High-Speed Optical Modulators and Data Communication Systems in Silicon Photonics

Abstract

Silicon photonics provides a promising platform for developing densely integrated, highly scalable and potentially very low cost solutions for various applications in the field of optical data communications. This thesis focuses on the technical challenges in silicon photonics on both the component and system levels. One of the most important components in optical transmitters is the electro-optic modulator. However, building high-speed efficient modulators in silicon remains to be one of the key challenges of silicon photonics. To achieve more efficient modulators, the first approach presented here is to incorporate new materials into the silicon platform with new device geometries. With highly efficient electro-optical polymers and low-loss silicon striploaded slot waveguide, we demonstrated the first silicon-polymer hybrid modulator operating with GHz bandwidth as well as the first sub-1 Vπ device at RF frequency. The second approach is innovative RF design, through which we demonstrated 40 Gb/s power-efficient silicon pn-junction traveling-wave Mach-Zehnder modulators showing compelling performance compared to commercial Lithium Niobate modulators. At the time of writing, system level designs in silicon photonics are far from mature. A critical barrier toward system design is the lack of established stable fabrication processes and process design kits (PDKs). I participated in and lead the testing effort of the early development of an monolithic silicon photonics platform (OpSIS-IME). High-speed (50 Gb/s) modulators and detectors as well as high-performance passive components co-exist in the same process with consistent performance and high yield. This opens up tremendous opportunities for systems. Upon this platform, we demonstrated various kinds of high-speed high-performance transmitters and receivers using different topologies and device approaches, showing a level of integration beyond the state-of-the-art. For a power-efficient and high-performance photonics system, electronics and in particular the high-speed analog front-end that directly interfaces with the photonic devices is an integral part and to a great extent determines system-level performance. Furthermore, close-integration and co-design offer potentially significant improvement to the overall system performance. Among several other high-speed analog circuits results, we have demonstrated on both the optical transmitter and the receiver sides, that ultra-high data rate (100 Gb/s non-return-to-zero) is plausible in existing silicon-based photonics and electronics technology.