Thermal and optical characterization of micro-LED probes for in vivo optogenetic neural stimulation

Within optogenetics there is a need for compact light sources that are capable of delivering light with excellent spatial, temporal, and spectral resolution to deep brain structures. Here, we demonstrate a custom GaN-based LED probe for such applications and the electrical, optical, and thermal properties are analyzed. The output power density and emission spectrum were found to be suitable for stimulating channelrhodopsin-2, one of the most common light-sensitive proteins currently used in optogenetics. The LED device produced high light intensities, far in excess of those required to stimulate the light-sensitive proteins within the neurons. Thermal performance was also investigated, illustrating that a broad range of operating regimes in pulsed mode are accessible while keeping a minimum increase in temperature for the brain (0.5°C). This type of custom device represents a significant step forward for the optogenetics community, allowing multiple bright excitation sites along the length of a minimally invasive neural probe

Active-matrix GaN micro light-emitting diode display with unprecedented brightness

Displays based on microsized gallium nitride light-emitting diodes possess extraordinary brightness. It is demonstrated here both theoretically and experimentally that the layout of the n-contact in these devices is important for the best device performance. We highlight, in particular, the significance of a nonthermal increase of differential resistance upon multipixel operation. These findings underpin the realization of a blue microdisplay with a luminance of 10⁶ cd/m²

Individually addressable AlInGaN micro-LED arrays with CMOS control and subnanosecond output pulses

We report the fabrication and characterization of an ultraviolet (370 nm) emitting AlInGaN-based micro-light- emitting diode (micro-LED) array integrated with complementary metal-oxide-semiconductor control electronics. This configuration allows an 8 × 8 array of micro-LED pixels, each of 72-mum diameter, to be individually addressed. The micro-LED pixels can be driven in direct current (dc), square wave, or pulsed operation, with linear feedback shift registers (LFSRs) allowing the output of the micro-LED pixels to mimic that of an optical data transmitter. We present the optical output power versus drive current characteristics of an individual pixel, which show a micro-LED output power of up to 570 muW in dc operation. Representative optical pulse trains demonstrating the micro-LEDs driven in square wave and LFSR modes, and controlled optical pulsewidths from 300 ps to 40 ns are also presented

Fabrication and characterisation of microscale air bridges in conductive gallium nitride

Abstract Fabrication and electrical characterisation of microscale air bridges consisting of GaN heavily doped with silicon is described. These were made from GaN-AlInNGaN epitaxial trilayers on sapphire substrates, in which the AlInN was close to the composition lattice matched to GaN at ∼17% InN fraction. The start of the fabrication sequence used inductively coupled plasma etching with chlorine chemistry to define mesas. In situ monitoring by laser reflectometry indicated an AlInN vertical etch rate of 400 nm/minute, ∼70% of the etch rate of GaN. Processing was completed by lateral wet etching of the AlInN in hot nitric acid to leave GaN microbridges supported between anchor posts at both ends. Deposition of Ti-Au contact pads onto the anchor posts allowed study of the electrical characteristics. At low applied voltages, vertical conduction through the undoped AlInN layers was minimal in comparison with the current path through the Si:GaN bridges. Typical structures showed highly linear currentvoltage characteristics at low applied voltages, and had resistances of 1050 . The observed resistance values are compared with the predicted value based on materials parameters and an idealised geometry. The microbridges showed damage from Joule heating only at current densities above 2 × 10 5 A cm −2

Etude de la compatibilité WDM d'un régénérateur tout-optique 2R basé sur un module absorbant saturable à 8 canaux

session Affiches [P54]National audienceDans cet article, nous présentons pour la première fois un module absorbant saturable pigtailisé avec 8 fibres indépendantes. Nous montrons expérimentalement ses qualités pour une régénération 2R à 42.6 Gbit/s et son accordabilité en longueur d'onde

La Validación Lingüística en los Principales Cuestionarios de Salud y Calidad de Vida

The goals of this article are to summarize the problems and solutions found in translating seven Health-Related Quality of Life (HRQOL) questionnaires from English into Spanish which have used a common international protocol based on back-translation techniques. The methodology used is based on the linguistic validation model including both the linguistic and the sociopragmatic equivalence. Five questionnaires from seven have obtained good results, not so two of them. Considering linguistic questions, there were more problems than good solutions on the lexical-semantic level. With respect to the sociocultural questions, there were more solutions than problems. The Spanish translated questionnaires still present deficiencies to be corrected, so both linguistic and sociocultural questions have to be studied more carefully in order not to allow differences between the translated versions and the source questionnaires

Composant Passif à Absorbants Saturables sur InP pour le Régénération Tout-Optique de Signaux à Très Hauts-Débits

The work carried out during this PhD focus on the fabrication and the investigation of an InP-based saturable absorber (SA) device for high bit rate all-optical reshaping. The principle of operation of this all-optical and passive device is based on the non-linear absorption of quantum well (QW) suitably inserted inside a Fabry-Perot microcavity. Besides its polarisation-insensitive operation and its response time compatible with the futures high bit rate signals, the SA device may process several wavelength simultaneously thanks to its large bandwidth, making it as a promising candidate for future low cost all-optical regenerator for high bit rate WDM links.Due to an optimised structure, we were able to make a device with a response time as short as the picoseconde and with a saturation fluence of only a few µJ/cm2. The experimental results allowed us to validate the SA-based microcavity autosaturation model developed during this work, as well as the one describing the SA device working at high bit rate by taking into account the important thermal effects.Thanks to its optimisation and to a better management of the thermal effect, we were able to demonstrate for the first time the extinction ratio enhancement of a 160 GHz signal (+6 dB on 8 nm bandwidth) and the reshaping of a 160 Gbits/s signal with a SA device. Finally, 2R regeneration results got from a recirculating loop experiment at 10 Gbits/s and 43 Gbits/s are also presented and show a factor enhancement of the propagation distance of 9.5 (on 13 nm) and of 6 respectively.Ce manuscrit est consacré à la réalisation et à l'étude d'un composant à base d'absorbants saturables (AS) sur InP pour la remise en forme de signaux optiques à très hauts-débits. Le fonctionnement de ce composant tout-optique et passif est basé sur la non-linéarité d'absorption de puits quantiques (PQ) insérés dans une microcavité Fabry-Perot. Outre son insensibilité à la polarisation et son temps de réponse compatible avec les futurs signaux à hauts-débits, le composant AS présente aussi une large bande passante (BP) lui permettant de traiter plusieurs longueurs d'onde simultanément, faisant de lui un bon candidat pour les futurs dispositifs de régénération tout-optique à faible coût pour les liaisons à hauts-débits multiplexés en longueur d'onde (WDM).Grâce à une structure optimisée, nous avons pu obtenir un composant avec un temps de réponse aussi court que la picoseconde et une fluence de saturation de seulement quelques µJ/cm2. Les résultats expérimentaux ont permis de valider le modèle de l'autosaturation des PQ en microcavité développé lors de cette thèse, ainsi que celui décrivant le fonctionnement du composant AS à hauts-débits et tenant compte des effets-thermique.Grâce à son optimisation et à une meilleure gestion des effets thermo-optiques, nous avons pu démontrer pour la 1iére fois l'amélioration du taux d'extinction de signaux à 160 GHz (+6 dB sur une BP de 8 nm) et la remise en forme à 160 Gbits/s par un composant AS. Enfin, des résultats de régénération 2R en boucle de recirculation à 10 Gbits/s et à 43 Gbits/s sont aussi présentés et montrent une amélioration de la distance de propagation de 9,5 (sur 13 nm) et de 6 respectivement

Composant passif à absorbants saturables sur InP pour la régénération tout-optique à très hauts-débits

Ce manuscrit est consacré à la réalisation et à l étude d un composant a base d absorbants saturables (AS) sur InP pour la remise en forme de signaux optiques à très hauts-débits. Le fonctionnement de ce composant tout-optique et passif est basé sur la non-linéarité d absorption de puits quantiques (PQ) insérés dans une microcavité Fabry-Perot. Outre son insensibilité à la polarisation et son temps de réponse compatible avec les futurs signaux à hauts-débits, le composant AS présente aussi une large bande passante (BP) lui permettant de traiter plusieurs longueurs d onde simultanément, faisant de lui un bon candidat pour les futurs dispositifs de régénération tout-optique à faible coût pour les liaisons à hauts-débits multiplexés en longueur d onde (WDM).Grâce à une structure optimisée, nous avons pu obtenir un composant avec un temps de réponse aussi court que la picoseconde et une fluence de saturation de seulement quelques J/cm2. Les résultats expérimentaux ont permis de valider le modèle de l autosaturation des PQ en microcavité développé lors de cette thèse, ainsi que celui décrivant le fonctionnement du composant AS à hauts-débits et tenant compte des effets-thermique.Grâce à son optimisation et à une meilleure gestion des effets thermo-optiques, nous avons pu démontrer pour la 1iére fois l amélioration du taux d extinction de signaux à 160 GHZ (+ 6 dB sur une BP de 8 nm) et la remise en forme à 160 Gbits/s par un composant AS. Enfin, des résultats de régénération 2R en boucle de recirculation à 10 Gbits/s et à 43 Gbits/s sont aussi présentés et montrent une amélioration de la distance de propagation de 9,5 (sur 13 nm) et de 6 respectivement.The work carried out during this PhD focus on the fabrication and the investigation of an InP-based saturable absorber (SA) device for high bit rate all-optical reshaping. The principle of operation of this all-optical and passive device is based on the non-linear absorption of quantum well (QW) suitably inserted inside a Fabry-Perot microcavity. Besides its polarisation-insensitive operation and its response time compatible with the futures high bit rate signals, the SA device may process several wavelength simultaneously thanks to its large bandwidth, making it as a promising candidate for future low cost all-optical regenerator for high bit rate WDM links. Due to an optimised structure, we were able to make a device with a response time as short as the picoseconde and with a saturation fluence of only a few J/cm2. The experimental results allowed us to validate the SA-based microcavity autosaturation model developed during this work, as well as the one describing the SA device working at high bit rate by taking into account the important thermal effects. Thanks to its optimisation and to a better management of the thermal effect, we were able to demonstrate for the first time the extinction ratio enhancement of a 160 GHz signal (+ 6 dB on 8 nm bandwidth) and the reshaping of a 160 Gbits/s signal with a SA device. Finally, 2R regeneration results got from a recirculating loop experiment at 10 Gbits/s and 43 Gbits/s are also presented and show a factor enhancement of the propagation distance of 9.5 (on 13 nm) and of 6 respectively.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Thermal conductance of laterally-wet-oxidised GaAs/AlxOy Bragg reflectors

Thermal resistivity measurements were carried out on GaAs-based monolithic saturable absorber microcavities. Two-types of microcavity mirrors were compared: GaAs/AlAs against GaAs/AlxOy Bragg reflectors processed by lateral-wet-oxidation of Al(Ga)As layers. It is found that GaAs/AlxOy mirrors are not efficient heat dissipators, the GaAs/AlxOy microcavity structure showing a thermal resistivity more than ten times higher than the GaAs/AlAs structure. Using modelling to fit the experimental data, thermal conductivity of the 250 nm AlxOy layers is estimated to be approximately 0.007 WK–1cm–1. These results illustrate a significant drawback related to the use of thick wet-oxidised Al(Ga)As/GaAs layer

Cascadability and efficiency of a saturable absorber device inserted into a SMF transmission line for future 160-Gbit/s all-optical reshaping applications.

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