Phase Control of Transient Optical Properties of Double Coupled Quantum-Dot Nanostructure via Gaussian Laser Beams

We theoretically analyze the transient properties of a probe field absorption and dispersion in a coupled semiconductor double-quantum-dot nanostructure.We show that in the presence of the Gaussian laser beams,absorption and dispersion of the probe field can be dramatically influenced by the relative phase between applied fields and intensity of the Gaussian laser beams.Transient and steady-state behaviors of the probe field absorption and dispersion are discussed to estimate the required switching time.The estimated range is between 5-8 ps for subluminal to superluminal light propagation.

Symmetry and size effects on energy and entanglement of an exciton in coupled quantum dots

We study theoretically the essential properties of an exciton in vertically coupled Gaussian quantum dots in the presence of an external magnetic field. The ground state energy of a heavy-hole exciton is split into four energy levels due to the Zeeman effect. For the symmetrical system, the entanglement entropy of the exciton state can reach a value of 1. However, for a system with broken symmetry, it is close to zero. Our results are in good agreement with previous studies.

Silicon micromirrors with three-dimensional curvature enabling lensless efficient coupling of free-space light

Miniaturized optical benches process free-space light propagating in-plane with respect to the substrate and have a large variety of applications,including the coupling of light through an optical fiber.High coupling efficiency is usually obtained using assembled micro-optical parts,which considerably increase the system cost and integration effort.In this work,we report a high coupling efficiency,monolithically integrated silicon micromirror with controlled three-dimensional(3D)curvature that is capable of manipulating optical beams propagating in the plane of the silicon substrate.Based on our theoretical modeling,a spherical micromirror with a microscale radius of curvature as small as twice the Gaussian beam Rayleigh range provides a 100%coupling efficiency over a relatively long optical path range.Introducing dimensionless parameters facilitates the elucidation of the role of key design parameters,including the mirror’s radii of curvature,independent of the wavelength.A micromachining method is presented for fabricating the 3D micromirror using fluorinated gas plasmas.The measured coupling efficiency was greater than 50%over a 200-mm optical path,compared to less than 10%afforded by a conventional flat micromirror,which was in good agreement with the model.Using the 3D micromirror,an optical cavity was formed with a round-trip diffraction loss of less than 0.4%,resulting in one order of magnitude enhancement in the measured quality factor.A nearly 100%coupling was also estimated when matching the sagittal and tangential radii of curvature of the presented micromirror’s surface.The reported class of 3D micromirrors may be an advantageous replacement for the optical lenses usually assembled in silicon photonics and optical benches by transforming them into real 3D monolithic systems while achieving wideband high coupling efficiency over submillimeter distances.