RF Signal Processing using Light-Sound Interactions in Silicon Photonic Integrated Circuits

Abstract

Since the idea of guiding and manipulating light in silicon waveguides was investigated in the 1980s, silicon photonic integrated circuits have been rapidly growing for applications in wide-bandwidth communications, sensors, and nonlinear and quantum optics. For wideband communications, radio-frequency (RF) signal processing in the optical domain, called microwave photonics, is an emerging application in silicon integrated photonic circuits. Manipulation of optical fields can be achieved by nonlinear optical effects, for example, GHz silicon modulators based on plasma dispersion effect are used for the up-conversion of RF signal to optical frequency. Among various nonlinear optical effects in silicon, Brillouin scattering, which is the coherent interaction between light and traveling sound, is a prominent method for combining RF, optical, and acoustic domains. In conventional RF signal processing, acoustic waves are used for high-quality filters and delays. Mixing RF, acoustic, and optical domains has shown not only high-quality filters and delays, but also low-noise RF and optical sources, non-reciprocal devices, and sensors. In this thesis, we discuss our novel approaches for Brillouin-based RF signal processing in silicon photonic integrated circuits. In chapter 1, we review silicon photonics and forward Brillouin scattering in a silicon chip. In chapter 2, we study the design and fabrication of silicon Brillouin-active-membrane (BAM) waveguides. In chapter 3, we describe experimental methods to measure optical losses and Brillouin resonances in silicon BAM waveguides. In chapter 4, we introduce our novel demonstration of coherent control of optically driven acoustic waves in silicon waveguides. In chapter 5, based on our demonstration of coherent acoustic control, we develop on-chip RF signal-shaping devices by using acoustic interferences. In chapter 6, we demonstrate fine-tunable narrowband Brillouin RF filters based on coupled acoustic cavities in silicon.