Brillouin- and Kerr-mediated parametric light sources in scalable photonic platforms

This thesis investigates Brillouin- and Kerr-active light sources in scalable silicon nitride platforms. We design waveguides that support both Brillouin scattering, a nonlinear optical process mediated by an acoustic wave, and the Kerr nonlinearity, an intensity-dependent refractive index. Using these waveguides, high spectral purity Brillouin lasers and broadband microcomb sources are realized by forming optical microresonators. In this work, we demonstrate an enhancement of Brillouin strength by several orders of magnitude, present multiple Brillouin photonic applications, realize Brillouin lasers and microcomb sources, and theoretically examine the interaction of competing Brillouin and Kerr gain in a single microcavity.
Chapter 2 establishes the theoretical and technical background, covering nonlinear optics in integrated photonics, microring resonators, microcomb generation, and the principles of Brillouin scattering.
In Chapter 3, we evaluate silicon nitride geometries including thick, symmetric dual-stripe, and asymmetric dual-stripe waveguides for SBS and Kerr nonlinearity. Optimized symmetric dual-stripe designs enabled low-loss fabrication (7 dB/m) and supported both Brillouin lasing and Brillouin-induced Kerr frequency combs.
Chapter 4 introduces a numerical model of competing Brillouin and Kerr gain in microresonators. Simulations show that Brillouin microcombs can form in forward or backward directions depending on the free spectral range (FSR) and pump conditions. Acoustic detuning was found to be critical, as FSR values slightly below the Brillouin shift prevent suppression of Brillouin lasing by Kerr induced cross-phase modulation.
In Chapter 5, we enable enhanced Brillouin gain by integrating silicon nitride with tellurite glass and coupling to surface acoustic waves (SAWs). This hybrid approach improved Brillouin strength by over two orders of magnitude, enabling demonstrations of a 10-dB optical amplifier, a tunable microwave notch filter with 2.2-MHz linewidth, and a Brillouin phonon laser with a record-low 7-Hz acoustic linewidth.
Together, these results demonstrate that Brillouin and Kerr nonlinear sources can be integrated in silicon nitride, offering scalable routes to high-coherence lasers, frequency combs, and multifunctional microwave photonic devices. This establishes a foundation for applications ranging from optical frequency division to coherent phonon sources and advanced signal processing.