Soliton ensembles in a laser cavity: collective behaviors, phase transitions and application to the generation of optical pulses with high repetition-rate – SOLICRISTAL

The study of collective behaviors for large sets of dissipative solitons is an unexplored and challenging area of fundamental research in nonlinear optics that we plan to investigate experimentally, numerically and theoretically. We expect to find strong analogies between these collective behaviors and the description of the states of matter, including phase transitions between them. Although these dissipative soliton ensembles could live in various nonlinear systems, we shall focus on their manifestation in mode-locked fiber lasers, for which all the project partners have complementary experience. Dissipative solitons manifest in the fiber laser cavity as optical pulses with given, and identical, phase and amplitude profiles. One goal will be to determine the conditions of formation for large soliton “crystals”, in which dissipative solitons are stably bound to each other, with fixed relative pulse-to-pulse separations and phase relationships. This vast fundamental task also prepares for the applied tasks in which we aim at developing novel high-repetition-rate pulsed fiber laser sources. It will be addressed by both academic partners, namely ICB Dijon and LPA Angers.
We propose the development of two types of pulsed fiber laser sources of high-repetition rates, which would address complementary ranges of repetition rates, namely the range 10-to-100 GHz on the one hand, and 100 GHz-to-1THz on the second hand. These repetition rates should be obtained without involving complicate electro-optic drivers: this represents the challenge and the potential innovation relative to these more applied parts. Naturally, the development of these sources at the experimental level will be coupled to theoretical and numerical investigations, using different model levels, from detailed propagation models to mean-field effective models and multi-scale analysis.
The first type of source will mainly use power-scaling laws, extrapolated from preliminary results as well as from the results obtained in the fundamental task of the project, in order to find the appropriate cavity design and pumping conditions where the entire fiber laser cavity can be filled with a large “crystal” of dissipative solitons, hence providing a stable repetition rate fixed by the nonlinear interactions between soliton pulses. This source will be developed experimentally at LPA, using also the expertise of ICB for the characterization of the pulsed output of the source.
The second type of source, which addresses higher repetition rates in the 100 GHz-to-1THz range, is based on triggering the pulsing regime by using a key nonlinear mechanism called modulational instability, and benefiting from a stabilization of pulsing through dissipative nonlinear processes. The source will be designed numerically and developed experimentally at ICB, owing to Dijon’s expertise in the fields of modulational instability and mode-locked fiber laser cavities. The expertise of LPA in high-power-handling components and fiber cavity designs will also be added into the experimental part. In addition to the use of “scalar” modulational instability, we shall focus on innovative cavity design using “vectorial” modulational instability. This strategy has never been tested inside a cavity and we anticipate that it would bring enhanced repetition-rate stability, a major feature which is lacking to the few high-repetition-rate fiber lasers that have been tested to date in research laboratories.

The overall project represents an ambitious program of research which combines the exploration of new soliton physics in fundamental nonlinear science, fiber-laser physics, and applications to the development of innovative fiber laser designs for an undeveloped niche of optical pulse sources that could become available for telecom market as well as for other emerging markets such as sensing applications and metrology.