Impact of Sampling Source Repetition Frequency in Linear Optical Sampling

We report the repetition frequency constraint of a passively mode-locked fiber laser (PMFL) for linear optical sampling based M-ary phase-shift keying (PSK) constellation characterization, based on the commonly used Viterbi-Viterbi carrier phase estimation algorithm. Referred to the error vector magnitude (EVM) value by the conventional high-speed electronic coherent detection, we put forward a benchmark of EVM
_{RMS_error}
to evaluate the accuracy of constellation characterization by linear optical sampling. Due to the repetition frequency constraint of the PMFL, the EVM
_{RMS_error}
will reach an ultimate value of 0.25% for the purpose of PSK constellation characterization, while it is insensitive to the signal symbol rate. The analytical results of a typical 28-GBaud QPSK signal well agree with those of the simulation and the experiment, therefore providing guidance for the repetition frequency optimization of PMFL-based linear optical sampling.