Optimisation of nonlinear photonic devices: design of optical fibre spectra and plasmonic systems

El propósito de esta tesis es diseñar y optimizar dispositivos fotónicos en el régimen no lineal. En particular, se han elegido dos tipos de dispositivos, que se clasifican según los fenómenos físicos de interés. La primera clase corresponde a fibras convencionales o de cristal fotónico, diseñadas para que la dinámica temporal de los paquetes de onda que se propagan en su interior genere espectros con las características deseadas, en el contexto del supercontinuo. La segunda clase explota la fenomenología espacial asociada a las ondas electromagnéticas que se propagan sobre la superficie de un metal. Estas ondas permiten, desde diseñar dispositivos tipo chip fotónico cuyas dimensiones típicas están muy por debajo de la longitud de onda de la luz, hasta la generación de estados no lineales híbridos de dinámica singular. Todos estos efectos tienen lugar dentro del marco proporcionado por las ecuaciones de Maxwell macroscópicas, las cuales han sido resueltas numéricamente. En algunos casos se emplean grandes aproximaciones teóricas para estudiar sistemas 1D, mientras que en otros se integran directamente en 3D. En el caso en el que la optimización del dispositivo resulta no trivial tras haber adquirido un conocimiento teórico profundo del mismo, se emplea una novedosa herramienta numérica que nace de la combinación de algoritmos genéticos con plataforma Grid.Milián Enrique, C. (2012). Optimisation of nonlinear photonic devices: design of optical fibre spectra and plasmonic systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14670Palanci

Robust ultrashort light bullets in strongly twisted waveguide arrays

We introduce a new class of stable light bullets that form in twisted waveguide arrays pumped with ultrashort pulses, where twisting offers a powerful knob to tune the properties of localized states. We find that, above a critical twist, three-dimensional wave packets are unambiguously stabilized, with no minimum energy threshold. As a consequence, when the higher-order perturbations that accompany ultrashort pulse propagation are at play, the bullets dynamically adjust and sweep along stable branches. Therefore, they are predicted to feature an unprecedented experimental robustness.Peer ReviewedPostprint (published version

Cavity solitons in a microring dimer with gain and loss

© 2018 Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.We address a pair of vertically coupled microring resonators with gain and loss pumped by a single-frequency field. Coupling between microrings results in a twofold splitting of the single microring resonance that increases when gain and losses decrease, giving rise to two cavity soliton (CS) families. We show that the existence regions of CSs are tunable and that both CS families can be stable in the presence of an imbalance between gain and losses in the two microrings. These findings enable experimental realization of frequency combs in configurations with active microrings and contribute toward the realization of compact multisoliton comb sources.Peer ReviewedPostprint (author's final draft

Solitons and frequency combs in silica microring resonators: Interplay of the Raman and higher-order dispersion effects

The influence of Raman scattering and higher order dispersions on solitons and frequency comb generation in silica microring resonators is investigated. The Raman effect introduces a threshold value in the resonator quality factor above which the frequency locked solitons can not exist and, instead, a rich dynamics characterized by generation of self-frequency shift- ing solitons and dispersive waves is observed. A mechanism of broadening of the Cherenkov radiation through Hopf instability of the frequency locked solitons is also reported.Comment: 12 pages, 10 figure

Energy deposition dynamics of femtosecond pulses in water

We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV. We also introduce an equation for the Raman gain valid for ultra-short pulses that validates our experimental procedure.Comment: 4 pages, 5 figures, submitted to Applied Physics Letter

Superfilamentation in air

The interaction between a large number of laser filaments brought together using weak external focusing leads to the emergence of few filamentary structures reminiscent of standard filaments, but carrying a higher intensity. The resulting plasma is measured to be one order of magnitude denser than for short-scale filaments. This new propagation regime is dubbed superfilamentation. Numerical simulations of a nonlinear envelope equation provide good agreement with experiments.Comment: 5 pages, 4 figure

Underwater acoustic wave generation by filamentation of terawatt ultrashort laser pulses

Acoustic signals generated by filamentation of ultrashort TW laser pulses in water are characterized experimentally. Measurements reveal a strong influence of input pulse duration on the shape and intensity of the acoustic wave. Numerical simulations of the laser pulse nonlinear propagation and the subsequent water hydrodynamics and acoustic wave generation show that the strong acoustic emission is related to the mechanism of superfilamention in water. The elongated shape of the plasma volume where energy is deposited drives the far-field profile of the acoustic signal, which takes the form of a radially directed pressure wave with a single oscillation and a very broad spectrum.Comment: 9 pages, 12 figure

Dissipative light bullets in externally driven multimode Kerr cavity with parabolic 3D potential

We study the formation of dissipative light bullets in externally driven multimode GRIN fiber cavity with chirped pulse pumping. Numerical simulations show the generation of stable bullets, with a spatiotemporal shape controlled via the pump chirp

Photonic Snake States in Two-Dimensional Frequency Combs

Taming the instabilities inherent to many nonlinear optical phenomena is of paramount importance for modern photonics. In particular, the so-called snake instability is universally known to severely distort localized wave stripes, leading to the occurrence of transient, short-lived dynamical states that eventually decay. The phenomenon is ubiquitous in nonlinear science, from river meandering to superfluids, and to date it remains apparently uncontrollable. However, here we show that optical snake instabilities can be harnessed by a process that leads to the formation of stationary and robust two-dimensional zigzag states. We find that such new type of nonlinear waves exists in the hyperbolic regime of cylindrical micro-resonators and it naturally corresponds to two-dimensional frequency combs featuring spectral heterogeneity and intrinsic synchronization. We uncover the conditions of the existence of such spatiotemporal photonic snakes and confirm their remarkable robustness against perturbations. Our findings represent a new paradigm for frequency comb generation, thus opening the door to a whole range of applications in communications, metrology, and spectroscopy.Comment: 6 figures, 11 page