Multi-core hollow photonic band gap fiber

Abstract

The invention relates to the technical field of microstructure optical fibers, in particular to a multi-core hollow photonic band gap optical fiber. The multi-core hollow-core photonic band gap optical fiber comprises an optical fiber body, the optical fiber body comprises a fiber core layer, a cladding is arranged outside the fiber core layer, an outer cladding is arranged outside the cladding, and the outer cladding is a quartz layer; n fiber core holes are formed in the fiber core layer, the number of cladding layers from the center of the optical fiber body to the inner sides of the fiber core holes is Nin, the number of cladding layers from the outer sides of the fiber core holes to the edge of the first cladding layer is Nout, and the number of cladding layers between the two fiber core holes is Nd, so that the transmission loss is not obviously increased, and optical signals can be transmitted by kilometer-level length; the HOMER is obviously increased, and quasi-single-mode transmission can be realized in a bending state; meanwhile, transmission channels are obviously increased, and the effective optical path of the optical fiber sensitive ring can be increased.

Description

Technical Field

[0001] The invention relates to the technical field of microstructure optical fibers, and in particular to a multi-core hollow-core photonic bandgap optical fiber. Background Art

[0002] Hollow-core photonic bandgap fibers have low temperature, irradiation, magnetic field sensitivity, and extremely low bending losses, and have been successfully used in fiber optic gyroscopes. Fiber optic gyroscopes require optical fibers with small fiber diameters and long distances. However, due to the complex multi-layer air hole structure of hollow-core photonic bandgap fibers, their fiber diameters are usually greater than 100 μm; due to the changes in air holes during the drawing process, their lengths are usually only a few kilometers. These shortcomings limit the application of hollow-core photonic bandgap fibers in high-precision miniaturized fiber optic gyroscopes.

[0003] In recent years, multi-core optical fiber has been used in fiber optic gyroscopes due to its high spatial efficiency. It can increase the effective optical path of the fiber sensitive ring, thereby improving the gyroscope accuracy and reducing temperature sensitivity. In traditional multi-core optical fibers for optical communications, mode coupling between cores will produce crosstalk. For this reason, two optical fiber solutions are proposed. One is a weakly coupled multi-core optical fiber structure, which reduces the coupling strength by increasing the core spacing or changing the core refractive index; the other is a strongly coupled multi-core optical fiber structure, which forms a stable transmission supermode in the optical fiber by reducing the core spacing, and obtains the required signal through mode demodulation at the output end. For fiber optic gyroscope applications, since it is necessary to accurately detect the Sagnac phase change in the optical path, it is necessary to select a weakly coupled multi-core optical fiber structure to reduce the coupling between cores. The weakly coupled multi-core optical fiber structure can be divided into two structural schemes: homogeneous core and heterogeneous core. The homogeneous core structure reduces coupling by increasing the core spacing, and the heterogeneous core structure reduces coupling by changing the core refractive index.

[0004] Due to the relatively complex structure and preparation process, there are currently no reports on multi-core hollow-core photonic bandgap fibers. In 2020, the OFS Laboratory in the United States reported a 3.1km long quasi-single-mode transmission hollow-core photonic bandgap fiber cable (DOI: 10.1364 / OFC.2020.Th4B.3), which has a "19cell" type core surrounded by 6 "7cell" type "leakage holes" to couple high-order modes in the core. This structure is similar to a "multi-core" structure. However, since the "leakage hole" is close to the edge of the cladding, the leakage loss is large and light cannot be guided, but this still proves the feasibility of preparing multi-core hollow-core photonic bandgap fibers. Summary of the invention

[0005] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide a multi-core hollow-core photonic bandgap fiber with excellent characteristics of low loss, quasi-single mode, low crosstalk, and low bending sensitivity, which can be applied to high-precision miniaturized fiber optic gyroscopes, increase the effective optical path of the fiber sensitive ring, thereby improving the gyroscope accuracy, and reducing the temperature sensitivity of the gyroscope.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: a multi-core hollow-core photonic bandgap optical fiber, comprising an optical fiber body, the optical fiber body comprising a core layer, a cladding layer is arranged outside the core layer, N core holes are arranged inside the core layer, and the number of cladding layers from the center of the optical fiber body to the inner side of the core hole is N in The number of cladding layers from the outside of the core hole to the edge of the first cladding is N out , the number of cladding layers between the two core holes is N d .

[0007] Furthermore, the optical fiber body structure is homogeneous or heterogeneous.

[0008] Furthermore, the configuration of the core hole includes one or more of 3 cells, 7 cells, and 19 cells.

[0009] Furthermore, the core hole has a hexagonal structure.

[0010] Furthermore, the structural parameters of the optical fiber body include the number of cladding layers along the opposite sides of the hexagonal cladding hole, the number of cladding layers along the diagonal sides of the hexagonal cladding hole, the ratio of the core hole diameter to the original core hole diameter S c , S of adjacent core holes c The difference ΔS c The counts of the number of side cladding layers and the number of diagonal cladding layers are respectively set to N in1 、N in2 、N out1 、N out2 、N d1 、N d2 .

[0011] Furthermore, the structural parameters of the homogeneous optical fiber body are N=3, N in1 =4, N out1 =5, N d2 =7.

[0012] Furthermore, the structural parameters of the homogeneous optical fiber body are N=3, N in2 =5, N out2 =5, N d1 =6.

[0013] Furthermore, the structural parameters of the heterogeneous optical fiber body are N=6, N in1 =4, N out1=5, N of adjacent core holes d1 =2, S of 6 core holes c Alternately 0.95, 1.05, ΔS c =0.1.

[0014] Furthermore, the structural parameters of the heterogeneous optical fiber body are N=6, N in2 =5, N out2 =5, N d2 =3, S of 6 core holes c Alternating to 0.925, 1.05, ΔS c =0.125.

[0015] Furthermore, it also includes an outer cladding, which is arranged outside the cladding; and the outer cladding is a quartz layer.

[0016] It can be seen from the above description of the present invention that, compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. Compared with the traditional hollow-core photonic bandgap optical fiber, the multi-core hollow-core photonic bandgap optical fiber of the present invention has no significant increase in transmission loss, and the optical signal can be transmitted over a kilometer-level length; the HOMER is significantly increased, and quasi-single-mode transmission can be achieved in a bent state; at the same time, the transmission channels are significantly increased, which can increase the effective optical path of the optical fiber sensitive ring.

[0018] 2. The structural complexity of the multi-core hollow-core photonic bandgap fiber of the present invention is not significantly increased, and the preparation process is basically the same as that of the traditional hollow-core photonic bandgap fiber, which has high feasibility.

[0019] 3. The heterogeneous multi-core hollow-core photonic bandgap optical fiber provided by the present invention can make different cores of different sizes by simply controlling the gas pressure of different cores during the fiber drawing process, thereby reducing the difficulty of manufacturing the heterogeneous structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure and parameters of the multi-core hollow-core photonic bandgap optical fiber of the present invention;

[0021] Figure 2 It is a schematic diagram of a counting method of two types of cladding layer numbers in a multi-core hollow-core photonic bandgap optical fiber of the present invention;

[0022] Figure 3 It is a core structure diagram of the multi-core hollow-core photonic bandgap optical fiber of the present invention when Sc=0.9, 1, and 1.1;

[0023] Figure 4 is a structural diagram of two homogeneous multi-core hollow-core photonic bandgap optical fibers in this embodiment;

[0024] Figure 5is a structural diagram of two heterogeneous multi-core hollow-core photonic bandgap optical fibers in this embodiment;

[0025] Reference numerals: 1, core hole, 2, cladding, 3, outer cladding. DETAILED DESCRIPTION

[0026] The technical solutions in the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] Reference Figure 1 As shown, a preferred embodiment of the present invention is a multi-core hollow-core photonic bandgap optical fiber, comprising an optical fiber body, wherein the optical fiber body comprises a core layer 1, a cladding layer 2 is arranged outside the core layer 1, an outer cladding layer 3 is arranged outside the cladding layer 2, and the outer cladding layer 3 is a quartz layer; N core holes are arranged in the core layer 1, and the number of cladding layers from the center of the optical fiber body to the inner side of the core hole is N in The number of cladding layers from the outside of the core hole to the edge of the first cladding is N out , the number of cladding layers between the two core holes is N d , so that its transmission loss does not increase significantly, and the optical signal can be transmitted at a kilometer-level length; and the HOMER is significantly increased, and quasi-single-mode transmission can be achieved in a bent state; at the same time, the transmission channels are significantly increased, which can increase the effective optical path of the optical fiber sensitive ring.

[0029] Its specific structure and parameter design are as follows

[0030] The multi-core hollow-core photonic bandgap fiber has N core holes, each of which has three configurations, namely "3cell", "7cell" and "19cell" structures. The core size increases successively, the corresponding mode field size increases successively, the transmission loss decreases successively, but the single-mode transmission characteristics also decrease successively. Considering the requirements of the fiber optic gyroscope for the mode field size, transmission loss and single-mode characteristics of the optical fiber, the preferred core hole configuration is the "7cell" structure.

[0031] There are two structural types of the multi-core hollow-core photonic bandgap optical fiber. One is a homogeneous multi-core hollow-core photonic bandgap optical fiber, whose cores are of the same size, so the effective refractive index of the fundamental mode transmitted by each core is basically the same; the other is a heterogeneous multi-core hollow-core photonic bandgap optical fiber, whose cores are slightly different in size, so the effective refractive index of the fundamental mode transmitted by each core is different, which can reduce the crosstalk between cores.

[0032] Figure 2 Schematic diagram of two ways of counting the number of cladding layers in the multi-core hollow-core photonic bandgap fiber. The first way is to count along the opposite side of the hexagonal cladding hole, recorded as direction "1" 4, and three layers are counted along this direction, namely the first layer 41, the second layer 42, and the third layer 43; the second way is to count along the diagonal direction of the hexagonal cladding hole, recorded as direction "2" 5, and three layers are counted along this direction, namely the first layer 51, the second layer 52, and the third layer 53.

[0033] The number of cladding layers from the center of the multi-core hollow-core photonic bandgap fiber to the inner side of the core hole 1 is recorded as N in , the number of cladding layers from the outside of the core hole 1 to the edge of the cladding 2 is recorded as N out , the number of cladding layers between the two cores is recorded as N d The above cladding layer numbers include two counting methods: direction "1" and direction "2", which are recorded as N in1 、N in2 、N out1 、N out2 、N d1 、N d2 .

[0034] The structural parameters of the heterogeneous multi-core hollow-core photonic bandgap optical fiber include, in addition to the above parameters, the ratio of the core diameter to the original core diameter S c , S of adjacent cores c The difference ΔS c . Figure 2 The S in the multi-core hollow-core photonic bandgap optical fiber of the present invention is c Fiber core structure diagram when =0.9, 1, and 1.1.

[0035] First, for N out In the hollow-core photonic bandgap fiber, the periodic hexagonal cladding holes form the cladding 2, which produces the photonic bandgap effect to confine the light wave in the core hole 1 for low-loss transmission. out If N is smaller, the photonic bandgap effect is weaker, resulting in an increase in the CL of the optical fiber. out If N is larger, the limiting loss will be reduced, but the number of cladding holes will increase, which will increase the difficulty of manufacturing multi-core hollow-core photonic bandgap fibers. After simulation optimization design, for the cladding in direction "1", N out1The preferred value is 5. At this time, CL = 0.42 dB / km, which is less than the scattering loss of hollow-core photonic bandgap fiber ~ 25 dB / km, so the total loss is almost unchanged. And compared with the traditional "7cell" structure hollow-core photonic bandgap fiber, its HOMER increases from 1.49 dB to 1.81 dB, indicating that its single-mode transmission characteristics have improved. For the cladding in direction "2", N out2 Preferably, it is 5. At this time, CL = 2.9 dB / km, which is less than the scattering loss of the hollow-core photonic bandgap fiber, which is 25 dB / km. Therefore, the total loss is 27.9 dB / km, which is slightly increased. Compared with the traditional "7-cell" structure hollow-core photonic bandgap fiber, its HOMER increases from 1.49 dB to 2.32 dB, indicating that its single-mode transmission characteristics have increased.

[0036] Then, for N in When the optical fiber is bent, the equivalent refractive index of its cross section changes gradually along the bending direction. The farther away from the center, the greater the change. In traditional hollow-core photonic bandgap fibers, the core is located at the center, that is, N in = 0, bending has almost no effect on its loss and mode characteristics. In a multi-core hollow-core photonic bandgap fiber, the core is no longer located at the center, that is, N in is no longer 0. At this time, bending will affect the loss and mode characteristics. After simulation optimization design, when the bending radius R is 1cm, for the cladding in direction "1", N in1 The preferred value is 4. In this bending state, the loss is almost unchanged, and HOMER increases to 5.58 dB, indicating that it can transmit in quasi-single mode. Similarly, for the cladding in direction "2", N in2 The preferred value is 5. In this bending state, the loss remains almost unchanged, HOMER increases to 6.23dB, and quasi-single-mode transmission is also possible.

[0037] Secondly, for homogeneous structures, for N d Optimize the design. Simulate different N d The mode coupling coefficient C between the fundamental modes of two adjacent fiber cores is C. For multi-core hollow-core photonic bandgap fibers used in fiber optic gyroscopes, the length is usually hundreds of meters or kilometers. When C<0.05, the crosstalk between the cores can be reduced to meet the use requirements of fiber optic gyroscopes. After simulation optimization design, when N d1 >5,N d2 >6, C<0.05, the degree of coupling between cores is small.

[0038] Finally, for heterogeneous structures, for N d , S c , ΔS c Optimize the design. When the sizes of the fiber cores are different, that is, S c When taking different values, the fundamental mode n of their respective transmission effDifferent, can reduce the core mode coupling. Simulation shows that when 0.9 c <1.1, the loss remains almost unchanged, n eff Follow S c The rate of change of is 0.00875. So we can let S c Taking different values ​​in [0.9, 1.1], the fundamental mode n of each fiber core eff Different, effectively reducing the core mode coupling. d >1 can reduce the core coupling. However, in the bent state, the equivalent refractive index of the fiber fundamental mode changes with the bending radius R. For two d , the average effective mode refractive index is n eff , the effective mode refractive index difference is Δn eff When R approaches the critical bending radius R c =n eff Λ d / Δn eff When N d1 ≤5 or N d2 ≤6, mode coupling will occur. eff Follow S c The change in Δn is very small, while eff With ΔS c Change, Λ d Follow N d Therefore, it is necessary to optimize the design of the ΔS of the two fiber cores. c With N d , so that R c The value of is far away from the bending radius R of the heterogeneous multi-core hollow-core photonic bandgap fiber in the fiber gyroscope to reduce the mode coupling between the cores. Usually, R>25mm in the hollow-core photonic bandgap fiber gyroscope, so let R c <25mm can meet the requirements.

[0039] Figure 4 These are two homogeneous multi-core hollow-core photonic bandgap fibers obtained based on the above optimization design results. Figure 4 The structural parameters of the homogeneous multi-core hollow-core photonic bandgap fiber in (a) are N=3, N in1 =4, N out1 =5, N d2 =7, its transmission loss is 25.3dB / km, HOMER in the bending state is 5.58dB, and the core-to-core mode coupling coefficient C is 0.026. Figure 4 The structural parameters of the homogeneous multi-core hollow-core photonic bandgap fiber in (b) are N=3, N in2 =5, N out2 =5, N d1 ​=6, its transmission loss is 28.1dB / km, HOMER is 6.23dB in the bending state, and the core mode coupling coefficient C is 0.055. Both can achieve low-loss quasi-single-mode transmission with low crosstalk between cores.

[0040] Figure 5 Based on the above optimization design results, two heterogeneous multi-core hollow-core photonic bandgap fibers are obtained. Figure 5 The structural parameters of the heterogeneous multi-core hollow-core photonic bandgap fiber in (a) are N=6, N in1 =4, N out1 =5, N of adjacent cores d1 =2, S of 6 cores c Alternately 0.95, 1.05, ΔS c = 0.1, the maximum transmission loss is 28.94dB / km, the HOMER in the bending state is 5.58dB, and the R corresponding to the adjacent cores is c It is 22.18mm. Figure 5 The structural parameters of the homogeneous multi-core hollow-core photonic bandgap fiber in (b) are N=6, N in2 =5, N out2 =5, N d2 =3, S of 6 cores c Alternating to 0.925, 1.05, ΔS c =0.125, the maximum transmission loss is 29.85dB / km, HOMER is 6.23dB in the bending state, R c is 17.86mm. Both can achieve low-loss quasi-single-mode transmission, and when the bending radius R is far away from R c When the core is connected to the MOSFET, the crosstalk between the cores is extremely small.

[0041] Under the premise that no conflict occurs, those skilled in the art may freely combine and superimpose the above-mentioned additional technical features.

[0042] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A multi-core hollow-core photonic bandgap optical fiber, characterized in that: The optical fiber body includes a core layer, a cladding layer is arranged outside the core layer, N core holes are arranged inside the core layer, and the number of cladding layers from the center of the optical fiber body to the inner side of the core hole is N in The number of cladding layers from the outside of the core hole to the edge of the first cladding is N out , the number of cladding layers between the two core holes is N d .

2. The multi-core hollow-core photonic bandgap optical fiber according to claim 1, characterized in that: The optical fiber body structure is homogeneous or heterogeneous.

3. The multi-core hollow-core photonic bandgap optical fiber according to claim 1, characterized in that: The configuration of the core hole includes one or more of 3 cells, 7 cells, and 19 cells.

4. The multi-core hollow-core photonic bandgap optical fiber according to claim 2, characterized in that: The fiber core hole is in a hexagonal structure.

5. The multi-core hollow-core photonic bandgap optical fiber according to claim 4, characterized in that: The structural parameters of the optical fiber body include the number of cladding layers along the opposite sides of the hexagonal cladding hole, the number of cladding layers along the diagonal sides of the hexagonal cladding hole, the ratio of the core hole diameter to the original core hole diameter S c , S of adjacent core holes c The difference ΔS c The counts of the number of side cladding layers and the number of diagonal cladding layers are respectively set to N in1 、N in2 、N out1 、N out2 、N d1 、N d2 .

6. The multi-core hollow-core photonic bandgap optical fiber according to claim 5, characterized in that: The structural parameters of the homogeneous optical fiber body are N=3, N in1 =4, N out1 =5, N d2 =7.

7. The multi-core hollow-core photonic bandgap optical fiber according to claim 5, characterized in that: The structural parameters of the homogeneous optical fiber body are N=3, N in2 =5, N out2 =5, N d1 =6.

8. The multi-core hollow-core photonic bandgap optical fiber according to claim 5, characterized in that: The structural parameters of the heterogeneous optical fiber body are N=6, N in1 =4, N out1 =5, N of adjacent core holes d1 =2, S of 6 core holes c Alternately 0.95, 1.05, ΔS c =0.

1.

9. The multi-core hollow-core photonic bandgap optical fiber according to claim 5, characterized in that: The structural parameters of the heterogeneous optical fiber body are N=6, N in2 =5, N out2 =5, N d2 =3, S of 6 core holes c Alternating to 0.925, 1.05, ΔS c =0.

125.

10. The multi-core hollow-core photonic bandgap optical fiber according to claim 1, characterized in that: It also includes an outer cladding layer, which is arranged outside the cladding layer; and the outer cladding layer is a quartz layer.

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