A segmented coupled mode division multiplexer based on microstructured optical fiber

Abstract

The present invention belongs to the field of optical fiber communication technology and relates to a segmented coupled mode division multiplexer based on microstructured optical fiber, comprising a substrate material and a central few-mode fiber core; a high refractive index ring is provided in the central few-mode fiber core; a first optical fiber segment is provided for LP to the central few-mode fiber core; 01 Mode conversion, LP 21 Mode conversion, LP 02 The first, second and third single-mode fiber cores of mode conversion and LP to the peripheral few-mode fiber cores 11 The fourth, fifth, and sixth single-mode cores for mode conversion and for transmitting LP 11 The seventh, eighth, and ninth few-mode cores of the mode; the second fiber segment is used to conduct LP to the central few-mode core 11 The tenth few-mode core for mode conversion, used for LP to the central few-mode core 12 The eleventh few-mode core for mode conversion and LP to the central few-mode core 31 The twelfth few-mode fiber core for mode conversion has the characteristics of a large number of conversion modes, high space utilization, low insertion loss and high flux.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber communication and relates to a segmented coupling mode division multiplexer based on microstructure optical fiber. Background Art

[0002] With the rapid development of the internet and 5G mobile communications, the majority of global information data is transmitted at high speeds via optical networks, and demand for data transmission speeds is increasing. This growing demand has also created a bandwidth bottleneck for traditional fiber-optic communication systems, with traditional cable transmission no longer able to meet the demand for high-speed data transmission. Fiber-optic communication, with its advantages of high speed, large capacity, and low loss, has become a mainstream modern communication technology. Within optical communication systems, mode division multiplexing (MDM) is one of the most promising methods for significantly increasing channel capacity by adding a new multiplexing dimension. MDM technology is also gaining increasing attention due to its advantages, such as wide bandwidth, long transmission distances, and high system reliability. In optical communication technology, the performance of MDMs is crucial. MDMs combine or separate multiple optical signals, significantly simplifying optical signal transmission systems. However, traditional technologies have many limitations, such as low efficiency, high noise, and high loss. To improve the performance of traditional mode division multiplexers, a new type of segmented coupled microstructured fiber mode division multiplexer module is created by connecting multiple couplers together, which can significantly improve the performance of the system.

[0003] At present, all-fiber mode converters include long-period fiber grating mode converters, photon lantern mode converters, tapered fiber mode converters, and all-fiber fused-taper structure mode converters. The premise for achieving mode conversion in these schemes is to destroy the fiber waveguide structure (adiabatic taper, cladding polishing, etc.), which leads to difficulties such as poor flexibility, non-reconfigurability, and high manufacturing difficulty.

[0004] Compared to segmented-coupled mode division multiplexers, cascaded mode converters are suitable for weakly coupled mode division multiplexing systems. These optical couplers consist of a near-single-mode and few-mode waveguides, coupling two modes with the same effective refractive index. However, various factors can lead to low coupling efficiency during laboratory fabrication. Furthermore, the multiplexers are bulky, difficult to move, and have a high risk of damage during later use. Summary of the Invention

[0005] In order to overcome the problems existing in the above-mentioned prior art, the present invention proposes a segmented coupled mode division multiplexer based on microstructured optical fiber, which has the advantages of a large number of mode conversions, high space utilization, low insertion loss and high throughput.

[0006] The technical solution of the present invention to solve the above problems is: a segmented coupled mode division multiplexer based on microstructured optical fiber, which is special in that:

[0007] The mode division multiplexer adopts a segmented design, which includes a first optical fiber segment and a second optical fiber segment;

[0008] The first optical fiber segment and the second optical fiber segment both include a base material and a central few-mode core located in the base material;

[0009] The central few-mode fiber core includes a fiber core base and a high refractive index ring located in the fiber core base;

[0010] A segmented design is adopted, which includes a first optical fiber segment and a second optical fiber segment;

[0011] The first optical fiber segment and the second optical fiber segment both include a base material and a central few-mode core located in the base material;

[0012] The central few-mode fiber core includes a fiber core base and a high refractive index ring located in the fiber core base;

[0013] In the first optical fiber segment, the periphery of the central few-mode fiber core is divided into a first layer and a second layer from the inside to the outside; a plurality of single-mode fiber cores and few-mode fiber cores are distributed in the first layer, wherein the few-mode fiber core is a transition fiber core, and a plurality of single-mode fiber cores are distributed in the second layer;

[0014] In the second optical fiber segment, a plurality of few-mode fiber cores are distributed around the central few-mode fiber core;

[0015] The single-mode core input LP of the first layer in the first fiber segment 01 mode, respectively coupling LP to the central core 01 Mode, LP 21 Mode and LP 02 Mode; Single-mode fiber core input LP on the second layer 01 mode, and then mode coupled to the transition core to convert to LP 11 mode, which is finally coupled to the central core in the second section of optical fiber to become LP 11 Mode, LP 12 Mode, LP 31 model;

[0016] The few-mode core in the second optical fiber segment is used for high-order mode conversion to the central few-mode core.

[0017] Furthermore, in the first optical fiber segment, the peripheral portion of the central few-mode core is provided with: 01 The first single-mode core of the mode conversion is used for LP to the central few-mode core 21 The second single-mode core for mode conversion is used to conduct LP to the central few-mode core02 The third single-mode fiber core for mode conversion is used to conduct LP to the peripheral few-mode fiber core 11 The fourth single-mode fiber core for mode conversion is used to conduct LP to the peripheral few-mode fiber core 11 The fifth single-mode core for mode conversion is used to conduct LP to the peripheral few-mode core 11 The sixth single-mode core for mode conversion is used to transmit the transition mode LP 11 The seventh few-mode fiber core is used to transmit the transition mode LP 11 The eighth few-mode core and the transition mode LP for transmission 11 The ninth few-mode core;

[0018] In the second optical fiber segment, the peripheral portion of the central few-mode core is provided with: 11 The tenth few-mode core for mode conversion, used for LP to the central few-mode core 12 The eleventh few-mode core for mode conversion and LP to the central few-mode core 31 Twelfth few-mode core for mode conversion.

[0019] Furthermore, the angle between the center line of the first single-mode fiber core and the central minority-mode fiber core and the center line of the second single-mode fiber core and the central minority-mode fiber core is 120°, the angle between the center line of the second single-mode fiber core and the central minority-mode fiber core and the center line of the third single-mode fiber core and the central minority-mode fiber core is 120°, the angle between the center line of the third single-mode fiber core and the central minority-mode fiber core and the center line of the first single-mode fiber core and the central minority-mode fiber core is 120°; the angle between the center line of the fourth single-mode fiber core and the central minority-mode fiber core and the center line of the fifth single-mode fiber core and the central minority-mode fiber core is 120°, the angle between the center line of the fifth single-mode fiber core and the central minority-mode fiber core and the center line of the sixth single-mode fiber core and the central minority-mode fiber core is 120°, the angle between the center line of the sixth single-mode fiber core and the central minority-mode fiber core and the center line of the fourth single-mode fiber core and the central minority-mode fiber core is 120°. °; the angle between the line connecting the centers of the seventh few-mode core and the central few-mode core and the line connecting the centers of the eighth few-mode core and the central few-mode core is 120°, the angle between the line connecting the centers of the eighth few-mode core and the central few-mode core and the line connecting the centers of the ninth few-mode core and the central few-mode core is 120°, the angle between the line connecting the centers of the ninth few-mode core and the central few-mode core and the line connecting the centers of the seventh few-mode core and the central few-mode core is 120°; the angle between the line connecting the centers of the tenth few-mode core and the central few-mode core and the line connecting the centers of the eleventh few-mode core and the central few-mode core is 120°, the angle between the line connecting the centers of the eleventh few-mode core and the central few-mode core and the line connecting the centers of the twelfth few-mode core and the central few-mode core is 120°, and the angle between the line connecting the centers of the twelfth few-mode core and the central few-mode core and the line connecting the centers of the tenth few-mode core and the central few-mode core is 120°.

[0020] Furthermore, the distances between the centers of the first single-mode core, the second single-mode core, the third single-mode core, the fourth single-mode core, the fifth single-mode core, the sixth single-mode core, the seventh few-mode core, the eighth few-mode core, the ninth few-mode core, the tenth few-mode core, the eleventh few-mode core and the twelfth few-mode core to the exact center of the central few-mode core are: L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, L11, L12, L13, L14, L15, L16, L17, L18, L19, L20, L21, L22, L23, L24, L25, L26, L27, L28, L29, L30, L31, L32, L33, L34, L35, L36, L37, L38, L39, L40, L41, L42, L43, L44, L45, L46, L47, L48, L49, L50, L51, L52, L53, L54, L55 10 、L 11 and L 12 , where L7 = L 10 , L8=L 11 , L9=L 12 .

[0021] Furthermore, the above L1 is 13.42 μm, L2 is 15.79 μm, L3 is 16.11 μm, L4 is 30.33 μm, L5 is 38.06 μm, L6 is 32.70 μm, L7, L 10 All are 15.79μm, L8, L 11 All are 23.52μm, L9, L 12 Both are 18.16μm.

[0022] Furthermore, the diameters and core refractive indexes of the fourth single-mode fiber core, the fifth single-mode fiber core and the sixth single-mode fiber core are equal, and the diameters and core refractive indexes of the seventh few-mode fiber core, the eighth few-mode fiber core and the ninth few-mode fiber core are equal.

[0023] Furthermore, the diameter of the first single-mode fiber core is 5 μm, and the core refractive index is 1.4629 at a wavelength of 1550 nm;

[0024] The diameter of the second single-mode fiber core is 5 μm, and the core refractive index is 1.4570 at a wavelength of 1550 nm;

[0025] The diameter of the third single-mode fiber core is 5 μm, and the core refractive index is 1.4554 at a wavelength of 1550 nm;

[0026] The diameters of the fourth single-mode fiber core, the fifth single-mode fiber core, and the sixth single-mode fiber core are 7 μm, and the core refractive index is 1.4512 at a wavelength of 1550 nm;

[0027] The diameters of the seventh few-mode fiber core, the eighth few-mode fiber core, and the ninth few-mode fiber core are 7 μm, and the core refractive index is 1.4600 at a wavelength of 1550 nm;

[0028] The diameter of the tenth few-mode fiber core is 7 μm, and the core refractive index is 1.4664 at a wavelength of 1550 nm;

[0029] The diameter of the eleventh few-mode fiber core is 7 μm, and the core refractive index is 1.4554 at a wavelength of 1550 nm;

[0030] The diameter of the twelfth few-mode fiber core is 7 μm, and the core refractive index is 1.4583 at a wavelength of 1550 nm.

[0031] Furthermore, the diameter of the above-mentioned central few-mode fiber core is 16μm, the base refractive index is 1.4550 at a wavelength of 1550nm, the center of the high refractive index ring is the center of the optical fiber, the inner circle diameter of the high refractive index ring is 8μm, the ring width is 2μm, and the refractive index of the high refractive index ring is 1.4560 at a wavelength of 1550nm.

[0032] Furthermore, the base material is made of silicon dioxide, and its refractive index is 1.4440 at a wavelength of 1550 nm; the total length of the mode division multiplexer is 16500 μm, the length of the first optical fiber segment is 9000 μm, and the length of the second optical fiber segment is 7500 μm.

[0033] Advantages of the present invention:

[0034] ① The present invention proposes a segmented coupling solution for the first time, achieving control separation in the coupling process of mode multiplexing, effectively reducing the crosstalk impact of traditional multi-mode simultaneous coupling;

[0035] ② The present invention is based on a segmented multi-core optical fiber structure and couples six modes of mode division multiplexer. Compared with the traditional cascade mode multiplexer, it can multiplex six modes simultaneously, greatly improving the number of modes and space utilization;

[0036] ③ The present invention can realize LP through the outer single-mode fiber core and the outer few-mode fiber core in the two-section optical fiber structure. 01 LP 11 LP 02 LP 21 LP 12 LP 31 Six modes can be converted and reused simultaneously. Compared with traditional mode converters, more modes can be converted and integrated in a minimal range.

[0037] ④ The present invention effectively converts LP into 02 and LP 21 The effective refractive index difference of the modes is distinguished to avoid serious crosstalk during mode conversion, which is extremely effective for the high-purity conversion of six modes simultaneously multiplexed by the multiplexer;

[0038] ⑤ The segmented coupled mode division multiplexer designed by the present invention is LP at a wavelength of 1550nm 01 LP 21 LP02 LP 11 LP 12 and LP 31 The mode conversion efficiencies are 99.7%, 98.6%, 98.3% and 92.0%, 86.6%, 97.4% respectively.

[0039] ⑥ The total length of the segmented coupled mode division multiplexer designed by the present invention is 16500μm, the length of the first optical fiber segment is 9000μm, and the length of the second optical fiber segment is 7500μm. The optical fiber used is short and the production cost is low. At the same time, the device produced is small in size, light in weight, and easy to carry.

[0040] ⑦ The present invention solves the contradiction that strongly coupled optical fibers require the side cores to be very close to the central core, while the space near the central core is very limited. While greatly improving the spatial utilization of the optical fiber cross-section, it also realizes the conversion of more high-order modes. The improvement in spatial utilization is also conducive to reducing the difficulty of preparing the space-division multiplexing interface device at the input end. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the cross-sectional structure and mode conversion of the mode division multiplexer of the present invention;

[0042] Figure 2 Schematic diagram of the positional relationship between the single-mode fiber core and the few-mode fiber core in the mode division multiplexer of the present invention;

[0043] Figure 3 Schematic diagram of the diameters of the single-mode fiber core and the few-mode fiber core in the mode division multiplexer of the present invention;

[0044] Figure 4 Schematic diagram of the distances between the single-mode fiber core and the few-mode fiber core and the fiber core center in the mode division multiplexer of the present invention;

[0045] Figure 5 This is a schematic diagram of the method of using the present invention in actual operation;

[0046] Figure 6 The mode division multiplexer of the present invention is LP at a wavelength of 1550nm 01 LP 21 LP 02 LP 11 LP 12 and LP 31 Schematic diagram of the variation of mode coupling efficiency with coupling length.

[0047] Wherein: 1. base material, 2. fiber core base, 3. high refractive index ring, 4. first single-mode fiber core, 5. second single-mode fiber core, 6. third single-mode fiber core, 7. fourth single-mode fiber core, 8. seventh few-mode fiber core, 9. fifth single-mode fiber core, 10. eighth few-mode fiber core, 11. sixth single-mode fiber core, 12. ninth few-mode fiber core, 13. tenth few-mode fiber core, 14. eleventh few-mode fiber core, 15. twelfth few-mode fiber core. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is claimed, but merely represents selected embodiments of the present invention.

[0049] The main feature of the segmented-coupled microstructured fiber mode division multiplexer is the use of microstructured fiber couplers as coupling and separation elements, enabling efficient mode division multiplexing, thereby improving the performance of traditional multimode and single-mode multiplexers. The basic principle of the segmented-coupled microstructured fiber mode division multiplexer is to connect two microstructured elements to a single device, abandoning traditional coupling methods to ensure that the mode propagation on the centerline is unaffected, thereby achieving mode division multiplexing. Microstructured coupler elements each have a certain coupling range. The segmented coupling design allows for two-segment data conversion within the same mode division multiplexer, forming a combined mode division multiplexer module with input and output terminals that can achieve different couplings, resulting in different mode division multiplexing functions depending on the coupling position.

[0050] The present invention provides a segmented coupled mode division multiplexer based on microstructured optical fiber, which adopts a segmented design. Figure 1 As shown, it includes a first optical fiber segment and a second optical fiber segment; the first optical fiber segment and the second optical fiber segment both include a base material 1 and a central few-mode core located in the base material 1.

[0051] The central few-mode core comprises a core substrate 2 and a high refractive index ring 3. The core substrate 2 is the main material of the few-mode core. The high refractive index ring 3 is located inside the central few-mode core substrate 2. The high refractive index ring 3 is used to increase the LP 21 and LP 02 The mode effective refractive index difference of the mode.

[0052] In the first optical fiber segment, the periphery of the central few-mode fiber core is divided into a first layer and a second layer from the inside to the outside; a plurality of single-mode fiber cores and few-mode fiber cores are distributed in the first layer, wherein the few-mode fiber core is a transition fiber core, and a plurality of single-mode fiber cores are distributed in the second layer; in the second optical fiber segment, a plurality of few-mode fiber cores are distributed around the central few-mode fiber core.

[0053] The single-mode core input LP of the first layer in the first fiber segment 01 mode, respectively coupling LP to the central core 01 Mode, LP 21 Mode and LP 02 Mode; Single-mode fiber core input LP on the second layer 01 mode, and then coupled to the transition core to convert it into LP 11 mode, which is finally coupled to the central core in the second section of optical fiber to become LP 11 Mode, LP 12 Mode and LP 31 The few-mode core in the second fiber segment is used to convert high-order modes to the central few-mode core.

[0054] In the first optical fiber segment, the peripheral portion of the central few-mode fiber core includes: 01 The first single-mode fiber core 4 of the mode conversion is used to conduct LP to the central few-mode fiber core 21 The second single-mode fiber core 5 of mode conversion is used to conduct LP to the central few-mode fiber core 02 The third single-mode fiber core 6 of mode conversion is used to conduct LP to the peripheral few-mode fiber core 11 The fourth single-mode fiber core 7 of mode conversion is used to conduct LP to the peripheral few-mode fiber core 11 The fifth single-mode fiber core 9 of mode conversion is used to conduct LP to the peripheral few-mode fiber core 11 The sixth single-mode fiber core 11 for mode conversion is used to transmit the transition mode LP 11 The seventh few-mode core 8 is used to transmit the transition mode LP 11 The eighth few-mode core 10 and the transition mode LP for transmission 11 The ninth few-mode fiber core 12.

[0055] In the second optical fiber segment, the peripheral portion of the central few-mode core is provided with: 11 The tenth few-mode core 13 of the mode conversion is used to conduct LP to the central few-mode core 12 The eleventh few-mode core 14 for mode conversion and the LP 31 The twelfth few-mode fiber core 15 for mode conversion.

[0056] The present invention is a strongly coupled optical fiber, and the distance between each fiber core is relatively close. If you want to use only one section of optical fiber to multiplex six modes at the same time, all side cores must be coupled to the central core. At the same time, the coupling will cause more serious mode crosstalk between the fiber cores, which is not conducive to distinguishing the various modes and is more difficult to prepare.

[0057] Therefore, the present invention adopts segmented coupling. The seventh few-mode core 8, the eighth few-mode core 10, and the ninth few-mode core 12 are transition cores. As mode conduction media, the LP is first input from the fourth single-mode core 7, the fifth single-mode core 9, and the sixth single-mode core 11. 01 mode, and then coupled to the transition core to convert it into LP 11 mode, which is finally coupled to the central core in the second section of optical fiber to become LP 11 Mode, LP 12 Mode and LP 31 mode, thereby improving space utilization and mode stability. The LP in the seventh few-mode fiber core 8, the eighth few-mode fiber core 10, and the ninth few-mode fiber core 12 11 The mode enters the second fiber segment, and the tenth few-mode core 13, the eleventh few-mode core 14 and the twelfth few-mode core 15 of the second fiber segment input the LP from the first fiber segment. 11 mode, and couples to the central core to become LP 11 LP 12 LP 31 model.

[0058] In the first section of optical fiber, LP is simultaneously input to the first single-mode fiber core 4, the second single-mode fiber core 5, the third single-mode fiber core 6, the fourth single-mode fiber core 7, the fifth single-mode fiber core 9 and the sixth single-mode fiber core 11. 01 Mode, because of the addition of transition fiber core, the input distance between fundamental modes is increased, providing a larger operating space when the fundamental mode is input, and at the same time avoiding mutual interference and mode instability between modes during coupling.

[0059] As a preferred embodiment of the present invention, see Figure 2, the angle between the center line of the first single-mode fiber core 4 and the central minority mode core and the center line of the second single-mode fiber core 5 and the central minority mode core is 120°, the angle between the center line of the second single-mode fiber core 5 and the central minority mode core and the center line of the third single-mode fiber core 6 and the central minority mode core is 120°, the angle between the center line of the third single-mode fiber core 6 and the central minority mode core and the center line of the first single-mode fiber core 4 and the central minority mode core is 120°; the angle between the center line of the fourth single-mode fiber core 7 and the central minority mode core and the center line of the fifth single-mode fiber core 9 and the central minority mode core is 120°, the angle between the center line of the fifth single-mode fiber core 9 and the central minority mode core and the center line of the sixth single-mode fiber core 11 and the central minority mode core is 120°, the angle between the center line of the sixth single-mode fiber core 11 and the central minority mode core and the center line of the fourth single-mode fiber core 7 and the central minority mode core is 120°; the angle between the center line of the seventh minority mode core The angle between the center line of the fiber core 8 and the central few-mode fiber core and the center line of the eighth few-mode fiber core 10 and the central few-mode fiber core is 120°, the angle between the center line of the eighth few-mode fiber core 10 and the central few-mode fiber core and the center line of the ninth few-mode fiber core 12 and the central few-mode fiber core is 120°, the angle between the center line of the ninth few-mode fiber core 12 and the central few-mode fiber core and the center line of the seventh few-mode fiber core 8 and the central few-mode fiber core is 120°; the angle between the center line of the tenth few-mode fiber core 10 and the central few-mode fiber core and the center line of the ninth few-mode fiber core 12 and the central few-mode fiber core is 120°; The angle between the center line of the core 13 and the central few-mode core and the center line of the eleventh few-mode core 14 and the central few-mode core is 120°, the angle between the center line of the eleventh few-mode core 14 and the central few-mode core and the center line of the twelfth few-mode core 15 and the central few-mode core is 120°, and the angle between the center line of the twelfth few-mode core 15 and the central few-mode core and the center line of the tenth few-mode core 13 and the central few-mode core is 120°. The outer core positions are distributed in such a way that the inner cores of the first section are arranged in a regular hexagonal structure and the outer cores are distributed in a regular triangle; the outer cores of the second section are distributed in a regular triangle, wherein each core is located at one of the vertices of the hexagon or triangle.

[0060] As a preferred embodiment of the present invention, the diameters and core refractive indexes of the fourth single-mode fiber core 7, the fifth single-mode fiber core 9 and the sixth single-mode fiber core 11 are equal, and the diameters and core refractive indexes of the seventh few-mode fiber core 8, the eighth few-mode fiber core 10 and the ninth few-mode fiber core 12 are equal.

[0061] The diameters of the first single-mode fiber core 4, the second single-mode fiber core 5 and the third single-mode fiber core 6 are equal, and the core refractive indices are different; the core diameters of the fourth single-mode fiber core 7, the fifth single-mode fiber core 9, and the sixth single-mode fiber core 11 are equal, and the refractive indices are equal; the diameters of the seventh few-mode fiber core 8, the eighth few-mode fiber core 10, and the ninth few-mode fiber core 12 are equal, and the refractive indices are the same; the core diameters of the tenth few-mode fiber core 13, the eleventh few-mode fiber core 14, and the twelfth few-mode fiber core 15 are equal, and the refractive indices are different; the diameters of the fourth single-mode fiber core 7, the fifth single-mode fiber core 9, the sixth single-mode fiber core 11, the seventh few-mode fiber core 8, the eighth few-mode fiber 10, the ninth few-mode fiber 12, the tenth few-mode fiber 13, the eleventh few-mode fiber 14, and the twelfth few-mode fiber 15 are equal.

[0062] As a preferred embodiment of the present invention, Figure 2 、 3 As shown, the diameter d1 of the first single-mode fiber core 4 is 5 μm, and the core refractive index n1 is 1.4629 at a wavelength of 1550 nm; the diameter d2 of the second single-mode fiber core 5 is 5 μm, and the core refractive index n2 is 1.4570 at a wavelength of 1550 nm; the diameter d3 of the third single-mode fiber core 6 is 5 μm, and the core refractive index n3 is 1.4554 at a wavelength of 1550 nm; the diameters of the fourth single-mode fiber core 7, the fifth single-mode fiber core 9, and the sixth single-mode fiber core 11 are d4, d5, and d6, respectively. 5, d6, d4, d5, d6 are all 7 μm, and the core refractive index at a wavelength of 1550 nm is n4, n5, n6, and n4, n5, n6 are all 1.4512; the diameters of the seventh few-mode core 8, the eighth few-mode core 10, and the ninth few-mode core 12 are d7, d8, d9, and d7, d8, d9 are all 7 μm, and the core refractive index at a wavelength of 1550 nm is n7, n8, n9, and n7, n8, n9 are all 1.4600; the diameter of the tenth few-mode core 13 is d 10 The core refractive index n is 7μm and 1550nm wavelength. 10 The diameter d of the eleventh few-mode core 14 is 1.4664; 11 The core refractive index n is 7μm and 1550nm wavelength. 11 The diameter d of the twelfth few-mode core 15 is 1.4554; 12 The core refractive index of the fiber is n at 7μm and 1550nm wavelength. 12 is 1.4583; the diameter of the central few-mode fiber core is 16μm, the substrate refractive index is 1.4550 at a wavelength of 1550nm, the center of the high refractive index ring is the center of the optical fiber, the inner diameter of the high refractive index ring is 8μm, the ring width is 2μm, and the refractive index of the high refractive index ring is 1.4560 at a wavelength of 1550nm.

[0063] refer to Figure 4The distances between the centers of the first single-mode fiber core 4, the second single-mode fiber core 5, the third single-mode fiber core 6, the fourth single-mode fiber core 7, the fifth single-mode fiber core 9, the sixth single-mode fiber core 11, the seventh few-mode fiber core 8, the eighth few-mode fiber core 10, the ninth few-mode fiber core 12, the tenth few-mode fiber core 13, the eleventh few-mode fiber core 14, and the twelfth few-mode fiber core 15 and the center of the central few-mode fiber core are: L1, L2, L3, L4, L5, L6, L7, L8, L9, L 10 、L 11 and L 12 , where L7 = L 10 , L8=L 11 , L9=L 12 The above L1 is 13.42μm, L2 is 15.79μm, L3 is 16.11μm, L4 is 30.33μm, L5 is 38.06μm, L6 is 32.70μm, L7, L 10 All are 15.79μm, L8, L 11 All are 23.52μm, L9, L 12 Both are 18.16μm.

[0064] As a preferred embodiment of the present invention, the base material 1 of the optical fiber is silicon dioxide, and its refractive index is 1.4440 at a wavelength of 1550 nm.

[0065] As a preferred embodiment of the present invention, Figure 2 As shown, the central few-mode core includes a core substrate 2 and a high-refractive index ring 3 located on the core substrate. The diameter d0 of the central few-mode core is 16 μm, the substrate refractive index n0 is 1.4550 at a wavelength of 1550 nm, the center of the high-refractive index ring 3 is the center of the optical fiber, the inner diameter of the high-refractive index ring 3 is 8 μm, the ring width is 2 μm, and the refractive index n0 of the high-refractive index ring 3 at a wavelength of 1550 nm is 1.4550. 13 It is 1.456.

[0066] Preferably, if Figure 5 As shown, the total length x of the mode division multiplexer is 16500 μm, the length x1 of the first optical fiber segment is 9000 μm, and the length x2 of the second optical fiber segment is 7500 μm.

[0067] The working performance of the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0068] A segmented coupled mode division multiplexer based on microstructured optical fiber, such as Figure 1As shown, it includes a base material 1, a central few-mode core, a peripheral single-mode core, and a peripheral few-mode core. The central few-mode core includes a core base 2 and a high-refractive-index ring 3. The core base 2 is the main material of the few-mode core, and the high-refractive-index ring 3 is used to distinguish the LP in the few-mode core. 21 and LP 02 The effective refractive index difference between the modes. The total length x of the mode division multiplexer is 16500 μm.

[0069] The angle between the center line of the first single-mode fiber core 4 and the central minority-mode fiber core and the center line of the second single-mode fiber core 5 and the central minority-mode fiber core is 120°, the angle between the center line of the second single-mode fiber core 5 and the central minority-mode fiber core and the center line of the third single-mode fiber core 6 and the central minority-mode fiber core is 120°, the angle between the center line of the third single-mode fiber core 6 and the central minority-mode fiber core and the center line of the first single-mode fiber core 4 and the central minority-mode fiber core is 120°; the angle between the center line of the fourth single-mode fiber core 7 and the central minority-mode fiber core and the center line of the fifth single-mode fiber core 9 and the central minority-mode fiber core is 120°, the angle between the center line of the fifth single-mode fiber core 9 and the central minority-mode fiber core and the center line of the sixth single-mode fiber core 11 and the central minority-mode fiber core is 120°, the angle between the center line of the sixth single-mode fiber core 11 and the central minority-mode fiber core and the center line of the fourth single-mode fiber core 7 and the central minority-mode fiber core is 120°; The angle between the center lines of the core 8 and the central few mode core and the center lines of the eighth few mode core 10 and the central few mode core is 120°, the angle between the center lines of the eighth few mode core 10 and the central few mode core and the center lines of the ninth few mode core 12 and the central few mode core is 120°, the angle between the center lines of the ninth few mode core 12 and the central few mode core and the center lines of the seventh few mode core 8 and the central few mode core is 120°; the angle between the center lines of the tenth few mode core 13 and the central few mode core and the center lines of the eleventh few mode core 14 and the central few mode core is 120°, the angle between the center lines of the eleventh few mode core 14 and the central few mode core and the center lines of the twelfth few mode core 15 and the central few mode core is 120°, and the angle between the center lines of the twelfth few mode core 15 and the central few mode core and the center lines of the tenth few mode core 13 and the central few mode core is 120°. The outer core positions are distributed in such a way that the inner cores of the first section are arranged in a regular hexagonal structure and the outer cores are distributed in a regular triangle; the outer cores of the second section are distributed in a regular triangle, wherein each core is located at one of the vertices of the hexagon or triangle.

[0070] refer to Figure 4The distances between the centers of the first single-mode fiber core 4, the second single-mode fiber core 5, the third single-mode fiber core 6, the fourth single-mode fiber core 7, the fifth single-mode fiber core 9, the sixth single-mode fiber core 11, the seventh few-mode fiber core 8, the eighth few-mode fiber core 10, the ninth few-mode fiber core 12, the tenth few-mode fiber core 13, the eleventh few-mode fiber core 14, and the twelfth few-mode fiber core 15 and the center of the central few-mode fiber core are: L1, L2, L3, L4, L5, L6, L7, L8, L9, L 10 、L 11 and L 12 , among which L1 is 13.42μm, L2 is 15.79μm, L3 is 16.11μm, L4 is 30.33μm, L5 is 38.06μm, L6 is 32.70μm, L7, L 10 All are 15.79μm, L8, L 11 All are 23.52μm, L9, L 12 Both are 18.16μm. The base material 1 of the optical fiber is silica, and its refractive index is 1.4440 at a wavelength of 1550nm. The central few-mode core includes a core substrate 2 and a high-refractive-index ring 3 located on the core substrate. The diameter d0 of the central few-mode core is 16μm, and the base refractive index n0 is 1.4550 at a wavelength of 1550nm. The center of the high-refractive-index ring 3 is the center of the optical fiber. The inner diameter of the high-refractive-index ring is 8μm, the ring width is 2μm, and the refractive index n0 of the high-refractive-index ring at a wavelength of 1550nm is 1.4550. 13 It is 1.4560.

[0071] See also Figure 2 、 3 The diameter d1 of the first single-mode fiber core 4 is 5 μm, and the core refractive index n1 is 1.4629 at a wavelength of 1550 nm; the diameter d2 of the second single-mode fiber core 5 is 5 μm, and the core refractive index n2 is 1.4570 at a wavelength of 1550 nm; the diameter d3 of the third single-mode fiber core 6 is 5 μm, and the core refractive index n3 is 1.4554 at a wavelength of 1550 nm; the diameters of the fourth single-mode fiber core 7, the fifth single-mode fiber core 9, and the sixth single-mode fiber core 11 are d4, d5, and d6, respectively. , d6, d4, d5, d6 are all 7 μm, and the core refractive index at a wavelength of 1550 nm is n4, n5, n6, and n4, n5, n6 are all 1.4512; the diameters of the seventh few-mode core 8, the eighth few-mode core 10, and the ninth few-mode core 12 are d7, d8, d9, and d7, d8, d9 are all 7 μm, and the core refractive index at a wavelength of 1550 nm is n7, n8, n9, and n7, n8, n9 are all 1.4600; the diameter of the tenth few-mode core 13 is d 10 The core refractive index n is 7μm and 1550nm wavelength. 10The diameter d of the eleventh few-mode core 14 is 1.4664; 11 The core refractive index n is 7μm and 1550nm wavelength. 11 The diameter d of the twelfth few-mode core 15 is 1.4554; 12 The core refractive index of the fiber is n at 7μm and 1550nm wavelength. 12 is 1.4583; the diameter of the central few-mode fiber core is 16μm, the substrate refractive index is 1.4550 at a wavelength of 1550nm, the center of the high refractive index ring is the center of the optical fiber, the inner diameter of the high refractive index ring is 8μm, the ring width is 2μm, and the refractive index of the high refractive index ring is 1.4560 at a wavelength of 1550nm.

[0072] This example calculates the crosstalk and loss problems caused by mode conversion in the present invention:

[0073] The present invention is based on a multi-core optical fiber, in which inter-core crosstalk is an important criterion for evaluating device quality. The inter-core crosstalk is specifically manifested as the mode coupling efficiency between the various cores.

[0074] The present invention is calculated and analyzed by using the beam propagation method, and LP at a wavelength of 1550nm is injected into the peripheral single-mode fiber core. 01 mode, and observe the power changes of all other fiber cores in the mode division multiplexer at the same time, as shown in Table 1. Table 1 shows the output power in other fiber cores when each peripheral single-mode optical fiber performs mode conversion at a wavelength of 1550 nm in Example 1.

[0075] We analyze the extinction ratio data given in Table 1. In this invention, the sixth-order linear polarization mode (LP 01 LP 21 LP 02 LP 11 LP 12 and LP 31 ) on the desired mode. Through the simulation of mode coupling, it was found that when only one of the cores at the input end of the optical fiber is passed through, the extinction ratio of the corresponding mode to be converted at the output end of the optical fiber is calculated. The larger the extinction ratio, the smaller the crosstalk of the undesired conversion mode on the desired conversion mode; the smaller the extinction ratio, the greater the crosstalk of all other undesired modes taken into account on the desired mode. 01 LP 21 and LP 02 The values ​​of the third-order mode are that as the transmission length increases, the mode extinction ratio of each expected conversion mode shows an upward trend. After the length is 9000μm, because no mode conversion occurs, the extinction ratio curve tends to be flat; the third-order mode LP 11 LP 12 and LP31 Because the outermost fundamental mode is coupled to the transition core at the total length of 9000μm, and no energy is converted to the central core, the curve tends to be flat. When the transmission length reaches 9000μm, because it is at the junction of the first and second fiber segments, and the corresponding side core parameters are different, the loss increases, and the extinction ratio of the third-order mode begins to rise rapidly. When the transmission length reaches 12000μm from 9000μm, the mode conversion occurs, so the upward trend slows down and still rises. When the transmission distance of the second fiber segment reaches 7500μm, that is, when the total length reaches 16500μm, the three modes reach their maximum value. As the transmission length increases, LP 31 The pattern shows a sharp downward trend, LP 11 and LP 12 There is also a slow decline, indicating that the optimal coupling length has been reached, so the total length of the optical fiber cut is 16500μm.

[0076] Table 1

[0077]

[0078] By analyzing the conversion efficiency of each mode in Table 1, it is obvious that the present invention has very small crosstalk during each mode conversion process at the working wavelength of 1550nm, and can achieve high mode purity for mode modulation and multiplexing.

[0079] The structural parameters designed by the present invention have a high mode conversion efficiency at a wavelength of 1550nm, but in practical applications, considering the adaptability and tolerance of the device, Figure 6 The conversion efficiency variation curves of each mode of the mode division multiplexer at a wavelength of 1550nm are given.

[0080] The above descriptions are merely embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied to other related system fields, are also included in the scope of protection of the present invention.

Claims

1. A segmented coupled mode division multiplexer based on microstructured optical fiber, characterized by: A segmented design is adopted, which includes a first optical fiber segment and a second optical fiber segment; The first optical fiber segment and the second optical fiber segment both comprise a base material (1) and a central few-mode core located in the base material (1); The central few-mode fiber core comprises a fiber core base (2) and a high refractive index ring (3) located in the fiber core base (2); In the first optical fiber segment, the periphery of the central few-mode fiber core is divided into a first layer and a second layer from the inside to the outside; a plurality of single-mode fiber cores and few-mode fiber cores are distributed in the first layer, wherein the few-mode fiber core is a transition fiber core, and a plurality of single-mode fiber cores are distributed in the second layer; In the second optical fiber segment, a plurality of few-mode fiber cores are distributed around the central few-mode fiber core; The single-mode core input LP of the first layer in the first fiber segment 01 mode, respectively coupling LP to the central core 01 Mode, LP 21 Mode and LP 02 Mode; Single-mode fiber core input LP on the second layer 01 mode, and then mode coupled to the transition core to convert to LP 11 mode, which is finally coupled to the central core in the second section of optical fiber to become LP 11 Mode, LP 12 Mode and LP 31 model; The few-mode core in the second optical fiber segment is used for high-order mode conversion to the central few-mode core.

2. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 1, characterized in that: In the first optical fiber segment, the peripheral portion of the central few-mode fiber core includes: 01 The first single-mode fiber core (4) for mode conversion is used to conduct LP to the central few-mode fiber core 21 The second single-mode fiber core (5) for mode conversion is used to conduct LP to the central few-mode fiber core 02 The third single-mode fiber core (6) for mode conversion is used to conduct LP to the peripheral few-mode fiber core 11 The fourth single-mode fiber core (7) for mode conversion is used to conduct LP to the peripheral few-mode fiber core 11 The fifth single-mode fiber core (9) for mode conversion is used to conduct LP to the peripheral few-mode fiber core 11 The sixth single-mode fiber core (11) for mode conversion is used to transmit the transition mode LP 11 The seventh few-mode core (8) is used to transmit the transition mode LP 11 The eighth few-mode core (10) and the transition mode LP for transmission 11 The ninth few-mode fiber core (12).

3. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 2, characterized in that: In the second optical fiber segment, the peripheral portion of the central few-mode core is provided with: 11 The tenth minority mode core (13) for mode conversion is used to conduct LP to the central minority mode core. 12 The eleventh few-mode core (14) for mode conversion and LP to the central few-mode core 31 The twelfth few-mode fiber core (15) for mode conversion.

4. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 3, characterized in that: The angle between the center line of the first single-mode fiber core (4) and the central minority-mode fiber core and the center line of the second single-mode fiber core (5) and the central minority-mode fiber core is 120°, the angle between the center line of the second single-mode fiber core (5) and the central minority-mode fiber core and the center line of the third single-mode fiber core (6) and the central minority-mode fiber core is 120°, and the angle between the center line of the third single-mode fiber core (6) and the central minority-mode fiber core and the center line of the first single-mode fiber core (4) and the central minority-mode fiber core is 120°; The angle between the center line of the single-mode fiber core (7) and the central minority-mode fiber core and the center line of the fifth single-mode fiber core (9) and the central minority-mode fiber core is 120°, the angle between the center line of the fifth single-mode fiber core (9) and the central minority-mode fiber core and the center line of the sixth single-mode fiber core (11) and the central minority-mode fiber core is 120°, the angle between the center line of the sixth single-mode fiber core (11) and the central minority-mode fiber core and the center line of the fourth single-mode fiber core (7) and the central minority-mode fiber core is 120°; the angle between the center line of the seventh minority-mode fiber core (9) and the central minority-mode fiber core and the center line of the sixth single-mode fiber core (11) and the central minority-mode fiber core is 120°; The angle between the center line of the eighth minority mode fiber core (10) and the center minority mode fiber core is 120°, the angle between the center line of the eighth minority mode fiber core (10) and the center minority mode fiber core is 120°, the angle between the center line of the ninth minority mode fiber core (12) and the center minority mode fiber core is 120°, the angle between the center line of the ninth minority mode fiber core (12) and the center minority mode fiber core is 120°, and the angle between the center line of the seventh minority mode fiber core (8) and the center minority mode fiber core is 120°; the angle between the center line of the tenth minority mode fiber core (10) and the center minority mode fiber core is 120°. The angle between the center line of the core (13) and the central minority mode fiber core and the center line of the eleventh minority mode fiber core (14) and the central minority mode fiber core is 120°, the angle between the center line of the eleventh minority mode fiber core (14) and the central minority mode fiber core and the center line of the twelfth minority mode fiber core (15) and the central minority mode fiber core is 120°, and the angle between the center line of the twelfth minority mode fiber core (15) and the central minority mode fiber core and the center line of the tenth minority mode fiber core (13) and the central minority mode fiber core is 120°.

5. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 4, characterized in that: The distances between the centers of the first single-mode fiber core (4), the second single-mode fiber core (5), the third single-mode fiber core (6), the fourth single-mode fiber core (7), the fifth single-mode fiber core (9), the sixth single-mode fiber core (11), the seventh few-mode fiber core (8), the eighth few-mode fiber core (10), the ninth few-mode fiber core (12), the tenth few-mode fiber core (13), the eleventh few-mode fiber core (14) and the twelfth few-mode fiber core (15) to the exact center of the central few-mode fiber core are: L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, L11, L12, L13, L14, L15, L16, L17, L18, L19, L20, L21, L22, L23, L24, L25, L26, L27, L28, L29, L30, L31, L32, L33, L34, L35, L36, L37, L38, L39, L40, L41, L42, L43, L44, L45, L46, L47, L48, L49, L50, L51, L52, L53, L54, L55 10 、L 11 and L 12 , where L7 = L 10 , L8=L 11 , L9=L 12 .

6. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 5, characterized in that: The L1 is 13.42 μm, L2 is 15.79 μm, L3 is 16.11 μm, L4 is 30.33 μm, L5 is 38.06 μm, L6 is 32.70 μm, L7, L 10 All are 15.79μm, L8, L 11 All are 23.52μm, L9, L 12 Both are 18.16μm.

7. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 6, characterized in that: The diameters and core refractive indexes of the fourth single-mode fiber core (7), the fifth single-mode fiber core (9) and the sixth single-mode fiber core (11) are equal, and the diameters and core refractive indexes of the seventh few-mode fiber core (8), the eighth few-mode fiber core (10) and the ninth few-mode fiber core (12) are equal.

8. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 7, characterized in that: The diameter of the first single-mode fiber core (4) is 5 μm, and the core refractive index is 1.4629 at a wavelength of 1550 nm; The diameter of the second single-mode fiber core (5) is 5 μm, and the core refractive index is 1.4570 at a wavelength of 1550 nm; The diameter of the third single-mode fiber core (6) is 5 μm, and the core refractive index is 1.4554 at a wavelength of 1550 nm; The diameters of the fourth single-mode fiber core (7), the fifth single-mode fiber core (9) and the sixth single-mode fiber core (11) are 7 μm, and the core refractive index is 1.4512 at a wavelength of 1550 nm; The diameters of the seventh few-mode fiber core (8), the eighth few-mode fiber core (10) and the ninth few-mode fiber core (12) are 7 μm, and the core refractive index is 1.4600 at a wavelength of 1550 nm; The diameter of the tenth few-mode fiber core (13) is 7 μm, and the core refractive index is 1.4664 at a wavelength of 1550 nm; The diameter of the eleventh few-mode fiber core (14) is 7 μm, and the core refractive index is 1.4554 at a wavelength of 1550 nm; The diameter of the twelfth few-mode fiber core (15) is 7 μm, and the core refractive index is 1.4583 at a wavelength of 1550 nm.

9. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 8, characterized in that: The diameter of the central few-mode fiber core is 16 μm, the base refractive index is 1.4550 at a wavelength of 1550 nm, the center of the high refractive index ring (3) is the center of the optical fiber, the inner diameter of the high refractive index ring (3) is 8 μm, the ring width is 2 μm, and the refractive index of the high refractive index ring is 1.4560 at a wavelength of 1550 nm.

10. The segmented coupled mode division multiplexer based on microstructured optical fiber according to claim 9, characterized in that: The base material (1) is made of silicon dioxide, and its refractive index is 1.4440 at a wavelength of 1550 nm; the total length of the mode division multiplexer is 16500 μm, the length of the first optical fiber segment is 9000 μm, and the length of the second optical fiber segment is 7500 μm.

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