Embedded anti-resonance photonic band gap hollow-core fiber

Abstract

The embedded anti-resonance photonic band gap hollow-core optical fiber is composed of an outer sleeve with the highest refractive index, a honeycomb-shaped outer cladding with the high refractive index, a composite negative curvature inner cladding and a fiber core with the low refractive index from outside to inside. Wherein the honeycomb-shaped outer wrapping layer is composed of hexagonal capillary tubes and is periodically and tightly arranged on the inner wall of the outer-layer sleeve in a melting and bonding mode; the composite negative-curvature inner cladding layer is composed of special-shaped capillary tubes, is embedded into the inner layer of the honeycomb-shaped outer cladding layer and is fused and bonded with the honeycomb-shaped outer cladding layer; the special-shaped capillary tube is composed of a negative curvature tube wall facing the fiber core and a polygonal tube wall embedded in the honeycomb-shaped outer cladding. The cellular outer cladding is used for constructing the photonic band gap, the negative curvature inner cladding pipe wall is used for constructing the anti-resonance unit, the transmission loss of the hollow-core optical fiber is further reduced, meanwhile, the bending sensitivity of the optical fiber is reduced, low-loss bending resistance of the hollow-core optical fiber is achieved, and the optical fiber can be widely applied to the fields of optical fiber communication, optical fiber sensing, optical fiber energy transmission, aerospace and the like.

Description

Technical Field

[0001] The present invention relates to the fields of optical fiber technology and laser technology, and particularly relates to a class of embedded anti-resonant photonic bandgap hollow-core optical fibers. Background Art

[0002] In recent years, hollow-core optical fibers have once become a research hotspot in the fields of optical fiber communication and fiber lasers. Due to their unique light guiding mechanism, light can be confined to the core air region for transmission, creating new application scenarios, and it is a disruptive optical fiber technology that has emerged in recent years. Hollow-core optical fibers have various advantages such as low transmission loss, low latency, low nonlinearity, ultra-low absorption, and high damage threshold. Compared with silica optical fibers, they can meet more requirements and have more application scenarios. According to different light guiding mechanisms, hollow-core optical fibers can be divided into photonic bandgap hollow-core optical fibers and anti-resonant hollow-core optical fibers.

[0003] Photonic bandgap hollow-core optical fibers form a photonic bandgap by constructing a periodically distributed photonic crystal structure in the cladding region, confining the light in the core region within the photonic bandgap. Due to its special cladding structure, photonic bandgap hollow-core optical fibers have the advantages of low bending loss, high birefringence, a wide range of temperature sensitivity coefficients, and can resist low-loss transmission, and can be widely applied to applications such as fiber optic sensing and fiber optic gyroscopes. Since the emergence of photonic bandgap optical fibers, researchers have carried out different studies on the modes, losses, and polarization characteristics of such optical fibers, and have fabricated various photonic bandgap hollow-core optical fibers with different structures. According to the reported photonic bandgap hollow-core optical fibers, the lowest transmission loss that can be achieved is 1.2 dB / km, and the highest birefringence can be 2.5×10 -2 and a wide temperature sensitivity coefficient range of -5 to 9 ps / km / °C can be obtained.

[0004] Anti-resonant hollow-core optical fibers, by constructing an anti-resonant cladding wall structure with negative curvature and using the anti-resonant reflection waveguide, can confine light well in the core air region. Since the invention of anti-resonant hollow-core optical fibers, their transmission losses have gradually decreased. Currently, the lowest transmission loss of the reported anti-resonant hollow-core optical fibers has been lower than 0.11 dB / km, breaking the loss limit of traditional silica single-mode optical fibers. In addition, anti-resonant hollow-core optical fibers have a wider transmission band, which also enables this type of optical fiber to be applied to gas nonlinearity, fabricating high-power gas lasers, and serving as a good carrier for the interaction between gas and laser. Since anti-resonant hollow-core optical fibers often have a relatively large core, the overlapping area between the core internal mode and the quartz material is greatly reduced, which is beneficial to improving the laser damage threshold and is a good medium for high-power laser transmission.

[0005] However, both of these two types of optical fibers have obvious disadvantages. For photonic bandgap hollow-core optical fibers, the surface scattering loss on the inner wall of the core limits the further reduction of their transmission loss. At the same time, surface modes are likely to be generated on the core wall of photonic bandgap hollow-core optical fibers. The existence of surface modes will result in high-loss peaks within the transmission band of the optical fiber, affecting the available bandwidth of the optical fiber. For anti-resonant hollow-core optical fibers, due to their simple cladding structure and less supporting material, this type of optical fiber has extremely high bending sensitivity. When the optical fiber is bent, adverse effects such as mode hopping inside the optical fiber and increased transmission loss will occur. In addition, polarization-maintaining anti-resonant hollow-core optical fibers mainly introduce birefringence by changing the thickness of the anti-resonant quartz wall inside the core. However, due to limitations such as preparation processes, the preparation of this type of optical fiber is extremely difficult. The highest birefringence value of the reported polarization-maintaining anti-resonant hollow-core optical fibers is only on the order of 10 -4 magnitude, and this shortcoming limits the application of this type of optical fiber in fields such as fiber optic sensing. Summary of the Invention

[0006] To overcome the above problems, the present invention provides a type of embedded anti-resonant photonic bandgap hollow-core optical fiber. This hollow-core optical fiber can not only meet the requirements of low-loss transmission, but also has a stable special cladding structure, can obtain extremely low bending sensitivity, and reduce bending loss.

[0007] The technical solution of the present invention is as follows:

[0008] The present invention provides a type of embedded anti-resonant photonic bandgap hollow-core optical fiber, which is characterized in that the hollow-core optical fiber is composed of four parts from outside to inside: an outer sleeve with the highest refractive index, a honeycomb-shaped outer cladding with a relatively high refractive index, a composite negative-curvature inner cladding, and a core with a relatively low refractive index. They are concentrically distributed in the radial direction and extend in the axial direction; wherein the honeycomb-shaped outer cladding is composed of hexagonal capillaries and is periodically and tightly arranged and fused on the inner wall of the outer sleeve; the composite negative-curvature inner cladding is composed of special-shaped capillaries, which are embedded in the inner layer of the honeycomb-shaped outer cladding and fused with it, and are centrosymmetrically distributed with respect to the core axis; wherein the special-shaped capillary is composed of a negative-curvature tube wall facing the core and a polygonal tube wall embedded in the honeycomb-shaped outer cladding.

[0009] Preferably, the hexagonal capillaries in the honeycomb-shaped outer cladding are arranged layer by layer from outside to inside, and the number of arranged layers is M layers, and M can be an integer such as 1, 2, 3...

[0010] Preferably, the honeycomb-shaped outer cladding structure can be embedded with L large-diameter capillaries of different shapes, and L can be a positive integer such as 0, 1, 2... to filter out high-order modes in the core region. The outer wall of the capillary is fused with the outer wall of the hexagonal capillary without gaps.

[0011] Preferably, the number of special-shaped capillaries in the composite negative-curvature inner cladding is N, and N is greater than or equal to 2.

[0012] Preferably, the inner wall of the profiled capillary of the composite negative curvature inner cladding can nest K thin-walled circular capillaries with different diameters, and K can be an integer such as 0, 1, 2, etc. The outer walls of the K thin-walled circular capillaries with different diameters are internally tangent to the inner wall of the profiled capillary polygonal tube wall and are fused and bonded.

[0013] Preferably, the wall thickness, size and arrangement period of the hexagonal capillary satisfy the requirements for constructing a specific photonic bandgap.

[0014] Preferably, the wall thickness t of the negative curvature tube wall of the profiled capillary satisfies the principle of the anti-resonant reflection waveguide, that is:

[0015]

[0016] where λ is the operating wavelength of the optical fiber; n 1 is the outer sleeve, honeycomb outer cladding, and average refractive index of the composite negative curvature inner cladding; n 0 is the refractive index of the gas filled in the core region; m is the anti-resonant reflection order.

[0017] Preferably, the materials of the outer sleeve outer cladding, honeycomb outer cladding and composite negative curvature inner cladding can be materials such as silica and soft glass, and the core material can be materials such as vacuum, air and inert gas.

[0018] The advantages of the present invention are as follows:

[0019] The present invention provides a class of embedded anti-resonant photonic bandgap hollow-core optical fibers. By combining the principles of anti-resonant reflection waveguide and photonic bandgap, a stable microstructured cladding is constructed, which has excellent bending characteristics while achieving low-loss transmission.

[0020] The present invention combines anti-resonant reflection and photonic bandgap principles by embedding a designed composite negative curvature capillary in the honeycomb outer cladding region, reducing the manufacturing process difficulty of low-loss and bend-resistant hollow-core optical fibers.

[0021] The present invention embeds a circular capillary with a larger diameter inside the honeycomb outer cladding, which can couple the high-order modes in the core to the cladding to achieve single-mode transmission.

[0022] The present invention can realize an adjustable shift of the transmission window from visible light to infrared light by adjusting the wall thickness of the negative curvature tube wall of the profiled capillary and the hole spacing between the hexagonal capillaries.

[0023] The present invention can reflect light to the core region through the negative curvature tube wall of the profiled capillary, reduce the overlap between the core quartz wall and the light field, reduce the scattering loss of the light field on the quartz wall, and at the same time reduce the generation of surface modes to achieve a wide transmission band. Description of the Drawings

[0024] Figure 1 It is a schematic cross-sectional structure diagram of Embodiment 1 of a kind of embedded anti-resonant photonic bandgap hollow-core optical fiber of the present invention.

[0025] Figure 2 It is a schematic cross-sectional structure diagram of Embodiment 2 of a kind of embedded anti-resonant photonic bandgap hollow-core optical fiber of the present invention.

[0026] Figure 3 It is a schematic cross-sectional structure diagram of Embodiment 3 of a kind of embedded anti-resonant photonic bandgap hollow-core optical fiber of the present invention.

[0027] Figure 4 It is the calculation result of the mode field distribution of Embodiment 1 of a kind of embedded anti-resonant photonic bandgap hollow-core optical fiber of the present invention. Figure 5 It is the transmission loss diagram of Embodiment 1 of a kind of embedded anti-resonant photonic bandgap hollow-core optical fiber of the present invention. Specific Embodiments

[0028] To make the purpose, technical solutions and advantages of the present invention clearer, the following will further describe the embodiments of the present invention in conjunction with the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0029] Embodiment 1

[0030] Figure 1 It is a schematic cross-sectional structure diagram of Embodiment 1 of a kind of embedded anti-resonant photonic bandgap hollow-core optical fiber of the present invention. Its structure from outside to inside is successively the outer sleeve 1 of the optical fiber, the honeycomb-shaped outer cladding 2, the composite negative-curvature inner cladding 3 and the core region 4.

[0031] The described honeycomb-shaped outer cladding 2 is fused and bonded tightly to the inner wall of the outer sleeve 1; the honeycomb-shaped outer cladding is composed of hexagonal capillaries 2-1. The hexagonal capillaries 2-1 are adjacent to each other two by two, arranged closely, and their outer walls are fused and bonded to each other seamlessly, forming a 5-layer honeycomb-shaped hexagonal structure from outside to inside. The described composite negative-curvature inner cladding 3 is composed of special-shaped capillaries 3-1. The part of the special-shaped capillary 3-1 facing the core is the negative-curvature tube wall 3-1-1, and the part embedded in the honeycomb-shaped outer cladding is the polygonal tube wall 3-1-2. The polygonal tube wall 3-1-2 of the special-shaped capillary is fused and bonded to the hexagonal capillary 2-1 closest to the core side without gaps. The number of special-shaped capillaries 3-1 in the described composite negative-curvature inner cladding 3 is 6, and the six special-shaped capillaries 3-1 do not contact each other.

[0032] In this example, the curvature of the negative-curvature tube wall 3-1-1 of the special-shaped capillary 3-1 is 8 μm.

[0033] The honeycomb-shaped outer cladding 2 and the composite negative-curvature inner cladding 3 are made of silica. The wall thickness t of the negative-curvature tube wall 3-1-1 of the special-shaped capillary 3-1 satisfies the principle of the anti-resonant reflection waveguide, that is:

[0034] where λ is the working wavelength; n 1 is the average refractive index of the outer sleeve 1, the honeycomb-shaped outer cladding 2, and the composite negative-curvature inner cladding 3; n 0 is the refractive index of the gas filled in the core region; m is the anti-resonant reflection order. In this embodiment, the working band is the infrared band, the working wavelength λ is taken as 1550 nm, the refractive index n 1 of the cladding tube is taken as 1.45, the refractive index n 0 of air is taken as 1, and m is taken as 1. Therefore, the calculated wall thickness is 813.75 nm.

[0035] Embodiment 2

[0036] Figure 2 is a schematic cross-sectional structure diagram of Embodiment 2 of a kind of embedded anti-resonant photonic bandgap hollow fiber of the present invention. Its structure from outside to inside is successively the outer sleeve 1 of the optical fiber, the honeycomb-shaped outer cladding 2, the composite negative-curvature inner cladding 3, and the core region 4.

[0037] The honeycomb-shaped outer cladding 2 is tightly bonded and fused with the inner wall of the outer sleeve 1; the honeycomb-shaped outer cladding is composed of hexagonal capillaries 2-1. The hexagonal capillaries 2-1 are adjacent to each other and are closely arranged. Their outer walls are fused and bonded to each other seamlessly, forming a 5-layer honeycomb-shaped hexagonal structure from outside to inside. The composite negative-curvature inner cladding 3 is composed of special-shaped capillaries 3-1. The part of the special-shaped capillary 3-1 facing the core is the negative-curvature tube wall 3-1-1, and the part embedded in the honeycomb-shaped outer cladding is the polygonal tube wall 3-1-2. The inner wall of the special-shaped capillary 3-1 of the composite negative-curvature inner cladding 3 nests a thin-walled circular capillary 3-2 with a smaller diameter. The outer wall 3-2 of the thin-walled circular capillary with a smaller diameter is tangent to and fused with the inner wall of the polygonal tube wall 3-1-2 to form a circular capillary complex. The number of special-shaped capillaries 3-1 of the composite negative-curvature inner cladding 3 is 4. The four special-shaped capillaries 3-1 are divided into two groups. Two special-shaped capillaries 3-1 within the group are fused and bonded into a union through adjacent nodes. There is no gap between the two unions and the innermost hexagonal capillary 2-1.

[0038] In this example, the curvature of the negative-curvature tube wall 3-1-1 of the special-shaped capillary 3-1 is 13 μm, and the curvature of the smaller-diameter capillary 3-2 nested in the special-shaped capillary 3-1 is 8 μm.

[0039] The honeycomb-shaped outer cladding 2 and the composite negative-curvature inner cladding 3 are made of silica. The wall thickness t of the negative-curvature tube wall 3-1-1 of the shaped capillary satisfies the principle of the anti-resonant reflection waveguide, that is:

[0040]

[0041] where λ is the working wavelength; n 1 is the average refractive index of the outer sleeve 1, the honeycomb-shaped outer cladding 2, and the composite negative-curvature inner cladding 3; n 0 is the refractive index of the gas filled in the core region; m is the anti-resonant reflection order. In this embodiment, the working band is the infrared band, the working wavelength λ is taken as 1550 nm, the refractive index n 1 of the cladding tube is taken as 1.45, the refractive index n 0 of air is taken as 1, and m is taken as 1. Therefore, the calculated wall thickness is 813.75 nm

[0042] Embodiment 3

[0043] Figure 3 is a schematic cross-sectional structure diagram of Embodiment 3 of a kind of embedded anti-resonant photonic bandgap hollow-core optical fiber of the present invention. Its structure from outside to inside is successively the outer sleeve 1 of the optical fiber, the honeycomb-shaped outer cladding 2, the composite negative-curvature inner cladding 3, and the core region 4

[0044] The honeycomb-shaped outer cladding 2 is tightly bonded and fused with the inner wall of the outer sleeve 1; the honeycomb-shaped outer cladding is composed of hexagonal capillaries 2-1. The hexagonal capillaries 2-1 are adjacent to each other and closely arranged, and their outer walls are fused and bonded to each other seamlessly, forming a 7-layer honeycomb-shaped hexagonal structure from outside to inside. Six circular capillaries 2-2 with larger diameters are embedded in the honeycomb-shaped outer cladding 2, and are fused and bonded with the adjacent hexagonal capillaries 2-1 without gaps. The composite negative-curvature inner cladding 3 is composed of six shaped capillaries 3-1. The part of the shaped capillary 3-1 facing the core is the negative-curvature tube wall 3-1-1, and the part embedded in the honeycomb-shaped outer cladding is the polygonal tube wall 3-1-2, and the six shaped capillaries 3-1 do not contact each other. The composite negative-curvature inner cladding 3 has a thin-walled circular capillary 3-2 with a smaller diameter nested inside the inner wall of the shaped capillary 3-1. The outer wall of the thin-walled circular capillary 3-2 with a smaller diameter is tangent to and fused with the inner wall of the polygonal tube wall 3-1-2 to form a circular capillary complex. The polygonal tube wall 3-1-2 of the shaped capillary is fused and bonded with the hexagonal capillary 2-1 closest to the core side without gaps.

[0045] In this example, the curvature of the negative-curvature tube wall 3-1-1 of the shaped capillary is 8 μm, the curvature of the smaller-diameter capillary 3-2 nested inside the shaped capillary is 5 μm, and the curvature of the larger-diameter circular capillary 2-2 is 13.5 μm.

[0046] The honeycomb-shaped outer cladding 2 and the composite negative-curvature inner cladding 3 are made of silica. The wall thickness t of the negative-curvature tube wall 3-1-1 of the shaped capillary satisfies the principle of the anti-resonant reflection waveguide, that is:

[0047]

[0048] where λ is the working wavelength; n 1 is the average refractive index of the outer sleeve 1, the honeycomb-shaped outer cladding 2, and the composite negative-curvature inner cladding 3; n 0 is the refractive index of the gas filled in the core region; m is the anti-resonant reflection order. In this embodiment, the working band is the infrared band, the working wavelength λ is taken as 1550 nm, the refractive index n of the cladding tube 1 is taken as 1.45, the refractive index n of air 0 is taken as 1, and m is taken as 1. Therefore, the calculated wall thickness is 813.75 nm

[0049] Embodiment 4

[0050] Figure 4 is the simulated fundamental mode field distribution diagram of Embodiment 1 of a kind of embedded anti-resonant photonic bandgap hollow-core optical fiber of the present invention. Figure 5 is the transmission loss result of the fundamental mode simulated and calculated in Embodiment 1 in the range of 1500 - 1600 nm.

[0051] The finite element simulation software COMSOL Multiphysics is used to perform simulation tests on Embodiment 1. In the simulation process, mode analysis is performed on the cross-section of the optical fiber. The cross-section of the optical fiber is divided using triangular meshes with a maximum mesh element of λ / 5, and a perfectly matched layer is used to simulate the larger silica glass outer cladding. The perfectly matched layer is divided using mapped meshes with a maximum mesh element of λ / 5. The fundamental mode field distribution at 1550 nm in the simulation results is as Figure 4 shown. The fundamental mode field is well confined in the core region by the designed anti-resonant reflection wall and the cladding with the photonic bandgap structure without leakage. The transmission loss of the optical fiber with this structure in Embodiment 1 in the range of 1500 - 1600 nm in the simulation results is as Figure 5 shown. In a certain bandwidth near the wavelength of 1550 nm, the transmission loss of the mode is between 10 -1 -10 -2 dB / km, indicating that this kind of optical fiber can maintain low-loss transmission. After calculation, the loss of the high-order mode at the wavelength of 1550 nm is more than two orders of magnitude larger than that of the fundamental mode, and the purpose of single-mode transmission can be achieved in actual use.

[0052] The above embodiments only represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these should all fall within the protection scope of the present invention.

Claims

1. A type of embedded antiresonant photonic bandgap hollow core fiber, characterized in that: The hollow-core optical fiber is composed of four parts from the outside to the inside: an outer sleeve (1) with the highest refractive index, a honeycomb outer cladding (2) with a relatively high refractive index, a composite negative curvature inner cladding (3) and a core (4) with a relatively low refractive index, and the parts are concentrically distributed in the radial direction and extend in the axial direction; wherein the outer sleeve (1) is a thick-walled annular base material layer; the honeycomb outer cladding (2) is formed by periodically and closely arranging hexagonal capillaries (2-1) on the inner wall of the outer sleeve (1) and melt-bonding them, and there is no gap between the outer walls of adjacent hexagonal capillaries (2-1); the composite negative curvature inner cladding (3) is arranged in a circular manner; and the inner wall of the composite negative curvature inner cladding (4) is formed by closely arranging hexagonal capillaries (2-1) on the inner wall of the outer sleeve (1) and melt-bonding them. The curvature inner cladding (3) is composed of a plurality of special-shaped capillaries (3-1), the special-shaped capillaries (3-1) are embedded in the honeycomb outer cladding (2) and melt-bonded thereto without gaps, and are centrally symmetrically distributed relative to the axis of the fiber core (4), the special-shaped capillaries (3-1) comprising a negative curvature tube wall (3-1-1) facing the fiber core (4), and a polygonal tube wall (3-1-2) embedded in the honeycomb outer cladding (2); the fiber core (4) is composed of a central gap formed by the honeycomb outer cladding (2) and the composite negative curvature inner cladding (3).

2. The embedded antiresonant photonic bandgap hollow core optical fiber according to claim 1, characterized in that: The hexagonal capillaries (2-1) are arranged in layers from outside to inside, and the number of layers is M, where M is a positive integer greater than 3.

3. The embedded antiresonant photonic bandgap hollow core optical fiber according to claim 1, characterized in that: The honeycomb outer cladding (2) is embedded with L circular capillaries (2-2) of different shapes and with a diameter greater than that of the hexagonal capillaries (2-1), where L is 0 or a positive integer. The outer wall of the circular capillary (2-2) is melt-bonded to the outer wall of the adjacent hexagonal capillary (2-1) without a gap, so as to filter out the high-order modes of the fiber core (4).

4. The embedded antiresonant photonic bandgap hollow core optical fiber according to claim 1, characterized in that: The number N of the special-shaped capillaries (3-1) is a positive integer greater than or equal to 2.

5. The type of embedded antiresonant photonic bandgap hollow core optical fiber according to claim 1, characterized in that: K thin-walled circular capillaries (3-2) of different diameters are nested on the inner wall of the special-shaped capillary (3-1), where K is 0 or a positive integer. The outer wall of the thin-walled circular capillary (3-2) is tangent to the inner wall of the polygonal tube wall (3-1-2) and is melt-bonded.

6. The type of embedded antiresonant photonic bandgap hollow core fiber as claimed in claim 1, characterized in that: The wall thickness, size and arrangement period of the hexagonal capillary (2-1) meet the requirements for constructing a specific photonic band gap.

7. The type of embedded antiresonant photonic bandgap hollow core fiber according to claim 1, characterized in that: The wall thickness t of the negative curvature tube wall (3-1-1) of the special-shaped capillary tube (3-1) satisfies the following conditions: Wherein, λ is the working wavelength of the optical fiber, n1 is the average refractive index of the outer sleeve (1), the honeycomb outer cladding (2) and the composite negative curvature inner cladding (3), n0 is the refractive index of the filling medium in the core (4) region, and m is the order of anti-resonance reflection.

8. The type of embedded antiresonant photonic bandgap hollow core optical fiber according to claim 1, characterized in that: The outer sleeve (1), the honeycomb outer cladding (2) and the composite negative curvature inner cladding (3) are made of silicon dioxide or soft glass, and the fiber core (4) is filled with a vacuum, air or an inert gas.

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