High-speed all-optical constellation add-drop multiplexer for 16-QAM based on constellation update in elastic optical networks

An all-optical constellation add-drop multiplexer (CADM) based on constellation update is proposed, aiming to improve the flexibility in the elastic optical switch. We use QPSK as the minimum granularity of the switch to realize the constellation add/drop for 16-QAM. In this scheme, a bi-directional phase-sensitive amplification (PSA) is employed to de-multiplex the 16-QAM into two PAM-4s simultaneously. Then the recovered two PAM-4s can be converted to a QPSK signal representing the quadrant symbol of the original 16-QAM through saturated four-wave mixing (FWM) and coherent addition. Finally, a brand new 16-QAM can be obtained through the FWM between the converted QPSK, an added QPSK, and the original 16-QAM signals. The feasibility of the scheme can be confirmed by the transfer functions and input–output constellations. The error vector magnitude (EVM) and bit error ratio (BER) of the updated 16-QAM and converted QPSK signals are calculated to evaluate the performance of the scheme.