Advanced optical modulators with hybrid configuration of silica-based PLC and LiNbO3 phase-shifter array for ultra-high-speed transport networks

Future optical transport networks should offer 10-Tb/s- class total capacity, and must be able to transport 100- Gb/s-class client signal transparently as well. Advanced modulation schemes for optical signals, such as differential quadrature phase-shift keying (DQPSK) and orthogonal frequency-division multiplexing (OFDM), are promising for such large-capacity networking. In this paper, highspeed optical modulators with a hybrid configuration of silica-based planar lightwave circuits and LiNbO₃ phase shifters are presented. Combining the advantages of the two components, the hybrid modulators offer high-speed responses as well as complex configurations and low optical losses. Using this technique, a DQPSK modulator, a return-to-zero- (RZ-) DQPSK modulator, and a two- subcarrier-OFDM-DQPSK modulator have been fabricated. Demonstrations of 10-Tb/s-class wavelength-division-multiplexing (WDM) transmission with 100-Gb/s- class data rate per channel using them are successfully achieved.