We describe a novel SOA-based all-optical pure-phase modulator, and show
how deleterious cross-gain modulation from the SOAs can be suppressed
by utilizing an integrated interferometer structure. We experimentally
demonstrate the use of the optical gate as a π/4 phase modulator
producing 21.3 Gbaud 8PSK from 21.3 Gbit/s OOK and 21.3 Gbaud QPSK
inputs. The modulator produces 3 dB of gain and coherent detection-based
bit error rate measurements indicate a 2.4 dB excess penalty.