Cavity Solitons in Silicon Nitride Microresonators
Joshi, Chaitanya Suhas
Silicon Photonics is a field of research that has attracted a lot of interest in the past few decades and has led to the development of compact structures on chip for the confinement and manipulation of light. The ability to confine light in a small mode area in waveguides has enabled the exploration of nonlinear optical phenomena on chip including frequency conversion using four wave mixing. Recently, demonstrations of chip-based optical frequency combs generated in microresonators fabricated using CMOS compatible materials and fabrication processes has become a rapidly developing field of research. The ability to generate a broadband optical spectrum on-chip by injecting a single frequency continuous wave laser into the microresonator holds promise in enabling applications of these combs in spectroscopy, metrology, and optical data communications. The ability to precisely control the generation of an optical frequency comb and repeatedly achieve low-noise operation is especially important to these applications. In this dissertation we set out to solve the problem of precise control and repeatable low-noise frequency comb generation in microresonators. In the first part of the dissertation, we investigate thermally controlled cavity soliton generation in silicon nitride microresonators by means of current control of integrated heaters. We report a method to stably and repeatably access cavity soliton states in a silicon nitride microresonator and control the detuning dependent properties of the soliton states using the integrated heaters. We characterize the RF noise characteristics of these soliton modelocked states and study the ability to generate single and multiple solitons within one cavity round trip. In the second part of the dissertation we investigate some of the applications of cavity solitons in silicon nitride microresonators. We study the bidirectionally pumped regime of operation of silicon nitride microresonators and demonstrate tunable generation of counter-rotating solitons in a single cavity. We also study the tunability of the soliton trains in opposite directions as a function of pump power ratio in the two directions. We also study a dual comb source consisting of soliton trains generated in two distinct microresonators by maintaining them at a fixed offset in their repetition rates determined by electircal feedback on one of the heaters. The tunability of the offset frequency between the two soliton trains is studied. The tunable dual comb source is applied to a distance ranging measurement where the ambiguity imposed by the fixed repetition rate of the signal comb is lifted by tuning it with respect to the other comb that acts as a local oscillator. The work presented in this dissertation paves the way for further exploration of applications of cavity solitons generated in silicon nitride microresonators in a reliable and precisely controlled manner.
soliton; Optics; Silicon Photonics; Physics; Frequency combs
Gaeta, Alexander L.
Lipson, Michal; Wise, Frank William
Ph.D., Applied Physics
Doctor of Philosophy
Attribution-NonCommercial 4.0 International
dissertation or thesis
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