arXiv subjects

Sébastien Cueff

Publications and source records attributed to Sébastien Cueff.

18 recordsLinked to original sources

arXiv2026

Photo-induced Wavelength-tuning of Telecom-band Quantum Dot Nanowires Embedded in a Phase Change Material

Scalable quantum-photonic technologies require spatially separated emitters to emit at the same wavelength, yet epitaxially grown quantum dots naturally exhibit emitter-to-emitter variations in their emission energies. Here, we demonstrate a contact-free post-growth tuning approach for InAs quantum dots embedded in InP nanowires using the photo-induced transformation of an amorphous Sb2S3 shell. This photoinduced effect leads to a progressive relaxation of the strain imposed on the InP core, enabling controlled spectral tuning of the quantum-dot emission. The effect is observed both at room temperature and under cryogenic conditions for quantum dots emitting in the O-band of the telecommunications spectrum. Strain-induced redshifts of approximately 7 meV at room temperature and 28 meV under cryogenic conditions are observed, respectively. The use of an amorphous chalcogenide shell therefore provides a route to achieve local wavelength tuning at the single quantum-dot-in-a-nanowire level after growth. This approach could enable spectrally matched emitters for scalable quantum-photonic architectures.

cond-mat.mes-hall↗

arXiv2025

A formalism for giant Goos-Hänchen shift in metasurface sensors with phase singularity

The Goos-Hänchen (GH) shift becomes giant in resonant photonic structures, making it promising for refractive index sensors with ultimate sensitivities. We provide here a complete formalism to analytically describe the GH shift and its associated sensitivity around the critical coupling regime in photonic structures. This analytical framework quantitatively connects physical parameters such as the quality factor, the angular dispersion, the beam size and the phase singularity to the GH shift. We numerically confirm this theory in two practical designs: a surface plasmon resonance sensor and a Bloch surface wave (BSW) metasurface sensor. Coupling our theory with numerical simulations, we design a BSW metasurface whose GH sensitivity ($10^{13} μm/RIU$) is more than 5 orders of magnitude higher than the current state-of-the art.We also reveal that the main practical limitation to reach ultimate GH sensitivities is the beam size. However, taking into account realistic beam sizes and introducing engineering dispersion for the metasurface, we calculate limits of detection for GH sensors as low as $10^{-13} RIU$ that still surpass current sensors. These results open the way for new sensing application needing high sensitivity and low limit of detection.

physics.optics↗

arXiv2025

Spatially-Controlled Planar Guided Crystallization of Low-Loss Phase Change Materials for Programmable Photonics

Photonic integrated devices are progressively evolving beyond passive components into fully programmable systems, notably driven by the progress in chalcogenide phase-change materials (PCMs) for non-volatile reconfigurable nanophotonics. However, the stochastic nature of their crystal grain formation results in strong spatial and temporal crystalline inhomogeneities. Here, we propose the concept of spatially-controlled planar guided crystallization, a novel method for programming the growth of optically homogeneous low-loss Sb2S3 PCM, leveraging the seeded directional and progressive crystallization within confined channels. This guided crystallization method is experimentally shown to circumvent the current limitations of conventional PCM-based nanophotonic devices, including a multilevel non-volatile optical phase-shifter exploiting a silicon nitride-based Mach-Zehnder interferometer, and a programmable metasurface with spectrally reconfigurable bound state in the continuum. Precisely controlling the growth of PCMs to ensure optically uniform crystalline properties across devices is the cornerstone for the industrial development of non-volatile reconfigurable photonic integrated circuits.

physics.optics↗

arXiv2025

Strong and Engineerable Optical Anisotropy in Easily Integrable Epitaxial SrO(SrTiO 3 ) N Ruddlesden--Popper Thin Layers

Optical anisotropy is a key property for numerous photonic devices. However, bulk anisotropic materials suitable for such applications remain relatively scarse and are often challenging to synthesize as thin films. Additionally, the optical losses as well as the complex structuration of anisotropic metamaterials hinder their integrability in photonic devices. Based on ellipsometry measurements coupled with reflectance, it is demonstrated here that Ruddlesden-Popper (RP) SrO(SrTiO 3 ) N phases (STO-RP N ), epitaxial thin films composed of a SrTiO 3 lattice periodically interrupted by one SrO atomic plane every N unit cells, exhibit pronounced dichroism and birefringence over a broad spectral range. Notably, this anisotropy is tunable by adjusting the RP order N. In contrast to most other anisotropic materials reported in the literature, STO-RP N thin layers can be fabricated using industry-standard growth processes. As it can be epitaxially grown on Si and GaAs using SrTiO 3 templates, the work paves the way for their compact integration on these photonic platforms.

cond-mat.mtrl-sci↗

arXiv2025

Tailoring Flatband Dispersion in Bilayer Moiré Photonic Crystals

In this study, we experimentally investigate the photonic dispersion in one-dimensional moiré structures formed by stacking two photonic crystal slabs with slightly different periods, separated by a carefully controlled subwavelength optical spacer. Angle-resolved reflectivity measurements reveal moiré bands arising from the interplay between intra- and inter-layer coupling mechanisms of guided modes mediated by the moiré superlattice corrugation. By precisely adjusting the refractive index contrast through the filling factor of the photonic crystals, we continuously tune intralayer coupling while keeping interlayer coupling constant. Consequently, we experimentally demonstrate the evolution of moiré minibands into flatbands characterized by minimal dispersion bandwidth. All experimental results show good agreement with numerical simulations. Our findings not only confirm theoretical predictions but also provide a practical approach for realizing photonic flatbands in silicon-based moiré superlattices operating in the telecom wavelength range. This work paves the way toward harnessing flatband physics in advanced optoelectronic applications such as lasers and optical sensors.

physics.optics↗

arXiv2024

Reversible single-pulse laser-induced phase change of Sb$_2$S$_3$ thin films: multi-physics modeling and experimental demonstrations

Phase change materials (PCMs) have gained a tremendous interest as a means to actively tune nanophotonic devices through the large optical modulation produced by their amorphous to crystalline reversible transition. Recently, materials such as Sb$_2$S$_3$ emerged as particularly promising low loss PCMs, with both large refractive index modulations and transparency in the visible and NIR. Controlling the local and reversible phase transition in this material is of major importance for future applications, and an appealing method to do so is to exploit pulsed lasers. Yet, the physics and limits involved in the optical switching of Sb$_2$S$_3$ are not yet well understood. Here, we investigate the reversible laser-induced phase transition of Sb$_2$S$_3$, focusing specifically on the mechanisms that drive the optically induced amorphization, with multi-physics considerations including the optical and thermal properties of the PCM and its environment. We theoretically and experimentally determine the laser energy threshold for reversibly changing the phase of the PCM, not only between fully amorphous and crystalline states but also between partially recrystallized states. We then reveal the non-negligible impact of the material's polycrystallinity and anisotropy on the power thresholds for optical switching. Finally, we address the challenges related to laser amorphization of thick Sb$_2$S$_3$ layers, as well as strategies to overcome them. These results enable a qualitative and quantitative understanding of the physics behind the optically-induced reversible change of phase in Sb$_2$S$_3$ layers.

physics.app-ph↗

arXiv2024

Super Bound States in the Continuum on Photonic Flatbands: Concept, Experimental Realization, and Optical Trapping Demonstration

In this work, we theoretically propose and experimentally demonstrate the formation of a super bound state in a continuum (BIC) on a photonic crystal flat band. This unique state simultaneously exhibits an enhanced quality factor and near-zero group velocity across an extended region of the Brillouin zone. It is achieved at the topological transition when a symmetry-protected BIC pinned at $k=0$ merges with two Friedrich-Wintgen quasi-BICs, which arise from destructive interference between lossy photonic modes of opposite symmetries. As a proof-of-concept, we employ the super flat BIC to demonstrate three-dimensional optical trapping of individual particles. Our findings present a novel approach to engineering both the real and imaginary components of photonic states on a subwavelength scale for innovative optoelectronic devices.

physics.optics↗

arXiv2023

How many supercells are required to achieve unconventional light confinement effects in moiré photonic lattices?

Moiré structures are receiving increasing attention in nanophotonics as they support intriguing optical phenomena. In the so-called "magic configuration", one-dimensional moirés give rise to fully dispersionless energy bands known as "flatbands", where the light is tightly localized within each supercell of the periodic moiré. The goal of this investigation is to determine to what extent the confinement of light, observed in periodic structures, is preserved in microcavities of finite size. Here we analyze the optical response of finite moiré structures consisting of one, two, or more supercells of 1D moiré. Our calculations reveal that for single-supercell cavity, the magic configuration does not impact the electric field confinement at the wavelength of the flat band modes. However, when three or more supercells are connected, we show that the coupling between supercells is canceled at the "magic configuration", resulting in highly confined modes with a quality factor greater than $10^6$ and exhibiting the characteristics of a quasi-bound state in the continuum where optical losses are eliminated through a destructive interference process.

physics.optics↗

arXiv2023

A simple method for programming and analyzing multilevel crystallization states in phase-change materials thin film

We propose and demonstrate a simple method to accurately monitor and program arbitrary states of partial crystallization in phase-change materials (PCMs). The method relies both on the optical absorption in PCMs as well as on the physics of crystallization kinetics. Instead of raising temperature incrementally to increase the fraction of crystallized material, we leverage the time evolution of crystallization at constant temperatures and couple this to a real-time optical monitoring to precisely control the change of phase. We experimentally demonstrate this scheme by encoding a dozen of distinct states of crystallization in two different PCMs: GST and Sb2S3. We further exploit this time-crystallization for the in-situ analysis of phase change mechanisms and demonstrate that the physics of crystallization in Sb2S3 is fully described by the so-called Johnson-Mehl-Avrami-Kolmogorov formalism. The presented method not only paves the way towards real-time and model-free programming of non-volatile reconfigurable photonic integrated devices, but also provides crucial insights into the physics of crystallization in PCMs.

physics.app-ph↗

arXiv2023

Femtosecond laser induced creation of G and W-centers in silicon-on-insulator substrates

The creation of fluorescent defects in silicon is a key stepping stone towards assuring the integration perspectives of quantum photonic devices into existing technologies. Here we demonstrate the creation, by femtosecond laser annealing, of W and G-centers in commercial silicon on insulator (SOI) previously implanted with 12C+ ions. Their quality is comparable to that found for the same emitters obtained with conventional implant processes; as quantified by the photoluminescence radiative lifetime, the broadening of their zero-phonon line (ZPL) and the evolution of these quantities with temperature. In addition to this, we show that both defects can be created without carbon implantation and that we can erase the G-centers by annealing while enhancing the W-centers' emission. These demonstrations are relevant to the deterministic and operando generation of quantum emitters in silicon.

physics.optics↗

arXiv2022

Unveiling the Enhancement of Spontaneous Emission at Exceptional Points

Exceptional points (EPs), singularities of non-Hermitian physics where complex spectral resonances degenerate, are one of the most exotic features of nonequilibrium open systems with unique properties. For instance, the emission rate of quantum emitters placed near resonators with EPs is enhanced (compared to the free-space emission rate) by a factor that scales quadratically with the resonance quality factor. Here, we verify the theory of spontaneous emission at EPs by measuring photoluminescence from photonic-crystal slabs that are embedded with a high-quantum-yield active material. While our experimental results verify the theoretically predicted enhancement, it also highlights the practical limitations on the enhancement due to material loss. Our designed structures can be used in applications that require enhanced and controlled emission, such as quantum sensing and imaging.

physics.optics↗

arXiv2021

Ultimate Phase Sensitivity in Surface Plasmon Resonance Sensors by Tuning Critical Coupling with Phase Change Materials

Plasmonic sensing is an established technology for real-time biomedical diagnostics and air-quality monitoring. While intensity and wavelength tracking are the most commonly used interrogation methods for Surface Plasmon Resonance (SPR), several works indicate the potential superiority of phase interrogation in detection sensitivity. Here, we theoretically and numerically establish the link between ultra-high sensitivities in phase interrogation SPR sensors and the critical coupling condition. However, reaching this condition requires a technically infeasible angstrom-level precision in the metal layer thickness. We propose a robust solution to overcome this limitation by coupling the SPR with a phase-change material (PCM) thin film. By exploiting the multilevel reconfigurable phase states of PCM, we theoretically demonstrate ultra-high phase sensitivities with a limit of detection as low as $10^{-10}$ refractive index unit (RIU). Such a PCM-assisted SPR sensor platform paves the way for unprecedented sensitivity sensors for the detection of trace amounts of low molecular weight species in biomedical sensing and environmental monitoring.

physics.optics↗

arXiv2019

VO2 Nanocrystals for Designer Phase-Change Metamaterials

Subwavelength nanoparticles can support electromagnetic resonances with distinct features depending on their size, shape and nature. For example, electric and magnetic Mie resonances occur in dielectric particles, while plasmonic resonances appear in metals. Here, we experimentally demonstrate that the multipolar resonances hosted by VO2 nanocrystals can be dynamically tuned and switched thanks to the insulator-to-metal transition of VO2. Using both Mie theory and Maxwell Garnett effective medium theory, we retrieve the complex refractive index of the effective medium composed of a slab of VO2 nanospheres embedded in SiO2 and show that such a resulting metamaterial presents distinct optical tunability compared to unpatterned VO2. We further show that this provides a new degree of freedom to design low-loss phase-change metamaterials with designer optical tunability and actively controlled light scattering.

physics.optics↗

arXiv2019

InAs quantum dot in a needlelike tapered InP nanowire: a telecom band single photon source monolithically grown on silicon

Realizing single photon sources emitting in the telecom band on silicon substrates is essential to reach complementary-metal-oxide-semiconductor (CMOS) compatible devices that secure communications over long distances. In this work, we propose the monolithic growth of needlelike tapered InAs/InP quantum dot-nanowires (QD-NWs) on silicon substrates with a small taper angle and a nanowire diameter tailored to support a single mode waveguide. Such a NW geometry is obtained by a controlled balance over axial and radial growths during the gold-catalyzed growth of the NWs by molecular beam epitaxy. This allows us to investigate the impact of the taper angle on the emission properties of a single InAs/InP QD-NW. At room temperature, a Gaussian far-field emission profile in the telecom O-band with a 30° beam divergence angle is demonstrated from a single InAs QD embedded in a 2° tapered InP NW. Moreover, single photon emission is observed at cryogenic temperature for an off-resonant excitation and the best result, $g^2(0) = 0.05$, is obtained for a 7° tapered NW. This all-encompassing study paves the way for the monolithic growth on silicon of an efficient single photon source in the telecom band based on InAs/InP QD-NWs.

physics.app-ph↗

arXiv2018

Tailoring the Local Density of Optical States and directionality of light emission by symmetry-breaking

We present a method to simultaneously engineer the energy-momentum dispersion and the local density of optical states. Using vertical symmetry-breaking in high-contrast gratings, we enable the mixing of modes with different parities, thus producing hybridized modes with controlled dispersion. By tuning geometric parameters, we control the coupling between Bloch modes, leading to flatband, M- and W-shaped dispersion as well as Dirac dispersion. Such a platform opens up a new way to control the direction of emitted photons, and to enhance the spontaneous emission into desired modes. We then experimentally demonstrate that this method can be used to redirect light emission from weak emitters -- defects in Silicon -- to optical modes with adjustable density of states and angle of emission.

physics.optics↗

arXiv2018

Directional lasing at high oblique angle from metasurface exhibiting multivalley dispersion

We report on a metasurface laser emitting at the valley extremum of a multivalley energy-momentum dispersion. Such peculiar dispersion shape is obtained by hybridizing high quality factor photonic modes of different symmetry and opposite effective mass. The lasing effect takes place at high oblique angle ($\sim$20 degrees), in the telecom wavelength range ($\sim$1580 nm), on silicon substrate and operating at room temperature. Our results show the potential of multivalley dispersion for micro-laser in integrated photonic and beam-steering applications. It also opens the way to study various features of valleytronic physics such as spontaneous momentum symmetry breaking, two-mode squeezing and Josephson oscillation in momentum space.

physics.optics↗

arXiv2017

Symmetry Breaking in Photonic Crystals: On-Demand Dispersion from Flatband to Dirac Cones

We demonstrate that symmetry breaking opens a new degree of freedom to tailor the energy-momentum dispersion in photonic crystals. Using a general theoretical framework in two illustrative practical structures, we show that breaking symmetry enables an on-demand tuning of the local density of states of a same photonic band from zero (Dirac cone dispersion) to infinity (flatband dispersion), as well as any constant density over an adjustable spectral range. As a proof-of-concept, we experimentally demonstrate the transformation of a very same photonic band from conventional quadratic shape to Dirac dispersion, flatband dispersion and multivaley one, by finely tuning the vertical symmetry breaking. Our results provide an unprecedented degree of freedom for optical dispersion engineering in planar integrated photonic devices.

physics.optics↗

arXiv2014

Quantifying and controlling the magnetic dipole contribution to 1.5 $μ$m light emission in erbium-doped yttrium oxide

We experimentally quantify the contribution of magnetic dipole (MD) transitions to the near-infrared light emission from trivalent erbium-doped yttrium oxide (Er$^{3+}$:Y$_2$O$_3$). Using energy-momentum spectroscopy, we demonstrate that the $^4$I$_{13/2}{\to}^4$I$_{15/2}$ emission near 1.5 $μ$m originates from nearly equal contributions of electric dipole (ED) and MD transitions that exhibit distinct emission spectra. We then show how these distinct spectra, together with the differing local density of optical states (LDOS) for ED and MD transitions, can be leveraged to control Er$^{3+}$ emission in structured environments. We demonstrate that far-field emission spectra can be tuned to resemble almost pure emission from either ED or MD transitions, and show that the observed spectral modifications can be accurately predicted from the measured ED and MD intrinsic emission rates.

physics.optics↗