Multi-core polarization-maintaining microstructure photonic crystal fiber

Abstract

The invention relates to a multi-core polarization-maintaining microstructure photonic crystal fiber, which comprises a common cladding and a plurality of polarization-maintaining core areas, each polarization-maintaining core area comprises a fiber core and an air hole dot matrix which is tightly arranged around the fiber core, the fiber core is positioned at the center of the air hole dot matrix, at least one pair of small-diameter air holes is arranged at the air hole dot matrix positions on the left side and the right side adjacent to the fiber core, at least one pair or one large-diameter air hole is formed in the upper side air hole dot matrix and the lower side air hole dot matrix adjacent to the fiber core, the diameter of the small-diameter air holes is smaller than that of the air holes in the air hole dot matrixes, and the diameter of the large-diameter air holes is larger than that of the air holes in the air hole dot matrixes. By flexibly adjusting the aperture change of the air holes, the symmetry of the optical fiber structure is destroyed, and the high birefringence performance of stress-free layer addition is realized. The microstructure multi-core optical fiber for simultaneous transmission of multiple independent channels is formed, the spectrum efficiency can be greatly enhanced, and the transmission capacity of the optical fiber is multiplied; meanwhile, a receiving end system is simplified, system cost is saved, time delay is shortened, and high-frequency exchange of data is facilitated.

Description

Technical Field

[0001] The present invention relates to a multi-core polarization-maintaining microstructure photonic crystal fiber, which has both polarization-maintaining characteristics and multi-channel transmission performance, and belongs to the field of optical fiber technology. Background Art

[0002] Driven by the digitalization process, digital switching industries such as artificial intelligence and the Internet of Things have developed rapidly. The wide spread of new digital networks has put forward strict requirements for the communication industry and key media. The transmission capacity of single-mode optical fibers, the traditional communication medium, has approached the physical limit. Therefore, it is urgent to explore optical fiber communication technologies with high spectral efficiency, ultra-large capacity, high signal quality, and high stable transmission performance.

[0003] Multi-core fiber (Multi-core Fiber) based on space-division multiplexing technology is one of the most promising solutions for the development of high-capacity coherent communication technology. Different from the single-core channel of traditional step-type optical fibers, multi-core fibers use the same cladding space to simultaneously transmit multiple core channels, and adopt self-coherent detection technology to greatly enhance the spectral efficiency and double the transmission capacity of optical fiber communication. In addition, the homodyne self-coherent communication system with multi-core fiber as the core can reduce the space requirement of the communication network laying project based on the high cladding space utilization rate of the transmission medium, forming an economic cost advantage; on the other hand, based on the high-efficiency spectral advantage of coherent optical communication, it can reduce the complexity of the DSP calculation process and form power consumption savings.

[0004] In actual situations, as described in Patent CN103399374A, the optical fiber medium used in the self-coherent detection system lacks the ability to maintain polarization characteristics. It is necessary to add a polarization control device to the detection system to achieve the characterization of random polarization modes, which additionally increases the structural complexity of the self-coherent detection system, forms a longer signal processing time delay, and is not conducive to high-frequency data exchange in a short time. Although the ring-doped four-core photonic crystal fiber proposed in Patent Application No. CN102819062A can support multi-core transmission, it lacks polarization-maintaining ability and cannot achieve polarization control of the signal light, which is also not conducive to the simplification of the self-coherent detection system. The proposed design of multi-core polarization-maintaining fiber requires the introduction of a doped stress area in the fiber cladding. The polarization-maintaining multi-core fiber designed based on the stress principle in Patent Application No. CN201910539234.6 needs to introduce a large stress area in the fiber cladding by doping, which limits the evolution of the small diameter of the fiber size. Patent Application No. CN113075763B proposes a design of multi-core panda-type polarization-maintaining fiber. This fiber co-axially configures multi-point stress rods outside the core layer to achieve polarization maintenance, and a special flexible fiber coupling connection device must be configured to ensure good polarization effect, which additionally increases the structural complexity of the self-coherent transmission system. In Invention Patent CN 114185126 A, a stress-type polarization-maintaining multi-core photonic crystal fiber design is adopted. Outside the structure of the traditional multi-core photonic crystal fiber, a large boron-doped stress area is introduced to achieve characteristics such as multi-core, polarization-maintaining, and dispersion tunability. The complex micro-structure arrangement of the multi-core photonic crystal in the core area and the introduction of a large stress area force this fiber to be drawn multiple times during the preparation process, making the preparation process complicated and not conducive to actual production. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a multi-core polarization-maintaining micro-structure photonic crystal fiber in view of the deficiencies of the above-mentioned existing technologies. Without adding a stress layer, it still has high birefringence performance and multi-core transmission ability, which is conducive to the simplification of the system structure for high-frequency data exchange in the self-coherent detection system.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: It includes a common cladding and multiple polarization-maintaining core areas. The polarization-maintaining core area is characterized in that it includes a core and an air-hole lattice closely arranged around the core. The core is located at the center of the air-hole lattice. At least one pair of small-diameter air holes is arranged at the air-hole lattice positions on both sides adjacent to the core, and at least one pair or one large-diameter air hole is arranged at the air-hole lattice positions on the other two sides perpendicular to the small-diameter air holes adjacent to the core. The aperture of the small-diameter air holes is smaller than the aperture of the air holes in the air-hole lattice, and the aperture of the large-diameter air holes is larger than the aperture of the air holes in the air-hole lattice.

[0007] According to the above solution, the air-hole lattice is a regular quadrilateral air-hole lattice, and the regular quadrilateral air-hole lattice is 2 to 5 layers.

[0008] According to the above solution, the pore diameters of each pore in the pore lattice are the same, and the spacing between adjacent pore lattice positions is the same.

[0009] According to the above solution, a pair (one on each side) or two pairs (two on each side) of small-diameter pores are arranged in parallel on both sides adjacent to the core.

[0010] According to the above solution, a pair (one on each side) or two pairs (two on each side) of large-diameter pores are arranged in parallel on the other two sides adjacent to the core (the two sides perpendicular to the direction of the small-diameter pores).

[0011] According to the above solution, a large-diameter pore is arranged at a pore lattice position on one side adjacent to the core, and a quartz rod is installed in the corresponding pore lattice on the other side. The quartz rod and the large-diameter pore are symmetrically arranged.

[0012] According to the above solution, a quartz coupling channel is arranged between adjacent polarization-maintaining core regions. The quartz coupling channel is composed of at least one layer of quartz rods with diameters and spacings equivalent (the same or basically the same) to the pore diameters and spacings in the pore lattice, and is used to reduce the coupling effect between the cores.

[0013] According to the above solution, the pore diameter D of the pores in the pore lattice is 1.6 - 10 μm.

[0014] According to the above solution, the spacing Λ between adjacent pore lattice positions in the pore lattice is 4 - 12 μm.

[0015] According to the above solution, the duty cycle D / Λ of the pores in the pore lattice is 0.3 - 0.85.

[0016] According to the above solution, the pore diameter d of the large-diameter pores b is D < d b < (2Λ - D).

[0017] According to the above solution, the pore diameter d of the small-diameter pores s is 0 < d s ≤ 2D / 3.

[0018] According to the above solution, the common cladding diameter is 100 - 300 μm.

[0019] According to the above solution, the common cladding is a pure silica glass layer.

[0020] According to the above solution, the number of polarization-maintaining core regions is 2 - 8.

[0021] According to the above solution, the core is a germanium-doped silica glass layer, or a rare-earth-doped silica glass layer, or a pure silica glass layer.

[0022] The beneficial effects of the present invention are as follows: 1. Based on the capillary stacking foundation of microstructured optical fibers, the core position layout of multi-core optical fibers can be flexibly designed to form a microstructured multi-core optical fiber with multiple independent channels transmitting simultaneously, which can significantly enhance the spectral efficiency and multiply expand the optical fiber transmission capacity. 2. In the air hole area of the polarization-maintaining core region, the air hole aperture can be flexibly adjusted to break the symmetry of the optical fiber structure, achieve the high birefringence performance of adding a stress-free layer, maintain the polarization characteristics of optical signals in the data center, simplify the receiving-end system, save system costs and shorten the time delay, which is beneficial to high-frequency data exchange. 3. Fill the quartz glass rod to construct the quartz coupling channel between the microstructured groups surrounding the core, weaken the influence of optical signal coupling between the cores, and improve the transmission quality of multi-core optical fibers. 4. The square arrangement within the core unit has a stronger cross-sectional area utilization rate and more zoning methods, which is conducive to enriching the adjustment freedom of the core unit and improving the birefringence performance. 5. The single-layer circular arrangement between the core units is conducive to achieving the farthest spacing between the core units and weakening the mutual coupling influence. 6. The original pipes required in different regions designed by the present invention are all circular, with a simple structure, and the change of the air hole aperture can be prepared by using different specifications of capillary tubes or controlling the stretching air pressure in different regions. The circular pipes and the pressure-dividing control process are relatively mature, which is beneficial to realizing mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the end face structure of an embodiment of the present invention.

[0024] Figure 2 Schematic enlarged view of the structure of the polarization-maintaining core region in an embodiment of the present invention.

[0025] Figure 3 Fundamental mode of the x polarization state of the optical fiber in an embodiment of the present invention.

[0026] Figure 4 Fundamental mode of the y polarization state of the optical fiber in an embodiment of the present invention.

[0027] Figure 5 Schematic diagram of the end face structure of Embodiment 11 of the present invention.

[0028] Figure 6 Schematic enlarged view of the structure of the polarization-maintaining core region in Embodiment 12 of the present invention.

[0029] Figure 7 Schematic enlarged view of the structure of the polarization-maintaining core region in Embodiment 13 of the present invention.

[0030] Figure 8 Schematic enlarged view of the structure of the polarization-maintaining core region in Embodiment 14 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The present invention will be further described in detail below in conjunction with the embodiments and drawings of the present invention.

[0032] As shown in one embodiment of the present invention Figure 1 , Figure 2 , it includes a common cladding b and 4 polarization-maintaining core regions a. The cross-section of the common cladding is circular, and the common cladding is a pure silica glass layer; the 4 polarization-maintaining core regions are symmetrically arranged. The polarization-maintaining core region includes a core 1 and an air hole lattice 2 closely arranged around the core. The core is located at the center of the air hole lattice. The core is a pure silica glass layer or other doped quartz glass layer. The diameter of the core is the same as or substantially the same as the pore diameter of the air hole lattice. The air hole lattice is a regular quadrilateral air hole lattice, and the regular quadrilateral air hole lattice has 3 layers. The pore diameter of each air hole in the air hole lattice is the same, and the spacing between adjacent air hole lattice positions is the same. A pair of small-diameter air holes 4 are arranged at the air hole lattice positions on the left and right sides adjacent to the core, and a pair of large-diameter air holes 3 are arranged at the air hole lattice positions on the upper and lower sides adjacent to the core (perpendicular to the direction of the small-diameter air holes). The pore diameter of the small-diameter air holes is smaller than the pore diameter of the air holes in the air hole lattice, and the pore diameter of the large-diameter air holes is larger than the pore diameter of the air holes in the air hole lattice. The small-diameter air holes and the large-diameter air holes are both symmetrically distributed, and the center connection line of the small-diameter air holes intersects with the center connection line of the large-diameter air holes at the core center. A quartz coupling channel c is arranged between adjacent polarization-maintaining core regions. The quartz coupling channel is composed of a layer of quartz rods with a diameter and spacing the same as or substantially the same as the pore diameter and spacing of the air holes in the air hole lattice, forming a quartz coupling channel for reducing the coupling influence between the cores. The fundamental mode of the x polarization state of the polarization-maintaining multi-core microstructure optical fiber (4-core) provided in this embodiment is as Figure 3 shown, and the fundamental mode of the y polarization state is as Figure 4 shown.

[0033] Taking the above embodiment as the basic structure, the structural parameters and polarization-maintaining performance of the polarization-maintaining multi-core microstructure optical fiber (4-core) provided by the present invention will be described in combination with specific numerical values. Table 1 lists the optical fiber structure profiles and birefringence performance parameters of the preferred embodiments 1-10 of the present invention.

[0034] Table 1 Structure of Four-Core Polarization-Maintaining Photonic Crystal Fiber

[0035]

[0036] Based on Table 1, it can be seen that the birefringence coefficients of the optical fiber at a wavelength of 1550 nm are all greater than 1E-5, indicating that the optical fiber has excellent birefringence performance.

[0037] Example 11: Provide a polarization-maintaining multi-core microstructure optical fiber, and the end face structure of the optical fiber is as Figure 5As shown, the multi-core polarization-maintaining microstructure optical fiber includes 3 polarization-maintaining core regions and a common cladding. The 3 polarization-maintaining core regions are arranged such that the center connection lines form an equilateral triangle. The coupling channels are composed of 3 layers of quartz rods with diameters and spacings equivalent to those of the lattice air holes, and are arranged between adjacent polarization-maintaining core regions. The structure of the polarization-maintaining core regions and the rest is the same as that of the previous embodiment.

[0038] Embodiment 12: Provide a polarization-maintaining multi-core microstructure optical fiber. The polarization-maintaining core region is as Figure 6 shown. In the polarization-maintaining core region, there are two pairs of small-diameter air holes arranged at the air hole lattice positions on the left and right sides adjacent to the core, and one pair of large-diameter air holes arranged at the air hole lattice positions on the upper and lower sides adjacent to the core. The regular quadrilateral air hole lattice is 3 layers, and the other structures are the same as those of the previous embodiment, and it can be a 4-core or 3-core structure.

[0039] Embodiment 13: Provide a polarization-maintaining multi-core microstructure optical fiber. The polarization-maintaining core region is as Figure 7 shown. The difference from Embodiment 12 is that in the polarization-maintaining core region, there are two pairs of small-diameter air holes arranged at the air hole lattice positions on the left and right sides adjacent to the core, and two pairs of large-diameter air holes arranged at the air hole lattice positions on the upper and lower sides adjacent to the core. The regular quadrilateral air hole lattice is 3 layers, and the other structures are the same as those of the previous embodiment.

[0040] Embodiment 14: Provide a schematic diagram of the core unit of a polarization-maintaining multi-core microstructure optical fiber. The polarization-maintaining core region is as Figure 8 shown. The difference from Embodiment 1 is that in the polarization-maintaining core region, there are two pairs of small-diameter air holes arranged at the air hole lattice positions on the left and right sides adjacent to the core, and one large-diameter air hole arranged at the air hole lattice position on the lower side adjacent to the core. A quartz rod 5 is installed in the upper air hole lattice, and the quartz rod and the large-diameter air hole are symmetrically arranged up and down. The regular quadrilateral air hole lattice is 3 layers, and the other structures are the same as those of the first embodiment.

Claims

1. A multi-core polarization-maintaining microstructure photonic crystal fiber, comprising a common cladding and a plurality of polarization-maintaining core regions, characterized in that The polarization-maintaining core region includes a core and an air-hole lattice closely arranged around the core. The core is located at the center of the air-hole lattice. At least one pair of small-diameter air holes are arranged at the air-hole lattice positions on both sides adjacent to the core. At least one pair or one large-diameter air hole is arranged at the air-hole lattice positions on the other two sides perpendicular to the small-diameter air holes adjacent to the core. The aperture of the small-diameter air hole is smaller than the aperture of the air holes in the air-hole lattice, and the aperture of the large-diameter air hole is larger than the aperture of the air holes in the air-hole lattice.

2. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1, characterized in that The air-hole lattice is a regular quadrilateral air-hole lattice, and the regular quadrilateral air-hole lattice has 2 to 5 layers.

3. The multi-core polarization-maintaining microstructured photonic crystal fiber according to claim 1 or 2, characterized in that The aperture of each air hole in the air-hole lattice is the same, and the distance between adjacent air-hole lattice positions is the same.

4. The multi-core polarization-maintaining microstructured photonic crystal fiber according to claim 1 or 2, characterized in that One pair or two pairs of the small-diameter air holes are arranged in parallel on both sides adjacent to the core.

5. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1 or 2, characterized in that One pair or two pairs of the large-diameter air holes are arranged in parallel on the other two sides adjacent to the core.

6. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1 or 2, characterized in that One large-diameter air hole is arranged at the air-hole lattice position on one side adjacent to the core, and a quartz rod is installed in the corresponding air-hole lattice on the other side. The quartz rod and the large-diameter air hole are symmetrically arranged.

7. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1 or 2, characterized in that A quartz coupling channel is arranged between adjacent polarization-maintaining core regions. The quartz coupling channel is composed of at least one layer of quartz rods with diameters and spacings equivalent to the aperture and spacing of the air holes in the air-hole lattice, and is used to reduce the coupling effect between the cores.

8. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1 or 2, characterized in that The aperture D of the air holes in the air-hole lattice is 1.6 to 10 μm.

9. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 8, characterized in that The spacing Λ between adjacent air-hole lattice positions in the air-hole lattice is 4 to 12 μm.

10. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 9, characterized in that The duty cycle D / Λ in the air-hole lattice is 0.3 to 0.

85.

11. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 9, characterized in that The large-diameter pore diameter d b is D < d b < (2Λ - D).

12. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 9, characterized in that The aperture diameter d of the small-diameter air holes s is 0 < d s ≤ 2D / 3.

13. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1 or 2, characterized in that The common cladding diameter is 100 to 300 μm.

14. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1 or 2, characterized in that The common cladding is a pure silica glass layer.

15. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1 or 2, characterized in that The number of polarization-maintaining core regions is 2 to 8.

16. The multi-core polarization-maintaining microstructure photonic crystal fiber according to claim 1 or 2, characterized in that The core is a germanium-doped silica glass layer, or a rare-earth-doped silica glass layer, or a pure silica glass layer.

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