Blind Modulation Format Identification Using the DC Component

We propose a blind modulation format identification (MFI) method based on direct-current (DC) component for coherent receivers. The DC value is affected by the distributions of received signal's modulated phase and amplitude. A monitoring factor R is defined as the ratio of DC value with and without phase rotation of a partial received signal. Simulation and experimental results for three commonly used modulation formats QPSK, 16-QAM, and 64-QAM demonstrate that the proposed MFI method can perform an identification with lower optical signal-to-noise ratio values than 7% forward error correction thresholds. The proposed MFI method needs no extensive training process and can tolerate the phase noise and fiber nonlinearity.