Optical PAM-4 generation via electromagnetically induced transparency in nitrogen-vacancy centers

A scheme of optical four-level pulse amplitude modulation (PAM-4) is proposed based on phase-dependent electromagnetic-induced transparency (EIT) in nitrogen-vacancy (NV) centers. For a closed structure, its transmission depends on the relative phase of applied fields. Based on EIT, the PAM-4 may be achieved by encoding the relative phase and decoding the amplitude of the transmission field. Simulation results show that the differential nonlinearity and the integral nonlinearity of the proposed scheme could be reduced by two orders of magnitude compared with that based on Mach-Zehnder modulator scheme, and the ratio of level separation mismatch is closer to the ideal value 1. Furthermore, the improvement of the system at different probe field detunings and coupling field strengths is investigated.