说明：  tA scheme of format conversion optical 16-ary quadrature amplitude modulation (16QAM) toquadrature phase shift keying (QPSK) signal based on cascaded four-wave mixing (FWM) in semiconduc-tor optical amplifiers (SOAs) is proposed. Theoretical analysis and simulations of the format conversionscheme are conducted to validate the feasibility of the proposal. In this proposal, the phase conjugatedof 16QAM signal is generated after the first FWM process in an SOA, and then the QPSK signal is con-verted due to the second non-degenerate FWM (ND-FWM) process in another SOA. The performance andthe optimal design of the 10 Gbit/s format conversion system under various key parameters of SOAs are uated and discussed. Simulation results present useful to enable interconnection between backbonenetwork and access network.