An Effective Modulation Format Identification Based on Intensity Profile Features for Digital Coherent Receivers

An effective and blind modulation format identification (MFI) scheme based on intensity profile features is proposed for digital coherent receivers of elastic optical networks. Here, different modulation format types present different profile features, which can be regarded as a classification metric. The proposed scheme requires no prior training and is independent of carrier phase noise or frequency offset. Besides, optical signal noise ratio (OSNR) values do not need to be pre-known in the identification process. In this paper, the first step of our scheme is to classify different classes based on different numbers of peak points, and then the second step is to apply height and width ratios between peak points to achieve the final identification process in each class. The feasibility is first demonstrated via numerical simulations in 28GBaud polarization division multiplexing (PDM)-quadrature phase shift keying (QPSK)/-8 quadrature amplitude modulation (QAM)/-16QAM/-32QAM/-64 QAM systems. The results show that the lowest required OSNR values to achieve 100% recognition rate for all modulation formats signals are much lower than the corresponding theoretical 7% forward error correction (FEC) limit (bit error ratio (BER) = 3.8 × 10
^-3
). Furthermore, that of PDM-QPSK/-8QAM/-16QAM signals are even lower than or close to 20% FEC limit (BER = 2.4 × 10
^-2
). Subsequently, the performance is further verified by proof-of-concept experiments among 28GBaud PDM-QPSK/-8QAM/-16QAM, and 21.5GBaud PDM-32QAM systems under back-to-back and long-distance links (from 400 km to 2000 km).