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Effect of laser frequency offset on optical minimum-shift keying transmission system

As a special case of continuous phase frequency-shift-keying (FSK), minimum-shift keying (MSK) exhibits some different properties compared with the traditional optical phase modulation formats, such as return-to-zero (RZ) differential-phase-shift-keying (DPSK) and differential-quadrature-phase-shift-keying (DQPSK). In this paper, we investigated the receiver performance degradation caused by laser frequency offset between laser frequency and delay interferometer (DI) phase, which is found to be the most critical impairment for the receiver performance in a practical optical phase modulated system. Results show that MSK system is about double times and six times more robust to frequency offsets than RZ-DPSK and RZ-DQPSK systems operating at the same 10Gb/s bit rate, respectively.