128-Gb/s Monolithic Silicon Optical Modulator for Digital Coherent Communication

Silicon photonic waveguides are promising in small-footprint low-cost monolithic photonic integrated circuits with capability of high-yield mass production using large-diameter wafers. Design, fabrication and performance characterization of a small-footprint monolithic dualpolarization quadrature phase-shift keying silicon-based optical modulator for digital coherent communication, which plays major roles in high-speed optical transport networks, are reported. The monolithic dual-polarization quadrature phase-shift keying silicon optical modulator consists basically of device blocks for quadrature phase-shift keying and a polarization-multiplexing optical circuit, which are monolithically integrated on silicon chip. The polarization-multiplexing optical circuit is based on silicon waveguides which are based on silicon cores and silica clads only, thereby suitable for mass production because the circuit can be fabricated simultaneously with silicon rib waveguides in the blocks for quadrature phaseshift keying. Low-loss monolithic silicon dual-polarization quadrature phase-shift keying optical modulator realized by integration with the polarization-multiplexing optical circuit is shown to have low optical loss. Dual-polarization quadrature phase-shift keying with bit rate as fast as 128 Gb/s is demonstrated based on constellation and bit-error-rate measurements.