Research On Short-Reach Optical Communication System Based On Probabilistic Shaping Modulation Technology

With the rapid development of high-bandwidth applications such as cloud computing,Internet of Things technology,and multimedia services,users have put forward higher requirements for data transmission rate,which promotes an exponential increase in the demand for communication bandwidth.In the context of the large-scale commercialization of 5G networks and the exploded in global Internet traffic,the realization of large-capacity and high-speed information communication under the condition of limited bandwidth resources has become the research goal of the nextgeneration fiber-optic communication systems.We introduced probabilistic shaping(PS)technology and advance modulation formats in short-reach optical communication systems with intensity modulation direct detection(IM/DD)to investigate the improvement of channel capacity,spectral efficiency,optical receiver power sensitivity and signal tolerance to fiber nonlinear effects.The specific research work and innovation are as follows:1.Due to high computation complexity of the classic PS schemes based on arithmetic coding,a novel bit-weighted distribution matching(BWDM)algorithm based on bitlevel processing has been proposed.The algorithm which has simple implementation and lower hardware complexity can directly cascade low-density parity-check(LDPC)coding.The BWDM algorithm is introduced into the 4-level pulse amplitude modulation(PAM4)and the 8-level pulse amplitude modulation(PAM8)signals for PS-PAM4 and the PS-PAM8 signal generation with Gaussian-like distribution.The theoretical simulation results show that the signal with probabilistic shaping is closer to the Shannon limit in the low signal-to-noise ratio(SNR)region.2.The key digital-processing(DSP)algorithms such as the constant modulus algorithm(CMA)and decision-directed least mean square(DD-LMS)algorithm have been applied in PS-PAM4 IM/DD optical interconnect system and PS-PAM8wavelength-division-multiplexing passive-optical-network(WDM-PON)system.The experiment results show that the blind equalization algorithm can effectively compensate for the signal high frequency component loss caused by the limited bandwidth of optical modulators and electrical drives.Therefore,the bit error rate(BER)of system can be improved.3.In order to obtain cost-efficient systems,intensity modulation-direct detection technology with simple structure and low-cost has been applied in our work.The transmission performance of PS-PAM4 signal based on BWDM in short-reach optical interconnection system and PS-PAM8 signal in WDM-PON system have been investigated,respect.According to the experiment results,optical receiver power sensitivity,BER of system and signal tolerance to optical fiber nonlinear can be improved by the PS technology employing BWDM algorithm.In addition,different values of PS parameters,which can lead to different symbol probability distributions and directly influence optical receiver power sensitivity,are also investigated.