Isabelle Robert-Philip

Optomechanical coupling in a two-dimensional photonic crystal defect cavity

We experimentally investigate the optomechanical properties of a conventional two-dimensional suspended photonic crystal defect cavity. Particularly, we measure localized mechanical modes in the GHz regime exhibiting high values of the optomechanical vacuum coupling rate exceeding 250 kHz.

Single photon emission from site-controlled pyramidal quantum dots

We demonstrate that a single photoexcited InGaAs semiconductor quantum dot (QD) grown by organo-metallic chemical vapor deposition on prepatterned substrates emits one photon at a time, with no uncontrolled background photon emission, making it an excellent single photon emitter. Moreover, our fabrication technique offers complete site control and small inhomogeneous broadening of QD arrays, which is essential for the practical implementation of QDs in efficient solid-state single photon emitting devices.

Indistinguishable single photons from a single-quantum dot in a two-dimensional photonic crystal cavity

We report on the spontaneous emission of a single-quantum dot embedded in a two-dimensional photonic crystal cavity. The resonant coupling between the dot and the strongly localized optical mode significantly shortens the spontaneous emission lifetime, so that the coherence time of the emitted photons is dominated by radiative effects: The emitted photons are indistinguishable, with a mean wave-packet overlap as high as 72%.

Efficient photonic mirrors for semiconductor nanowires

Using a fully vectorial frequency-domain aperiodic Fourier modal method, we study nanowire metallic mirrors and their photonic performance. We show that the performance of standard quarter-wave Bragg mirrors at subwavelength diameters is surprisingly poor, while engineered metallic mirrors that incorporate a thin dielectric adlayer may offer reflectance larger than 90% even for diameters as small as lambda/5.

Electro-osmotic propulsion of helical nanobelt swimmers

Micro and nanoscale mobile agents capable of self-propulsion in low Reynolds number fluids would have a great technological impact in many fields. Few known mechanisms are able to propel such devices. Here we describe helical nanobelt (HNB) swimmers actuated by an electric field-generated electro-osmotic force. These HNB swimmers are designed with a head and a tail, similar to natural micro-organisms such as bacteria and their flagella. We show that these electro-osmotic propulsion of HNB swimmers achieve speeds (24 body lengths per second), force (1.3 nN), and pressure (375.5 Pa) above those demonstrated by other artificial swimmers based on physical energy conversion. Although nature’s bacteria are still more dynamic, this paper reports that the demonstrated electro-osmotic HNB microswimmers made a big step toward getting closer to their performances. Moreover, an unusual swimming behavior with discontinuous pumping propulsion, similar to jellyfish, was revealed at or above the speculated marginal limit of linear propulsion. These electro-osmosis propelled HNB swimmers might be used as biomedical carriers, wireless manipulators, and as local probes for rheological measurements.

Single photon emission from individual GaAs quantum dots

We report on photon correlation measurements on a single quantum dot formed at fluctuations of the interface of a GaAs/GaAlAs quantum well. We demonstrate that under pulsed nonresonant excitation, the quantum dot emits a single photon per pulse. This shows that after the photon emission, there is no refill of the quantum dot by the nearby two-dimensional reservoir of delocalized states. The possibility of delivering Fourier transform limited single photons makes this system a good candidate for exciton- and photon-based quantum information processing schemes.

Thermo-optical dynamics in an optically pumped Photonic Crystal nano-cavity

Linear and non-linear thermo-optical dynamical regimes were investigated in a photonic crystal cavity. First, we have measured the thermal relaxation time in an InP-based nano-cavity with quantum dots in the presence of optical pumping. The experimental method presented here allows one to obtain the dynamics of temperature in a nanocavity based on reflectivity measurements of a cw probe beam coupled through an adiabatically tapered fiber. Characteristic times of 1.0+/-0.2 micros and 0.9+/-0.2 micros for the heating and the cooling processes were obtained. Finally, thermal dynamics were also investigated in a thermo-optical bistable regime. Switch-on/off times of 2 micros and 4 micros respectively were measured, which could be explained in terms of a simple non-linear dynamical representation.

Metal organic vapor phase epitaxy of InAsP/InP(001) quantum dots for 1.55μm applications: Growth, structural, and optical properties

This contribution reports the metal organic vapor phase epitaxy of InAsP/InP(001) quantum dots with a voluntary V-alloying obtained owing to an additional phosphine flux during InAs quantum dot growth. The quantum dots were studied by photoluminescence and transmission electron microscopy. We show that the additional phosphine flux allows to tune quantum dot emission around 1.55 μm while improving their optical properties. The comparison of the optical and structural properties of the InAsP quantum dots allows to deduce their phosphorus composition, ranging from 0% to 30% when the phosphine/arsine flow ratio is varying between 0 and 50. On the basis of the compositions deduced, we discuss on the effects of the phosphine flow and of the alloying on the quantum dot growth, structural, and optical properties.

Submicron-diameter semiconductor pillar microcavities with very high quality factors

Pillar microcavities are subject to two common fabrication artifacts: Bragg mirror corrugation and oxide deposit cladding. In this letter the authors investigate the impact of these features on the quality factor. A quasiperiodic variation of the quality factor as a function of the pillar diameter is experimentally observed and well described by theory. Moreover, observation of quality factors in excess of 1500, close to the theoretical limit, is reported for 600-nm-diameter GaAs micropillars bounded by AlGaAs∕GaAs Bragg mirrors.

Optimizing H1 cavities for the generation of entangled photon pairs

We report on the theoretical investigation of photonic crystal cavities etched on a suspended membrane for the generation of polarization entangled photon pairs using the biexciton cascade in a single quantum dot. The implementation of the spontaneous emission enhancement effect increases the entanglement visibility, while the concomitant preferential funneling of the emission in the cavity mode increases the collection of both entangled photons. We demonstrate and quantify that standard cavity designs present a polarization-dependent emission diagram, detrimental to entanglement. The optimization of H1 cavities allows us to obtain both high collection efficiencies and polarization-independent emission, while keeping the high Purcell factors necessary for high-quality entangled photon sources.