A fiber amplifier with gain-balanced six-mode erbium-doped fiber
By designing a six-mode erbium-doped fiber and fiber amplifier with gain equalization, the problem of excessive gain of the differential mode during multi-mode amplification is solved, and efficient fiber communication is achieved.
Patent Information
- Application Number
- CN202310414216.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-04-18
- Publication Date
- 2025-08-12
- Estimated Expiration
- 2043-04-18
AI Technical Summary
The existing low-mode erbium-doped fiber amplifiers have excessive gain in the differential mode during the multi-mode amplification process, resulting in increased difficulty in long-distance fiber communication.
Using a six-mode erbium-doped fiber with gain equalization, the central downward trench structure of the six-mode erbium-doped fiber is designed, combined with a pump source, isolator and beam combiner to achieve simultaneous amplification of the six mode signals and reduce the differential mode gain.
The fiber amplification with high gain and low differential mode gain is achieved, reducing costs and improving the transmission efficiency of fiber communication.
Smart Images
Figure CN116387949B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to an optical fiber amplifier containing a gain-balanced six-mode erbium-doped optical fiber, belonging to the technical field of optical fiber communication. Background Art
[0002] With the continuous emergence of new technologies such as mobile internet, big data, and cloud computing, the transmission capacity of traditional single-mode optical fiber has approached the theoretical limit defined by Shannon's theorem. The ever-increasing demand for data capacity has become a core issue in optical fiber communication research. Optical fiber has been studied from multiple dimensions, including wavelength, polarization, and space. Among them, mode division multiplexing (MDM) under space division multiplexing (SDM) is considered a key technology that is expected to be used in the next generation of high-capacity optical fiber communications. MDM achieves the goal of increasing optical fiber capacity by increasing the number of modes by superimposing multiple mutually orthogonal spatial modes, with each mode being considered an independent channel. Therefore, MDM technology using few-mode fiber transmission is one of the effective solutions for increasing the transmission capacity of long-distance optical fiber communication systems.
[0003] However, when optical fibers are used for long-distance information transmission, they inevitably encounter problems such as optical signal attenuation, dispersion, crosstalk, and nonlinearity, which greatly complicates signal processing at the receiving end. Few-mode erbium-doped fiber amplifiers (FMAs) effectively compensate for losses in optical signal transmission and significantly reduce costs by simultaneously amplifying multiple modes. However, competition between these multiple modes leads to high differential mode gain, which is detrimental to long-distance optical fiber communication. Therefore, improving the modal gain of optical fiber amplifiers while reducing differential mode gain is a pressing issue. Summary of the Invention
[0004] In order to overcome the deficiencies of the prior art, the present invention provides an optical fiber amplifier containing a gain-balanced six-mode erbium-doped optical fiber.
[0005] A fiber amplifier containing a gain-balanced six-mode erbium-doped fiber comprises: a pump source, a first isolator, a second isolator, a few-mode erbium-doped fiber, and a beam combiner. The input end of the first isolator is connected to the transmission fiber. After passing through the first isolator, signal light is input into the beam combiner together with pump light generated by the pump source. The output end of the beam combiner is connected to the few-mode erbium-doped fiber. The other end of the few-mode erbium-doped fiber is connected to the second isolator. Light after fundamental mode forward pumping is output through the second isolator.
[0006] The few-mode erbium-doped fiber is a six-mode erbium-doped fiber. The core layer of the six-mode erbium-doped fiber is divided into four layers from the inside to the outside, namely the first circular layer, the second annular layer, the third annular layer and the fourth annular layer. The refractive index is from high to low in the order of the second layer, the first layer, the third layer and the fourth layer. The first and second layers are doped with erbium ions. The second layer is divided into the second I layer and the second II layer. The doping concentration is from high to low in the order of the second II layer, the first layer and the second I layer.
[0007] Six-mode erbium-doped fiber supports LP 01 Mode, LP 11a Mode, LP 11b Mode, LP 21a Mode, LP 21b Mode and LP 02 The six modes have a first-layer circular radius of 0.5 μm to 3 μm, a second-layer ring outer circle radius of 6.8 μm to 7.8 μm, a third-layer ring outer circle radius of 8 μm to 11 μm, and a fourth-layer ring width of 1 μm to 3 μm.
[0008] The refractive index distribution of the six-mode erbium-doped fiber is a step-index distribution. The refractive index of the first layer is 1.447 to 1.45, the refractive index of the second layer is 1.451 to 1.453, the refractive index of the third layer is consistent with the refractive index of the cladding, the refractive index of the fourth layer is 1.44 to 1.442, and the refractive index of the cladding is 1.444.
[0009] The erbium ion doping concentration of the first layer is 9×10 24 m -3 to 1×10 25 m -3 , the erbium ion doping concentration of the second layer I is 4×10 24 m -3 to 6×10 24 m -3 , the erbium ion doping concentration of the second layer II is 2×10 25 m -3 to 2.5×10 25 m -3 The ratio of the width of the second I layer ring to the width of the second II layer ring is 3:1.
[0010] The first and second layers of the six-mode erbium-doped optical fiber are made of silicon dioxide material doped with germanium dioxide or phosphorus pentoxide, the third layer is made of silicon dioxide material, and the fourth layer is made of silicon dioxide material doped with boron trioxide.
[0011] The refractive index n4 of the fourth layer 104 of the six-mode erbium-doped optical fiber 504 is equal to the refractive index n3 of the third layer 103. The silicon dioxide material is not doped with boron trioxide. The core layer is divided into two layers from four layers, and the structure is a center-depressed type.
[0012] The effects of the present invention are as follows: a gain-balanced six-mode erbium-doped optical fiber and an optical fiber amplifier are proposed. The central depressed groove auxiliary structure of the six-mode erbium-doped optical fiber can effectively reduce the fusion loss between the six-mode erbium-doped optical fiber and the few-mode gradient-index transmission optical fiber, and by simultaneously amplifying six mode signals, the cost is greatly reduced. At the same time, it also has the amplification characteristics of high gain and low differential mode gain, and can be widely used in optical fiber communications. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] When considered in conjunction with the accompanying drawings, the present invention can be more completely and better understood and its many attendant advantages can be easily known by referring to the following detailed description. However, the drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention, as shown in the figure:
[0014] Figure 1 Schematic diagram of the structure of the six-mode erbium-doped optical fiber of the present invention.
[0015] Figure 2 FIG. 1 is a schematic diagram of the refractive index of the six-mode erbium-doped optical fiber of the present invention.
[0016] Figure 3 Schematic diagram of the gain of the six-mode erbium-doped optical fiber of the present invention.
[0017] Figure 4 FIG2 is a second schematic diagram of the refractive index of the six-mode erbium-doped optical fiber of the present invention.
[0018] Figure 5 It is a structural schematic diagram of the present invention.
[0019] Figure 6 Schematic diagram of the erbium ion doping concentration distribution of the six-mode erbium-doped optical fiber of the present invention. DETAILED DESCRIPTION
[0020] The present invention will be further described below with reference to the accompanying drawings and examples.
[0021] Obviously, many modifications and variations made by those skilled in the art based on the purpose of the present invention fall within the protection scope of the present invention.
[0022] The terms "first" and "second" are used for descriptive purposes only and should not be construed to indicate or imply relative importance or implicitly specify the quantity of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. In the description, "plurality" means two or more, unless otherwise specifically defined.
[0023] Unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," and "fixed" should be interpreted broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.
[0024] Those skilled in the art will understand that unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by those skilled in the art.
[0025] Example 1: Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 and Figure 6 As shown, a fiber amplifier containing a gain-balanced six-mode erbium-doped fiber includes: a pump source 502, isolators 501 and 505, a few-mode erbium-doped fiber 504, and a combiner 503. The input end of the isolator 501 is connected to the transmission fiber. After passing through the isolator 501, the signal light is input into the combiner 503 together with the pump light generated by the pump source 502. The output end of the combiner 503 is connected to the few-mode erbium-doped fiber 504. The light after fundamental mode forward pumping is output through the isolator 505.
[0026] The few-mode erbium-doped fiber 504 is a gain-balanced six-mode erbium-doped fiber. Its core is divided into four layers from the inside out: the first circular layer 101, the second annular layer 102, the third annular layer 103, and the fourth annular layer 104. The refractive indexes, from highest to lowest, are: the second layer 102, the first layer 101, the third layer 103, and the fourth layer 104. The first and second layers 101, 102 are doped with erbium ions. The second layer 102 is divided into a second I layer 601 and a second II layer 602. The doping concentrations, from highest to lowest, are: the second II layer 602, the first layer 101, and the second I layer 601.
[0027] This six-mode erbium-doped fiber supports LP 01 LP 11a LP 11b LP 21a LP 21b and LP 02 Six modes.
[0028] The circular radius r1 of the first layer 101 is 0.5 μm to 3 μm.
[0029] The radius r2 of the outer circle of the annular shape of the second layer 102 is 6.8 μm to 7.8 μm.
[0030] The radius r3 of the outer circle of the annular third layer 103 is 8 μm to 11 μm.
[0031] The fourth layer 104 has a ring width w of 1 μm to 3 μm.
[0032] The refractive index n1 of the first layer 101 is 1.447 to 1.45.
[0033] The refractive index n2 of the second layer 102 is 1.451 to 1.453.
[0034] The refractive index n3 of the third layer 103 is consistent with the refractive index n5 of the cladding layer 105 .
[0035] The refractive index n4 of the fourth layer 104 is 1.44 to 1.442.
[0036] The refractive index n5 of the cladding 105 is 1.444.
[0037] The erbium ion doping concentration N1 of the first layer 101 is 9×10 24 m -3 to 1×10 25 m -3 , the erbium ion doping concentration N2 of the second I layer 601 is 4×10 24 m -3 to 6×10 24 m -3 , the erbium ion doping concentration N3 of the second II layer 602 is 2×10 25 m -3 to 2.5×10 25 m -3 The ratio of the annular width of the second I layer 601 to the annular width of the second II layer 602 is 3:1.
[0038] The first layer 101 and the second layer 102 of the six-mode erbium-doped optical fiber are made of silicon dioxide doped with germanium dioxide or phosphorus pentoxide, the third layer 103 is made of silicon dioxide, and the fourth layer 104 is made of silicon dioxide doped with boron trioxide.
[0039] The optical fiber amplifier uses the six-mode erbium-doped optical fiber of the present invention to generate LP through the pump light 502 01 The fundamental mode is forward pumped and amplified, and the LP generated by the transmission fiber is 01 LP 11a LP 11b LP 21a LP 21b and LP 02After passing through the isolator 501, the six modes of light are input to the input end of the combiner 503 together with the pump light 502. The output end of the combiner 503 injects the signal light and the pump light into the six-mode erbium-doped fiber 504 mentioned in the first aspect of the present invention. The amplified light is output through the isolator 505.
[0040] The present invention optimizes the structure of the six-mode erbium-doped fiber 504 according to different pump light 502 powers by using a genetic algorithm in Matlab software. After analyzing the mode field distribution, the six-mode erbium-doped fiber doping structure is optimized through processes such as individual encoding, population initialization, individual fitness calculation, individual selection, crossover mutation, and population evolution. The optimal solution for achieving a fiber amplifier with high gain and low differential mode gain is calculated.
[0041] Figure 3 This is a gain plot for a 10m-long six-mode erbium-doped fiber 504 at 400mW pump power. As can be seen, pump light 502 is fully utilized, with gains in all modes exceeding 25dB, and the differential mode gain reduced to 0.277dB. This demonstrates that the six-mode erbium-doped fiber of the present invention exhibits excellent gain equalization, contributing to the advancement of optical fiber communications.
[0042] The refractive index n4 of the fourth layer 104 of the six-mode erbium-doped fiber 504 is equal to the refractive index n3 of the third layer 103, and no boron trioxide-doped silica material is required. That is, the core layer structure changes from four layers to two layers, and the structure becomes a center-depressed type.
[0043] As described above, the embodiments of the present invention have been described in detail. However, it is obvious to those skilled in the art that many variations are possible without departing from the spirit and effects of the present invention. Therefore, all such variations are included within the scope of protection of the present invention.
Claims
1. A fiber amplifier containing a gain-balanced six-mode erbium-doped fiber, characterized in that: include: The pump source, the first isolator, the second isolator, the few-mode erbium-doped fiber, and the combiner are connected. The input end of the first isolator is connected to the transmission fiber. The signal light passes through the first isolator and is input into the combiner together with the pump light generated by the pump source. The output end of the combiner is connected to the few-mode erbium-doped fiber. The other end of the few-mode erbium-doped fiber is connected to the second isolator. The light after the fundamental mode forward pumping is output through the second isolator. The refractive index distribution of the six-mode erbium-doped fiber is a step-index distribution. The refractive index of the first layer is 1.447 to 1.45, the refractive index of the second layer is 1.451 to 1.453, the refractive index of the third layer is consistent with the refractive index of the cladding, the refractive index of the fourth layer is 1.44 to 1.442, and the refractive index of the cladding is 1.
444. The refractive index n4 of the fourth layer of the six-mode erbium-doped fiber is equal to the refractive index n3 of the third layer. The silicon dioxide material is not doped with boron trioxide. The core layer is divided into two layers from the four-layer structure. The few-mode erbium-doped fiber is a six-mode erbium-doped fiber. The core layer of the six-mode erbium-doped fiber is divided into four layers from the inside to the outside, namely the first circular layer, the second annular layer, the third annular layer and the fourth annular layer. The refractive index is from high to low in the order of the second layer, the first layer, the third layer and the fourth layer. The first and second layers are doped with erbium ions. The second layer is divided into the second I layer and the second II layer. The doping concentration is from high to low in the order of the second II layer, the first layer and the second I layer.
2. The optical fiber amplifier containing a gain-balanced six-mode erbium-doped fiber according to claim 1, characterized in that: Six-mode erbium-doped fiber supports LP 01 Mode, LP 11a Mode, LP 11b Mode, LP 21a Mode, LP 21b Mode and LP 02 The six modes have a first-layer circular radius of 0.5 μm to 3 μm, a second-layer ring outer circle radius of 6.8 μm to 7.8 μm, a third-layer ring outer circle radius of 8 μm to 11 μm, and a fourth-layer ring width of 1 μm to 3 μm.
3. The optical fiber amplifier containing a gain-balanced six-mode erbium-doped fiber according to claim 1, characterized in that: The erbium ion doping concentration of the first layer is 9×10 24 m -3 to 1×10 25 m -3 , the erbium ion doping concentration of the second layer I is 4×10 24 m -3 to 6×10 24 m -3 , the erbium ion doping concentration of the second layer II is 2×10 25 m -3 to 2.5×10 25 m -3 The ratio of the width of the second I layer ring to the width of the second II layer ring is 3:
1.
4. The optical fiber amplifier containing a gain-balanced six-mode erbium-doped fiber according to claim 1, characterized in that: The first and second layers of the six-mode erbium-doped optical fiber are made of silicon dioxide material doped with germanium dioxide or phosphorus pentoxide, the third layer is made of silicon dioxide material, and the fourth layer is made of silicon dioxide material doped with boron trioxide.