High-Speed Silicon Photonics Modulators

The realization of gigahertz bandwidth modulators out of silicon-based technology in the early 2000s marked a cornerstone of silicon photonics development. While modulation speeds have since progressed well above 50 GHz and satisfy the bandwidth requirements of current and emerging modulation formats, concurrently obtaining low drive voltages and low insertion losses remains a very active area of research. While modulators generally come in two categories, direct absorption and those relying on embedded phase shifters, the focus of this paper lies on the latter capable of supporting both complex-valued modulation and optically broadband operation. The paper provides an overview of the current state of the art, as well as of currently explored improvement paths. First, common phase shifter configurations, aspects related to electrical driving, and associated power consumption are reviewed. Slow-wave, resonant, and plasmonic enhancements are further discussed. The reader is familiarized with the optimization of these devices and provided with a sense of the limitations of current technology and the potential of novel hybrid material integration.