All-optical technique for modulation format conversion from NRZ-OOK to RZ-16QAM employing nonlinear optical loop mirror with 1:2 coupler.

All-optical technique for modulation format conversion from 4 channels non-return-to-zero on-off-keying (OOK) to return-to-zero 16 quadrature amplitude modulation (16QAM) employing nonlinear optical loop mirror with 1:2 coupler configuration is proposed and experimentally demonstrated at 10Gs/s. The experimentally converted 16QAM signal was distorted in its phase by cross-phase modulation induced amplitude-to-phase noise conversion. The effect of amplified spontaneous emission noise in the amplified OOK signals to the converted 16QAM's phase was theoretically discussed.