Radiatively Broadened Incandescent Sources

We study the incandescence of a semiconductor system characterized by a radiatively broadened material excitation. We show that the shape of the emission spectrum and the peak emissivity value are determined by the ratio between radiative and nonradiative relaxation rates of the material mode. Our system is a heavily doped quantum well, exhibiting a collective bright electronic excitation in the mid-infrared. The spontaneous emission rate of this collective mode strongly depends on the emission direction and, uncommonly for an intersubband system, can dominate nonradiative scattering processes. Consequently the incandescence spectrum undergoes strong modifications when the detection angle is varied. Incandescence is modeled solving quantum Langevin equations, including a microscopic description of the collective excitations, decaying into electronic and photonic baths. We demonstrate that the emissivity reaches unity value for a well-defined direction and presents an angular radiative pattern that is very different from that of an oscillating dipole

Supplementary document for Temporal Localized Turing Patterns in Mode-locked Semiconductor Lasers - 6108005.pdf

details on the pape

Elliptical micropillars for efficient generation and detection of coherent acoustic phonons

Coherent acoustic phonon generation and detection assisted by optical resonances are at the core of efficient optophononic transduction processes. However, when dealing with a single optical resonance, the optimum generation and detection conditions take place at different laser wavelengths, i.e. different detunings from the cavity mode. In this work, we theoretically propose and experimentally demonstrate the use of elliptical micropillars to reach these conditions simultaneously at a single wavelength. Elliptical micropillar optophononic resonators present two optical modes with orthogonal polarizations at different wavelengths. By employing a cross-polarized scheme pump-probe experiment, we exploit the mode splitting and couple the pump beam to one mode while the probe is detuned from the other one. In this way, at a particular micropillar ellipticity, both phonon generation and detection processes are enhanced. We report an enhancement of a factor of ~3.1 when comparing the signals from elliptical and circular micropillars. Our findings constitute a step forward in tailoring the light-matter interaction for more efficient ultrahigh-frequency optophononic devices

Direct Band Gap Germanium Microdisks Obtained with Silicon Nitride Stressor Layers

Germanium is an ideal candidate to achieve a monolithically integrated laser source on silicon. Unfortunately bulk germanium is an indirect band gap semiconductor. Here, we demonstrate that a thick germanium layer can be transformed from an indirect into a direct band gap semiconductor by using silicon nitride stressor layers. We achieve 1.75% (1.67%) biaxial tensile strain in 6 (9) μm diameter microdisks as measured from photoluminescence. The modeling of the photoluminescence amplitude vs temperature indicates that the zone-center Γ valley has the same energy as the L valley for a 9 μm diameter strained microdisk and is even less for the 6 μm diameter microdisk, thus demonstrating that a direct band gap is indeed obtained. We deduce that the crossover in germanium from indirect to direct gap occurs for a 1.67% ± 0.05% biaxial strain at room temperature, the value of this parameter varying between 1.55% and 2% in the literature

3048512.pdf

The Supplemental Document provides details on the theoretical model used to simulate the polarization tomography experiment

Giant optical polarisation rotations induced by a single quantum dot spin

This dataset contains the measured data, and their corresponding simulated values (fits), used in the analysis of our experimental results. Normalized intensities and corresponding Stokes components are included for all six polarisations (H, V, D, A, R, L), as a function of the detuning between the incoming laser and the QD transition

Origin of optical nonlinearity in plasmonic semiconductor nanostructures

The development of nanoscale nonlinear elements in photonic integrated circuits is hindered by the physical limits to the nonlinear optical response of dielectrics, which requires that the interacting waves propagate in transparent volumes for distances much longer than their wavelength. Here we present experimental evidence that optical nonlinearities in doped semiconductors are due to free-electron and their efficiency could exceed by several orders of magnitude that of conventional dielectric nonlinearities. Our experimental findings are supported by comprehensive computational results based on the hydrodynamic modeling, which naturally includes nonlocal effects, of the free-electron dynamics in heavily doped semiconductors. By studying third-harmonic generation from plasmonic nanoantenna arrays made out of heavily n-doped InGaAs with increasing levels of free-carrier density, we discriminate between hydrodynamic and dielectric nonlinearities. As a result, the value of maximum nonlinear efficiency as well as its spectral location can now be controlled by tuning the doping level. Having employed the common material platform InGaAs/InP that supports integrated waveguides, our findings pave the way for future exploitation of plasmonic nonlinearities in all-semiconductor photonic integrated circuits

Supplement 1: Scalable performance in solid-state single-photon sources

We deduce area distribution; show visibility power-dependence; deduce a model for visibility versus temporal distance; and describe how indistinguishability is obtained with the resonant-excitation method. Originally published in Optica on 20 April 2016 (optica-3-4-433