BUNEL Thomas : Generation of multiple frequency combs in few mode passive fiber resonators

Résumé de thèse :

Optical frequency combs are light sources that revolutionized the science of precision measurements in the beginning of the 21st century. The applications extend to different fields of the detection of pollutants by measuring distances for autonomous cars or the detection of exoplanets. More recently, implementing multiple frequency combs has added speed and precision, making it possible to gain several orders of magnitude in the speed of analysis compared to single comb systems to access ultra-precise dynamic characterizations.

The objective of this project is to develop multiple frequency comb light sources from simple short fiber resonators supporting several transverse modes or cores. This additional degree of freedom generates a rich and original dynamic to be studied from a fundamental point of view before being able to optimize these sources for one of the aforementioned applications.

The used resonators are fiber Fabry-Perot cavities made from optical fibers with a fiber length of around 6 to 10 cm. Both fiber ends are mounted in ceramic ferrules and Bragg mirrors are deposited at each extremity. An experimental setup was made to pump the cavity with a laser which is stabilized on a cavity resonance. That way, nonlinear effects occur in the cavity making possible frequency comb generations. Several studies could be conducted. First, the modulation instability process was investigated in a cavity with an anomalous dispersion and characterized in intensity and phase with a high resolution. It was shown that the cross-phase modulation effect occurring in Fabry-Pérot cavities, due to the temporal overlap between the forward and the backward waves, have a significant impact on the modulation instability process which therefore depends on the input pulse duration. Secondly, frequency comb generation was studied as a function of pumping (pulsed or continuous), dispersion (normal or anomalous), and cavity length. Thus, cavity solitons, switching waves, and Brillouin frequency combs with a line spacing of 10 GHz were generated in 1 GHz free spectral range cavities.

For the future, we plan to transfer our knowledge in frequency comb generation in a single mode cavity to multimode or multicore cavities allowing to develop a multiple frequency comb light source.

Doctorant : BUNEL Thomas

Directeur(s) de thèse : MUSSOT Arnaud, CONFORTI Matteo