Mode multiplexer / demultiplexer based on multi-ring-core few-mode fiber

Abstract

The invention discloses a mode multiplexer / demultiplexer based on a multi-ring-core few-mode optical fiber, and belongs to the technical field of optical fiber communication. In order to solve the problems that an existing mode multiplexing and demultiplexing device is high in crosstalk and narrow in working wave band, a multi-ring-core few-mode optical fiber structure and a matched single-mode optical fiber design are mainly adopted, effective refractive index difference distribution of an optical fiber mode is optimized by adjusting the radius and the refractive index of a fiber core, and machined mode selection couplers are combined in a symmetric cascade mode. According to the invention, the inter-mode crosstalk can be obviously reduced, and the working wave band range is widened, so that the information transmission capacity and the multiplexing and demultiplexing performance of a single optical fiber are improved.

Description

Technical Field

[0001] The invention relates to a mode multiplexer / demultiplexer based on a multi-ring core few-mode optical fiber, belonging to the technical field of optical fiber communication. Background Art

[0002] In recent years, with the continuous development of mode division multiplexing technology, mode multiplexer / demultiplexer has become one of the research hotspots in the field of optical fiber communication. At present, the mainstream mode multiplexer / demultiplexer solutions include free space optical type, photon lantern type, multi-plane optical conversion type and all-fiber cascade type. Among them, the all-fiber cascade mode multiplexer / demultiplexer has attracted widespread attention due to its advantages such as low loss, high conversion efficiency, easy cascading and simple processing. This type of multiplexer / demultiplexer realizes mode multiplexing and demultiplexing by converting the fundamental mode in single-mode fiber into the high-order mode in few-mode fiber, and converting the high-order mode in few-mode fiber into the fundamental mode in single-mode fiber. However, the current research work lacks in-depth research on the crosstalk reduction and working band expansion of all-fiber cascade mode multiplexers / demultiplexers.

[0003] The all-fiber cascade mode multiplexer / demultiplexer is composed of multiple mode selective couplers cascaded. Among them, each mode selective coupler includes a few-mode fiber and a corresponding matching single-mode fiber. Its working principle is the matching between the effective refractive index of each mode in the few-mode fiber and the matching single-mode fiber base mode. However, the current mode multiplexer / demultiplexer is often made based on single-ring core few-mode fiber and ordinary single-mode fiber. This will bring the following two problems: First, there are often some adjacent modes with a small effective refractive index difference in single-ring core few-mode fiber, which makes the crosstalk of the mode multiplexing and demultiplexing device at a large level. Second, due to the inconsistent effective refractive index change trend of each mode in each optical fiber at different wavelengths, the mode selective coupler can only achieve perfect matching of the effective refractive index at a specific wavelength. Therefore, when the mode multiplexer / demultiplexer works at other wavelengths, problems such as increased loss, reduced conversion efficiency, and increased crosstalk usually occur, and the farther away from the matching wavelength, the more serious the problem is, which is not conducive to the compatibility of mode division multiplexing technology with the current wavelength division multiplexing system. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention proposes a mode multiplexer / demultiplexer based on multi-ring core few-mode optical fiber, aiming to reduce the crosstalk level in the mode multiplexing and demultiplexing process and broaden the working band, thereby improving the information transmission capacity of a single optical fiber.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A mode multiplexer / demultiplexer based on multi-ring core few-mode optical fiber, comprising:

[0007] Multi-ring core few-mode fiber: As the main channel, it adopts a multi-ring core structure. Different rings have different refractive index distributions, supporting multiple high-order modes. The effective refractive index difference between adjacent modes is evenly distributed.

[0008] Multiple matching single-mode optical fibers: each matching single-mode optical fiber is coupled with a mode of the multi-ring core few-mode optical fiber, and the effective refractive index of the matching single-mode optical fiber is matched with the effective refractive index of the corresponding high-order mode of the multi-ring core few-mode optical fiber;

[0009] Among them, a mode selective coupler is made of a multi-ring core few-mode optical fiber and a corresponding matching single-mode optical fiber. The mode selective coupler is used to perform mode coupling or decoupling of optical signals between the multi-ring core few-mode optical fiber and the matching single-mode optical fiber; multiple mode selective couplers are connected in a symmetrical cascade manner to form a mode multiplexer / demultiplexer structure.

[0010] Furthermore, the core refractive index of the multi-ring-core few-mode optical fiber is in the range of 1.447-1.458 at 1550 nm.

[0011] Further, the core refractive index of the matched single-mode optical fiber is in the range of 1.446-1.459 at 1550 nm.

[0012] Furthermore, the matching single-mode optical fiber makes its own fundamental mode match the effective refractive index of the corresponding mode in the multi-ring core few-mode optical fiber by adjusting the optical fiber core radius and the core refractive index.

[0013] Furthermore, the effective refractive index matching refers to the effective refractive index matching within the wavelength range of 1460-1630 nm.

[0014] Furthermore, the mode selective coupler is made by combining a multi-ring core few-mode optical fiber and a corresponding matching single-mode optical fiber through side polishing or D-type optical fiber processing.

[0015] Furthermore, a single-mode jumper is fused onto the multi-ring core few-mode optical fiber core of a mode selective coupler of the cascaded mode multiplexer / demultiplexer to achieve base mode multiplexing / demultiplexing.

[0016] The beneficial effects achieved by the present invention are as follows:

[0017] 1. The present invention adopts a multi-ring core few-mode optical fiber structure to make the effective refractive index difference between adjacent modes of the optical fiber evenly distributed, reduce inter-mode crosstalk, significantly enhance the selectivity of mode multiplexing and demultiplexing, achieve ultra-low inter-mode crosstalk, and improve system performance.

[0018] 2. The present invention designs a matching step-structured single-mode optical fiber for each mode supported by the few-mode optical fiber, and by adjusting the core radius and refractive index, makes the effective refractive index difference between the matching single-mode optical fiber base mode and the few-mode optical fiber mode as small as possible within an ultra-wide wavelength range, thereby broadening the operating band range of the mode multiplexer / demultiplexer.

[0019] 3. The present invention processes the multi-ring core few-mode optical fiber and the matching single-mode optical fiber into a mode selective coupler, and assembles the multiplexer / demultiplexer in a symmetrical cascade manner, so that it has the advantages of ultra-wideband, ultra-low crosstalk and high selectivity, thereby greatly improving the information transmission capacity and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural diagram of a mode multiplexer / demultiplexer based on multi-ring core few-mode optical fiber of the present invention.

[0021] Figure 2 It is a refractive index profile diagram of the multi-ring core few-mode optical fiber and the matching single-mode optical fiber of the present invention.

[0022] Figure 3 This is a diagram showing the effective refractive index matching between the LP-m mode of the multi-ring core few-mode optical fiber of the present invention and the base mode of the matching single-mode optical fiber.

[0023] Figure 4 It is a structural diagram of the mode multiplexer / demultiplexer of the 4-LP mode of the embodiment.

[0024] Figure 5 FIG. 4 is a refractive index profile diagram of a 4-LP mode three-ring core few-mode optical fiber and a matching single-mode optical fiber according to an embodiment.

[0025] Figure 6 It is a diagram showing the effective refractive index matching between the higher-order modes of the three-ring core few-mode optical fiber of the 4-LP mode of the embodiment and the fundamental mode of the matching single-mode optical fiber. DETAILED DESCRIPTION

[0026] In order to make the various technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and easy to understand, they are described in detail below with reference to the accompanying drawings.

[0027] The present invention discloses a mode multiplexer / demultiplexer based on multi-ring core few-mode optical fiber, the overall structure of which is as follows: Figure 1 As shown, a multi-ring core few-mode fiber and multiple matching single-mode fibers (SMFs) are used, and the mode multiplexer couples the optical signals in the multiple single-mode fibers to specific high-order modes in the multi-ring core few-mode fibers through a mode selective coupler (MSC); the mode demultiplexer decouples the specific modes in the multi-ring core few-mode fibers back to the matching single-mode fibers through the mode selective coupler.

[0028] 1. Multi-ring core few-mode optical fiber

[0029] Since the crosstalk between modes is mainly related to the effective refractive index difference between modes, the present invention uses a multi-ring core structure to make the effective refractive index difference between adjacent modes of the optical fiber more evenly distributed, reduce the inter-mode crosstalk caused by the mode multiplexer / demultiplexer, and enhance the selectivity of mode multiplexing and demultiplexing. The multi-ring core few-mode optical fiber designed by the present invention uses a multi-ring core structure. Figure 2 The left part shows the refractive index profile of the multi-ring core of the multi-ring core few-mode optical fiber, and different refractive indices correspond to different modes LP-m (LP-1, LP-2, ..., LP-k). The core refractive index of the multi-ring core few-mode optical fiber designed by the present invention ranges from 1.447 to 1.458 at 1550nm.

[0030] 2. Matching single-mode optical fiber

[0031] The present invention designs a matching single-mode optical fiber for each mode of the multi-ring core few-mode optical fiber. Figure 2 The right part shows the measured refractive index profiles of multiple matched single-mode fibers.

[0032] The present invention designs a matching single-mode optical fiber by adjusting the optical fiber core radius and the core refractive index. Figure 3 As shown, for the LP-m mode, the effective refractive index of the LP-m mode and the LP-1 mode of the matching single-mode fiber under the ultra-wide band range is calculated by scanning the parameters of the core radius and the core refractive index, and finally the matching single-mode fiber parameters that meet the approximately equal effective refractive index with the LP-m mode in the ultra-wide wavelength range are determined. The core refractive index of the matching single-mode fiber designed by the present invention ranges from 1.446 to 1.459 at 1550nm.

[0033] The designed multi-ring core few-mode optical fiber and the corresponding matching single-mode optical fiber can be processed into a mode selective coupler by side polishing, D-type optical fiber, etc. The processed mode selective coupler is symmetrically cascaded into a mode multiplexer / demultiplexer.

[0034] For a mode multiplexer / demultiplexer based on a multi-ring core few-mode optical fiber of the present invention, the following embodiments are specifically described by taking a 4-LP mode three-ring core few-mode optical fiber and a matching single mode as an example.

[0035] Figure 4The structure diagram of the mode multiplexer / demultiplexer of the 4-LP mode is composed of two LP11, LP21, and LP02 mode selection couplers and two sections of single-mode fiber jumpers. The multiplexing order is LP01 mode, LP11 mode, LP21 mode, and LP02 mode. The demultiplexing order is symmetrical. Since the LP01 mode mode field of the 4-LP mode three-ring core few-mode fiber used in this embodiment is not much different from the LP01 mode mode field of the ordinary single-mode fiber, the multiplexing and demultiplexing of the LP01 mode is realized by the method of few-mode fiber center injection.

[0036] Figure 5 The left part is the core refractive index profile of the designed 4-LP mode three-ring core few-mode fiber. The effective refractive index difference between adjacent modes is 1.93×10 -3 , 2.99×10 -3 , 1.90×10 -3 . Figure 5 The right part shows the measured refractive index profiles of three matched single-mode fibers.

[0037] Figure 6 The effective refractive index matching between the high-order modes of the three-ring core few-mode fiber and the three matching single-mode fiber base modes in the range of 1460-1630nm is shown. It can be seen that in the range of 1460-1630nm, the effective refractive indexes of the three high-order modes and the corresponding matching single-mode fiber LP01 base mode are basically equal. The maximum difference of the LP11 mode is 7×10 -5 , the maximum difference in LP21 mode is 3.8×10 -4 , the maximum difference in LP02 mode is 4.1×10 -4 .

[0038] This embodiment adopts the side polishing method to make the mode selection coupler. The prepared mode selection coupler is fused with multi-ring core few-mode optical fibers in the order of LP11, LP21, and LP02 modes, and cascaded into a high-order mode multiplexer. At the same time, a high-order mode demultiplexer is cascaded by fusing multi-ring core few-mode optical fibers in the order of LP02, LP21, and LP11 modes. In the cascaded mode multiplexer / demultiplexer, the multi-ring core few-mode optical fibers of the LP11 mode selection coupler are respectively expanded and fused with a single-mode jumper to realize the multiplexing and demultiplexing of the LP01 base mode. At this point, a 4-LP mode mode multiplexer / demultiplexer is made.

[0039] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions of the technical solutions of the present invention made by ordinary technicians in the field should all be included in the protection scope of the present invention. The protection scope of the present invention shall be based on what is defined in the claims.

Claims

1. A mode multiplexer / demultiplexer based on multi-ring core few-mode optical fiber, characterized in that: include: Multi-ring core few-mode fiber: As the main channel, it adopts a multi-ring core structure. Different rings have different refractive index distributions, supporting multiple high-order modes. The effective refractive index difference between adjacent modes is evenly distributed. Multiple matching single-mode optical fibers: each matching single-mode optical fiber is coupled with a mode of the multi-ring core few-mode optical fiber, and the effective refractive index of the matching single-mode optical fiber is matched with the effective refractive index of the corresponding high-order mode of the multi-ring core few-mode optical fiber; Among them, a mode selective coupler is made of a multi-ring core few-mode optical fiber and a corresponding matching single-mode optical fiber. The mode selective coupler is used to perform mode coupling or decoupling of optical signals between the multi-ring core few-mode optical fiber and the matching single-mode optical fiber; multiple mode selective couplers are connected in a symmetrical cascade manner to form a mode multiplexer / demultiplexer structure.

2. The mode multiplexer / demultiplexer according to claim 1, characterized in that: The refractive index of the core of the multi-ring core few-mode optical fiber is in the range of 1.447-1.458 at 1550nm.

3. The mode multiplexer / demultiplexer according to claim 1, characterized in that: The core refractive index of the matched single-mode fiber is in the range of 1.446-1.459 at 1550nm.

4. The mode multiplexer / demultiplexer according to claim 1, characterized in that: Matching single-mode optical fiber adjusts the fiber core radius and the core refractive index to match its own fundamental mode with the effective refractive index of the corresponding mode in the multi-ring core few-mode optical fiber.

5. The mode multiplexer / demultiplexer according to claim 4, characterized in that: The effective refractive index matching refers to the effective refractive index matching within the wavelength range of 1460-1630nm.

6. The mode multiplexer / demultiplexer according to claim 1, characterized in that: The mode selective coupler is made by combining a multi-ring core few-mode optical fiber and a corresponding matching single-mode optical fiber through side polishing or D-type optical fiber processing.

7. The mode multiplexer / demultiplexer according to claim 1, characterized in that: A single-mode jumper is fused onto the multi-ring core few-mode optical fiber core of a mode selective coupler of a cascaded mode multiplexer / demultiplexer to realize base mode multiplexing / demultiplexing.

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