Solitons in non-linear ring micro-resonators

We studied with the LugiatoLefever spatiotemporal formalism the existence, formation and dynamics of solitons in non-linear Kerr micro-resonators. For anomalous and normal dispersion we find different types of solitons, bright and dark respectively. We have determined the region of existence and stability for both types of structures and have studied the introduction of third order dispersion which gives a velocity to the solitons and stabilises them. In the normal GVD regime, we could not find the recently proposed flat top solitons. Ideas why this is the case are discussed

Thermal radiation measurements of Silicon microspheres

La solución de Mie a las ecuaciones de Maxwell describe la interacción de una onda luminosa con una esfera. Esta solución - para dimensiones de esfera comparables a la longitud de onda de la luz - tiene un resultado muy interesante. Para algunas frecuencias de resonancia y radios de la esfera, la sección de scattering puede ser más de diez veces mayor que la sección geométrica real. Además, en algunas condiciones, la sección de absorción también puede ser mayor que la real. Esto significaría que la microesfera absorbería más luz que la que incidía en su superficie. Esto tendría una consecuencia muy impresionante en el aprovechamento de la luz en placas solares. Para probar esta capacidad y aplicando la ley de Kirchhoff de radiación térmica - que establece que la emisividad es igual a la absorbancia - hemos de medir la radiación térmica de una sola microesfera. En este proyecto diseñamos un set-up óptico que formará parte de la configuración final utilizada para medir la radiación térmica de una sola microesfera. Para realizar la medición se utilizaron tecnicas de espectroscopia FT-IR combinada con técnicas de lock-in. Hemos podido medir un área de 10?m de radio en contraste con los pocos milímetros que el FT-IR normal mide.Mie’s solution to Maxwell’s equations describes the interaction of a light wave with a sphere. This solution - for sphere dimensions comparable to the light wavelength- has a very a interesting result. For some resonant frequencies and sphere radii, scattering section can be more than ten times greater than actual geometric section. Furthermore, under some conditions, the absorption cross section can also be larger than the real one. This means that the microsphere would absorb more light than the one impinging on its surface. This would have a very impressive consequence on light harvesting. In order to test this ability and applying Kirchho↵’s law of thermal radiation - which states that the emissivity is equal to the absorptivity - we would measure thermal radiation of a single microshpere. In this project we design a optical set-up that will be part of the final set-up used to measure the thermal radiation of a single microsphere. In order to perform the measurement Step-Scan FT-IR spectroscopy combined with lock-in techniques were used. We where able to measure an area of 10µm radius’ circle in contrast to the few millimetres that normal FT-IR measures

Optical turbulence control by non-Hermitian potentials

We propose a method for a control of turbulence by modifying the excitation cascade leading to turbulence. The method is based on the asymmetric coupling between the spatiotemporal excitation modes by non-Hermitian potentials. The non-Hermitian potentials are recently known to enable unidirectional coupling between modes. We demonstrate that such unidirectional coupling towards larger (smaller) wave numbers can increase (reduce) the energy flow in turbulent states, and therefore, influence the character of turbulence. The study is based on the complex Ginzburg-Landau equation, a universal model for pattern formation and turbulence in a wide range of systems including nonlinear optical resonators. We show that enhancement or reduction of turbulence is indeed dependent on the imposed direction of the energy flow, controlled by the phase shift between the real and imaginary parts of the temporal oscillation of the non-Hermitian potential.Peer ReviewedPostprint (published version

Turbulence control by non-Hermitian potentials

We propose a method to control turbulence by the introduction a non-Hermitian spatiotemporal modulation, based on the energy redirection from unstable to stable modes by the unidirectional coupling induced by these potentials and so, influence and slow down the excitation cascade of turbulenceObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (author's final draft

Non-Hermitian control of optical turbulence in systems with fractional dispersion

We show an efficient mechanism to control optical turbulence in systems with different dispersion laws, including parabolic, sub-diffractive, hyper-diffractive or general fractional dispersion. The method is based on the modification of the energy cascade through spatial scales leading to turbulence: a non-Hermitian spatio-temporal periodic potential allows unidirectional coupling between modes in the excitation process. We prove a significant increase and reduction of the energy flow in turbulent states, by either condensing the excitation towards small wave-numbers or affecting the energy transfer towards large wave-number. The study is based on the complex Fractional Ginzburg–Landau equation, a universal model for pattern formation and turbulence in a wide range of systems. The enhancement or reduction of turbulence is indeed dependent on the imposed direction of the energy flow, controlled by the phase shift between the real and imaginary parts of the temporal oscillation of the non-Hermitian potential.Peer ReviewedPostprint (published version

Light control by Non-Hermitian modulation in multimode fiber

We show that a non-Hermitian modulation of the potential along the nonlinear multimode fibers controls dynamics of propagating radiation. Specifically we consider simultaneous modulation of the refraction index and gain/loss profile. We observe that the non-Hermitian modulation introduces a unidirectional and controllable coupling towards the lower/higher order transverse modes, depending on the potential parameters. Such effect may enhance the beam self-cleaning phenomena. On the contrary, coupling towards higher order modes may enhance pulsing, turbulence and, eventually help in super-continuum generation.Peer ReviewedObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (published version

Non-Hermitian mode cleaning in periodically modulated multimode fibers

We show that the simultaneous modulation of the propagation constant and of the gain/loss coefficient along the multimode fibers results in unidirectional coupling among the modes, which, depending on the modulation parameters, leads to the enhancement or reduction of the excitation of higher order transverse modes. In the latter case, effective mode-cleaning is predicted, in ideal case resulting in single-mode spatially coherent output. The effect is semi-analytically predicted on a simplified Gaussian beam approximation and numerically proven by solving the wave propagation equation introducing the modulated potential.Peer ReviewedObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPreprin

Thermal radiation measurements of Silicon microspheres

La solución de Mie a las ecuaciones de Maxwell describe la interacción de una onda luminosa con una esfera. Esta solución - para dimensiones de esfera comparables a la longitud de onda de la luz - tiene un resultado muy interesante. Para algunas frecuencias de resonancia y radios de la esfera, la sección de scattering puede ser más de diez veces mayor que la sección geométrica real. Además, en algunas condiciones, la sección de absorción también puede ser mayor que la real. Esto significaría que la microesfera absorbería más luz que la que incidía en su superficie. Esto tendría una consecuencia muy impresionante en el aprovechamento de la luz en placas solares. Para probar esta capacidad y aplicando la ley de Kirchhoff de radiación térmica - que establece que la emisividad es igual a la absorbancia - hemos de medir la radiación térmica de una sola microesfera. En este proyecto diseñamos un set-up óptico que formará parte de la configuración final utilizada para medir la radiación térmica de una sola microesfera. Para realizar la medición se utilizaron tecnicas de espectroscopia FT-IR combinada con técnicas de lock-in. Hemos podido medir un área de 10?m de radio en contraste con los pocos milímetros que el FT-IR normal mide.Mie’s solution to Maxwell’s equations describes the interaction of a light wave with a sphere. This solution - for sphere dimensions comparable to the light wavelength- has a very a interesting result. For some resonant frequencies and sphere radii, scattering section can be more than ten times greater than actual geometric section. Furthermore, under some conditions, the absorption cross section can also be larger than the real one. This means that the microsphere would absorb more light than the one impinging on its surface. This would have a very impressive consequence on light harvesting. In order to test this ability and applying Kirchho↵’s law of thermal radiation - which states that the emissivity is equal to the absorptivity - we would measure thermal radiation of a single microshpere. In this project we design a optical set-up that will be part of the final set-up used to measure the thermal radiation of a single microsphere. In order to perform the measurement Step-Scan FT-IR spectroscopy combined with lock-in techniques were used. We where able to measure an area of 10µm radius’ circle in contrast to the few millimetres that normal FT-IR measures

Solitons in non-linear ring micro-resonators

We studied with the LugiatoLefever spatiotemporal formalism the existence, formation and dynamics of solitons in non-linear Kerr micro-resonators. For anomalous and normal dispersion we find different types of solitons, bright and dark respectively. We have determined the region of existence and stability for both types of structures and have studied the introduction of third order dispersion which gives a velocity to the solitons and stabilises them. In the normal GVD regime, we could not find the recently proposed flat top solitons. Ideas why this is the case are discussed

Stabilisation of spatially periodic states by non-Hermitian potentials

We uncover new families of stable periodic solutions by the introduction of non-Hermitian potentials in the universal complex Ginzburg–Landau equation. We perform a comprehensive analysis on the dynamics and stability of the system by determining and following these new solutions for a one-dimensional system, and demonstrate that the results hold for higher spatial dimensions and for the corresponding complex Ginzburg–Landau fractional order equation. We prove the robustness of the stabilisation within a broad range in parameter space. The universality of the CGLE allows extending these results to different actual systems described by other specific models. In particular, we provide results on the stabilisation for Vertical Cavity Surface Emitting Lasers.Peer ReviewedPostprint (author's final draft