Amplitude variance and 4th power transformation based modulation format identification for digital coherent receiver

This paper demonstrates the use of amplitude variance in combination with only one time of 4th power transformation and fast Fourier transform (FFT) for modulation format identification (MFI) in digital coherent receiver. The incoming signals are firstly classified into two main categories, polarization-division multiplexing (PDM) m-ary phase-shift keying modulation (mPSK) and m-ary quadrature amplitude modulation (mQAM), based on the amplitude variance after constant modulus algorithm (CMA) equalization. Then, the sub-categories of PDM-mPSK or PDM-mQAM are further identified by utilizing the logical regression (LR) algorithm on a two-dimensional (2-D) plane which is constructed by using the mean and maximum value after 4th power transformation and FFT. The feasibility is firstly verified via numerical simulation for 28GBaud/s PDM-QPSK/8PSK/16QAM/32QAM signals transmitted through additive Gaussian noise channel as well as long-distance standard single mode fiber (SSMF) channel. The simulation results demonstrate that 100% identification accuracy for all these modulation formats can be achieved at the optical signal noise ratio (OSNR) much lower than their respective 7% FEC thresholds and as high as 99% identification accuracy can be achieved even at the OSNR much lower or close to their respective 20% FEC thresholds. 100% identification accuracy can be also obtained in the presence of obviously nonlinear impairments. Proof-of-concept experiments are finally implemented to evaluate the MFI performance among 28GBaud/s PDM-QPSK/8PSK/16QAM, and 21.5GBaud/s PDM-32QAM signals, which further confirm the feasibility of our proposed MFI scheme.