Frequency Stabilization and Frequency Conversion in High-Q Silicon Nitride Microresonators

Integrated photonics is an active research field in the recent decade. Silicon nitride is a prominent platform that features low optical loss and can be fabricated in a high-volume complementary metal–oxide–semiconductor (CMOS) foundry. The first part of the thesis focuses on taking advantage of these two mature properties to create integrated lasers with high frequency stability, which possibly has the lowest frequency noise among integrated lasers at the time when this thesis is written. Silicon nitride is also popular in the four-wave-mixing applications as it has an inherent high third-order optical nonlinearity. In the second part of this thesis, however, I present advancement and applications of the second order optical nonlinearity in this material. The second order nonlinearity is not inherent but rather induced by optical signals through photogalvanic effect. This effect is presented as weak historically, but efficient applications are made available in this thesis through the high enhancement of low loss microresonators. Applications include efficient generation of low-noise and tunable lasers through second harmonic generation and demonstrating the quantum nature of correlated photon-pairs generated through spontaneous down conversion.