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

In this Letter, 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 the destructive interference between lossy photonic modes of opposite symmetries. As a proof of concept, we employ the ultraflat super 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.

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 beam divergence angle θ = 30° is demonstrated using 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, g2(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.

Probing the Combined Electromagnetic Local Density of Optical States with Quantum Emitters Supporting Strong Electric and Magnetic Transitions.

We experimentally demonstrate that the radiative decay rate of a quantum emitter is determined by the combined electric and magnetic local density of optical states (LDOS). A Drexhage-style experiment was performed for two distinct quantum emitters, divalent nickel ions in magnesium oxide and trivalent erbium ions in yttrium oxide, which both support nearly equal mixtures of isotropic electric dipole and magnetic dipole transitions. The disappearance of lifetime oscillations as a function of emitter-interface separation distance confirms that the electromagnetic LDOS refers to the total mode density, and thus similar to thermal emission, these unique electronic emitters effectively excite all polarizations and orientations of the electromagnetic field.

Dynamic control of light emission faster than the lifetime limit using VO2 phase-change.

Modulation is a cornerstone of optical communication, and as such, governs the overall speed of data transmission. Currently, the two main strategies for modulating light are direct modulation of the excited emitter population (for example, using semiconductor lasers) and external optical modulation (for example, using Mach-Zehnder interferometers or ring resonators). However, recent advances in nanophotonics offer an alternative approach to control spontaneous emission through modifications to the local density of optical states. Here, by leveraging the phase-change of a vanadium dioxide nanolayer, we demonstrate broadband all-optical direct modulation of 1.5 µm emission from trivalent erbium ions more than three orders of magnitude faster than their excited state lifetime. This proof-of-concept demonstration shows how integration with phase-change materials can transform widespread phosphorescent materials into high-speed optical sources that can be integrated in monolithic nanoscale devices for both free-space and on-chip communication.

Modeling the anisotropic electro-optic interaction in hybrid silicon-ferroelectric optical modulator.

We present a numerical method to accurately model the electro-optic interaction in anisotropic materials. Specifically, we combine a full-vectorial finite-difference optical mode solver with a radio-frequency solver to analyze the overlap between optical modes and applied electric field. This technique enables a comprehensive understanding on how electro-optic effects modify individual elements in the permittivity tensor of a material. We demonstrate the interest of this approach by designing a modulator that leverages the Pockels effect in a hybrid silicon-BaTiO3 slot waveguide. Optimized optical confinement in the active BaTiO3 layer as well as design of travelling-wave index-matched electrodes is presented. Most importantly, we show that the overall electro-optic modulation is largely governed by off-diagonal elements in the permittivity tensor. As most of active electro-optic materials are anisotropic, this method paves the way to better understand the physics of electro-optic effects and to improve optical modulators.

Electrically tailored resistance switching in silicon oxide.

Resistive switching in a metal-free silicon-based material offers a compelling alternative to existing metal oxide-based resistive RAM (ReRAM) devices, both in terms of ease of fabrication and of enhanced device performance. We report a study of resistive switching in devices consisting of non-stoichiometric silicon-rich silicon dioxide thin films. Our devices exhibit multi-level switching and analogue modulation of resistance as well as standard two-level switching. We demonstrate different operational modes that make it possible to dynamically adjust device properties, in particular two highly desirable properties: nonlinearity and self-rectification. This can potentially enable high levels of device integration in passive crossbar arrays without causing the problem of leakage currents in common line semi-selected devices. Aspects of conduction and switching mechanisms are discussed, and scanning tunnelling microscopy (STM) measurements provide a more detailed insight into both the location and the dimensions of the conductive filaments.

Structural factors impacting carrier transport and electroluminescence from Si nanocluster-sensitized Er ions.

We present an analysis of factors influencing carrier transport and electroluminescence (EL) at 1.5 µm from erbium-doped silicon-rich silica (SiOx) layers. The effects of both the active layer thickness and the Si-excess content on the electrical excitation of erbium are studied. We demonstrate that when the thickness is decreased from a few hundred to tens of nanometers the conductivity is greatly enhanced. Carrier transport is well described in all cases by a Poole-Frenkel mechanism, while the thickness-dependent current density suggests an evolution of both density and distribution of trapping states induced by Si nanoinclusions. We ascribe this observation to stress-induced effects prevailing in thin films, which inhibit the agglomeration of Si atoms, resulting in a high density of sub-nm Si inclusions that induce traps much shallower than those generated by Si nanoclusters (Si-ncs) formed in thicker films. There is no direct correlation between high conductivity and optimized EL intensity at 1.5 µm. Our results suggest that the main excitation mechanism governing the EL signal is impact excitation, which gradually becomes more efficient as film thickness increases, thanks to the increased segregation of Si-ncs, which in turn allows more efficient injection of hot electrons into the oxide matrix. Optimization of the EL signal is thus found to be a compromise between conductivity and both number and degree of segregation of Si-ncs, all of which are governed by a combination of excess Si content and sample thickness. This material study has strong implications for many electrically-driven devices using Si-ncs or Si-excess mediated EL.

Thickness-dependent optimization of Er3+ light emission from silicon-rich silicon oxide thin films.

This study investigates the influence of the film thickness on the silicon-excess-mediated sensitization of Erbium ions in Si-rich silica. The Er3+ photoluminescence at 1.5 µm, normalized to the film thickness, was found five times larger for films 1 µm-thick than that from 50-nm-thick films intended for electrically driven devices. The origin of this difference is shared by changes in the local density of optical states and depth-dependent interferences, and by limited formation of Si-based sensitizers in "thin" films, probably because of the prevailing high stress. More Si excess has significantly increased the emission from "thin" films, up to ten times. This paves the way to the realization of highly efficient electrically excited devices.