Microcombs for ultrafast optical interferometry

Doctoral thesis, 2023

The optical frequency comb has revolutionized the field of laser spectroscopy. This type of laser, characterized by an array of uniformly spaced and coherent laser lines, finds promise in photonic platforms for the integration of chip-scale spectrometers. On-chip frequency comb generation can be achieved through microresonators, driven by a single-frequency laser, yielding ultrashort light pulses with a broad spectral bandwidth.

In this thesis, linear interferometry techniques using frequency combs are analyzed, particularly the dual-comb configuration. By using two-frequency combs, this technique enables the optical sampling of a device under test with high resolution and short measurement times. The interest for implementing this technique using microcombs has attracted a high interest, however, its realization is still challenging.

This work studies the dynamics of microcomb generation and their impact on its spectral properties. As a result, it is proposed different methods to stabilize their output which has allowed us to implement dual-comb interferometry for the first time using platicon microcombs. Additionally, a method to tune a microcomb is proposed, potentially overcoming the limitation imposed by sparse spectral sampling, primarily determined by the comb spacing.

Furthermore, the dynamics of spectral broadening are investigated, resulting in the generation of coherent octave-spanning spectra using ultra-low loss nano-photonic waveguides. Overall, the results of this thesis underline the capacity of chip-scale frequency combs to offer extensive spectral coverage, high resolution, sensitivity, and rapid measurement times in optical interferometry.