High-Speed Silicon Optical Modulators

Abstract

High-speed silicon optical modulators are reviewed with respect to applications of optical signal generation in two major modulation formats in optical-fiber telecommunications: on-off keying as a common modulation format in commercialized 10-Gbit/s optical-fi ber networks and quadrature phaseshift keying as an advanced modulation format in cutting-edge 64-Gbit/s and 128-Gbit/s coherent optical-fiber networks. The silicon optical modulators in this review consist of Mach-Zehnder interferometer waveguides having lateral PN-junction rib-waveguide phase shifters and are suitable to highly integrated monolithic optical modulators with small footprint and low optical insertion loss. We present the performance of a 10-Gbit/s on-off keying silicon optical modulator in a fiber-pig-tailed package with a bit error rate as low as that for a commercialized lithium-niobate optical modulator. We describe a nested silicon Mach-Zehnder optical modulator for 64-Gbit/s quadrature phase-shift keying and characterize it with a constellation diagram and bit-error-rate characteristics. The progress and the prospects for 128-Gbit/s dual-polarization quadrature phase-shift keying are presented.