Time Domain Analysis Of High-Speed Signals Based On Linear Optical Sampling

With the rapid development of fiber optic communication system toward the goal of ultra-high speed,ultra-large capacity and ultra-long distance,the optical signal transmission rate is also increasing,while the measurement technology of high-speed optical signal has put forward higher requirements.Most of the current measurement of optical signals using electrical sampling method,that is,the use of high-speed photodetector and high-speed analog-to-digital converter(ADC)for sampling measurement of optical signals.Due to the "electronic bottleneck" constraints,the measurement bandwidth of electrical sampling is limited.All-optical sampling technology with its low cost and high measurement bandwidth advantages in the field of optical signal measurement has received widespread attention.As a branch of all-optical sampling,linear optical sampling is considered a reliable optical signal measurement technique because of its ability to measure the amplitude,phase,and polarization information of optical signals.This thesis focuses on the principle of linear optical sampling technology and related digital signal processing algorithms,analyzing and improving the algorithms,using the linear optical sampling experimental platform to measure optical signals in different modulation formats,and finally realizing the development of the high-speed optical signal measurement system.The main research contents of this thesis are as follows:(1)A synchronous fast peak extraction algorithm is proposed to determine the search interval by using the tunable repetition frequency range of the passive mode-locked laser for fast iterative extraction of peak points.To address the problem of I and Q mismatch caused by the peak extraction algorithm,an I and Q synchronization module is implemented in the algorithm to avoid the problem of eye diagram reconstruction failure.(2)A software integration extraction algorithm is proposed.This thesis analyzes the phenomenon that the sampling point of the data acquisition card is not synchronized with the peak point of the pulse will introduce the sampling error,and designs a software integration extraction algorithm for digital signals.The software integration of pulses without integration hardware circuit reduces the sampling error and makes the reconstructed eye diagram more realistic.The maximum reduction of error vector magnitude(EVM)in the measurement experiment of 32Gbaud polarization-division multiplexed quadrature phase shift keying(PDMQPSK)signal is about 6.4%.(3)A packet carrier recovery algorithm is proposed.It can effectively compensate the damage caused by frequency drift while ensuring the data length.In the measurement experiment of 32Gbaud PDM-QPSK signal,the EVM obtained by the packet carrier recovery algorithm is reduced by about 13.7%compared with the traditional carrier recovery algorithm.The characterization capability of the linear optical sampling system is greatly improved.(4)A linear optical sampling simulation platform and an experimental platform have been built.Measurements of 32 Gbaud PDM-QPSK signals have been achieved in a laboratory environment.Based on this algorithm,the algorithm is replaced and the measurement of 8 Gbaud polarizationdivision multiplexed 8 phase shift keying(PDM-8PSK)and 8 Gbaud polarization-division multiplexed 16 quadrature amplitude modulation(PDM-16QAM)signals is realized.Finally,based on the linear optical sampling technology,a high-speed optical signal measurement system is developed.Benchmarked with a high-speed oscilloscope,the system achieves real-time measurement of PDM-QPSK signals at 50 Gbaud.