120-Gb/s NRZ-DQPSK signal generation by a thin-lithium-niobate- substrate modulator

A high-speed DQPSK optical modulator is fabricated with a thin lithium niobate substrate. Decrease in the propagation loss of electrodes and a low half-wave voltage, which can be realized by fabrication of a ridge-type optical waveguide structure, can help achieve 120-Gb/s (60-Gbaud) NRZ-DQPSK modulation with full electrical-time-division-multiplexing technique.