Negative curvature annular optical fiber mode selection coupler

Abstract

The invention relates to the technical field of optical fibers, in particular to a negative curvature annular optical fiber mode selection coupler which is formed by bonding two negative curvature annular optical fibers of the same structure, the bonding part is a coupling area, and the non-bonding part forms four ports which serve as input and output ports respectively. The power ratio of the collinear output end to the cross output end is determined by the coupling length L; the tangent planes of the two negative curvature annular optical fibers are ground and then bonded through refractive index matching glue. The coupler can generate high-order OAM modes, including 12 OAM modes including OAM01, OAM11, OAM21 and OAM31, by reasonably designing the structural parameters of the optical fibers and properly selecting the center spacing distance and the coupling length of the two optical fibers. Compared with a traditional optical fiber coupler, the optical fiber coupler can still achieve high coupling efficiency in a high-order mode, and the splitting ratio and the coupling mode can be adjusted by adjusting the coupling distance and the input mode.

Description

Technical Field

[0001] The invention relates to the technical field of optical fibers, and in particular to a negative curvature annular optical fiber mode selective coupler. Background Art

[0002] The commonly used fiber optic devices in fiber optic communication systems are mainly couplers, polarization controllers, gratings and multiplexers. The most classic fiber optic device is the fiber optic coupler, which plays a key role in lasers, fiber optic communications and sensors. A coupler is a passive device used for transmission and splitting, which can realize functions such as coupling, interference and separation in a fiber optic link. According to the type of generated mode, common couplers can be divided into couplers for generating linear polarization mode (LP) mode and couplers for generating orbital angular momentum (OAM) mode.

[0003] At present, the most common fiber structure used in OAM couplers is conventional ring fiber. The high refractive index region of the ring fiber can make the effective refractive index separation between adjacent modes larger, thereby avoiding the coupling of high-order vector modes into LP modes, thereby ensuring the stable transmission of OAM modes. However, the high refractive index region is achieved through a relatively complex doping process, which not only makes the fiber manufacturing process difficult, but also causes high mode transmission loss. In addition, the stress-strain characteristics of traditional ring fiber OAM couplers are poor, and they are easily affected by external forces during the manufacturing process. Summary of the invention

[0004] The purpose of the present invention is to provide a negative curvature annular optical fiber mode selective coupler, and to provide a mode selective coupler structure with a stable structure, capable of generating a high-order OAM mode and having a low transmission loss.

[0005] To achieve the above object, the present invention provides a negative curvature annular fiber mode selective coupler, which is composed of two negative curvature annular fibers of the same structure bonded together, the bonded portion is a coupling region, the unbonded portion forms four ports as input and output ports respectively, and the power ratio of the collinear output end and the cross output end is determined by the coupling length L;

[0006] The cut surfaces of the two negative curvature annular optical fibers are both ground and then bonded using refractive index matching glue.

[0007] There is a cladding air hole outside the ring core of the negative curvature annular optical fiber, 6 hollow capillaries with a thickness of t1 are arranged on the outer layer of the cladding air holes, and the outer cladding is a hollow capillary with a thickness of t2.

[0008] The base material of the negative curvature annular optical fiber is pure silica, and the refractive index n0 is 1.444 at a wavelength of 1.55 μm.

[0009] The inner circle radius of the ring core is r0=1.2 μm, and the outer circle radius is r1=3.3 μm.

[0010] The rectangular air holes of the outer cladding of the ring core have a width of d1 = 1.6 μm, a height of d2 = 1.4 μm, a spacing distance between two air holes of k = 2 μm, and a radius of r2 = 4.8 μm.

[0011] The thickness t1 of the hollow capillary outside the cladding air hole is 0.72 μm, and the outer radius is r3 = 4.8 μm.

[0012] The center spacing distance D of the two ring cores in the coupling zone is adjustable, and D is 8-9.6 μm.

[0013] The present invention provides a negative curvature annular optical fiber mode selective coupler, which is composed of two negative curvature annular optical fibers of the same structure bonded together. The bonded part is the coupling area, and the unbonded part forms four ports as input and output ports respectively. The power ratio of the collinear output end and the cross output end is determined by the coupling length L. The cut surfaces of the two negative curvature annular optical fibers are polished and then bonded with refractive index matching glue. By reasonably designing the optical fiber structural parameters and appropriately selecting the center spacing distance and coupling length of the two optical fibers, the coupler can generate high-order OAM modes, including OAM 01 (<0, ±1>), OAM 11 (<±1, 1>), OAM 21 (<±2, ±1>), OAM 31 Compared with the traditional fiber coupler, the present invention can still achieve higher coupling efficiency in high-order modes, and can also achieve adjustable splitting ratio and coupling mode by adjusting the coupling distance and input mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 It is a structural schematic diagram of a negative curvature annular optical fiber mode selective coupler of the present invention.

[0016] Figure 2 The OAM of the specific embodiment of the present invention 11 Mode field diagram, phase diagram, and coupling efficiency diagram of the mode.

[0017] Figure 3 The OAM of the specific embodiment of the present invention 21 Mode field diagram, phase diagram, and coupling efficiency diagram of the mode.

[0018] Figure 4 The OAM of the specific embodiment of the present invention 31 Mode field diagram, phase diagram, and coupling efficiency diagram of the mode. DETAILED DESCRIPTION

[0019] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0020] See also Figure 1 The present invention provides a negative curvature annular fiber mode selective coupler, which is composed of two negative curvature annular optical fibers of the same structure bonded together, the bonded portion is a coupling region, the unbonded portion forms four ports as input and output ports respectively, and the power ratio of the collinear output end and the cross output end is determined by the coupling length L;

[0021] The cut surfaces of the two negative curvature annular optical fibers are both ground and then bonded using refractive index matching glue.

[0022] The negative curvature annular optical fiber has a cladding air hole outside the ring core, 6 hollow capillaries with a thickness of t1 are arranged outside the cladding air hole, and the outer cladding is a hollow capillary with a thickness of t2.

[0023] The base material of the negative curvature annular optical fiber is pure silicon dioxide, and the refractive index n0 is 1.444 at a wavelength of 1.55 μm.

[0024] The inner circle radius of the ring core is r0=1.2 μm, and the outer circle radius is r1=3.3 μm.

[0025] The rectangular air holes of the outer cladding of the ring core have a width of d1 = 1.6 μm, a height of d2 = 1.4 μm, a spacing distance between two air holes of k = 2 μm, and a radius of r2 = 4.8 μm.

[0026] The thickness t1 of the hollow capillary outside the cladding air hole is 0.72 μm, and its outer radius is r3 = 4.8 μm.

[0027] The center spacing distance D between the two ring cores in the coupling zone is adjustable, and D is 8-9.6 μm.

[0028] The following is further described in conjunction with specific embodiments:

[0029] In this embodiment, the center spacing distance between the two annular fiber cores is D=8.3 μm.

[0030] Under the above parameters, the negative curvature annular fiber mode selective coupler of the present invention can support up to OAM 01 (<0, ±1>), OAM 11 (<±1, 1>), OAM 21 (<±2, ±1>), OAM 31 The stable generation and transmission of 12 OAM modes including (<±3, ±1>) are shown in the figure. Figures 2 to 4 shown.

[0031] Figure 2 OAM generated by the negative curvature ring fiber mode selective coupler at different lengths 11 Mode field diagram, phase diagram and coupling efficiency diagram of the (<+1,+1>) mode, the input light wavelength is 1.55μm, the spacing distance D=8.3μm, when the input port 1 inputs OAM 11 In mode, both output ports of the coupler (port 3 and port 4) can generate OAM 11 mode, the specific power distribution is related to the fiber coupling length L, and the coupling efficiency at the cross output end is as high as 99.3%.

[0032] Figure 3 OAM generated by the negative curvature ring fiber mode selective coupler at different lengths 21 Mode field diagram, phase diagram and coupling efficiency diagram of the (<+2,+1>) mode, the input light wavelength is 1.55μm, the spacing distance D=8.3μm, when the input port 1 inputs OAM 21 In mode, both output ends of the coupler can generate OAM 21 mode, the specific power distribution is related to the fiber coupling length L, and the coupling efficiency at the cross output end is as high as 98.8%.

[0033] Figure 4 OAM generated by the negative curvature ring fiber mode selective coupler at different lengths 31 Mode field diagram, phase diagram and coupling efficiency diagram of the (<+3,+1>) mode, with an input wavelength of 1.55 μm and a spacing of D = 8.3 μm. When OAM is input to input port 1 31 In mode, both output ends of the coupler can generate OAM 31 mode, the specific power distribution is related to the fiber coupling length L, and the coupling efficiency at the cross output end is as high as 80.6%.

[0034] In summary, the present invention has the following advantages:

[0035] 1. The structure is stable, which not only preserves the fiber structure originally used to transmit the OAM mode, but also does not affect the integrity of the mode in the coupling area.

[0036] 2. Compared with the current fiber couplers, it can achieve higher coupling efficiency and mode purity with low insertion loss in high-order OAM modes.

[0037] 3. By adjusting the coupling distance and input mode, the splitting ratio and coupling mode can be adjusted, laying the foundation for the construction of an all-fiber MDM communication system.

[0038] What is disclosed above is only one or more preferred embodiments of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiments and making equivalent changes according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A negative curvature annular fiber mode selective coupler, characterized in that: It is composed of two negative curvature annular optical fibers of the same structure bonded together. The bonded part is the coupling area, and the unbonded part forms four ports as input and output ports respectively. The power ratio of the collinear output end and the cross output end is determined by the coupling length L. The cut surfaces of the two negative curvature annular optical fibers are both ground and then bonded using refractive index matching glue.

2. The negative curvature annular fiber mode selective coupler according to claim 1, characterized in that: The negative curvature annular optical fiber has a cladding air hole outside the ring core, 6 hollow capillaries with a thickness of t1 are arranged outside the cladding air hole, and the outer cladding is a hollow capillary with a thickness of t2.

3. The negative curvature annular fiber mode selective coupler according to claim 2, characterized in that: The base material of the negative curvature annular optical fiber is pure silicon dioxide, and the refractive index n0 is 1.444 at a wavelength of 1.55 μm.

4. The negative curvature annular fiber mode selective coupler according to claim 3, characterized in that: The inner circle radius of the ring core is r0=1.2 μm, and the outer circle radius is r1=3.3 μm.

5. The negative curvature annular fiber mode selective coupler according to claim 4, characterized in that: The rectangular air holes of the outer cladding of the ring core have a width of d1 = 1.6 μm, a height of d2 = 1.4 μm, a spacing distance between two air holes of k = 2 μm, and a radius of r2 = 4.8 μm.

6. The negative curvature annular fiber mode selective coupler according to claim 5, characterized in that: The thickness t1 of the hollow capillary outside the cladding air hole is 0.72 μm, and its outer radius is r3 = 4.8 μm.

7. The negative curvature annular fiber mode selective coupler according to claim 6, characterized in that: The center spacing distance D between the two ring cores in the coupling zone is adjustable, and D is 8-9.6 μm.

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