Study On Distributed Raman Fiber Amplification In New High-speed Optical Fiber Transmission System

The traditional intensity modulation direct detection(IMDD)optical transmission system,represented by dense wavelength division multiplexing(DWDM)and erbium doped fiber amplifier(EDFA),is difficult to sustain the rapid growth of network traffic.Based on high order modulation pattern and digital signal processing(DSP)technology coherent detection optical transmission system has become a high-speed core network in the mainstream way.Higher transmission bit rates and complex high-order modulation formats increase the demand for optical signal-to-noise ratio(OSNR)margins for optical communication systems and are more sensitive to nonlinear effects in the link.Low noise distributed fiber Raman The amplifier is thus more widely concerned.In the traditional IMDD system,the gain spectrum optimization of Raman amplifier and the intensity noise caused by various effects have been studied in detail.In the coherent optical communication system of polarization multiplexing,it is worthy of further study and reflection that the complex signal of the complex amplitude modulation may have more abundant physical phenomena under Raman amplification.On the other hand,the capacity of the single-mode fiber-optic transmission system reported in the current experiment is close to the non-linearly limited Shannon limit,and the growth momentum of global network traffic caused by various new services continues.The new type of artificial channel transmission,represented by space division multiplexing(SDM)technology,is a hotspot in research and application.It is expected to break through the transmission limit of single fiber and increase the capacity of optical fiber transmission system.Raman amplifier is one of the attractive solutions for long-distance distributed signal amplification in space-division multiplexing optical fiber transmission media.Based on above,a new theoretical and experimental study on the new noise mechanism,system damage and performance improvement of the distributed Raman amplifier is carried out with the background of the new multi-dimensional multiplexing coherent optical transmission system.The main research work content and innovation contributions are summarized below:(1)In this thesis,a novel noise called relative phase noise(RPN)is introduced in the coherent optical transmission system due to the Raman pump relative intensity noise(RIN)and the cross phase modulation(XPM)effect in the fiber.The RPN noise is directly observed and measured in the forward pump condition for the first time.The experimental results are in good agreement with the theoretical model.However,it is difficult to directly observe the RPN under the backward pump condition,but the experimental results are consistent with the simulation results under the experimental conditions such as the phase noise of the laser,which proves the correctness of the theoretical model.On the other hand,for the first time,the presence of RPN noise is observed in the coherent optical orthogonal frequency division multiplexing(CO-OFDM)transmission system,and an RPN transfer function consistent with the continuous optical signal is obtained.This work proves the existence of RPN new Raman amplifier noise in coherent optical communication system and carries out detailed mechanism analysis,which points out the direction for optimizing the performance of coherent optical communication system under Raman amplification.(2)The high-capacity and long-distance CO-OFDM transmission platform is realized by optimizing the noise performance and nonlinear damage in the link using the two-way Raman amplification and mixed-amplification fiber loop structure.On this basis,an efficient and Low-complexity in-band OSNR monitoring method.The correlation calculation is performed using only one training sequence symbol(TS1)in the OFDM symbol to obtain the signal-to-noise ratio(ESNR)of the subcarrier,and the OSNR is estimated.This method can independently monitor OSNR on two polarization states and exhibit good estimation accuracy over a wide dynamic range.The influence factors of nonlinear noise on OSNR estimation accuracy are analyzed by experiment and simulation.Combined with the inhibitory effect of distributed Raman amplification on nonlinear effects,this method provides a suitable technique for OSNR monitoring of long-distance fiber links.(3)A novel crosstalk noise,called relative polarization noise(RPolN),is generated in the polarization multiplexing system due to Raman pumped RIN noise and the interaction of the crossed polarization modulation(XPolM)effect in the fiber.For the first time,RPolN experiments were carried out and the transfer function was measured.Compared with the theoretical model,it is found that the traditional CMA algorithm has a certain compensation effect on the crosstalk noise at low frequencies,but there is still a large effect of RPolN noise in the higher frequency range.The mechanism of the polarization state of Raman pump light on RPolN was studied experimentally.The anti-biasing effect of pump light was realized to achieve a better resistance to RPolN effect.(4)A CO-OFDM quasi-base mode transmission system based on low-mode and single-mode hybrid fiber-optic link Raman amplification is proposed and implemented.It is possible to resist the nonlinear damage of fiber transmission by using the large effective mode field of the quasi-base mode excited by the low-mode fiber and to resist the multi-path interference(MPI)effect in the quasi-base mode transmission by OFDM multi-carrier technique MPI Suppression Algorithm in Carrier Quasi-Base Mode Transmission System.In the single-wavelength signal light 800 km transmission experiment,the quasi-fundamental mode transmission system of the hybrid fiber is compared with the traditional single-mode transmission system,and the transmission performance of the system is optimized by using the hybrid fiber link to further reduce the MPI and the Raman amplifier.Good fiber power and Q value were improved by 2dB and 0.35 dB.This work provides an effective system evolution scheme for space-division multiplexing transmission technology based on low-mode fiber.