阅读说明：本技术 一种正交模式复用光信号的耦合保持方法及装置 (Coupling keeping method and device for orthogonal mode multiplexing optical signals ) 是由 刘博� 忻向军 任建新 毛雅亚 赵建业 王瑞春 沈磊 吴泳锋 孙婷婷 赵立龙 于 2020-12-15 设计创作，主要内容包括：本发明公开了一种正交模式复用光信号的耦合保持方法和装置,其中方法包括：将不同的正交模式光信号扇入到多芯光纤中进行纤内耦合,耦合之后的光信号以统一的正交模分复用信号形式输入到多模光纤中进行正交模分复用传输,在传输过程中采用中继节点对光信号进行整形补偿,保持模式之间的正交性。本发明通过中继节点对多模光信号的补偿,保持正交模式信号在传输过程中的耦合特性；通过减小多芯光纤之间的纤芯距来增加耦合系数,实现多芯光纤中纤芯之间的强耦合,实现正交模式的耦合。(The invention discloses a coupling keeping method and a coupling keeping device for orthogonal mode multiplexing optical signals, wherein the method comprises the following steps: the optical signals in different orthogonal modes are fanned into the multi-core optical fiber for in-fiber coupling, the coupled optical signals are input into the multi-mode optical fiber in a uniform orthogonal mode division multiplexing signal form for orthogonal mode division multiplexing transmission, the optical signals are shaped and compensated by adopting the relay nodes in the transmission process, and the orthogonality among the modes is kept. The invention keeps the coupling characteristic of the orthogonal mode signal in the transmission process by the compensation of the relay node on the multimode optical signal; the coupling coefficient is increased by reducing the fiber core distance between the multi-core fibers, so that strong coupling between the fiber cores in the multi-core fibers is realized, and the coupling of an orthogonal mode is realized.)

1. A method for maintaining coupling of an orthogonal mode multiplexed optical signal, comprising: the optical signals in different orthogonal modes are fanned into the multi-core optical fiber for in-fiber coupling, the coupled optical signals are input into the multi-mode optical fiber in a uniform orthogonal mode division multiplexing signal form for orthogonal mode division multiplexing transmission, the optical signals are shaped and compensated by adopting the relay nodes in the transmission process, and the orthogonality among the modes is kept.

2. The method of claim 1, wherein the shaping compensation comprises: the method comprises the steps of firstly carrying out wave front matching on transmitted orthogonal mode division multiplexing signals to reduce crosstalk among mode groups, then decoupling a unified orthogonal mode field, separating the unified orthogonal mode field into a plurality of different mode fields before coupling, respectively carrying out direct compensation on optical signals in different modes to enable the optical fields of the orthogonal mode signals to be identical in strength and in phase, and coupling the modes again through a coupler.

3. The method of claim 2, wherein the wavefront matching comprises: and detecting wavefront phase information to obtain the distortion drift information of the wavefront phase, reconstructing the wavefront phase information by using the conjugate beam as a control signal, and finally realizing phase compensation by changing the refractive index.

4. The method of claim 1, wherein the multicore optical fiber has a smaller core pitch than a conventional optical fiber.

5. A coupling maintaining apparatus for an orthogonal mode multiplexing optical signal, comprising:

the multi-core optical fiber performs in-fiber coupling on different orthogonal mode optical signals and then sends the optical signals to the multi-mode optical fiber;

the multimode optical fiber is connected with the multi-core optical fiber and carries out orthogonal mode division multiplexing transmission on the coupled optical signals in a uniform orthogonal mode division multiplexing signal form;

the wave front matching module is used for carrying out wave front matching on the transmitted orthogonal mode division multiplexing signals and reducing crosstalk among the mode groups;

the mode field separation module is used for decoupling the uniform orthogonal mode field and separating the uniform orthogonal mode field into a plurality of different mode fields before coupling;

the mode field shaping module is used for directly compensating optical signals in different modes respectively;

and the mode field recoupling module is used for coupling the compensated signals in different modes and performing one-way multimode transmission on a plurality of paths of optical signals.

6. The apparatus of claim 5, wherein the wavefront matching module comprises:

the wave-front detection module is used for detecting wave-front phase information, acquiring distortion drift information of the wave-front phase and making a basis for wave-front control;

the wavefront control module is used for reconstructing phase information of a wavefront by using the conjugate beam as a control signal;

and the wavefront correction module is used for realizing phase compensation by changing the refractive index.

Technical Field

The present invention relates to the field of optical communications, and in particular, to a method and an apparatus for maintaining coupling of an optical signal multiplexed in an orthogonal mode.

Background

With the increase of the demand of people on network capacity, the communication bandwidth is rapidly increased, the capacity of the traditional optical fiber communication technology such as high-order coded modulation, wavelength division multiplexing and polarization multiplexing is further improved, but the single-core single-mode optical fiber serving as a signal transmission carrier is difficult to meet the increasing capacity demand.

While the Mode Division Multiplexing (MDM) technology is considered as an important means for improving the optical communication capacity, when the conventional MDM is transmitted, signal light is usually subjected to crosstalk and distortion caused by mode coupling and modal dispersion in an optical fiber transmission device, and especially in long-distance transmission, the crosstalk between signals is more non-negligible, which greatly limits the capacity and the application environment of the MDM system.

Under ideal conditions, orthogonality is satisfied between any modes in the transmission process of the few-mode optical fiber, but in practical application, due to defects in the preparation process of the optical fiber and the influence of phenomena such as bending in use, mode fields in the transmission of the few-mode optical fiber are superposed, orthogonality of the modes is damaged, and mode crosstalk is caused, so that the transmission distance and the transmission quality are reduced.

Disclosure of Invention

The purpose of the invention is as follows: in view of the above problems, an object of the present invention is to provide a method for maintaining coupling of orthogonal mode multiplexing optical signals, in which strong coupling between fiber cores is achieved by using a multi-core optical fiber, and then mode shaping and compensation are performed on the optical signals by using a relay node, so as to ensure orthogonality of the multimode optical signals in a transmission process.

The technical scheme is as follows: the invention discloses a coupling maintaining method of an orthogonal mode multiplexing optical signal, which comprises the following steps: the optical signals in different orthogonal modes are fanned into the multi-core optical fiber for in-fiber coupling, the coupled optical signals are input into the multi-mode optical fiber in a uniform orthogonal mode division multiplexing signal form for orthogonal mode division multiplexing transmission, the optical signals are shaped and compensated by adopting the relay nodes in the transmission process, and the orthogonality among the modes is kept.

The shaping compensation comprises: the method comprises the steps of firstly carrying out wave front matching on transmitted orthogonal mode division multiplexing signals to reduce crosstalk among mode groups, then decoupling a unified orthogonal mode field, separating the unified orthogonal mode field into a plurality of different mode fields before coupling, respectively carrying out direct compensation on optical signals in different modes to enable the optical fields of the orthogonal mode signals to be identical in strength and in phase, and coupling the modes again through a coupler.

The wavefront matching comprises: and detecting wavefront phase information to obtain the distortion drift information of the wavefront phase, reconstructing the wavefront phase information by using the conjugate beam as a control signal, and finally realizing phase compensation by changing the refractive index.

The multi-core optical fiber has smaller fiber core distance than the conventional optical fiber and larger coupling coefficient, and the coupling coefficient is increased by reducing the fiber core distance.

The invention provides a coupling holding device of orthogonal mode multiplexing optical signal, comprising:

the multi-core optical fiber performs in-fiber coupling on different orthogonal mode optical signals and then sends the optical signals to the multi-mode optical fiber;

the multimode optical fiber is used for carrying out orthogonal mode division multiplexing transmission on the coupled optical signals in a uniform orthogonal mode division multiplexing signal form;

the wave front matching module is used for carrying out wave front matching on the transmitted orthogonal mode division multiplexing signals and reducing crosstalk among the mode groups;

the mode field separation module is used for decoupling the uniform orthogonal mode field and separating the uniform orthogonal mode field into a plurality of different mode fields before coupling;

the mode field shaping module is used for directly compensating optical signals in different modes respectively;

and the mode field recoupling module is used for coupling the compensated signals in different modes and performing one-way multimode transmission on a plurality of paths of optical signals.

The wavefront matching module comprises:

the wave-front detection module is used for detecting wave-front phase information, acquiring distortion drift information of the wave-front phase and making a basis for wave-front control;

the wavefront control module is used for reconstructing phase information of a wavefront by using the conjugate beam as a control signal;

and the wavefront correction module is used for realizing phase compensation by changing the refractive index.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:

1. compensating the multimode optical signal through the relay node, and keeping the coupling characteristic of the orthogonal mode signal in the transmission process; in long-distance multimode signal transmission, a plurality of relay nodes are arranged, so that low-loss, long-distance and high-quality transmission is realized;

2. by considering the discrete modes as orthogonal modes and establishing a uniform coding scheme, the cross correlation among different modes is zero, and the crosstalk in the transmission process is avoided;

3. the coupling coefficient is increased by reducing the fiber core distance between the multi-core fibers, so that strong coupling between the fiber cores in the multi-core fibers is realized, and the coupling of an orthogonal mode is realized.

Drawings

FIG. 1 is a flow chart of a coupling maintaining method for orthogonal mode multiplexing optical signals according to the present invention;

FIG. 2 is a cross-sectional view of a multi-core fiber and a conventional 19-core fiber in the present embodiment;

FIG. 3 is a schematic diagram of the propagation path of an orthomode coupled optical field;

FIG. 4 is a flow chart of the orthogonal mode coupling;

fig. 5 is a schematic flow chart of a relay node.

Detailed Description

A process of the coupling maintaining method for orthogonal mode multiplexing optical signals described in this embodiment is shown in fig. 1, and includes: firstly, optical signals of orthogonal modes are generated through a spatial light modulator, the modes of the orthogonal mode signals are not overlapped and are in a mode of combination of a plurality of annular mode fields, as shown in figure 3, different optical signals of the orthogonal modes are fanned into a multi-core optical fiber for in-fiber coupling, the optical signals of different modes in the single-mode optical fiber are subjected to mode coupling after a coupling distance by utilizing the condition of phase matching, and according to the mode coupling theory, the total electric field distribution of the optical fiber is expressed as

Wherein beta is_iTransmission constant of ith core, | A_i(z)|²Is the total optical power in the ith core, E is the transverse electric field profile, and z is the propagation direction.

In this embodiment, taking a 19-orthogonal-mode multiplexing transmission system as an example, the adopted multi-core fiber is a 19-core fiber, and as shown in fig. 2, the fiber core distance r is equal to that of a conventional 19-core fiber₁In contrast, the core pitch r of the multi-core optical fiber in the present embodiment₂Smaller, thereby increasing the coupling coefficient. The front end of the multi-core fiber is connected with the single-mode fiber, receives optical signals of different modes, couples different orthogonal modes together through strong coupling among the multiple cores, outputs the optical signals to the multi-mode fiber from the other end of the fiber for orthogonal mode division multiplexing transmission, and the total orthogonal mode field after coupling is shown in fig. 3, wherein fig. 4 is a coupling flow chart. And in the transmission process, the relay node is adopted to carry out shaping compensation on the optical signals and maintain the orthogonality among the modes.

The method is characterized in that the transmitted orthogonal mode division multiplexing signals are subjected to wave front matching, so that the phase of optical signals is suppressed, and the crosstalk among the signals is reduced, and the method mainly comprises three parts, namely wave front detection, wave front control and wave front correction: and detecting wavefront phase information to obtain the distortion drift information of the wavefront phase, reconstructing the wavefront phase information by using the conjugate beam as a control signal, and realizing phase compensation by changing the refractive index.

And reducing crosstalk among the mode groups, decoupling the uniform orthogonal mode field, separating the uniform orthogonal mode field into a plurality of different mode fields before coupling, respectively and directly compensating optical signals of different modes to ensure that the optical fields of the orthogonal mode signals have the same intensity and the same phase, and coupling the modes again through the coupler. The optical field variation throughout the orthogonal mode optical signal propagation path is shown in fig. 5.

A coupling maintaining apparatus for an orthogonal mode multiplexing optical signal, comprising:

the multi-core optical fiber is used for carrying out in-fiber coupling on different orthogonal mode optical signals;

the multimode optical fiber is used for carrying out orthogonal mode division multiplexing transmission on the coupled optical signals in a uniform orthogonal mode division multiplexing signal form;

the wave front matching module is used for carrying out wave front matching on the transmitted orthogonal mode division multiplexing signals and reducing crosstalk among the mode groups;

the mode field separation module is used for decoupling the uniform orthogonal mode field and separating the uniform orthogonal mode field into a plurality of different mode fields before coupling;

the mode field shaping module is used for directly compensating optical signals in different modes respectively;

and the mode field recoupling module is used for coupling signals in different modes and performing one-way multimode transmission on multiple paths of optical signals.

Wherein the wavefront matching module comprises:

the wave-front detection module is used for detecting wave-front phase information, acquiring distortion drift information of the wave-front phase and making a basis for wave-front control;

the wavefront control module is used for reconstructing phase information of a wavefront by using the conjugate beam as a control signal;

and the wavefront correction module is used for realizing phase compensation by changing the refractive index.