Frequency combs on chip for interferometry applications

Licentiate thesis, 2022

Optical frequency combs have revolutionized the field of laser spectroscopy. A frequency comb is a type of laser that generates an array of equally spaced coherent laser lines. Indeed, the  outstanding performance of frequency combs in terms of bandwidth and stability is readily attainable in bench-top systems. Integrated photonics offers a platform for the implementation of frequency combs relying on nonlinear optics processes.  This thesis explores the generation of chip-scale frequency combs based on supercontinuum and microcomb generation and its potential use for interferometry. This investigation covers the capabilities offered by supercontinuum generation in the normal dispersion regime. The spectral broadening is realized by pumping a straight waveguide with a short duration pulse meaning that the pump is a comb itself. Therefore, its performance in terms of coherence and the transferring of noise to the broadened spectra have been investigated. Microcombs can be generated  on a microresonator starting from a continuous wave laser. In this work, we study microcomb generation in the normal dispersion regime using a novel dual-cavity architecture.

 
The appended papers describe the nonlinear processes involved in the microcomb generation. We have studied its capabilities in terms of spectral flatness and symmetry, together with the coherence attained on these combs. It is found that these capabilities make microcombs a suitable spectral sources for spectroscopy. Furthermore, the capabilities of different interferometry techniques are analyzed in terms of resolution, sensitivity and measurement time in order to perform on-chip dual-comb spectroscopy.