Estudi sobre estructures disipatives en sistemes òptics no-lineals: estructures localitzades i fluctuacions quàntiques.

RESÚM La formació de patrons espacials en sistemes òptics té molts elements en comú amb altres sistemes formadors de patrons que trobem a la natura (hidrodinàmics, biològics, mecànics, químics). Ara bé, nhi ha trets particulars dels sistemes òptics que motiven encara més lestudi de la formació de patrons en aquests. Duna banda, les potencials aplicacions a la tecnologia de la informació i les telecomunicacions: la formació destructures en el pla transversal a la direcció de propagació de la llum en sistemes nolineals òptics obre la porta al processat òptic de la informació en parallel, amb la codificació i emmagatzemament de la informació en aquest pla transversal. Respecte a aquest fet, haurem de tindre en compte dos aspectes . El primer dells és la possibilitat de multiestabilitat espacial, és a dir, dexistència de més duna solució del sistema per a uns valors donats dels paràmetres : ja que parlem de sistemes extensos, implica la possibilitat dassolir diverses solucions estables en distintes regions transversals. Aquest fet possibilita no només la coexistència entre patrons extensos, sinò lexistència destructures localitzades, de gran interés per a les aplicacions pràctiques que comentàvem adés, on actuaríen com bits de informació. És per tant dimportància estudiar com controlar els patrons emergents, i més en concret, les estructures localitzades, així com la possibilitat de crear-les, moure-les i esborrar-les. Aquest control permetria la utilització pràctica de les estructures localitzades com components de memòries òptiques, on la informació podria codificar-se i processar-se. Daltra banda, en una interacció nolineal estan creant-se i destruint-se fotons del camp electromagnètic. Aquesta naturalesa quàntica de la llum es manifesta fins i tot a temperatura ambient, cosa que diferencia notablement els sistemes òptics de qualsevol altre sistema. Aquest fet ha motivat lestudi dels efectes quàntics en patrons espacials transversals i, més recentment, en les estructures localitzades. Aquesta tesi versa sobre un tipus destructures localitzades que suporten diverses cavitats òptiques nolineals : els solitons de cavitat. Pot dividir-se en dues grans seccions, agrupant els diversos articles que constitueixen el cos fonamental daquesta tesi : la primera està dedicada a lestudi clàssic daquestes estructures, en la segona sestudia, per primer cop, les fluctuacions quàntiques dels solitons de cavitat. La primera secció consta dun primer apartat, que engloba els articles Vectorial Kerr-cavity solitons, Opt.Lett. 25, 957 (2000) i Bright cavity solitons in anisotropic vectorial Kerr cavities, J.Opt.B : Quantum Semiclass. Opt. 3 S118 (2001), on sestudien les condicions dexistència i el tipus de solitó que trobem en cavitats Kerr anisòtropes i birrefringents i es relacionen amb les solucions duna equació de paràmetre dordre (nolineal dSchrödinger amb decaïment i forçament paramètric : PDNLS), que descriu la susdita cavitat en el límit de gran anisotropia. Un segon apartat, constituït pels treballs Domain Walls and Ising-Bloch Transition in Parametrically Driven Systems, Phys.Rev.Lett. 89, 164101 (2002), The Ising-Bloch transition in degenerate optical parametric oscillators, J.Opt.B: Quantum Semiclass. Opt. 6, S361 (2004) i Stabilizing and controlling domain walls and dark-ring cavity solitons, Opt.Exp. 12, 2130 (2004), tracta sobre les parets de domini. En particular sestudia la transició Ising-Bloch en la PDNLS i els oscilladors òptics paramètrics degenerats (DOPO). En aquest sistema, es presenten també dos mecanismes destabilització i control de les estructures en sistemes bidimensionals, on les parets no són estables. La segona secció tracta el problema de les fluctuacions quàntiques en aquests solitons, estudiant-se lespectre dsqueezing de solitons en DOPOs. El treball Squeezed quantum cavity solitons, arxiv:quant-ph/0405148, enviat per la seva publicació a Physical Review Letters, presenta un tractament general per lestudi daquestes fluctuaciones i estudia per primer cop les fluctuacions quàntiques dels solitons de cavitat, trobant reducció de soroll perfecta per qualsevol rang de paràmetres on existeix el solitó. ____________________________________________________________________________________________________ ABSTRAC The matter of this Thesis is the study of a type of localized structures (LS) supported by different nonlinear optical cavities, in particular, cavity solitons (CSs), both bright and dark domain walls- CSs. By a hand, we study the nonlinear dynamics of these cavities and the features and behavior of LSs semiclassically. By other hand, we investigate about the quantum fluctuations features of CSs. We study these CSs in anisotropic vectorial Kerr cavities, in optical parametric oscillators and in an order parametric equation the parametrically driven nonlinear Schrödinger equation-, also. We demonstrate two alternative techniques for controlling and stabilizing dark CSs. About the problem of quantum fluctuations in CSs, in particular, we study the squeezing spectrum of CSs in degenerate optical parametric oscillators, but the method can be used with any different cavity in a trivial way. The structure of the Thesis consists of two sections: -An introduction with two different parts. First one is a brief summary of the field of nonlinear dynamics in optical cavities: main concepts, techniques, beginning and evolution of quantum optics, taking special care about the spatial aspects. -The introduction to the synopsis of articles, the mean body of this Thesis, grouped in three subjects, each one emphasizes most important results and conclusions: - Vectorial Kerr-cavity solitons, Opt.Lett. 25, 957 (2000); Bright cavity solitons in anisotropic vectorial Kerr cavities, J.Opt.B : Quantum Semiclass. Opt. 3 S118 (2001), where bright CSs in Kerr cavities are studied. - Domain walls are treated in Domain Walls and Ising-Bloch Transition in Parametrically Driven Systems, Phys. Rev. Lett. 89, 164101 (2002), The Ising-Bloch transition in degenerate optical parametric oscillators, J.Opt.B: Quantum Semiclass.Opt. 6, S361 (2004) and Stabilizing and controlling domain walls and dark-ring cavity solitons, Opt.Exp. 12, 2130 (2004). - We develop the study of quantum fluctuations in CSs in Squeezed quantum cavity solitons, (Physical Review Letters, sent). At the end, we add some appendices for clarifying technical or mathematical points. The last appendix consists of the complete synopsis of articles

Numerical simulation of target strength measurements from near to far field of fish using the method of fundamental solutions

[EN] We propose the application of a numerical model based on the Method of Fundamental Solutions to the estimation of the target strength (TS) of single fish, a crucial parameter for evaluating fish abundance when using active acoustical techniques. We consider a realistic beam and the influence of the evolution of the scattered field with distance maintaining the target in the far field of the ultrasonic transducer. The cases of a fluid sphere and a prolate spheroid model for the swimbladder are used to verify the application of MFS against other analytical and numerical methods. Additionally, a model considering only the swimbladder and the fishbone is presented to evaluate the differences between dorsal and ventral aspect measurements, and to understand previous experimental works performed with Atlantic salmon (Salmo salar) in floating cages.I. Perez-Arjona and V. Espinosa acknowledge funding of ACUSTUNA project ref. CTM2015-70446-R (MINECO/FEDER, UE), and UPV grants of PAID-00-15 and GVA BEST/2015/270. L. Godinho acknowledges the funding by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT - Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633. The authors would like to thank Dr. Manuel Bou and Carlos Albino for the technical assistance with work-station procedures.Pérez Arjona, I.; Godinho, L.; Espinosa Roselló, V. (2018). Numerical simulation of target strength measurements from near to far field of fish using the method of fundamental solutions. Acta Acustica united with Acustica. 104(1):25-38. https://doi.org/10.3813/AAA.919142S2538104

Detection and target strength measurements of uneaten feed pellets with a single beam echosounder

[EN] The possibility of detecting uneaten food pellets in aquaculture floating cages using a scientific single beam echosounder is demonstrated. The applied methodology is based in a basic scheme with the ultrasonic beam facing upwards the sea surface from the cage bottom. The target strength of single pellets is measured resulting in a linear relationship between target strength and pellet size. These results are the basis to quantify the uneaten food falling and to develop an automated feeding system based on demand. (C) 2017 Elsevier B.V. All rights reserved.This work was developed with the financial support of project ARM/1790/010 of the Tecnological Develoment Program of MAGRAMA, Spanish Government. E. Soliveres acknowledges support of Spanish Government grant AP2009-4459 FPU Subprogram. The authors would like to,acknowledge Prof. Helge Balk of the University of Oslo for his assistance with the software and license's access to Sonar 5 Pro, and the collaboration of Simrad Spain S.L. for lending the used EK15 echosounder.Llorens-Escrich, S.; Pérez Arjona, I.; Soliveres, E.; Espinosa Roselló, V. (2017). Detection and target strength measurements of uneaten feed pellets with a single beam echosounder. Aquacultural Engineering. 78:216-220. https://doi.org/10.1016/j.aquaeng.2016.10.008S2162207

Nondiffractive sonic crystals

We predict theoretically the nondiffractive propagation of sonic waves in periodic acoustic media (sonic crystals), by expansion into a set of plane waves (Bloch mode expansion), and by finite difference time domain calculations of finite beams. We also give analytical evaluations of the parameters for nondiffractive propagation, as well as the minimum size of the nondiffractively propagating acoustic beams.Comment: 7 figures, submitted to J. Acoust. Soc. A

Horizontal target strength-size conversion equations for sea bass and gilt-head bream

[EN] Horizontal hydroacoustics is a technique of remote fish detection that has proved to efficiently determine fish density and biomass in shallow or superficial waters. This non-intrusive technique could render better results than those obtained by conventional sampling when monitoring shallow waters. To apply this technique, we need equations that relate the amount of sound returned by fish, known as target strength (TS in dB), with their length (mm) or weight (g). This study presents horizontal conversion equations for the species gilt-head bream (Sparus aurata) and sea bass (Dicentrarchus labrax), two of the most important species bred in aquaculture. Moreover, this study presents a new formula to calculate a mixed equation adjusted to the percentage of distribution of those species in case of mixed populations. The results in this research have been obtained by applying a simple setup that allows for high-quality acoustic data. These new equations will enable the application of this technique in order to estimate these species' density and biomass in shallow aquatic systems such as aquaculture ponds with semi-intensive production densities.This study's authors would like to thank the Superintendent of Economy and Knowledge (Andalusian Government) for the funding provided as part of the project (PI_57052) developed in collaboration with CTAQUA. We would like to thank the researchers Carlos Orduna Marin and Juan Ramon Cid Quintero for their selfless work to obtain the field data and to the company PIMSA for generously allowing us to use their facilities and fish. We would also like to thank the veterinarian JR Rodriguez for being kind enough to perform X-rays on the studied fish and Cristina Ocana for her careful proofreading of the English text.Rodríguez-Sánchez, V.; Rodríguez-Ruiz, A.; Pérez Arjona, I.; Encina-Encina, L. (2018). Horizontal target strength-size conversion equations for sea bass and gilt-head bream. Aquaculture. 490:178-184. https://doi.org/10.1016/j.aquaculture.2018.02.034S17818449

Domain wall dynamics in an optical Kerr cavity

An anisotropic (dichroic) optical cavity containing a self-focusing Kerr medium is shown to display a bifurcation between static --Ising-- and moving --Bloch-- domain walls, the so-called nonequilibrium Ising-Bloch transition (NIB). Bloch walls can show regular or irregular temporal behaviour, in particular, bursting and spiking. These phenomena are interpreted in terms of the spatio-temporal dynamics of the extended patterns connected by the wall, which display complex dynamical behaviour as well. Domain wall interaction, including the formation of bound states is also addressed.Comment: 15 pages Tex file with 11 postscript figures. Resubmitted to Phys. Rev.

Bistable and dynamic states of parametrically excited ultrasound in a fluid-filled cavity

In this paper we have considered the problem of parametric sound generation in an acoustic resonator flled with a fluid, taking explicitely into account the influence of the nonlinearly generated second harmonic. A simple model is presented, and its stationary solutions obtained. The main feature of these solutions is the appearance of bistable states of the fundamental field resulting from the coupling to the second harmonic. An experimental setup was designed to check the predictions of the theory. The results are consistent with the predicted values for the mode amplitudes and parametric thresholds. At higher driving values a self-modulation of the amplitudes is observed. We identify this phenomenon with a secondary instability previously reported in the frame of the theoretical model.Comment: 5 figures. Submitted to JAS

Squeezing spectra from s-ordered quasiprobability distributions. Application to dispersive optical bistability

It is well known that the squeezing spectrum of the field exiting a nonlinear cavity can be directly obtained from the fluctuation spectrum of normally ordered products of creation and annihilation operators of the cavity mode. In this article we show that the output field squeezing spectrum can be derived also by combining the fluctuation spectra of any pair of s-ordered products of creation and annihilation operators. The interesting result is that the spectrum obtained in this way from the linearized Langevin equations is exact, and this occurs in spite of the fact that no s-ordered quasiprobability distribution verifies a true Fokker-Planck equation, i.e., the Langevin equations used for deriving the squeezing spectrum are not exact. The (linearized) intracavity squeezing obtained from any s-ordered distribution is also exact. These results are exemplified in the problem of dispersive optical bistability.Comment: 15 pages, no figures, to be published in Journal of Modern Optic

Target strength measurements of gilthead sea bream with single-beam quantitative echosounder

[EN] Target strength (TS) measurements for ventral aspect of gilthead sea bream (Sparus aurata) have been performed in a scaled aquaculture cage. The measurements have been made with a Simrad EK-60 scientific echososunder working at 200 kHz with a single-beam composted transducer specific of the Simrad ES15 echosounder (aperture of 30 degrees), designed for aquaculture control among other applications. Linear relationships of TS versus the logarithms of length have been derived. It must been underlined the obtaining of high values of the correlation coefficients and a high resolution of the ventral expressions for fish size predictions. Lower mean values of TS distributions are obtained for single-beam mesurements respect split-beam measurements as expected.Llorens Escrich, S.; Soliveres, E.; Pérez Arjona, I.; Espinosa Roselló, V.; Puig Pons, V.; Ordoñez Cebrian, P. (2016). Target strength measurements of gilthead sea bream with single-beam quantitative echosounder. Universidade do Porto. 1-6. http://hdl.handle.net/10251/181090S1

Cavity solitons in bidirectional lasers

We show theoretically that a broad area bidirectional laser with slightly different cavity losses for the two counterpropagating fields sustains cavity solitons (CSs). These structures are complementary, i.e., there is a bright (dark) CS in the field with more (less) losses. Interestingly, the CSs can be written/erased by injecting suitable pulses in any of the two counterpropagating fields.Comment: 4 figure