R. Houdré

Optical and confinement properties of two-dimensional photonic crystals

We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs of these photonic crystals, including the case of in-plane Fabry-Perot cavities formed between two such crystals. The measurement method makes use of the guided photoluminescence of embedded quantum wells or InAs quantum dots to generate an internal probe beam. Out-of-plant, scattering losses are evaluated by various means. In a second part, in-plane micrometer-sized photonic boxes bounded by circular trenches or by two-dimensional photonic crystal are probed by exciting spontaneous emission inside them. The high quality factors observed in such photon boxes demonstrate the excellent photon confinement attainable in these systems and allow to access the detail of the modal structure. Last, some perspectives for applications are offered.

Optical investigation of highly strained InGaAs‐GaAs multiple quantum wells

Low‐temperature optical transmission spectra of several InxGa1−xAs/GaAs strained multiple quantum wells (MQWs) with different well widths and In mole fractions have been measured. The excitonic transitions up to 3C‐3H are observed. The notation nc‐mH(L) is used to indicate the transitions related to the nth conduction and mth valence heavy (light) hole subbands. Steplike structures corresponding to band‐to‐band transitions are also observed, which are identified as 1C‐1L transitions. The calculated transition energies, taking into account both the strain and the quantum well effects, are in good agreement with the measured values. In these calculations the lattice mismatch between the GaAs buffer and the InGaAs/GaAs MQW is taken into account and the valence‐band offset Qv is chosen as an adjustable parameter. By fitting the experimental results to our calculations, we conclude that the light holes are in GaAs barrier region (type II MQW) and the valence‐band offset Qv is determined to be 0.30. A possible ...

Low-loss channel waveguides with two-dimensional photonic crystal boundaries

We have used transmission measurements to estimate the propagation loss of submicron channels defined in two-dimensional photonic crystals patterned into a Ga(Al)As waveguide. The measured propagation loss of the fundamental mode is indistinguishable from the material absorption, setting an upper limit of 50 cm−1 (2 dB per 100 μm). We also find that, provided the etching is deep enough, propagation losses of these photonic crystal waveguides are lower than those of ridge waveguides etched in the same run.

Confined Electrons and Photons

The scientific fields of confined electrons and photons have become areas of major efforts worldwide. Their appeal originates in the many facets they offer in fundamental and applied science, in technology and device development, and to high technology, large-scale industries.

Polariton Superfluids Reveal Quantum Hydrodynamic Solitons

A condensed-matter system is used to study superfluid dynamics. A quantum fluid passing an obstacle behaves differently from a classical one. When the flow is slow enough, the quantum gas enters a superfluid regime, and neither whirlpools nor waves form around the obstacle. For higher flow velocities, it has been predicted that the perturbation induced by the defect gives rise to the turbulent emission of quantized vortices and to the nucleation of solitons. Using an interacting Bose gas of exciton-polaritons in a semiconductor microcavity, we report the transition from superfluidity to the hydrodynamic formation of oblique dark solitons and vortex streets in the wake of a potential barrier. The direct observation of these topological excitations provides key information on the mechanisms of superflow and shows the potential of polariton condensates for quantum turbulence studies.

Self-collimating photonic crystal polarization beam splitter

We present theoretical and experimental results of a polarization splitter device that consists of a photonic crystal (PhC) slab, which exhibits a large reflection coefficient for TE and a high transmission coefficient for TM polarization. The slab is embedded in a PhC tile operating in the self-collimation mode. Embedding the polarization-discriminating slab in a PhC with identical lattice symmetry suppresses the in-plane diffraction losses at the PhC-non-PhC interface. The optimization of the PhC-non-PhC interface is thereby decoupled from the optimization of the polarizing function. Transmissions as high as 35% for TM- and 30% for TE-polarized light are reported.

Miniband transmission in a photonic-crystal coupled-resonator optical waveguide

We demonstrate in the near infrared the coupled-resonator optical waveguide (CROW) concept that was recently proposed by Yariv et al. [Opt. Lett.24, 711 (1999)]. Two-dimensional photonic crystals have been used to define, in a GaAs-based waveguiding heterostructure, an array of micrometer-sized hexagonal cavities coupled through thin walls. With the photoexcitation of InAs quantum dots as an internal source, the transmission spectra of the coupled resonators show marked minibands and minigaps, in agreement with theoretical predictions.

All-optical polariton transistor

Optical technology has proved to be the best choice for the transmission of information at high data rate over long distances. However, the implementation of high-speed, low-energy, all-optical logics in semiconductors represents a formidable challenge due to the intrinsic difficulty of all-optical devices to satisfy the basic system requirements [1]. In particular, cascadability is difficult to obtain in optical systems, and it is assured only if the output of one stage is in the correct form to drive the input of the next stage. In this context, we demonstrate a scheme of all-optical transistor based on exciton polaritons in semiconductor microcavities, which exhibits full connectivity in the same chip plane.

Refractive index sensing with an air-slot photonic crystal nanocavity

We investigate an air-slot photonic crystal cavity for high-precision refractive index sensing. The high quality factor approximately 2.6x10(4) of the cavity, along with a strong overlap between the resonant mode and the hollow core region, allows us to achieve an experimental sensitivity of 510nm per refractive index unit (RUI) and a detection limit below 1x10(-5)RUI. The device has a remarkably low sensing volume of 40aliters, holding less than 1x10(6)molecules.

Effect of in situ and ex situ annealing on dislocations in GaAs on Si substrates

Gallium arsenide layers grown by molecular beam epitaxy on (100) Si substrates were subjected to annealing under As overpressure at 650, 750, and 850 °C for 1/2 h. A substantial reduction in the dislocation density near the interface and in the bulk of the epitaxial layers was observed for the 850 °C anneal. In situ annealing at 700 °C for 1/2 h after 1/2 h of growth followed by a deposition of InGaAs/GaAs strained‐layer superlattices and bulk layers also resulted in reduced dislocation densities.