CN112180499A - Three-layer core multilayer erbium ion-doped 4-mode optical fiber with extremely small gain difference - Google Patents

Abstract

The invention relates to a three-core multilayer erbium ion-doped 4-mode optical fiber with extremely small gain difference, which comprises a fiber core 1, a groove 2 and a cladding 3, wherein the fiber core 1 is positioned at the most center of the optical fiber, the cladding 3 is positioned outside the fiber core 1, and the groove 2 is arranged in the cladding 3 and is closer to the fiber core 1. The fiber core 1 is divided into three layers, namely a central layer 1-1, an annular layer 1-2 and an outer core layer 1-3 which are tightly connected. The ion doping is mainly concentrated in the area of the fiber core 1, the fiber core 1 is divided into three layers of rings for doping, and the three layers of ion filling areas are respectively the same as the refractive index distribution areas of the central layer 1-1, the ring layer 1-2 and the outer core layer 1-3 of the erbium ion-doped 4-mode fiber. The refractive index distribution assisted by the three-layer core groove ensures that the optical fiber has higher mode refractive index difference, can weaken the cross talk between modes and reduces the bending loss in application. Moreover, the refractive index distribution is beneficial to reducing the difference value of the power filling factors of all modules, the difficulty of optimizing the particle doping distribution can be greatly reduced, and the gain balance is easier to realize.

Description

Three-layer core multilayer erbium ion-doped 4-mode optical fiber with extremely small gain difference

Technical Field

The invention relates to a three-core multilayer erbium ion-doped 4-mode optical fiber with a small gain difference, belonging to the field of optical fiber laser amplifiers.

Background

With the rapid exponential increase of network data traffic, the information capacity of the conventional Single Mode Fiber (SMF) transmission system has not been able to meet the demand, and in order to further increase the communication capacity, a space division multiplexing system based on mode division multiplexing and core division multiplexing has been proposed and intensively studied in recent years. In the case of ultra-long distance communication, an on-line optical amplifier with high performance and low energy consumption is indispensable. In the mode division multiplexing system, the existing single mode fiber amplifier is no longer applicable due to the increase of signal modes. When information is transmitted independently in each mode, a large difference in gain between modes (DMG) causes signal distortion and an increase in error rate, thereby reducing system transmission capacity and increasing the probability of system transmission interruption. Therefore, in the few-mode fiber amplifier, the gain balance between modes becomes an important index for measuring the mode division multiplexing amplification system.

At present, there are 3 methods for realizing gain equalization between modes as follows: adjusting the pump mode composition, optimizing the dopant ion distribution in the fiber, and improving the refractive index distribution in the fiber. The pumping mode of the fiber gain amplifier mainly comprises core pumping and cladding pumping. The adjustment of the pumping mode composition is mainly used for core pumping, however, it is difficult to achieve gain equalization of more signal modes by the combination of pumping modes alone, and an extremely complex doped ion distribution structure is required. In modeling a cladding pumped amplifier, it can be assumed that the pump intensity distribution is uniform throughout the doped core. Therefore, fine optimization of the ion doping profile in few-mode active fibers and improvement of the refractive index profile in the fiber are critical to reducing DMG in cladding-pumped amplifiers. Based on this realization, gain-balanced few-mode fiber amplifiers with different types of refractive index profiles have been proposed so far. Among them, there are 4-mode and 6-mode active fibers based on step-index profile (q. kang et al. minimizing differential mode gain in clamped pumped MM-EDFAs for mode division multiplexing in C and L Bands, POEM' 14, Paper fth4 f.1). The DMG is about 1 dB. There are 5 spatial modes of fiber amplifiers based on the annular index profile (Y. Jung et al, Few Mode Ring-Core fiber Amplifier for Low Differential Module Gain,2017ECOC, Gothenburg, pp.1-3). The DMG is also about 1 dB. However, the optimization of the few-mode active gain optical fiber based on the step refractive index mainly depends on the optimization of the distribution of doped ions, and the optimization difficulty is high; the few-mode active gain optical fiber based on the annular refractive index distribution has smaller mode gain difference due to the special design of the refractive index distribution and the optimization of the ion filling distribution, but the upper limit of the gain amplitude of each mode in the optical fiber is lower.

Disclosure of Invention

In order to obtain a very small gain difference between modes and ensure a higher mode gain amplitude upper limit, a three-layer core multilayer erbium ion-doped 4-mode optical fiber with a very small gain difference is provided.

The purpose of the invention is realized by the following technical scheme:

a three-core multilayer erbium ion-doped 4-mode optical fiber with extremely small gain difference comprises a fiber core, a groove and a cladding, wherein the fiber core is positioned at the center of the optical fiber, the cladding is positioned outside the fiber core, and the groove is arranged in the cladding and is closer to the fiber core. Wherein, the fiber core is divided into three layers, which are respectively a central layer from inside to outside, the ring layer is closely connected with the outer core layer, the radius of the central layer is 4.025 mu m, and the difference between the refractive index of the central layer and the refractive index of the cladding is 0.01; the ring layer is positioned at 4.025-6.225 μm, and the difference between the refractive index of the ring layer and the refractive index of the cladding layer is 0.0121; the outer core layer is located at 6.225-7.75 μm, and the difference between the refractive index of the outer core layer and the refractive index of the cladding layer is 0.0113; the grooves are positioned at 8.55-14.75 mu m, and the difference between the refractive index of the grooves and the refractive index of the cladding is-0.00712; the cladding radius was 62.5 μm. Ion doping is mainly concentrated in a fiber core area, the fiber core is divided into three layers of rings for doping, from inside to outside, a doped inner layer, a doped middle layer and a doped outer layer are respectively arranged, the respective filling areas of the inner layer, the doped middle layer and the doped outer layer are respectively the same as the central layer, the ring layer and the outer core layer of the erbium ion-doped 4-mode optical fiber, the concentration ratio of the erbium ion-doped ions is 1: 0.9119: 1.3477. the concentration ratio of doped ions of each layer is different along with the difference of the dividing radius of each filling layer, and can also be changed into two layers of doping, and the finally obtained minimum gain difference between the modes is less than 0.1 dB.

The beneficial effects of the technology are as follows: the three-core multilayer erbium ion-doped 4-mode optical fiber with extremely small gain difference adopts three-core multilayer ion doping to realize extremely small inter-mode gain difference, and the optical fiber has higher mode refractive index difference due to the refractive index distribution assisted by the three-core groove, so that the inter-mode crosstalk is weakened, and the processing and manufacturing difficulty is reduced. The optical fiber has reduced bending loss in practical application due to the groove design, so that the optical fiber has higher application value. Moreover, the refractive index distribution is beneficial to reducing the difference value of the power filling factors of all modules, so that the difficulty of optimizing the ion doping distribution is greatly reduced, and the gain balance is easier to realize. The optical fiber realizes that the mode gain difference between 4 modes is smaller than 0.00082 on the basis of ensuring higher mode gain amplitude.

Drawings

Fig. 1 is a schematic diagram of an erbium-doped 4-mode fiber with three doped ion distribution regions aligned with the three core refractive index distribution regions.

Fig. 2 is a schematic diagram of an erbium-doped 4-mode fiber when the three-layer doped ion distribution region is not consistent with the three-layer core refractive index distribution region.

Fig. 3 is a schematic diagram of an erbium ion-doped 4-mode fiber with two layers of doped ion profiles.

Fig. 4 is a 4-module gain diagram obtained by simulation using the preferred parameters of the present invention.

Detailed Description

The invention will be illustrated and explained by the following non-limiting description of preferred embodiments. The embodiments are merely exemplary of the application of the invention, and any technical solutions formed by adopting equivalent substitutions or equivalent changes are within the scope of the invention as claimed.

The present technology is further described below with reference to the accompanying drawings.

Example one

In this example, a three-core multilayer erbium ion-doped 4-mode fiber with very small gain difference is shown in fig. 1. The erbium ion-doped 4-mode optical fiber comprises a fiber core 1, a groove 2 and a cladding 3, wherein the fiber core 1 is positioned at the center of the optical fiber, the cladding 3 is positioned outside the fiber core 1, and the groove 2 is positioned in the cladding 3 and is closer to the fiber core 1. The fiber core 1 is divided into three layers, namely a central layer 1-1, a ring layer 1-2 and an outer core layer 1-3 which are tightly connected from inside to outside. Wherein, the radius of the central layer 1-1 of the 4-mode erbium-doped fiber is 4.025 μm, and the difference between the refractive index of the central layer and the refractive index of the cladding 3 is 0.01; the ring layers 1-2 are positioned at 4.025-6.225 mu m, and the difference between the refractive index of the ring layers and the refractive index of the cladding layer 3 is 0.0121; the outer core layer 1-3 is located at 6.225-7.75 μm, and the difference between the refractive index of the outer core layer and the refractive index of the cladding layer 3 is 0.0113; the grooves 2 are positioned at 8.55-14.75 μm, and the difference between the refractive index of the grooves and the refractive index of the cladding 3 is-0.00712; the radius of the cladding 3 is 62.5 μm. Erbium ions are doped in a fiber core 1 region and are doped in three layers, the respective filling regions of the erbium ions are respectively the same as the refractive index distribution regions of a central layer 1-1, a ring layer 1-2 and an outer core layer 1-3 of a three-core multi-layer doped 4-mode erbium-doped fiber, and the concentration ratio of the doped ions is 1: 0.9119: 1.3477, all the ion doping concentrations that meet this concentration ratio satisfy the gain balance, except that different concentrations result in different gain amplitudes.

Example two

In this example, a three-core multilayer erbium ion-doped 4-mode fiber with very small gain difference is shown in fig. 2. The 4-mode erbium-doped fiber comprises a fiber core 1, a groove 2 and a cladding 3, wherein the fiber core 1 is positioned at the center of the fiber, the cladding 3 is positioned outside the fiber core 1, and the groove 2 is positioned in the cladding 3 and is closer to the fiber core 1. The fiber core 1 is divided into three layers, namely a central layer 1-1, a ring layer 1-2 and an outer core layer 1-3 which are tightly connected from inside to outside. Wherein, the radius of the central layer 1-1 of the 4-mode erbium-doped fiber is 4.025 μm, and the difference between the refractive index of the central layer and the refractive index of the cladding 3 is 0.01; the ring layers 1-2 are positioned at 4.025-6.225 mu m, and the difference between the refractive index of the ring layers and the refractive index of the cladding layer 3 is 0.0121; the outer core layer 1-3 is located at 6.225-7.75 μm, and the difference between the refractive index of the outer core layer and the refractive index of the cladding layer 3 is 0.0113; the grooves 2 are positioned at 8.55-14.75 μm, and the difference between the refractive index of the grooves and the refractive index of the cladding 3 is-0.00712; the radius of the cladding 3 is 62.5 μm. The ion doping of the 4-mode erbium-doped fiber is mainly concentrated in the fiber core 1 area, the fiber core 1 is doped by three layers of rings, namely a doped inner layer 51, a doped middle layer 52 and a doped outer layer 53 from inside to outside, the doped area at the moment is to divide the fiber core 1 into three layers arbitrarily, and different doping concentration ratios of the layers can be obtained according to different division conditions. The doped inner layer 51 shown in fig. 2 has a doping radius smaller than that of the central layer 1-1, the doped middle layer 52 has a doping radius larger than that of the ring layer 1-2 and smaller than that of the outer core layer 1-3, and the doped outer layer 53 has a doping radius equal to that of the outer core layer 1-3.

EXAMPLE III

In this example, a three-core multilayer erbium ion-doped 4-mode fiber with very small gain difference is shown in fig. 3. The 4-mode erbium-doped fiber comprises a fiber core 1, a groove 2 and a cladding 3, wherein the fiber core 1 is positioned at the center of the fiber, the cladding 3 is positioned outside the fiber core 1, and the groove 2 is positioned in the cladding 3 and is closer to the fiber core 1. The fiber core 1 is divided into three layers, namely a central layer 1-1, a ring layer 1-2 and an outer core layer 1-3 which are tightly connected from inside to outside. Wherein, the radius of the central layer 1-1 of the 4-module gain fiber is 4.025 μm, and the difference between the refractive index of the central layer and the refractive index of the cladding 3 is 0.01; the ring layers 1-2 are positioned at 4.025-6.225 mu m, and the difference between the refractive index of the ring layers and the refractive index of the cladding layer 3 is 0.0121; the outer core layer 1-3 is located at 6.225-7.75 μm, and the difference between the refractive index of the outer core layer and the refractive index of the cladding layer 3 is 0.0113; the grooves 2 are positioned at 8.55-14.75 μm, and the difference between the refractive index of the grooves and the refractive index of the cladding 3 is-0.00712; the radius of the cladding 3 is 62.5 μm. The ion doping of the 4-mode erbium-doped fiber is mainly concentrated in the fiber core 1 area, the fiber core 1 is divided into two layers of rings for doping, namely a doped inner layer 61 and a doped outer layer 62 from inside to outside, the fiber core 1 is divided into two layers at the moment, and different doping concentration ratios of all layers can be obtained according to different division conditions. The doped inner layer 61 shown in fig. 3 has a doping radius smaller than the radius of the outer core layers 1-3 and the doped outer layer 62 has a doping radius equal to the radius of the outer core layers 1-3.

There are numerous embodiments of the invention, and it will be apparent to those skilled in the art that variations may be made in the embodiments in accordance with the teachings of the invention without departing from the scope of the invention.

Claims (3)

1. a three-layer core multi-layer erbium ion-doped 4-mode optical fiber with extremely small gain difference is characterized in that: comprising a fiber core (1), a groove (2) and a cladding (3), and the fiber core (1) is located at In the center of the optical fiber, the cladding (3) is located outside the core (1), and the groove (2) is located in the cladding (3) which is closer to the core (1); wherein, the core (1) is further divided into There are three layers, from the inside to the outside, the center layer (1-1), the ring layer (1-2) and the outer core layer (1-3) are closely connected; the radius of the center layer (1-1) is 4.025μm, The difference between its refractive index and that of the cladding (3) is 0.01; the ring layer (1-2) is located at 4.025-6.225 μm, and the difference between its refractive index and that of the cladding (3) is 0.0121; the outer core layer (1-3) ) is located at 6.225-7.75μm, and the difference between its refractive index and that of the cladding (3) is 0.0113; the groove (2) is located at 8.55-14.75 μm, and the difference between its refractive index and that of the cladding (3) is -0.00712; The radius of the layer (3) is 62.5 μm; the erbium ions are doped in the core (1) region, which is doped in three layers, and their respective filling regions are respectively connected with the central layer 1 of the three-layer core three-layer erbium ion 4-mode fiber. -1. The refractive index distribution areas of the ring layer 1-2 and the outer core layer 1-3 are the same, and the doping ion concentration ratio is 1:0.9119:1.3477; the doping ion concentration ratio varies with the division radius of each filling layer. It can also be changed into two layers of doping, and the minimum gain difference between the final modes should be less than 0.1dB. 2. A three-layer core multi-layer erbium ion-doped 4-mode fiber with extremely small gain difference according to claim 1, characterized in that: the ion doping is mainly concentrated in the core (1) region, and the core (1) Doping is performed in three-layer rings, the doping radius of the doping inner layer (51) is greater than 0 and smaller than the radius of the outer core layer (1-3), and the doping radius of the doping middle layer (52) is larger than that of the doping inner layer (52). The layer (51) is smaller than the radius of the outer core layer (1-3), and the doping radius of the doped outer layer (53) is equal to the radius of the outer core layer (1-3). 3. A three-layer core multi-layer erbium ion-doped 4-mode fiber with extremely small gain difference according to claim 1, characterized in that: the ion doping is mainly concentrated in the core (1) area, and the core (1) Doping is performed in two layers, the doping radius of the doped inner layer (61) is greater than 0 and smaller than the radius of the outer core layer (1-3), and the doping radius of the doped outer layer (62) is equal to the outer core Radius of layers (1-3).

Images