CN103731211A - Dispersion compensation method suitable for fewer-mode type multiplexing system - Google Patents

Abstract

The invention relates to a dispersion compensation method suitable for a few-mode mode multiplexing system. The method realizes dispersion compensation between transmission modes by adopting a segmented cascade structure based on a specially designed graded few-mode fiber. The two kinds of few-mode fiber sections can exhibit opposite dispersion and dispersion slopes for the transmission in the C-band except for the basic mode, and the inter-mode dispersion compensation is realized by selecting the length ratio of the two few-mode fiber spans. The method of the invention can effectively compensate the inter-mode dispersion accumulated in the transmission at the node or line terminal of the few-mode multiplexing system, has high practicability and flexibility, and is efficiently applicable to the signal processing of the mode division multiplexing system and the system terminal.

Description

A Dispersion Compensation Method Applicable to Few-Mode Mode Multiplexing System

technical field

The invention relates to a dispersion compensation method suitable for a few-mode mode multiplexing system, in particular to an inter-mode dispersion compensation method based on a graded few-mode optical fiber.

technical background

In order to solve the bottleneck of the transmission capacity in the high-speed optical transmission system, the use of multi-core optical fiber and the mode multiplexing technology of different transmission modes in the newly designed multi-mode optical fiber such as few-mode optical fiber has gradually become the research of various scientific research institutions as an emerging solution. hotspot. Mode multiplexing technology is a new type of optical communication technology based on optical fiber waveguide transmission mode, using higher order modes as carrier in addition to the basic transmission mode for mode division multiplexing to achieve higher capacity and higher transmission rate.

But on the other hand, the few-mode multiplexing optical transmission system uses different modes of optical transmission to transmit signals in few-mode fibers. In actual communication systems, the optical transmission mode is inevitably affected by the manufacturing process of the actual optical fiber, such as mechanical pressure, deformation, The serious influence of factors such as microbending and fiber span mismatch causes the orthogonality between the transmission modes to be destroyed. At the same time, the energy concentration distribution of the fundamental mode and the high-order mode in the fiber core is different, which further causes the group velocity of different modes to be different. Intermodal group delay dispersion is generated, and the optical signal at the transmission terminal will be seriously disturbed.

Most of the mode-multiplexed optical transmission systems studied at the present stage use MIMO digital signal processing technology to equalize and compensate the inter-mode dispersion accumulated in the transmission or use multi-step few-mode fibers to equalize the dispersion in the optical channel. Although these technologies can reduce the intermodal dispersion value to a certain extent, they are all restricted by factors such as the actual environment, decoding complexity, and operational difficulties.

Contents of the invention

In order to overcome the severe impact on communication performance caused by the interference of transmission group rate differences between different modes in a few-mode multiplexing system, the invention provides an inter-mode dispersion compensation method based on graded few-mode optical fibers.

The present invention also provides an example of an optical transmission system based on a few-mode fiber used in the intermodal dispersion compensation method.

The present invention also provides a cumulative dispersion compensation structure in the above-mentioned few-mode optical fiber transmission line, which adopts a cross-connected structure with positive and negative dispersion few-mode optical fibers.

The technical solution of the present invention to solve the technical problem is to provide a method for compensating the intermodal dispersion accumulated in the transmission link of the mode multiplexing system based on the graded few-mode optical fiber. The method achieves intermodal dispersion compensation by cross-cascading few-mode fiber segments with positive and negative dispersions.

The present invention also provides an example of an optical transmission system based on a few-mode fiber used in the intermodal dispersion compensation method. Including an optical transmitter module, an optical receiving module and a section of the above-mentioned optical transmission line section, the optical transmitting module includes a signal generation module, mode excitation, mode conversion and mode multiplexing; the optical receiving module includes a signal receiving module, mode filtering, mode conversion and pattern demultiplexing. The optical transmission line section can realize intermodal dispersion compensation accumulated in the transmission link at the optical transmission terminal.

Compared with the prior art, the intermodal dispersion compensation method in the mode multiplexing system based on the few-mode fiber of the present invention does not require complex digital signal processing technology of the terminal, and does not need to change the basic transmission structure of the mode multiplexing system.

Description of drawings

Fig. 1 is an example of an optical transmission system based on a few-mode fiber used in the present invention.

Fig. 2 is a schematic diagram of the refractive index distribution of the few-mode fiber used in the present invention

Detailed ways

Please refer to FIG. 1 , which is an example of an optical transmission system based on a few-mode fiber used in the present invention. The mode division multiplexing optical transmission system includes an optical transmitting module, an optical receiving module and an optical transmission line section. The optical transmitter includes a signal generation module, a mode excitation module, a mode conversion module, and a mode multiplexing module; an optical receiver includes a signal receiving mode, a mode conversion module, and a mode demultiplexing module; Dispersion is composed of few-mode optical fiber segmented and cross-connected, and the optical fiber transmission includes other high-order modes besides the basic mode for real-time compensation of inter-modal dispersion.

Please refer to FIG. 2 , which is a schematic diagram of the refractive index distribution of the few-mode fiber used in the present invention. A few-mode fiber doped with 90% SiO ₂ is used in the design, and the core radius r ₀ and cladding radius r of the few-mode fiber are reasonably selected, and the relative refractive index between the core and the cladding is limited by weak waveguide Δ=(n ₁ -n ₂ )/n ₁ is extremely small, the refractive index distribution index α of the positive dispersion fiber is 2.1, and the refractive index α of the negative dispersion fiber is 1.8. With the transmission line structure of the present invention, the length ratio of the positive and negative dispersion optical fiber spans is 1:1.2. The total distance of the transmission system is up to 100km, and the total dispersion value can be controlled within the range of -6ps/nm/km～5ps/nm/km.

The at least two optical signal transmitters enveloped by the optical system are intended to generate optical signals in a predetermined spectral band-C band. The signal sent by one transmitter propagates in the basic mode LP01, and the signal sent by the other transmitter needs to pass through a mode conversion module after being propagated in the basic mode LP01, and is converted into a high-order mode such as LP11. The mode conversion module can be obtained using any known technology such as long period gratings or spatial light modulators. The obtained two modes are propagated along the optical transmission line segment through the alignment of the mode multiplexing module to the few-mode fiber. As previously defined, a transmission line section includes at least one section of optical fiber with positive dispersion and positive dispersion slope and one section of optical fiber with negative dispersion and negative dispersion slope. The transport nodes of the optical system may include optical amplifiers. At the optical receiver node, the optical signal must have close to zero transmission cumulative dispersion. The output signal is sequentially demultiplexed, converted, filtered, and decoded by the signal processing module to obtain two multiplexed signals of the basic mode LP01 and the high-order mode such as LP11.

The dispersion compensation method of the present invention is intended for high bit-rate transmission of long-distance, multiple transmission modes of higher-order modes of transmission envelope in addition to the basic transmission mode in a few-mode mode-division multiplexing system with multiple transmission line segments In the intermodal dispersion module in the system.

Claims (7)

1. the dispersion compensation method of a few mould modular system, the structure of many fiber span cascade is provided, at least comprises that a gradation type less fundamental mode optical fibre section with positive dispersion and positive dispersion slope and one have the gradation type less fundamental mode optical fibre section of negative dispersion and negative dispersion slope.

2. dispersion compensation method as claimed in claim 1, is characterized in that: the cascade of described two kinds of fiber segments intersection.

3. the optical transmission system based on above-mentioned less fundamental mode optical fibre, comprises light emission module and Optical Receivers, at least one section of transmission line section as described in claim 1 and 2.

4. as claimed in claim 3, the transmitter module of optical transmission system, is characterized in that: comprise at least two signal generating module, mode excitation module, pattern modular converter and mode multiplexing module, two signal generating module are connected with mode excitation module, excite basic transmission mode LP simultaneously ₀₁, wherein a road is connected with pattern modular converter, by basic transmission mode LP ₀₁be converted to higher order mode, for example LP ₁₁; The carrying communication mode of two paths of signals comprises after basic transmission mode and higher order mode access module Multiplexing module simultaneously, and two paths of signals is carried out multiplexing.

5. as claimed in claim 3, the Optical Receivers of optical transmission system, is characterized in that: comprise at least two signal receiving modules, pattern demultiplexing module, pattern modular converter, pattern filtering module and signal processing module; The signal that light emission module transmits is after above-mentioned transmission line section, through pattern demultiplexing module, obtain the light signal that two-way comprises fundamental mode and fine mode, wherein higher order mode is converted to fundamental mode through pattern modular converter again, and further pass through pattern filtering module, filtering higher order mode, makes conversion obtain basic transmission mode more pure; Such two paths of signals is carrying out information decoding through terminal signaling processing module.

6. an inter-modal dispersion compensation method for few mould mode multiplexing system, is characterized in that comprising following steps:

Light emission module is provided, produces at least two kinds of transmission modes that comprise that are suitable for the transmission line section as described in claim 1 and 2;

Optical Receivers is provided, receives two kinds of arq modes after inter-modal dispersion compensation;

Light emission module produces and comprises after at least two kinds of transmission modes, requires described transmission line section to be connected with claim 1 and 2, after certain transmission line length, is connected with Optical Receivers.

7. the inter-modal dispersion compensation method of few mould mode multiplexing photosystem as claimed in claim 6, is characterized in that: the dispersion in compensating light transmission system between basic transmission mode and higher order mode.

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