Harnessing Traveling-wave Photon-Phonon Interactions in Integrated Waveguides
By replacing chip-based electrical circuits with optical waveguides, the field of integrated photonics seeks to create next-generation technologies for information processing, high-speed communications, and precision sensing. To this end, a considerable body of work over the past two decades has demonstrated high-performance waveguide-integrated modulators, filters, light sources, and detectors with potential advantages in terms of size, power consumption, performance, and cost over conventional benchtop systems.
In this dissertation, we explore interactions between traveling photons and phonons within these integrated photonic circuits. By coupling optical and elastic degrees of freedom, we develop new functionalities not available within all-optical systems. We harness these techniques to demonstrate optical amplifiers, microwave filters, nonreciprocal devices, and signal processing techniques within integrated silicon waveguides.
Underpinning these interactions is a nonlinear optical effect called stimulated Brillouin scattering (SBS). While Kerr (electronic) and Raman (optical phonon-mediated) nonlinearities are well-known to be enhanced by sub-wavelength confinement in integrated waveguides, Brillouin nonlinearities, which are the strongest nonlinearity in optical fiber, were previously absent in semiconductor integrated photonic circuits. By designing new optomechanical waveguide structures which tightly confine light and sound, these nonlinearities become radically enhanced, making them not only measurable, but exceedingly strong and tailorable.