High quality factor nitride-based optical cavities: microdisks with embedded GaN/Al(Ga)N quantum dots

We compare the quality factor values of the whispery gallery modes of microdisks incorporating GaN quantum dots (QDs) grown on AlN and AlGaN barriers by performing room temperature photoluminescence (PL) spectroscopy. The PL measurements show a large number of high Q factor (Q) resonant modes on the whole spectrum which allows us to identify the different radial mode families and to compare them with simulations. We report a considerable improvement of the Q factor which reflect the etching quality and the relatively low cavity loss by inserting QDs into the cavity. GaN/AlN QDs based microdisks show very high Q values (Q > 7000) whereas the Q factor is only up to 2000 in microdisks embedding QDs grown on AlGaN barrier layer. We attribute this difference to the lower absorption below bandgap for AlN barrier layers at the energies of our experimental investigation

Silicon-on-Insulator RF Filter Based on Photonic Crystal Functions for Channel Equalization

International audienceA compact silicon-on-insulator 2-tap interferometer is demonstrated as a channel equalizer. The radiofrequency filter is reconfigurable thanks to thermally-controlled photonic crystal couplers and delay lines. The channel fading of a dispersive fiber link supporting a directly modulated telecommunication signal is successfully compensated for using the interferometer, leading to eye diagram opening and the possibility to recover the bit-error-rate of a reference signal with less than 1-dB power penalty

Effets d'optique non-linéaire d'ordre trois dans les cavités à cristaux photoniques en silicium (auto-oscillations GHz dues aux porteurs libres et diffusion Raman stimulée)

Dans ce travail de thèse, nous avons étudié des effets d'optique non-linéaire d'ordre trois dans les cavités à cristaux photoniques en silicium. Le premier d'entre eux est un phénomène d'auto-oscillations à haute fréquence (GHz) dans ces cavités, qui a pour origine une modulation de la transmission de la cavité due à l'interaction entre la dispersion due aux porteurs libres et l absorption à deux photons. Nous avons observé ces auto-oscillations, pour la première fois, dans les nanocavités à cristaux photoniques silicium avec une fréquence de l ordre de 3 GHz et une grande pureté spectrale. Nous avons développé un modèle pour analyser les mécanismes qui régissent l'apparition de ces auto-oscillations, ainsi que les amplitudes des fréquences fondamentale et harmoniques de ces oscillations. Ce phénomène d'auto-oscillations permettrait de réaliser des sources micro-ondes en silicium très compactes. Le deuxième phénomène étudié est celui de la diffusion Raman, qui est le seul moyen d'obtenir des lasers entièrement en silicium démontré jusqu'à présent. Cette diffusion Raman a été mesurée tout d'abord dans des guides d'onde à cristaux photoniques étroits (W0.63) de longueur 100 microns, où nous avons pu obtenir un nombre de photons Stokes allant jusqu'à 9, montrant ainsi que la diffusion Raman stimulée prédominait dans ces guides d'onde, bien que nous n ayons pas pu y obtenir un effet laser Raman franc. Nous avons ensuite mesuré la diffusion Raman dans des nanocavités doublement résonantes conçues spécifiquement à partir de ces guides d'ondes pour optimiser l'effet Raman, avec des facteurs de qualités allant jusqu'à 235000 pour la résonance Stokes. Bien que nous n'ayons pu mesurer que de la diffusion Raman spontanée dans ces cavités, avec un facteur de Purcell de 2.9, l'étude théorique que nous avons effectuée sur les lasers Raman, et qui s'accorde parfaitement avec les résultats expérimentaux, montre qu il serait possible d'obtenir un laser Raman dans ces cavités avec un seuil en dessous du milliwatt à condition de diminuer ces pertes dues à l'absorption par porteurs libres. Ceci pourrait être accompli en diminuant le temps de vie des porteurs libres, par exemple en les retirant du silicium à l aide d une jonction MSM.In this thesis, we studied third order nonlinear optical effects in photonic crystal cavities. The first of those effects is is the phenomenon of high frequency (GHz) self-pulsing in these cavities, which originates from a modulation of the transmission of the cavity due to the interaction between the free-carrier dispersion and the two-photon absorption. We have observed these self-induced oscillations for the first time in silicon photonic crystal nanocavities, with a frequency of about 3 GHz and a high spectral purity. We have developed a model to analyze the mechanisms that govern the onset of these oscillations, as well as the amplitudes of the fundamental and harmonic frequencies of these oscillations. This self-pulsing phenomenon would allow us to realize realize ultra-compact microwave sources made of silicon. The second phenomenon studied is that of Raman scattering, which is the only way to obtain lasers fully in silicon demonstrated so far. The Raman scattering was measured first in narrow photonic crystals waveguides (W0.63) of length 100 microns, where we could obtain a number of Stokes photons up to 9, showing that the stimulated Raman scattering predominated in these waveguides, although we have not been able to obtain a true Raman laser effect in them. We then measured the Raman scattering in doubly resonant nanocavities specifically designed from these waveguides to optimize the Raman effect, with quality factors up to 235000 for the Stokes resonance. Although we could only measure spontaneous Raman scattering in these cavities, with a Purcell factor of 2.9, the theoretical study that we conducted on the Raman lasers, which agrees perfectly with the experimental results, shows that it would be possible to obtain a Raman laser in these cavities with a threshold below the milliwatt, provided we reduce the losses due to the free-carrier absorption. This could be accomplished by decreasing the free-carrier lifetime, for example by removing the free carriers from the silicon using a MSM junction.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Solving thermal issues in tensile-strained Ge microdisks

International audienceWe propose to use a Ge-dielectric-metal stacking to allow one to address both thermal management with the metal as an efficient heat sink and tensile strain engineering with the buried dielectric as a stressor layer. This scheme is particularly useful for the development of Ge-based optical sources. We demonstrate experimentally the relevance of this approach by comparing the optical response of tensile-strained Ge microdisks with an Al heat sink or an oxide pedestal. Photoluminescence indicates a much reduced temperature rise in the microdisk (16 K with Al pedestal against 200 K with SiO 2 pedestal under a 9 mW continuous wave optical pumping). An excellent agreement is found with finite element modeling of the temperature rise. This original stacking combining metal and dielectrics is promising for integrated photonics where thermal management is an issue

Unidirectional band gaps in uniformly magnetized two-dimensional magnetophotonic crystals

By exploiting the concepts of magnetic group theory we show how unidirectional behavior can be obtained in two-dimensional magneto-photonic crystals (MOPhC) with uniform magnetization. This group theory approach generalizes all previous investigations of one-way MOPhCs including those based on the use of antiparallel magnetic domains in the elementary crystal cell. Here, the theoretical approach is illustrated for one MOPhC example where unidirectional behavior is obtained by appropriately lowering the geometrical symmetry of the elementary motifs. One-way transmission is numerically demonstrated for a photonic crystal slice.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Ultra-Low Threshold cw Lasing in Tensile Strained GeSn Microdisk Cavities

GeSn is proven as a good candidate to achieve CMOS-compatible laser sources on silicon. Lasing demonstrations in this alloy were based on directness of the band structure, this directness being increased with increasing the Sn content above 8 at.%. These past few years the research were consequently focused on incorporating the highest Sn content as possible to achieve high directness and high temperature laser operation. This unfortunately results is increased threshold. In this contribution we discuss the advantages in combining tensile strain engineering with lower Sn content alloys. This approach is motivated by the higher material quality in lower Sn content. The case with Sn content as small as 5.4 at.% Sn will be discussed. The alloy is initially compressively strained, and exhibits an indirect band gap that is turned to direct by applying tensile strain. A specific technology based on transfer On Insulator stressor layer on metal was developed to address strain engineering, thermal cooling and defective interface with the Ge-VS. This led to lasing in Ge0.95Sn0.05 microdisk cavities with dramatically reduced thresholds, by two order of magnitude, as compared to the case with high Sn alloys and as consequence enables cw operation

Superconducting single photon detectors integrated with diamond nanophotonic circuits

Photonic quantum technologies promise to repeat the success of integrated nanophotonic circuits in non-classical applications. Using linear optical elements, quantum optical computations can be performed with integrated optical circuits and thus allow for overcoming existing limitations in terms of scalability. Besides passive optical devices for realizing photonic quantum gates, active elements such as single photon sources and single photon detectors are essential ingredients for future optical quantum circuits. Material systems which allow for the monolithic integration of all components are particularly attractive, including III-V semiconductors, silicon and also diamond. Here we demonstrate nanophotonic integrated circuits made from high quality polycrystalline diamond thin films in combination with on-chip single photon detectors. Using superconducting nanowires coupled evanescently to travelling waves we achieve high detection efficiencies up to 66 % combined with low dark count rates and timing resolution of 190 ps. Our devices are fully scalable and hold promise for functional diamond photonic quantum devices.Comment: 28 pages, 5 figure