Research Of Long-haul Quasi-single-mode Transmission System

With the advent of the era of Internet,the need of the network capacity around the world is in the form of explosive growth.As the cornerstone of the Internet,the optical fiber communication is facing increasing pressure.By the limit of the single-mode fiber's spatial dimension,the transmission capacity of single-mode fiber will be approaching the Shannon limit in the foreseeable future.However,the crisis of future network capacity will be solved effectively due to the emergence of few-mode fiber.However,due to the immaturity of few-mode optical components,the practical application of few-mode fiber transmission system still need a long time.But,as an intermediate step towards the adoption of FMF transmissions,quasi-single-mode use the FMFs instead of large effective-area single-mode fibers.One can launch signals in the fundamental mode,for the large-effective-area nature of the LP₀₁mode in FMFs is able to considerably reduce the fiber nonlinearity and extend the transmission distance.This paper further study the long-span and long-haul quasi-single-mode transmission links.The main work will be arranged as follows:?1?We theoretically study that modes conducted in a fiber are orthonormal.The generation mechanism of mode coupling in the FMF is also studied and analyzed.Meanwhile,we establish the mathematical model of few-mode fiber link.And we have verified that the adaptive algorithm could be theoretically used to compensate the signal penalty resulting from mode coupling.?2?We analyses the basic principle of mode group delay measurement technology and set up practical system to measure mode group delay in the few-mode fiber,which is helpful to determine the number of taps in DSP algorithms.?3?We analyses the basic principle of coherent optical detection technology and develop a set of digital signal processing algorithms to demodulate signal in PM-QPSK quasi-single-mode transmission link.Based on multipath interference compensation algorithm,multipath interference penalty caused by mode coupling is effectively compensated in quasi-single-mode system.?4?We have demonstrated long-span and long-haul quasi-single-mode transmission experiments with EDFA amplification only or hybrid Raman-EDFA amplification.Moreover,we experimentally study long-haul bi-directional quasi-single-mode transmission.With multipath interference penalty compensation using the CMA algorithm with large number of taps,transmission distance of 2500 km,2100 km and 2200 km is realized,respectively.