Annular interdigital transducer focuses piezoelectric surface waves to a single point

We propose and demonstrate experimentally the concept of the annular interdigital transducer that focuses acoustic waves on the surface of a piezoelectric material to a single, diffraction-limited, spot. The shape of the transducing fingers follows the wave surface. Experiments conducted on lithium niobate substrates evidence that the generated surface waves converge to the center of the transducer, producing a spot that shows a large concentration of acoustic energy. This concept is of practical significance to design new intense microacoustic sources, for instance for enhanced acouto-optical interactions

Fast build up of photorefractive spatial solitons in iron doped indium phosphide

Conférence OralInternational audiencePhotorefractive (PR) spatial soliton propagation hints that all optical routing can be achieved through soliton interactions. This requires, however, fast build up and sensitivity to telecommunication wavelengths. We have investigated the build up of infrared (1,06m) photorefractive solitons in iron doped indium phosphide (InP:Fe) and shown that PR self focusing occurs at input powers of hundreds of W and intensities in the range of W/cm2, showing a build up time down to the microsecond

Auto-focalisation infrarouge dans le Phosphure d'Indium dopé fer

This work aims to studying the possible design of an all optical router compatible with intensities and wavelengths which are present in optical telecommunication networks. This implies studying the physics of photorefractive self-focusing and spatial solitons in Iron doped Indium Phosphide (InP:Fe) which was chosen for its speed and its sensitivity to telecommunication wavelengthsThe first part is devoted to characterizing our samples through conventional photorefractive two wave mixing to measure the resonance intensity around which, the literature says, self-focusing is expected to happen. The second part is thus devoted to the experimental study of spatial soliton formation and propagation in InP:Fe. We have there evidenced a build up time shorter than 1 ms.Parallel theoretical studies have been conducted on the basis of the transport equations taking into account the two carrier types characteristic of semi-conductors. Our analytical derivations have shown a link between two-carrier semi-conductors and one-carrier doped insulators. Numerical simulations with less approximations have confirmed these results. We have thus explained successfully our experimental observations, while showing the need for a partial re-thinking of the existing theory.and help to understand the experimental observations, both through analytical studies and numerics. Theses studies have led to partially reconsidering existing theories.L'objectif de mon travail est l'étude de la faisabilité d'un routeur tout optique à des longueurs d'onde et des intensités compatibles avec les réseaux optiques de télécommunication. Cette étude passe par celle des l'autofocalisation et des solitons spatiaux photoréfractif dans le Phosphure d'Indium dopé au fer (InP:Fe), matériau choisi pour sa vitesse et sa sensibilité aux longueurs d'ondes adéquates.Dans une première partie une caractérisation de nos échantillonsInP:Fe par la technique du mélange à deux ondes a été envisagée,afin de définir l'intensité de résonance nécessaire d'après labibliographie pour l'expérience d'auto-focalisation. Dans une seconde partie, un banc expérimental spécialement conçu et réalisé pour notre étude, nous a permis d'observer le phénomène d'auto-focalisation stationnaire à des temps inférieurs à la milliseconde.Nous avons mené en parallèle une étude théorique sur la base du modèle classique des équations de transport, en prenant en compte la nature semi-conductrice du phosphure d'indium. Des approximations usuelles nous ont permis de relier le comportement des semi-conducteurs à celui des isolants dopés, ou un seul type de porteur est pris en compte. Des simulations numériques nécessitant moins d'approximations sont venues conforter ces résultats. Nous avons ainsi expliqué avec succès les observations expérimentales, tout en remettant partiellement en cause la théorie existante sur le sujet

Photorefractive self focusing in near IR for optical communications

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Temporal Behavior of Photorefractive Self-Focusing in InP:Fe Crystals at Infrared Wavelengths

http://www.opticsinfobase.org//abstract.cfm?URI=PR-2007-MB25International audienceTemporal and spatial dependency of photorefractive self focusing in InP:Fe from intensity and temperature is compared to a theoretical model; self focusing and bending occur on a microseconds timescale for low beam intensities