arXiv subjects

Isabelle Sagnes

Publications and source records attributed to Isabelle Sagnes.

At least 55 records · Page 3Linked to original sources

arXiv2021

Relaxation mechanism of GaP grown on 001 Sisubstrates: influence of defects on the growth of AlGaPlayers on GaP/Si templates

The mechanical stability of commercial GaP/Si templates during thermal an-nealing and subsequent MOCVD growth of GaP and AlGaP is investigated.Although the GaP layer of the template originally presents an excellent surfacemorphology, annealing at high enough temperatures to remove the native oxideprior to growth leads to plastic relaxation, accompanied by a variety of defects,including a dense grid of micro-twins. These micro-twins detrimentally affectGaP and AlGaP layers grown subsequently on the template.

cond-mat.mtrl-sci↗

arXiv2020

Reduced lasing thresholds in GeSn microdisk cavities with defect management of the optically active region

GeSn alloys are nowadays considered as the most promising materials to build Group IV laser sources on silicon (Si) in a full complementary metal oxide semiconductor-compatible approach. Recent GeSn laser developments rely on increasing the band structure directness, by increasing the Sn content in thick GeSn layers grown on germanium (Ge) virtual substrates (VS) on Si. These lasers nonetheless suffer from a lack of defect management and from high threshold densities. In this work we examine the lasing characteristics of GeSn alloys with Sn contents ranging from 7 \% to 10.5 \%. The GeSn layers were patterned into suspended microdisk cavities with different diameters in the 4-\SI{8 }{\micro\meter} range. We evidence direct band gap in GeSn with 7 \% of Sn and lasing at 2-\SI{2.3 }{\micro\meter} wavelength under optical injection with reproducible lasing thresholds around \SI{10 }{\kilo\watt\per\square\centi\meter}, lower by one order of magnitude as compared to the literature. These results were obtained after the removal of the dense array of misfit dislocations in the active region of the GeSn microdisk cavities. The results offer new perspectives for future designs of GeSn-based laser sources.

physics.optics↗

arXiv2020

Optimization of laser dynamics for active stabilization of DF--VECSELs dedicated to cesium CPT clocks

We report the implementation and performance of a double servo-loop for intensity and phase-difference active stabilization of a dual-frequency vertical external--cavity surface-emitting laser (DF-VECSEL) for coherent population trapping (CPT) of cesium atoms in the framework of compact atomic clocks. In--phase fully correlated pumping of the two laser modes is identified as the best scheme for intensity noise reduction, and an analytical model allows the optimization of the active stabilization strategy. Optical phase-locking the beat-note to a local oscillator leads to a phase noise level below -103~dBc/Hz at 100~Hz from the carrier. The laser contribution to the short-term frequency stability of the clock is predicted to be compatible with a targeted Allan deviation below $σ_y = 5\,\times 10^{-13}$ over one second.

physics.ins-det↗

arXiv2020

Semiconductor quantum plasmons for high frequency thermal emission

Plasmons in heavily doped semiconductor layers are optically active excitations with sharp resonances in the 5-15 um wavelength region set by the doping level and the effective mass. Here we demonstrate that volume plasmons can form in doped layers of widths of hundreds of nanometers, without the need of potential barrier for electronic confinement. Their strong interaction with light makes them perfect absorber and therefore suitable for incandescent emission. Moreover, by injecting microwave current in the doped layer, we can modulate the temperature of the electron gas. We have fabricated devices for high frequency thermal emission and measured incandescent emission up to 50MHz, limited by the cutoff of our detector. The frequency dependent thermal emission is very well reproduced by our theoretical model that let us envision a frequency cutoff in the tens of GHz.

cond-mat.mes-hall↗

arXiv2020

Slow propagation of 2 GHz acoustical waves in a suspended GaAs on insulator phononic waveguide

Optoelectronic oscillators have dominated the scene of microwave oscillators in the last few years thanks to their great performances regarding frequency stability and phase noise. However, miniaturization of such a device is an up to date challenge. Recently, devices based on phonon-photon interaction gather a lot of interest thanks to their extreme compactness and working frequency directly in the GHz. In this frame, a still missing element to obtain long-term frequency stability performances is an on-chip delay within the feedback loop. Here, we experimentally show filtering and slow propagation of 2 GHz acoustic waves on a Gallium Arsenide membrane heterogeneously integrated on silicon wafer. By engineering the dispersion of an acoustical waveguide, we evidence a group velocity below 1000 m/s for the mode able to propagate. Thus, an integrated delay implementation is at reach for potential improvement of opto-acoustic devices such as optomechanical oscillators or wireless applications.

physics.app-ph↗

arXiv2019

Reproducibility of high-performance quantum dot single-photon sources

Single-photon sources based on semiconductor quantum dots have emerged as an excellent platform for high efficiency quantum light generation. However, scalability remains a challenge since quantum dots generally present inhomogeneous characteristics. Here we benchmark the performance of fifteen deterministically fabricated single-photon sources. They display an average indistinguishability of 90.6 +/- 2.8 % with a single-photon purity of 95.4 +/- 1.5 % and high homogeneity in operation wavelength and temporal profile. Each source also has state-of-the-art brightness with an average first lens brightness value of 13.6 +/- 4.4 %. Whilst the highest brightness is obtained with a charged quantum dot, the highest quantum purity is obtained with neutral ones. We also introduce various techniques to identify the nature of the emitting state. Our study sets the groundwork for large-scale fabrication of identical sources by identifying the remaining challenges and outlining solutions.

quant-ph↗

arXiv2019

Gallium phosphide as a piezoelectric platform for quantum optomechanics

Recent years have seen extraordinary progress in creating quantum states of mechanical oscillators, leading to great interest in potential applications for such systems in both fundamental as well as applied quantum science. One example is the use of these devices as transducers between otherwise disparate quantum systems. In this regard, a promising approach is to build integrated piezoelectric optomechanical devices, that are then coupled to microwave circuits. Optical absorption, low quality factors and other challenges have up to now prevented operation in the quantum regime, however. Here, we design and characterize such a piezoelectric optomechanical device fabricated from gallium phosphide in which a 2.9~GHz mechanical mode is coupled to a high quality factor optical resonator in the telecom band. The large electronic bandgap and the resulting low optical absorption of this new material, on par with devices fabricated from silicon, allows us to demonstrate quantum behavior of the structure. This not only opens the way for realizing noise-free quantum transduction between microwaves and optics, but in principle also from various color centers with optical transitions in the near visible to the telecom band.

quant-ph↗

arXiv2019

Multi-orbital tight binding model for cavity-polariton lattices

In this work we present a tight-binding model that allows to describe with a minimal amount of parameters the band structure of exciton-polariton lattices. This model based on $s$ and $p$ non-orthogonal photonic orbitals faithfully reproduces experimental results reported for polariton graphene ribbons. We analyze in particular the influence of the non-orthogonality, the inter-orbitals interaction and the photonic spin-orbit coupling on the polarization and dispersion of bulk bands and edge states.

cond-mat.mes-hall↗

arXiv2019

Equalization of pulse timings in an excitable microlaser system with delay

An excitable semiconductor micropillar laser with delayed optical feedback is able to regenerate pulses by the excitable response of the laser. It has been shown that almost any pulse sequence can, in principle, be excited and regenerated by this system over short periods of time. We show experimentally and numerically that this is not true anymore in the long term: rather, the system settles down to a stable periodic orbit with equalized timing between pulses. Several such attracting periodic regimes with different numbers of equalized pulse timing may coexist and we study how they can be accessed with single external optical pulses of sufficient strength that need to be timed appropriately. Since the observed timing equalization and switching characteristics are generated by excitability in combination with delayed feedback, our results will be of relevance beyond the particular case of photonics, especially in neuroscience.

physics.optics↗

arXiv2019

Photonic crystal nanobeam cavities with optical resonances around 800 nm

We report on the design and the fabrication of 1D photonic crystal (PhC) nanobeam cavities with optical resonances around 800 nm, compatible with Rubidium, Cesium or Argon atomic transitions. The cavities are made of Indium Gallium Phosphide (InGaP) material, a III-V semi-conductor compound which has a large index of refraction ($n \simeq 3.3$) favoring strong optical confinement and small mode volumes. Nanobeam cavities with inline and side coupling have been designed and fabricated, and quality factors up to $2\times 10^4$ have been measured.

physics.optics↗

arXiv2018

Orbital angular momentum bistability in a microlaser

Light's orbital angular momentum (OAM) is an unbounded degree of freedom emerging in helical beams that appears very advantageous technologically. Using a chiral microlaser, i.e. an integrated device that allows generating an emission carrying a net OAM, we demonstrate a regime of bistability involving two modes presenting distinct OAM (L = 0 and L = 2). Furthermore, thanks to an engineered spin-orbit coupling of light in the device, these modes also exhibit distinct polarization patterns, i.e. cirular and azimuthal polarizations. Using a dynamical model of rate euqations, we show that this bistability arises from polarization-dependent saturation of the gain medium. Such a bistable regime appears very promising for implementing ultrafast optical switches based on the OAM of light. As well, it paves the way to the exploration of dynamical processes involving phase and polarization vortices.

physics.optics↗

arXiv2018

Noise investigation of a dual-frequency VECSEL for application to Cesium clocks

We theoretically and experimentally study the noise of a class-A dual-frequency vertical external cavity surface emitting laser operating at Cesium clock wavelength. The intensity noises of the two orthogonally polarized modes and the phase noise of their beatnote are investigated. The intensity noises of the two modes and their correlations are well predicted by a theory based on coupled rate equations. The phase noise of the beatnote is well described by considering both thermal effects and the effect of phase-amplitude coupling. The good agreement between theory and experiment indicates possible ways to further decrease the laser noises.

physics.ins-det↗

arXiv2018

Optically controlling the emission chirality of microlasers

Orbital angular momentum (OAM) carried by helical light beams is an unbounded degree of freedom of photons that offers a promising playground in modern photonics. So far, integrated sources of coherent light carrying OAM are based on resonators whose design imposes a single, non-tailorable chirality of the wavefront (i.e. clockwise or counter clockwise vortices). Here, we propose and demonstrate the realization of an integrated microlaser where the chirality of the wavefront can be optically controlled. Importantly, the scheme that we use, based on an effective spin-orbit coupling of photons in a semiconductor microcavity, can be extended to different laser architectures, thus paving the way to the realization of a new generation of OAM microlasers with tunable chirality.

physics.optics↗

arXiv2017

Quench dynamics in strongly coupled laser cavities

Strongly coupled dissipative optical cavities with nonlinear interactions give new opportunities to explore symmetry breaking phenomena and phase transitions, Josephson dynamics and quantum criticality. Among the different experimental realizations, photonic crystal coupled nanocavities operating in the laser regime are outstanding systems since nonlinearity, gain/dissipation and intercavity coupling can be judiciously tailored. Yet, although most common scenarios emerge from quasi-dynamical equilibrium where the gain nearly compensates for losses, little is known about far out-of-equilibrium dynamics resulting, for instance, from short pulsed pumping inducing a classical "quench". Here we show that bimodal nanolasers generically display transient dynamics after quench which, when projected onto the nonlasing mode, exhibit superthermal light. Such a mechanism is akin to the fast cooling of a suspension of Brownian particles under gravity, with the intracavity intensity playing the role of the inverse temperature. We implement a simple experimental technique to access the probability density functions, that enabled quantifying the distance from thermal equilibrium --and hence the degree of residual order-- via the Gibbs entropy. This allowed us to further detect mixing of thermal states with coherent broken parity phases, thus paving the road for investigating far nonequilibrium thermodynamics with multimode optical oscillators.

physics.optics↗

arXiv2017

Reducing phonon-induced decoherence in solid-state single-photon sources with cavity quantum electrodynamics

Solid-state emitters are excellent candidates for developing integrated sources of single photons. Yet, phonons degrade the photon indistinguishability both through pure dephasing of the zero-phonon line and through phonon-assisted emission. Here, we study theoretically and experimentally the indistinguishability of photons emitted by a semiconductor quantum dot in a microcavity as a function of temperature. We show that a large coupling to a high quality factor cavity can simultaneously reduce the effect of both phonon-induced sources of decoherence. It first limits the effect of pure dephasing on the zero phonon line with indistinguishabilities above $97\%$ up to $18$ K. Moreover, it efficiently redirects the phonon sidebands into the zero-phonon line and brings the indistinguishability of the full emission spectrum from $87\%$ (resp. $24\%$) without cavity effect to more than $99\%$ (resp. $76\%$) at $0$ K (resp. $20$ K). We provide guidelines for optimal cavity designs that further minimize the phonon-induced decoherence.

quant-ph↗

arXiv2016

Single photon superradiance and cooperative Lamb shift in an optoelectronic device

Single photon superradiance is a strong enhancement of spontaneous emission appearing when a single excitation is shared between a large number of two-level systems. This enhanced rate can be accompanied by a shift of the emission frequency, the cooperative Lamb shift, issued from the exchange of virtual photons between the emitters. In this work we present a semiconductor optoelectronic device allowing the observation of these two phenomena at room temperature. We demonstrate experimentally and theoretically that plasma oscillations in spatially separated quantum wells interact through real and virtual photon exchange. This gives rise to a superradiant mode displaying a large cooperative Lamb shift.

cond-mat.mes-hall↗

arXiv2016

Phase-controlled bistability of a dark soliton train in a polariton fluid

We use a one-dimensional polariton fluid in a semiconductor microcavity to explore the rich nonlinear dynamics of counter-propagating interacting Bose fluids. The intrinsically driven-dissipative nature of the polariton fluid allows to use resonant pumping to impose a phase twist across the fluid. When the polariton-polariton interaction energy becomes comparable to their kinetic energy, linear interference fringes transform into a train of solitons. A novel type of bistable behavior controlled by the phase twist across the fluid is experimentally evidenced.

cond-mat.mes-hall↗

arXiv2016

Origins and control of the polarization splitting in exciton-polaritons microwires

We report on the experimental investigation of the polarization-dependent energy splitting in the lower exciton-polariton branches of a 1D microcavity. The splitting observed for the lowest branch can reach up to 1 meV. It does not result from low temperature thermal constraints but from anisotropic mechanical internal strains induced by etching. Those strains remove the degeneracy both in the photonic ($δE_{\mathrm{ph}}$) and excitonic ($δE_{\mathrm{exc}}$) components of the polariton but also in the photon-exciton coupling ($δΩ$). Those three contributions are accurately infered from experimental data. It appears that the sign and magnitude of the polarization splitting as well as the linear polarization of the corresponding polariton eigenstates can be tuned through the bare exciton-photon detuning. Moreover, no dependence on the width of the wire (from 3 to 7 $\mathrmμ$m) is observed. We propose a mechanical model explaining the universality of those observations paving the way to the engineering of polarization eigenstates in microwires exciton-polaritons.

cond-mat.mes-hall↗