Stephane Trebaol

Determination of coupling regime of high-Q resonators and optical gain of highly selective amplifiers

We present a simple method to determine simultaneously the main characteristics of passive or active high-Q optical resonators. The method is based on cavity ringdown spectroscopy, where the probe wavelength is rapidly swept across the resonance. It has already been shown that this technique allows the loaded cavity lifetime of passive resonators to be obtained. We show that we can also infer the coupling regime for passive resonators and the resonant gain for active resonators. The method is tested on Er3+ doped fiber resonators and also applied to determine the intrinsic and external Q-factors of an MgF2 whispering gallery mode resonator.

Polaritonic Feshbach resonance

Feshbach resonances provide a powerful tool for engineering interactions in ultracold atomic gases. The strong exciton–photon coupling in semiconductor microcavities facilitates the demonstration of a polaritonic Feshbach resonance with promising implications for manipulating polariton quantum fluids. A Feshbach resonance occurs when the energy of two interacting free particles comes into resonance with a molecular bound state. When approaching this resonance, marked changes in the interaction strength between the particles can arise. Feshbach resonances provide a powerful tool for controlling the interactions in ultracold atomic gases, which can be switched from repulsive to attractive1,2,3,4, and have allowed a range of many-body quantum physics effects to be explored5,6. Here we demonstrate a Feshbach resonance based on the polariton spinor interactions in a semiconductor microcavity. By tuning the energy of two polaritons with anti-parallel spins across the biexciton bound state energy, we show an enhancement of attractive interactions and a prompt change to repulsive interactions. A mean-field two-channel model quantitatively reproduces the experimental results. This observation paves the way for a new tool for tuning polariton interactions and to move forward into quantum correlated polariton physics.

Heterodyne spectroscopy of polariton spinor interactions

We report on spinor polariton interactions in GaAs based microcavities. This investigation is carried out by means of heterodyne polarized pump-probe spectroscopy. We show the dependence of the energy renormalization of the lower and upper polariton resonances with cavity detuning for different polariton densities. We use the exciton-photon based Gross-Pitaevskii equation to model the experiment for both lower and upper polariton modes. The theoretical results reproduce qualitatively the experimental observations revealing the magnitude and sign of the parallel and antiparallel spin interaction strength. We evidence the strong influence of the biexciton resonance on the antiparallel spin polariton energy shift and provide the exciton-biexciton coupling constant. We derive our results in the lower polariton basis using the Gross-Pitaevskii equation, from which we express analytically the spinor polariton interactions and identify the clear role of the biexciton resonance.

Miniaturized Optical Microwave Source Using a Dual-Wavelength Whispering Gallery Mode Laser

We report on the observation of a compact optical microwave source based on a whispering gallery mode (WGM) laser. The use of a single 160-¿m diameter erbium-doped glass microsphere and two half fiber tapers allows a dual single-mode laser emission around 1550 nm to be obtained. The generated beat note at 10.86 GHz has a linewidth of 22 kHz. This preliminary experimental demonstration shows the potentialities of erbium-doped WGM resonators for microwave generation.

Two-dimensional Fourier transform spectroscopy of exciton-polaritons and their interactions

We investigate polariton-polariton interactions in a semiconductor microcavity through two-dimensional Fourier transform (2DFT) spectroscopy. We observe, in addition to the lower-lower and the upper-upper polariton self-interactions, a lower-upper cross interaction. This appears as separated peaks in the on-diagonal and off-diagonal parts of 2DFT spectra. Moreover, we elucidate the role of the polariton dispersion through a fine structure in the 2DFT spectrum. Simulations, based on lower-upper polariton basis Gross-Pitaevskii equations including both self-and cross interactions, result in a 2DFT spectra in qualitative agreement with experiments.

Nonlinear relaxation and selective polychromatic lasing of confined polaritons

Integration of optical elements into scalable chips has been at the center of a large effort in recent years [1–3]. Concurrently, the separation between the diverse functions, namely switches, detectors or emitters [4–6] increases significantly the final number of components on chip. Such technical limitations may be overcome by introducing agile devices able, for example, to simultaneously detect, process and emit a coherent signal. Such a pathway has been explored with different approaches [7] that bear advantages and drawbacks. Polaritons have often been proposed as promising candidates for multifunctional devices [8]. Here we present an optical switch based on polariton lasing. An incident monochromatic signal is channeled into several polariton laser beams at different wavelengths by a novel relaxation mechanism which combines bistability, phonon interactions, long polariton lifetime and bosonic stimulation. We demonstrate spin logic operations conserving the original polarization state that is fully imprinted onto the coherently emitted signals.

Effect of a noisy driving field on a bistable polariton system

We report on the effect of noise on the characteristics of the bistable polariton emission system. The present experiment provides a time-resolved access to the polariton emission intensity. We evidence the noise-induced transitions between the two stable states of the bistable polaritons. It is shown that the external noise specifications, intensity and correlation time, can efficiently modify the polariton Kramers time and residence time. We find that there is a threshold noise strength that provokes the collapse of the hysteresis loop. The experimental results are reproduced by numerical simulations using Gross-Pitaevskii equation driven by a stochastic excitation.

High-gain wavelength-selective amplification and cavity ring down spectroscopy in a fluoride glass erbium-doped microsphere

We experimentally demonstrate a compact optical amplifier consisting of a rare-earth-doped whispering-gallery-mode microsphere coupled via a tapered fiber. A gain up to 20 dB is reported in an erbium-doped fluoride glass microsphere 135 μm in diameter. Below the amplification regime, the optical gain is used to compensate for unavoidable losses due to surface contamination or scattering. Quality factor as high as 2×10(9) has been measured by analyzing the transient response of the microsphere excited by a dynamically shifted frequency input signal.

Glass Microspherical Lasers

We report experimental results obtained in our laboratories in the development of Er3+- doped glass microspherical cavities for the fabrication of compact and low threshold laser sources at 1.55 μm. We investigate three different approaches in order to fabricate the microspheres including direct melting of Er3+-doped glass powders, coating of silica microspheres with an Er3+- doped sol-gel layer, and synthesis of Er3+-doped monolithic microspheres using the sol-gel route in acid catalysis. Details of the different fabrication processes are presented together with the photoluminescence characterization in free space configuration of the microspheres and of the glass precursor. We analyse the photoluminescence spectra of the whispering gallery modes of the microspheres exited using evanescent coupling and we demonstrate laser action in a wide range of wavelengths around 1.55 μm.

Transient effects in high-Q whispering gallery mode resonators: Modelling and applications

We analyse the transient transmission response of a high quality (Q) factor whispering gallery mode resonator when the probe laser frequency is rapidly swept across the resonance. The detailed comparison with a simple numerical linear model allows the coupling regime and the strength of the intracavity Rayleigh scattering to be measured. By including thermal nonlinearities in the model we show here that it can be possible to deduce the power launched in the high-Q mode by using this simple cavity ring-down spectroscopy technique.