阅读说明：本技术 正交模式复用信号的光放大系统 (Optical amplification system for orthogonal mode multiplexed signals ) 是由 刘博� 张丽佳 毛雅亚 姜蕾 忻向军 孙婷婷 赵立龙 吴泳锋 刘少鹏 宋真真 王 于 2020-08-11 设计创作，主要内容包括：本发明公开了一种正交模式复用信号的光放大系统,包括正交模式复用信号装置、模式光子灯笼复用器、模式光子灯笼解复用器,还包括正交模式泵浦光系统,输出与正交模式复用信号的模式和相位一致的泵浦光；还包括用于正交模式复用信号光放大的传输链路；正交模式复用信号装置输出端和正交模式泵浦光系统输出端与模式光子灯笼复用器输入端信号连接,模式光子灯笼复用器输出端与传输链路输入端信号连接,传输链路输出端与模式光子灯笼解复用器输入端信号连接。通过对泵浦光的正交模式匹配实现与信号光的耦合传输,对不同模式下的光信号进行放大,从而实现低模间耦合的光信号均衡,为正交模式复用信号长距离传输时提供了稳定的光放大系统。(The invention discloses an optical amplification system of orthogonal mode multiplexing signals, which comprises an orthogonal mode multiplexing signal device, a mode photon lantern multiplexer, a mode photon lantern demultiplexer and an orthogonal mode pump light system, wherein the orthogonal mode pump light system outputs pump light consistent with the mode and the phase of the orthogonal mode multiplexing signals; the optical amplifier also comprises a transmission link for optical amplification of the orthogonal mode multiplexing signals; the output end of the orthogonal mode multiplexing signal device and the output end of the orthogonal mode pumping light system are in signal connection with the input end of the mode photon lantern multiplexer, the output end of the mode photon lantern multiplexer is in signal connection with the input end of the transmission link, and the output end of the transmission link is in signal connection with the input end of the mode photon lantern demultiplexer. The coupling transmission with the signal light is realized by matching the orthogonal mode of the pump light, and the optical signals under different modes are amplified, so that the low-mode coupling optical signal balance is realized, and a stable optical amplification system is provided for the long-distance transmission of the orthogonal mode multiplexing signals.)

1. An optical amplification system of orthogonal mode multiplexing signals comprises an orthogonal mode multiplexing signal device, a mode photon lantern multiplexer and a mode photon lantern demultiplexer, and is characterized by further comprising an orthogonal mode pump optical system used for outputting pump light consistent with the mode and the phase of the orthogonal mode multiplexing signals; the optical amplifier also comprises a transmission link for optical amplification of the orthogonal mode multiplexing signals; the output end of the orthogonal mode multiplexing signal device and the output end of the orthogonal mode pumping light system are in signal connection with the input end of the mode photon lantern multiplexer, the output end of the mode photon lantern multiplexer is in signal connection with the input end of the transmission link, the output end of the transmission link is in signal connection with the input end of the mode photon lantern demultiplexer, the transmission link is composed of a ring core optical fiber and a ring core gain optical fiber, the ring core optical fiber and the ring core gain optical fiber structure comprise an optical fiber layer and a cladding layer, the cladding layers are arranged on two sides of the optical fiber layer, and the optical fiber layer in the ring core gain optical fiber is doped with a medium for optical amplification.

2. The optical amplification system for quadrature mode multiplexed signals of claim 1, wherein the quadrature mode pump optical system comprises a laser, a demultiplexer, a mode converter, a phase controller and a pump mode multiplexer, which are connected in sequence by a signal.

3. The optical amplification system for quadrature mode multiplexed signals of claim 1, wherein the mode photon lantern demultiplexer has an output connected to a quadrature mode pump light.

Technical Field

The invention relates to the field of communication transmission, in particular to an optical amplification system of an orthogonal mode multiplexing signal.

Background

With the rapid development of internet +, big data, cloud computing and 5G, the demand of users on network capacity is increasing day by day, and the capacity of optical communication is also required to be higher. However, the transmission capacity of the single-core single-mode fiber has a nonlinear shannon transmission limit of 100Tb/s, and cannot meet future communication requirements. Optical signal spatial multiplexing methods based on optical fibers themselves have been proposed.

Spatial multiplexing is an effective method for solving the broadband crisis of an optical transmission network. The existing optical fibers for realizing spatial multiplexing include: multi-core fibers, few-mode fibers, and combinations of multi-core fibers and few-mode fibers. Wherein, the transmission capacity of the multi-core few-mode optical fiber formed by combining the multi-core optical fiber and the few-mode optical fiber reaches 10.16 Pb/s. The transmission capacity can be greatly improved by using mode multiplexing in the multi-core few-mode optical fiber, so that the capacity crisis is effectively solved. For example, CN111399123A discloses a method and an apparatus for generating an orthogonal mode multiplexing optical signal, and the patent application discloses an orthogonal mode multiplexing signal apparatus in detail.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide an optical amplification system for orthogonal mode multiplexing signals in long-distance transmission, wherein the signals maintain mode orthogonality in the transmission process so as to inhibit crosstalk between modes, and a ring core gain optical fiber structure in a transmission link has extremely low mode gain difference.

The technical scheme is as follows: the invention provides an optical amplification system of orthogonal mode multiplexing signals, which comprises an orthogonal mode multiplexing signal device, a mode photon lantern multiplexer, a mode photon lantern demultiplexer, an orthogonal mode pump optical system and a transmission link for optical amplification of the orthogonal mode multiplexing signals. The mode and phase of the pump light output by the orthogonal mode pump light system are consistent with the orthogonal mode multiplexing signal. The output end of the orthogonal mode multiplexing signal device and the output end of the orthogonal mode pumping light system are in signal connection with the input end of the mode photon lantern multiplexer, the output end of the mode photon lantern multiplexer is in signal connection with the input end of the transmission link, and the output end of the transmission link is in signal connection with the input end of the mode photon lantern demultiplexer.

The transmission link is composed of a ring core optical fiber and a ring core gain optical fiber. The ring core optical fiber is a carrier for orthogonal mode multiplexing signal transmission, can simultaneously transmit a plurality of mode signals, and keeps the orthogonality of the modes. The orthogonal mode multiplexing signal is reduced in signal power due to loss after long-distance transmission, and the ring core gain optical fiber can realize relay amplification of the orthogonal mode multiplexing signal.

The optical fiber layer in the ring core gain optical fiber is doped with a medium for optical amplification, and the medium can be erbium ions.

The orthogonal mode pump optical system comprises a laser, a wave separator, a mode converter, a phase controller and a pump mode multiplexer which are sequentially connected through signals. The pump light is injected into the erbium-doped optical fiber, erbium ions in a ground state are pumped to an excited state, the erbium ions are unstable in the excited state, and radiationless transition is carried out to a metastable state energy level with long particle life, so that the distribution inversion of erbium ion particle numbers is realized, and the gain balance is carried out on optical signals.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: the orthogonal mode pump light system generates pump light multiplexed under different modes of 980nm, realizes coupling transmission of signal light and the pump light through orthogonal mode matching, and amplifies optical signals under different modes, so that low-mode coupled optical signal balance is realized, and a stable optical amplification system is provided for long-distance transmission of orthogonal mode multiplexed signals.

Drawings

FIG. 1 is a schematic diagram of the present invention;

fig. 2 is a view showing the structure of a gain optical fiber according to the present invention.

Detailed Description

The technical scheme of the invention is further explained by combining the attached drawings.

As shown in fig. 1, the optical amplification system for quadrature-mode multiplexed signals includes a quadrature-mode multiplexed signal device and a quadrature-mode pump optical system, where the quadrature-mode multiplexed signal output by the former is identical in mode and phase with the pump light output by the latter. The orthogonal mode multiplexing signal is input to a mode1-4 port of the mode photon lantern multiplexer, the pump light is input to a mode5 port, the pump light is input to a transmission link through the mode photon lantern multiplexer in a coupling mode, signal light amplification is carried out after long-distance transmission, and the mode photon lantern demultiplexer is guaranteed to effectively receive the orthogonal mode multiplexing signal.

The laser beam generated by the laser in the orthogonal mode pump light system is divided into a plurality of laser beams with the same power through the wave splitter, different laser beams are subjected to mode conversion through the mode converter, different mode lasers are subjected to phase control, a plurality of pump modes are integrated through the pump mode multiplexer, and a path of pump light is formed and coupled and input to a mode5 port.

The orthogonal mode multiplexing signal is input to a mode1-4 port, and the mode photon lantern multiplexer couples and multiplexes different orthogonal modes and pumping modes into one optical signal.

In order to realize the gain balance of the orthogonal mode multiplexing signals, a multi-layer ring core optical fiber structure needs to be established, so that an optical fiber gain section and a refractive index section are not completely overlapped, and extremely low mode gain difference is realized.

The mode field distribution u in the multilayer annular core optical fiber is expressed as follows in a cylindrical coordinate system:

where n (r) is the fiber refractive index distribution, k is the wavenumber, β is the longitudinal transmission constant of the mode, and r is the radius independent variable in a cylindrical coordinate system. Solving equation (1) using the scalar method, the following conclusions are reached:

① the guided mode exhibits a standing wave distribution in the core in the radial direction, i.e. n_i>β/ k（n_iRefractive index of the i-th layer mode field), the field distribution obtained by solving is as follows:

② in the cladding, the conduction mode decays in the radial direction, i.e. n_i<β/k, the resulting field distribution is:

wherein m is the order of Bessel equation, r,α is undetermined coefficient, J is imaginary unit, ai and bi are weight coefficients, J is coordinate independent variable in cylindrical coordinate system_m、N_mFirst and second class of mth order Bessel function, I_m、K_mModified m-th order shellfish of the first and second classes respectivelyThe Seal function. Normalized transverse phase parameter U in equations (2) and (3)_iAnd normalized transverse attenuation parameter W_iCan be expressed as

(4)

Where a is the radius of the core.

Therefore, the mode field distribution of each layer can be calculated according to the boundary conditions and the mode number m of each layer of the optical fiber and the formulas (2) to (4), so that the mode field distribution condition can be obtained. Because of the multi-layer fiber structure, the gain profile and the refractive index profile do not completely overlap.

And establishing a theoretical model between the parameters of the active optical fiber and the mode gain according to the mode field distribution characteristics of each layer of the ring-core optical fiber. Fig. 2 shows a cross-sectional view of a multi-layer structure of a ring-core optical fiber, which sequentially comprises a middle cladding 5, a first optical fiber layer 4, a first cladding 3, a second optical fiber layer 2, and a low-refractive-index groove 1 from inside to outside.

The transmission link is formed by sequentially combining a Ring Core Fiber (RCF), a ring core gain fiber (RC-EDF) and a Ring Core Fiber (RCF). In the ring core gain optical fiber, the optical fiber is doped with erbium ions.

The orthogonal mode multiplexing signals are transmitted in the ring core optical fiber, so that the orthogonality of the signals is not damaged, and the signals are amplified in the ring core gain optical fiber in a balanced manner, so that the long-distance transmission of the orthogonal mode multiplexing optical signals is ensured.

Pumping light is injected into the erbium-doped fiber, erbium ions in a ground state are pumped to an excited state, the erbium ions are unstable in the excited state, and radiationless transition is performed to a metastable state energy level with long particle life, so that the distribution inversion of erbium ion particle number is realized.

The orthogonal mode pump light system is respectively connected to two sides of the mode photon lantern multiplexer and the mode photon lantern demultiplexer, and pump light is relatively uniform at each position of the erbium-doped fiber and has the dual characteristics of high power and low noise.