Blind and Noise-Tolerant Modulation Format Identification

We propose and experimentally demonstrate a simple, blind digital modulation format identification scheme for a quadrature amplitude modulation (QAM) coherent optical communication system. In the proposed scheme, we utilize a density-peak clustering algorithm to determine the number of amplitude levels of the signal as the feature for modulation format identification. Simulations are carried out to investigate the application of the proposed scheme to various modulation signals. Experiments are performed to verify the robustness of the method to amplified spontaneous emission noise and fiber nonlinearities. We experimentally achieved a 95% identification accuracy for a quadrature phase shift keying signal with a lowest optical-signal-noise-ratio (OSNR) of 13.2 dB, a 16-QAM signal with a lowest OSNR of 13.3 dB, and a 64-QAM signal with a lowest OSNR of 19.7 dB.