form a group, and the anti-resonant sub-units closest to the hollow core region in two groups have different wall thicknesses. The beneficial effects are significant suppression of optical field leakage, substantial reduction of fiber confinement loss, stable polarization-maintaining function, and a simple overall structural design that eliminates the need for complex nesting structures, facilitating large-scale production and effectively controlling optical fiber manufacturing costs.

Description

Technical Field

[0001] This invention relates to the field of special optical fiber design and manufacturing technology, and in particular to an anti-resonant hollow optical fiber with polarization-maintaining performance. Background Technology

[0002] Hollow-core optical fiber uses air as the light guiding medium, which avoids the limitations of material properties in traditional quartz optical fiber. It exhibits outstanding advantages such as extremely low nonlinear effects and Rayleigh scattering, small transmission delay and high damage threshold, and has important potential in long-distance communication and high-power transmission.

[0003] Based on differences in light guiding principles, hollow-core optical fibers can be divided into two categories: photonic bandgap fibers and anti-resonant fibers. In polarization-sensitive systems such as fiber optic gyroscopes and quantum computing, the fiber must possess stable polarization-maintaining capabilities, i.e., high birefringence (typically required to reach 10). -4 (On the order of magnitude). However, hollow-core optical fibers lack the means to control polarization characteristics through doping, stress application, etc., found in traditional polarization-maintaining fibers, and the light field is mainly distributed in the air, resulting in a weak response to cladding geometric asymmetry. Therefore, achieving high birefringence is quite difficult.

[0004] While existing photonic bandgap fibers can introduce birefringence through surface mode coupling, their high loss and narrow bandwidth (typically less than 10 nm) severely limit their practicality and make it difficult to meet the demands of long-distance, high-performance transmission. Antiresonant fibers, on the other hand, can utilize the antiresonance effect of the cladding structure to more strongly confine the optical field within the hollow core region. Compared to photonic bandgap fibers, they exhibit lower loss potential and wider bandwidth tunability. By controlling the cladding thickness and utilizing the polarization-dependent coupling between the core mode and the cladding mode near the antiresonance point, high birefringence can be achieved within a bandwidth of hundreds of nanometers, becoming the mainstream direction in the current research and development of polarization-maintaining hollow core fibers.

[0005] However, existing polarization-maintaining anti-resonant fiber designs still face significant problems: high birefringence often leads to increased loss, while low-loss designs often rely on complex nested structures, which are difficult and costly to fabricate.

[0006] In addition, the cladding structure morphology has a significant impact on its performance, but current research is mostly limited to conventional configurations such as circles and ellipses. Many irregular structures with excellent simulation performance are difficult to actually fabricate due to their complex structural design and poor compatibility with fabrication processes.

[0007] Therefore, there is an urgent need for an anti-resonant hollow fiber with a simple structure, easy manufacturing, high birefringence, low loss, and wide bandwidth, which can maintain polarization performance and promote its application in high-end optical systems. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention provides an anti-resonant hollow fiber with polarization-maintaining performance, comprising four anti-resonant units uniformly attached to the inner surface of the outer cladding and together surrounding to form a hollow fiber core region. Each anti-resonant unit includes multiple anti-resonant sub-units arranged radially, wherein the wall thickness of each anti-resonant sub-unit closest to the outer cladding is the anti-resonant thickness corresponding to the working wavelength band of the anti-resonant hollow fiber. The anti-resonant units that are not adjacent to each other form a group, and the anti-resonant subunits that are closest to the hollow fiber core region in the two groups of anti-resonant units have different wall thicknesses.

[0009] Preferably, each of the anti-resonant units includes two radially intersecting circular rings, which serve as two anti-resonant subunits respectively; Among them, the ring closest to the hollow fiber core region is the inner ring, and the other ring is the outer ring. The wall thickness of each outer ring is the anti-resonance thickness corresponding to the working band of the anti-resonance hollow fiber. The inner rings in the two sets of anti-resonant units have different wall thicknesses.

[0010] Preferably, the wall thickness of the inner ring in one of the anti-resonance units is the non-anti-resonance thickness corresponding to the working band of the anti-resonance hollow fiber, and is greater than the wall thickness of the outer ring.

[0011] Preferably, the centers of the two rings in each anti-resonance unit are collinear with the center of the hollow fiber core region.

[0012] Preferably, the embedding depth of the two intersecting rings in each anti-resonant unit is 8μm-10μm.

[0013] Preferably, it further includes multiple filler rings, which are uniformly attached to the inner surface of the outer cladding and located between two adjacent anti-resonant units.

[0014] Preferably, the filling ring is a circular ring, and the thickness of each filling ring is equal and corresponds to the anti-resonance thickness of the working band of the anti-resonance hollow fiber.

[0015] Preferably, each of the anti-resonant units includes multiple arcs, and the two ends of each arc are attached to the inner surface of the outer cladding to enclose a closed region. A cross-ring structure is provided in the closed region, and the arcs and the cross-ring structure serve as two anti-resonant subunits, respectively. The intersecting ring structure includes two rings that intersect radially, with the ring closest to the outer cladding attached to the inner surface of the outer cladding.

[0016] Preferably, each of the rings in each of the cross-ring structures has the same wall thickness, and is an anti-resonant wall thickness.

[0017] The above technical solution has the following advantages or beneficial effects: 1) By designing the wall thickness of the anti-resonant sub-unit on the side furthest from the hollow fiber core in each anti-resonant unit as the anti-resonant thickness, the advantages of the anti-resonance effect can be fully utilized, effectively avoiding phase matching between the core mode field and the boundary radiation mode, thereby significantly suppressing optical field leakage and greatly reducing the confinement loss of the optical fiber. In the 1.5–1.75 μm wavelength range, the confinement loss of the optical fiber of this invention can be stably controlled below 1 dB / m, effectively ensuring efficient and low-loss transmission of optical signals within the optical fiber, and meeting the stringent requirements for optical fiber loss performance in scenarios such as long-distance communication and high-power transmission.

[0018] 2) While maintaining the overall circular symmetry of the optical fiber structure, the inner anti-resonator units near the hollow core region in the two sets of anti-resonant units have different wall thicknesses. This results in significant differences in the perceived effective cladding environment when the optical field propagates along the two orthogonal directions of the fiber, leading to a significant difference in the effective refractive index of the two orthogonal polarization states. Within the 1.5–2 μm wavelength range, the effective refractive index difference between the two orthogonal polarization states can be stably higher than 10. -4 The scale is large enough to achieve stable polarization-maintaining function, fully meeting the core requirements of polarization-sensitive high-end optical systems such as fiber optic gyroscopes and quantum computing for fiber polarization-maintaining performance. 3) The use of four anti-resonant units as the core structure of the cladding results in a simple overall structure design without the need for complex nesting structures. Compared with the complex design of existing low-loss polarization-maintaining anti-resonant fibers, this significantly reduces the difficulty of the fabrication process and the requirements for fabrication accuracy, making it easier to achieve large-scale production and effectively control the cost of fiber fabrication. At the same time, the fiber maintains circular symmetry, which can avoid fabrication deviations and performance fluctuations caused by asymmetric structures, further improving the stability and consistency of fiber performance. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of an anti-resonant hollow optical fiber with polarization-maintaining performance in Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the waveguide obtained from the fundamental simulation calculation of the vertical polarization state of the anti-resonant hollow fiber with polarization-maintaining performance at a wavelength of 1.55 μm in Embodiment 1 of the present invention. Figure 3 This is a schematic diagram of the waveguide situation obtained by the fundamental simulation calculation of the horizontal polarization state of the anti-resonant hollow fiber with polarization-maintaining performance at a wavelength of 1.55 μm in Embodiment 1 of the present invention. Figure 4 This is a broadband loss curve of an anti-resonant hollow-core optical fiber with polarization-maintaining properties in Embodiment 1 of the present invention. Figure 5 This is a graph of the real part of the effective refractive index of the fundamental mode for two polarization states in a wide spectral range of an anti-resonant hollow fiber with polarization-maintaining properties, as shown in Embodiment 1 of the present invention. Figure 6 This is a graph showing the difference in the real part of the effective refractive index of the fundamental mode for two polarization states in a wide spectral range of an anti-resonant hollow-core optical fiber with polarization-maintaining properties, as shown in Embodiment 1 of the present invention. Figure 7 This is a schematic diagram of an anti-resonant hollow fiber with polarization-maintaining properties in Embodiment 2 of the present invention.

[0020] Figure 8 This is a fundamental mode confinement loss curve for two polarization states in a wide spectral range of an anti-resonant hollow-core optical fiber with polarization-maintaining properties, as shown in Embodiment 2 of the present invention. Figure 9 This is a graph of the real part of the effective refractive index of the fundamental mode for two polarization states in a wide spectral range of an anti-resonant hollow fiber with polarization-maintaining properties, as shown in Embodiment 2 of the present invention. Figure 10 This is a graph showing the difference in the real part of the effective refractive index of the fundamental mode for two polarization states in a wide-spectrum anti-resonant hollow fiber with polarization-maintaining properties, as shown in Embodiment 2 of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment; other embodiments that conform to the spirit of the present invention may also fall within the scope of the present invention.

[0022] In a preferred embodiment of the present invention, based on the above-mentioned problems existing in the prior art, an anti-resonant hollow fiber with polarization-maintaining performance is provided, comprising four anti-resonant units arranged uniformly along the axis, so that the fiber cross-section exhibits symmetry with respect to the x-axis and y-axis, forming a quasi-quadruple symmetric structure. This symmetric structure can effectively avoid performance fluctuations caused by asymmetric arrangement, and at the same time provide a structural basis for the realization of birefringence.

[0023] Furthermore, the anti-resonant units that are not adjacent to each other form a group, and the anti-resonant oscillator units closest to the hollow fiber core region in the two groups of anti-resonant units have different wall thicknesses.

[0024] Example 1 like Figure 1 As shown, in this embodiment, each anti-resonant unit is a cross-ring structure, including two rings that intersect radially, which serve as two anti-resonant sub-units respectively; Two non-adjacent intersecting ring structures form a group, meaning the four intersecting ring structures can be divided into two groups: intersecting ring structure 1 and intersecting ring structure 2. All intersecting ring structures are uniformly attached to the inner surface of the outer cladding layer 3 and together surround and form the hollow fiber core region 4. Each group contains two intersecting ring structures, and the two groups of intersecting ring structures are arranged symmetrically. Each intersecting ring structure includes two rings that intersect radially, and the embedding depth of the two intersecting rings is 8μm-10μm to satisfy the anti-resonance condition.

[0025] Among them, the ring closest to the hollow fiber core region is the inner ring 5, and the other ring is the outer ring 6. The wall thickness of each outer ring 6 is the anti-resonance thickness corresponding to the working band of the anti-resonance hollow fiber with polarization-maintaining performance, so as to ensure the effective performance of the anti-resonance effect and suppress optical field leakage.

[0026] Furthermore, the inner rings 5 ​​in the two sets of intersecting circular structures have different wall thicknesses. For example... Figure 1 As shown, the wall thickness of the inner ring 5 in the cross-ring structure 1 is greater than the wall thickness of the outer ring 6. In this embodiment, the wall thickness of the inner ring 5, which is greater than the wall thickness of the outer ring 6, is the non-anti-resonant thickness corresponding to the working band of the anti-resonant hollow fiber with polarization-maintaining performance. In addition, the wall thickness of the inner ring 5 in the cross-ring structure 2 is the same as the wall thickness of the outer ring 6.

[0027] By varying the wall thickness of the inner ring 5, the anti-resonance conditions perceived by different polarization states are also different, thereby introducing a considerable birefringence. Furthermore, the cross-ring structure helps to push the boundary dielectric material further away, thus further reducing confinement loss. In addition, the diameter of the hollow core region 4 is preferably fixed at 12 μm; a smaller core diameter helps to increase the effective refractive index difference between the two polarization states.

[0028] In this embodiment, the outer diameter of the inner ring 5 in each intersecting ring structure is not much different from the outer diameter of the outer ring 6. Adjusting the interlacing depth makes the inner ring 5 closer to the hollow fiber core region 4, better participating in optical field confinement, while making the outer ring 6 tightly attached to the inner surface of the outer cladding layer 3, improving the overall structure.

[0029] Preferably, the outer diameter of the inner ring 5 is 16μm-18μm, and the outer diameter of the outer ring 6 is 17μm-19μm.

[0030] It also includes multiple filling rings 7, which are uniformly attached to the inner surface of the outer cladding layer 3 and located between two adjacent intersecting circular ring structures.

[0031] In this embodiment, the filling ring 7 is a circular ring, and the thickness of each filling ring 7 is equal and is the anti-resonant thickness corresponding to the working band of the anti-resonant hollow fiber with polarization-maintaining performance.

[0032] Specifically, by incorporating a filler ring 7, energy leakage from the gap between two adjacent intersecting circular ring structures can be reduced. The outer diameter of the filler ring 7 is preferably 10-12 μm, and the wall thickness is set to the anti-resonant thickness of the waveguide band.

[0033] By simulating the structure of this embodiment, such as... Figure 2 As shown, at a wavelength of 1.55 μm, the mode field distribution of its vertical polarization fundamental mode is approximately square with slightly rounded sides, and the overall shape is between a square and an ellipse.

[0034] like Figure 3 As shown, the mode field of the horizontally polarized fundamental mode of the anti-resonant hollow fiber with polarization-maintaining performance after the above structural optimization is displayed at a wavelength of 1.55 μm.

[0035] like Figure 4 As shown, the broadband transmission waveguide performance of the anti-resonant hollow fiber with polarization-maintaining performance after the above structural optimization is demonstrated. Simulation calculations were performed based on the finite element method and combined with the boundary conditions of the perfectly matched layer. The results show that the confinement loss is less than 1 dB / m in the 1.5–1.75 μm band, confirming that the structure has broadband light guiding capability.

[0036] like Figure 5 As shown, the curves of the effective refractive index of the fundamental mode of the two orthogonally polarized states of the anti-resonant hollow fiber with polarization-maintaining performance after the above structural optimization are displayed.

[0037] like Figure 6 As shown, the curves illustrating the effective refractive index difference of the two orthogonal polarization fundamental modes of an anti-resonant hollow fiber with polarization-maintaining properties as a function of wavelength are presented.

[0038] It can be seen that by configuring a cross-ring structure with different wall thicknesses in orthogonal directions, the effective refractive index of the two polarization states can have a large difference over a wide spectral range. Specifically, within the band where the loss is limited to less than 1 dB / m, the difference in effective refractive index is greater than 10. -4 .

[0039] Example 2 In this embodiment, as Figure 7 As shown, each anti-resonant unit includes multiple arcs 8. The two ends of each arc 8 are attached to the inner surface of the outer cladding layer 3 to enclose and form a closed area. A cross-ring structure 2 is provided in the closed area. The arcs 8 and the cross-ring structure 2 serve as two anti-resonant subunits, respectively. The intersecting ring structure 2 includes two rings that intersect radially, with the ring closer to the outer cladding 3 attached to the inner surface of the outer cladding 3.

[0040] In each of the intersecting circular ring structures 2, the shape and wall thickness of each ring are completely identical, and the wall thickness is anti-resonant.

[0041] Specifically, the wall thickness of the arc 8 in the two sets of anti-resonant units is different. The wall thickness of the arc 8 in one set of anti-resonant units is set to the anti-resonant thickness corresponding to the transmitted waveband, while the wall thickness of the arc in the other set of anti-resonant units is set to the non-anti-resonant thickness corresponding to the transmitted waveband.

[0042] Furthermore, since the wall thicknesses of the arcs 8 in the two sets of anti-resonant units are different, the first layer wall thickness conditions perceived by the horizontal and vertical polarization states of the optical field are different, in order to achieve a polarization-maintaining effect. It can be understood that the wall thickness of each layer of the intersecting ring structure 2 existing within the arc 8 is set as an anti-resonant wall thickness to ensure low overall confinement loss.

[0043] like Figure 8 As shown, this embodiment demonstrates the wide-spectrum range confinement loss of the two polarization state fundamental modes of the antiresonant hollow fiber with polarization-maintaining performance.

[0044] It can be observed that the limiting loss is less than 1 dB / km in the 1.55-1.68 μm range, indicating good waveguide performance.

[0045] Furthermore, Figure 9 and Figure 10 This embodiment demonstrates the effective refractive index difference between the two polarization states of an anti-resonant hollow fiber with polarization-maintaining properties.

[0046] It can be observed that within the low-loss window where the loss limit is below 1 dB / km, the effective refractive index difference between the two polarization fundamental modes is greater than 4 × 10⁻⁶. -5 .

[0047] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made using the content of this specification and illustrations should be included within the protection scope of the present invention.

Claims

1. An anti-resonant hollow-core optical fiber with polarization-maintaining properties, characterized in that, It includes four anti-resonance units, which are uniformly attached to the inner surface of the outer cladding and together surround to form a hollow fiber core region. Each anti-resonance unit includes multiple anti-resonance sub-units arranged radially, wherein the wall thickness of each anti-resonance sub-unit closest to the outer cladding is the anti-resonance thickness corresponding to the working band of the anti-resonance hollow fiber. The anti-resonant units that are not adjacent to each other form a group, and the anti-resonant subunits that are closest to the hollow fiber core region in the two groups of anti-resonant units have different wall thicknesses.

2. The anti-resonant hollow-core optical fiber according to claim 1, characterized in that, Each of the anti-resonant units includes two radially intersecting circular rings, which serve as two anti-resonant subunits respectively; Among them, the ring closest to the hollow fiber core region is the inner ring, and the other ring is the outer ring. The wall thickness of each outer ring is the anti-resonance thickness corresponding to the working band of the anti-resonance hollow fiber. The inner rings in the two sets of anti-resonant units have different wall thicknesses.

3. The anti-resonant hollow-core optical fiber according to claim 2, characterized in that, The wall thickness of the inner ring in one of the anti-resonance units is the non-anti-resonance thickness corresponding to the working band of the anti-resonance hollow fiber, and is greater than the wall thickness of the outer ring.

4. The anti-resonant hollow-core optical fiber according to claim 1, characterized in that, The centers of the two rings in each of the anti-resonant units are collinear with the center of the hollow fiber core region.

5. The anti-resonant hollow-core optical fiber according to claim 1, characterized in that, The embedding depth of the two intersecting rings in each anti-resonant unit is 8μm-10μm.

6. The anti-resonant hollow-core optical fiber according to claim 2, characterized in that, It also includes multiple filler rings, which are uniformly attached to the inner surface of the outer cladding and located between two adjacent anti-resonant units.

7. The anti-resonant hollow-core optical fiber according to claim 6, characterized in that, The filling ring is circular, and the thickness of each filling ring is equal and corresponds to the anti-resonance thickness of the working band of the anti-resonance hollow fiber.

8. The anti-resonant hollow-core optical fiber according to claim 1, characterized in that, Each of the anti-resonant units includes multiple arcs, and the two ends of each arc are attached to the inner surface of the outer cladding to enclose a closed region. A cross-ring structure is provided in the closed region, and the arcs and the cross-ring structure serve as two anti-resonant subunits, respectively. The intersecting ring structure includes two rings that intersect radially, with the ring closest to the outer cladding attached to the inner surface of the outer cladding.

9. The anti-resonant hollow-core optical fiber according to claim 8, characterized in that, Each of the rings in the described cross-ring structure has the same wall thickness, and it is an anti-resonant wall thickness.

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