Hollow-core negative curvature optical fiber type polarization filter

Abstract

The invention provides a hollow-core negative-curvature optical fiber type polarization filter. The hollow-core negative-curvature optical fiber type polarization filter comprises a base layer; the air fiber core is arranged in the center in the base layer, and a wrapping layer is further arranged between the air fiber core and the base layer; the cladding comprises a first cladding region, a third cladding region, a second cladding region and a fourth cladding region. According to the invention, due to the asymmetry of the cladding structure, the coupling of a fiber core mode and a cladding mode in the x direction is enhanced, and the structure of the negative curvature optical fiber reduces the limiting loss of light waves, so that not only is the polarization extinction ratio of the optical fiber improved, but also the limiting loss is reduced, the polarization extinction ratio of the provided optical fiber is greater than 100 in the wavelength range of 1547-1555nm, and the optical fiber can be applied to the optical fiber. When the working wavelength is 1550nm, the polarization extinction of the y polarization fundamental mode is up to 41511, and the loss is as low as 1.66 * 10 <-2 > dB / m; when the bending radius of the optical fiber in the x direction is 4 cm, the polarization filtering function can still be achieved, and the loss of an x polarization fundamental mode is as low as 1 dB / m.

Description

Technical Field

[0001] The present invention relates to the technical field of polarization filters, and particularly relates to a polarization filter of a hollow-core negative-curvature fiber type. Background Art

[0002] As an important optical fiber device, a polarization filter can effectively suppress the transmission of non-target polarization states, thereby avoiding polarization-related losses and crosstalk. Existing polarization filters can be divided into two categories according to different working principles: the first category is a mode-splitting polarization filter, which realizes single-polarization mode transmission by coupling non-target polarization modes into adjacent waveguides through the waveguide mode coupling effect; the second category is a loss-type polarization filter, which selectively attenuates specific polarization states based on the interaction between guided modes and the environment; compared with the mode-splitting filter, the loss-type filter can provide a higher polarization extinction ratio within a shorter transmission distance and is more suitable for device integration. Therefore, in recent years, the research on loss-type polarization filters has mainly focused on the hollow-core negative-curvature fiber structure.

[0003] It is found that Mousavi et al. achieved a polarization filtering effect with a polarization extinction ratio of 1000 and an x-polarization loss of 0.076 dB / m at a wavelength of 1550 nm by designing a single-ring four-tube hollow-core negative-curvature fiber in "Broadband high birefringence and polarizing hollow core antiresonant fibers"; Wei et al. designed a polarization filter based on a single-ring six-tube in "Polarization-filtering and polarization-maintaining low-loss negative curvature fibers" and obtained a polarization extinction ratio of 850 and a low loss of 0.02 dB / m at a wavelength of 1550 nm; Yan et al. achieved a polarization extinction ratio of 17662 at 1550 nm and a loss of only 0.04 dB / m for the x-polarization by using a double-ring hollow-core antiresonant fiber in "Single-polarization single-mode double-ring hollow-core anti-resonant fiber".

[0004] It can be seen that the hollow-core negative-curvature fiber type polarization filters in the prior art generally have the problems of relatively high transmission loss and relatively low polarization extinction ratio; therefore, how to achieve a hollow-core negative-curvature fiber type polarization filter with low loss and high polarization extinction ratio is still a challenge in the field of practical engineering applications. For polarization filters, reducing their confinement loss and improving the polarization extinction ratio have important engineering practical values. However, the loss and polarization extinction ratio characteristics of the hollow-core negative-curvature fiber type polarization filters in the prior art are not very ideal. Therefore, a hollow-core negative-curvature fiber type polarization filter is invented to improve the above problems. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects mentioned above, so as to provide a hollow-core negative-curvature fiber type polarization filter.

[0006] To solve the above problems, the present invention provides a hollow-core negative-curvature fiber type polarization filter, which includes: Base layer; Air core, disposed at the center within the base layer, and a cladding is further disposed between the air core and the base layer; The cladding includes: a plurality of cladding regions, each of the cladding regions is formed by an outer tangent ring group formed by at least two mutually outer tangent rings; the outer tangent ring group extends from the center position of the base layer towards the edge direction; the cladding regions include: a first cladding region, a second cladding region, a third cladding region, and a fourth cladding region: The first cladding region includes: an outer tangent ring group extending in the Y-axis direction with the air core as the coordinate origin; The third cladding region includes: an outer tangent ring group extending downward in the Y-axis direction with the air core as the coordinate origin, and is disposed opposite to the first cladding region. A glass plate is embedded in the center of the circular plate close to the air core in the first cladding region and the third cladding region respectively. Two small rings are externally tangent to the side of the glass plate close to the air core; The second cladding region and the fourth cladding region are both symmetrically disposed between the first cladding region and the third cladding region with the air core as the coordinate origin, and are both composed of three groups of two uniformly arranged externally tangent rings, and each group of the externally tangent rings is arranged along the radial direction of the air core.

[0007] Preferably, the radius r1 of the small ring is 2.22 μm to 2.5 μm.

[0008] Preferably, the ring close to the base layer is the first layer of ring, and the radius r2 of the first layer of ring is 9.88 μm to 10.14 μm.

[0009] Preferably, the ring close to the air core is the second-layer ring, and the radius r3 of the second-layer ring is 10.2 μm to 10.5 μm.

[0010] Preferably, the radius R of the air core is 29.1 μm to 29.25 μm.

[0011] Preferably, the thickness t1 of the first-layer ring and the second-layer ring is 1.12 μm.

[0012] Preferably, the thickness t2 of the glass plate and the small ring is 1.5 μm.

[0013] Preferably, the materials of the base layer, the ring, the small ring, and the glass plate are all silicon dioxide SiO2.

[0014] The hollow-core negative-curvature fiber type polarization filter provided by the present invention has the following beneficial effects: 1. In the present invention, the cladding and the air core are arranged in the base layer, and the air core is located at the center of the cladding. The cladding includes a first cladding region, a second cladding region, a third cladding region, and a fourth cladding region. The four regions together form the cladding region of the polarization filter. In this way, due to the asymmetry of the cladding structure, the coupling between the core mode and the cladding mode in the x direction is enhanced, and the structure of the negative-curvature fiber reduces the confinement loss of light waves, which not only improves the polarization extinction ratio of the fiber but also reduces the confinement loss; 2. The present invention also provides that for the fiber in the wavelength range of 1547 - 1555 nm, the polarization extinction ratio is greater than 100. When the working wavelength is 1550 nm, the polarization extinction of the y-polarized fundamental mode is as high as 41511, and the loss is as low as 1.66×10 -2 dB / m; when the bending radius of the fiber in the x direction is 4 cm, the polarization filtering function can still be achieved, and the loss of the x-polarized fundamental mode is as low as 1 dB / m. Description of the Drawings

[0015] Figure 1 It is a schematic cross-sectional structure diagram of the hollow-core negative-curvature fiber type polarization filter of the present invention; Figure 2 It is a graph showing the change of the polarization extinction ratio of the hollow-core negative-curvature fiber type polarization filter of the present invention with the radius of the embedded small ring; Figure 3 It is a graph showing the change of the polarization extinction ratio of the hollow-core negative-curvature fiber type polarization filter of the present invention with the radius of the first-layer ring; Figure 4 It is a graph showing the change of the polarization extinction ratio of the hollow-core negative-curvature fiber type polarization filter of the present invention with the radius of the second-layer ring; Figure 5Variation curve of polarization extinction ratio of the hollow negative curvature fiber type polarization filter of the present invention with the air core radius; Figure 6 Variation curve of confinement loss of the hollow negative curvature fiber type polarization filter of the present invention with wavelength; Figure 7 Variation curve of polarization extinction ratio of the hollow negative curvature fiber type polarization filter of the present invention with wavelength; Figure 8 Mode field distribution diagrams of the y-polarized fundamental mode, x-polarized fundamental mode and cladding mode of the present invention at 1550 nm; Figure 9 Variation curve of critical bending radius and confinement loss of the y-polarized fundamental mode under different bending directions of the hollow negative curvature fiber type polarization filter of the present invention; Figure 10 PER and birefringence values under different bending directions of the present invention.

[0016] The reference signs are shown as: 1, base layer; 2, cladding; 3, core; 4, first cladding region; 5, second cladding region; 6, third cladding region; 7, fourth cladding region; 8, small ring; 9, first layer of ring; 10, second layer of ring. Detailed implementation manners

[0017] As Figures 1-10 shown, the present invention provides a hollow negative curvature fiber type polarization filter, which includes: Base layer 1; An air core 3, which is arranged at the center inside the base layer, and a cladding 2 is further arranged between the air core and the base layer; The cladding includes: several cladding regions, and each cladding region is formed by an externally tangent ring group composed of at least two mutually externally tangent rings; the externally tangent ring group extends from the center position of the base layer to the edge direction; the cladding regions include: a first cladding region 4, a second cladding region 5, a third cladding region 6 and a fourth cladding region 7: The first cladding region includes: an externally tangent ring group extending in the Y-axis direction with the air core as the coordinate origin; The third cladding region includes: an externally tangent ring group extending downward in the Y-axis direction with the air core as the coordinate origin, and is arranged opposite to the first cladding region. A glass plate is embedded in the center of the circular plate close to the air core in the first cladding region and the third cladding region respectively. Two small rings 8 are externally tangent to the side of the glass plate close to the air core; The second cladding region and the fourth cladding region are symmetrically arranged between the first cladding region and the third cladding region with the air core as the coordinate origin, and each is composed of three groups of two externally tangent circular rings evenly arranged. Each group of the externally tangent circular rings is arranged along the radial direction of the air core. As Figure 1 shown, the first cladding region, the second cladding region, the third cladding region and the fourth cladding region together form the cladding region of the hollow negative curvature fiber type polarization filter. By precisely designing the shape and material of the cladding 2, the filtering of light with a specific polarization direction can be realized, so that only the light meeting specific polarization conditions can pass through the optical fiber. The design of the air core 3 helps to reduce the scattering and absorption losses of light during transmission and improve the light transmission efficiency; by introducing a glass plate and a specific cladding 2 structure, the propagation path and polarization state of light can be further controlled, thereby enhancing or introducing specific optical effects, such as the negative curvature effect, which helps to achieve more advanced functions in the fields of optical communication, sensing or signal processing, etc.; by adjusting the structural parameters of the cladding 2 (such as the size, position and number of the circular rings), the optical performance of the optical fiber can be flexibly adjusted to meet different application requirements.

[0018] Specifically, its first cladding region takes the center of the air core 3 as the coordinate origin and is composed of two externally tangent circular rings in the y-axis direction. The three groups of externally tangent circular rings of the second cladding region are respectively located at the 45°, 90° and 135° directions on the left side of the first cladding region; the third cladding region is composed of two externally tangent circular rings in the y-axis direction; the fourth cladding region is composed of three groups of two externally tangent circular rings, which are respectively located at the 45°, 90° and 135° directions on the right side of the first cladding region 4; through the coupling between the fundamental mode of the cladding 2 and the fundamental mode of the air core 3, the birefringence and loss difference of the fundamental mode of the air core 3 are enhanced, so that the polarization extinction ratio performance of the y-polarized fundamental mode is optimized; in the present invention, the cladding 2 is composed of different cladding regions, and the four regions together form the cladding region of a hollow negative curvature fiber type polarization filter based on a "gourd" structure; in this way, due to the asymmetry of the cladding 2 structure, the coupling between the core 3 mode in the x direction and the cladding 2 mode is enhanced, and the structure of the negative curvature fiber reduces the confinement loss of light waves, further improving the polarization extinction ratio of the hollow negative curvature fiber and reducing the confinement loss.

[0019] In some embodiments, the radius r1 of the small circular ring 8 is 2.22 μm to 2.5 μm. As Figure 2 shown, the radius r1 of the small circular ring 8 is 2.22 μm to 2.5 μm. When the value of r1 is 2.42 μm, it reaches the critical value, and at this time the polarization extinction ratio value reaches the maximum. When r1 continues to increase, the value of the polarization extinction ratio will rapidly decrease. From Figure 1 it can be concluded that when r1 is selected as 2.42 μm, the value of the polarization extinction ratio is the largest.

[0020] In some embodiments, the ring close to the base layer 1 is the first-layer ring 9, and the radius r2 of the first-layer ring 9 is 9.88 μm to 10.14 μm. As Figure 3 shown, the ring close to the base layer 1 is the first-layer ring 9, and the radius r2 of the first-layer ring 9 is 9.88 μm to 10.14 μm. When r2 varies within the range of 9.88 - 10.14 μm, the PER generally shows a trend of first increasing and then decreasing, and when r2 = 10.03 μm, the polarization extinction ratio reaches the maximum value, and the maximum value can reach 11166. Therefore, when r2 is taken as 10.03 μm, the value of the polarization extinction ratio is the largest.

[0021] In some embodiments, the ring close to the air core 3 is the second-layer ring 10, and the radius r3 of the second-layer ring 10 is 10.2 μm to 10.5 μm. As Figure 4 shown, the radius R of the air core 3 is 29.1 μm to 29.25 μm. When r3 varies within the range of 10.3 - 10.5 μm, the polarization extinction ratio generally shows a trend of first increasing and then decreasing, and at r3 = 10.41 μm, the polarization extinction ratio reaches the maximum value, and the maximum value can reach 12991. From Figure 4 it can be concluded that when r3 is selected as 10.41 μm, the value of the polarization extinction ratio is the largest.

[0022] In some embodiments, the radius R of the air core 3 is 29.1 μm to 29.25 μm. As Figure 5 shown, the radius R of the air core 3 is 29.1 μm to 29.25 μm. When R varies within the range of 29.1 μm - 29.25 μm, it shows a trend of first increasing and then decreasing, and at R = 29.19 μm, the polarization extinction ratio reaches the maximum value, and the maximum value can reach 41510.572. From Figure 5 it can be known that when R is selected as 29.19 μm, the value of the polarization extinction ratio is the largest.

[0023] In some embodiments, the thickness t1 of the first-layer ring 9 and the second-layer ring 10 is 1.12 μm.

[0024] In some embodiments, the thickness t2 of the glass plate and the small ring 8 is 1.5 μm.

[0025] In some embodiments, the materials of the base layer 1, the ring, the small ring 8, and the glass plate are all silicon dioxide SiO2.

[0026] Specifically, the refractive index of silicon dioxide in the C band (1530 nm to 1565 nm) is approximately 1.444.

[0027] Specifically, Figure 6It is the curve diagram of the variation of the confinement loss of the hollow-core negative-curvature fiber type polarization filter of the present invention with wavelength; Specifically, Figure 5 In [reference], the relationship between its confinement loss and wavelength was calculated when the fiber structure parameters were set as r1 = 2.42 μm, r2 = 10.03 μm, r3 = 10.41 μm, and R = 29.19 μm. From Figure 5 It can be concluded that when the optimized parameter values are selected, the confinement loss of the y-polarized fundamental mode at 1550 nm is only 1.66×10 -2 dB / m, while the confinement loss of the x-polarized fundamental mode is 689.83 dB / m.

[0028] Specifically, Figure 7 It is the curve diagram of the variation of the polarization extinction ratio of the hollow-core negative-curvature fiber type polarization filter of the present invention with wavelength; Figure 7 In [reference], when the fiber structure parameters were set as r1 = 2.42 μm, r2 = 10.03 μm, r3 = 10.41 μm, and R = 29.19 μm, the polarization extinction ratio curve of the proposed negative-curvature fiber type polarization filter after parameter optimization in the range of 1530 nm - 1570 nm was calculated; from Figure 7 It can be concluded that in the wavelength range of 1547 nm - 1554 nm, the polarization extinction ratio of the polarization filter is greater than 100, meeting the minimum working performance requirements of the polarization filter.

[0029] Specifically, Figure 8 It is the mode field distribution diagram of the y-polarized fundamental mode, x-polarized fundamental mode, and cladding 2 mode at 1550 nm provided by the present invention; when the fiber structure parameters are set as r1 = 2.42 μm, r2 = 10.03 μm, r3 = 10.41 μm, and R = 29.19 μm, the y-polarized fundamental mode, x-polarized fundamental mode, and cladding 2 mode; among them, Figure 8 a is the mode field distribution of the y-polarized fundamental mode; Figure 8 b is the mode field distribution of the x-polarized fundamental mode; Figure 8 c is the mode field distribution of the cladding 2 mode; the results show that the designed fiber can work normally.

[0030] Specifically, Figure 9 It is the curve diagram of the transformation of the critical bending radius and the confinement loss of the y-polarized fundamental mode under different bending directions; when the fiber structure parameters are set as r1 = 2.42 μm, r2 = 10.03 μm, r3 = 10.41 μm, and R = 29.19 μm, it can be seen that when the bending direction θ increases from 0° to 90°, the critical bending radius generally shows a gradually increasing trend, and when θ = 60°, the critical bending radius reaches the maximum value of 24 cm; in the range of the bending direction θ = 0° - 30°, the loss of the y-polarized fundamental mode increases rapidly with the increase of the bending angle and remains at a relatively large level.

[0031] Specifically, Figure 10 are the PER and birefringence values under different bending directions provided by the present invention, corresponding to Figure 9 All values are calculated at the critical bending radius corresponding to the bending direction. The PER is greater than 100, meeting the conditions for polarization filtering. When the bending direction is the y direction, the corresponding critical bending radius is 4 cm, and the corresponding PER is 145.

[0032] In this application, the cladding 2 and the air core 3 are arranged in the base layer 1, and the air core 3 is located at the center of the cladding 2. The cladding 2 includes a first cladding region, a second cladding region, a third cladding region, and a fourth cladding region. The four regions together form the cladding region of the polarization filter. In this way, due to the asymmetry of the structure of the cladding 2, the coupling between the core 3 mode in the x direction and the cladding 2 mode is enhanced, and the structure of the negative curvature fiber reduces the confinement loss of light waves, which not only improves the polarization extinction ratio of the fiber but also reduces the confinement loss. In addition, for the fiber provided by the present invention, in the wavelength range of 1547 - 1555 nm, the polarization extinction ratio is greater than 100. When the working wavelength is 1550 nm, the polarization extinction of the y-polarized fundamental mode is as high as 41511, and the loss is as low as 1.66×10 -2 dB / m; when the bending radius of the fiber along the x direction is 4 cm, the polarization filtering function can still be achieved, and the loss of the x-polarized fundamental mode is as low as 1 dB / m.

[0033] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. The above is only the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can still be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A hollow core negative curvature optical fiber polarization filter, characterized in that: include: Grassroots; An air core is arranged at the center of the base layer, and a cladding is arranged between the air core and the base layer; The cladding layer includes: a plurality of cladding regions, each of which is formed by at least two circumscribed circular ring groups formed by mutually circumscribed circular rings; the circumscribed circular ring groups extend from the center position of the base layer toward the edge direction; the cladding regions include: a first cladding region, a second cladding region, a third cladding region and a fourth cladding region: The first cladding region includes: a circumscribed circular ring group extending in the Y-axis direction with the air core as the coordinate origin; The third cladding region includes: a group of circumscribed circular rings extending downward in the Y-axis direction with the air core as the coordinate origin, and arranged opposite to the first cladding region, wherein the first cladding region and the third cladding region are respectively embedded with a glass plate in the center of the circular plate close to the air core, and two small circular rings are circumscribed on one side of the glass plate close to the air core; The second cladding region and the fourth cladding region are both symmetrically arranged between the first cladding region and the third cladding region with the air core as the coordinate origin, and are both composed of three groups of two evenly arranged circumscribed circular rings, and each group of the circumscribed circular rings is arranged along the radial direction of the air core.

2. The hollow core negative curvature optical fiber polarization filter according to claim 1, characterized in that: The radius r1 of the small ring is 2.22 μm to 2.5 μm.

3. The hollow core negative curvature optical fiber polarization filter according to claim 1, characterized in that: The circular ring close to the base layer is a first-layer circular ring, and the radius r2 of the first-layer circular ring is 9.88 μm-10.14 μm.

4. The hollow core negative curvature optical fiber polarization filter according to claim 3, characterized in that: The circular ring close to the air core is a second-layer circular ring, and the radius r3 of the second-layer circular ring is 10.2 μm-10.5 μm.

5. The hollow core negative curvature optical fiber polarization filter according to claim 1, characterized in that: The radius R of the air core is 29.1 μm to 29.25 μm.

6. The hollow core negative curvature optical fiber polarization filter according to claim 4, characterized in that: The thickness t1 of the first layer of circular rings and the second layer of circular rings is 1.12 μm.

7. The hollow core negative curvature optical fiber polarization filter according to claim 1, characterized in that: The thickness t2 of the glass plate and the small ring is 1.5 μm.

8. The hollow core negative curvature optical fiber polarization filter according to claim 1, characterized in that: The materials of the base layer, the ring, the small ring and the glass plate are all silicon dioxide SiO2.

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