Advanced Modulation Formats Signal Performance Monitoring By All-Optical Sampling Technique

With the extensive use of polarization division multiplexing, wavelength division multiplexing, advanced modulation formats together with coherent detection in large-capacity long-haul high speed fiber optical communication network, optical signal performance monitoring technique has been developed towards higher speed, higher fidelity and lower cost, which is undoubtedly a huge challenge for conventional electrical sampling based signal monitoring technique. Without the use of high-speed electronic devices, all-optical sampling techniques have demonstrated excellent performance in terms of signal sensitivity, timing jitter, temporal resolution as well as wide operating bandwidth, leading to a key technique for optical signal performance monitoring in next generation optical network.This thesis is focused on the linear all-optical sampling based advanced modulated optical signal monitoring technique. The research content includes a basic theory of the linear optical sampling technique, functional prototype equipment implementation and performance optimization. The main research outcomes are summarized as follows:(1) A theoretical analysis model of the linear optical sampling system is established. A detailed analysis of the principles governing coherent signal monitoring using linear optical sampling, as well as the verification that the linear optical sampling technique has the capability to obtain all information about the electric field is carried out. A self-developed linear optical sampling functional prototype is present to complete a signal monitoring test with a commercial 4 × 128 Gbps PDM-QPSK optical signal, with a comparison of results obtained by a commercial modulation format analyzer.(2) The repetition rate optimization of optical sampling pulse is conducted from the standard algorithm of linear optical sampling. The impact of the repetition rate on constellation characterization through linear optical sampling for M-ary PSK optical signal is carried out by both analytical and experimental investigation. It is found that for QPSK signal, when the ratio of signal linewidth to sampling rate is less than 1.5 × 10-3, linear optical sampling technique is able to obtain reliable measurement results, with the error vector magnitude(EVM) difference less than 1.5%, in the case of a comparison with the traditional modulation format analyzer.(3) Due to the repetition rate restriction of passively mode-locked fiber laser, the linear optical sampling technique can approach the results of the conventional modulation format analyzer. The constellation EVM difference can be as low as 0.25%. Meanwhile, it is found that this EVM difference is independent of the signal speed, indicating that linear optical sampling technique is particularly suitable for ultra-high-speed optical signal performance monitoring.