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Normal-mode splitting is the most evident signature of strong coupling between two interacting subsystems. It occurs when two subsystems exchange energy between themselves faster than they dissipate it to the environment. Here we experimentally show that a weakly coupled optomechanical system at room temperature can manifest normal-mode splitting when the pump field fluctuations are antisquashed by a phase-sensitive feedback loop operating close to its instability threshold. Under these conditions the optical cavity exhibits an effectively reduced decay rate, so that the system is effectively promoted to the strong coupling regime.

In dilute-nitride semiconductors, the possibility to selectively passivate N atoms by spatially controlled hydrogen irradiation allows for tailoring the effective N concentration of the host-and, therefore, its electronic and structural properties-with a precision of a few nanometers. In the present work, this technique is applied to the realization of ordered arrays of GaAs1-xNx/GaAs1-xNx: H wires oriented at different angles with respect to the crystallographic axes of the material. The creation of a strongly anisotropic strain field in the plane of the sample, due to the lattice expansion of the fully hydrogenated regions surrounding the GaAs1-xNx wires, is directly responsible for the peculiar polarization properties observed for the wire emission. Temperature-dependent polarization-resolved microphotoluminescence measurements, indeed, reveal a nontrivial dependence of the degree of linear polarization on the wire orientation, with maxima for wires parallel to the [110] and [1 (1) over bar0] directions and a pronounced minimum for wires oriented along the [100] axis. In addition, the polarization direction is found to be precisely perpendicular to the wire when the latter is oriented along high-symmetry crystal directions, whereas significant deviations from a perfect orthogonality are measured for all other wire orientations. These findings, which are well reproduced by a theoretical model based on finite-element calculations of the strain profile of our GaAs1-xNx/GaAs1-xNx:H heterostructures, demonstrate our ability to control the polarization properties of dilute-nitride micro- and nanostructures via H-assisted strain engineering. This additional degree of freedom may prove very useful in the design and optimization of innovative photonic structures relying on the integration of dilute-nitride-based light emitters with photonic crystal microcavities.

Images of semiconductor `dot in rods' and their small clusters are studied by measuring the second-order correlation function with a spatially resolving ICCD camera. This measurement allows one to distinguish between a single dot and a cluster and, to a certain extent, to estimate the number of dots in a cluster. A more advanced measurement is proposed, based on higher-order correlations, enabling more accurate determination of the number of dots in a small cluster. Nonclassical features of the light emitted by such a cluster are analyzed., Comment: 4 pages, 4 figures

Most current methods for the engineering of photonic crystal (PhC) cavities rely on cumbersome, computationally demanding trial-and-error procedures. In the present work, we take a different approach to the problem of cavity design, by seeking to establish a direct, semianalytic relationship between the target electromagnetic field distribution and the dielectric constant of the PhC structure supporting it. We find that such a relationship can be derived by expanding the modes of L-N-type cavities as a linear combination of the one-dimensional (1D) Bloch eigenmodes of a PhC W1 waveguide. Thanks to this expansion, we can also ascertain the presence of a well-defined 1D character in the modes of relatively short cavities (e.g., L9-15), thus confirming recent theoretical predictions and experimental findings. Finally, we test our method through the successful design of a cavity supporting a mode with Gaussian envelope function and ultralow radiative losses (quality factor of 17.5 x 10(6)).

We demonstrate the nonresonant magnetic interaction at optical frequencies between a photonic crystal microcavity and a metallized near-field microscopy probe. This interaction can be used to map and control the magnetic component of the microcavity modes. The metal coated tip acts as a microscopic conductive ring, which induces a magnetic response opposite to the inducing magnetic field. The resulting shift in resonance frequency can be used to measure the distribution of the magnetic field intensity of the photonic structure and fine-tune its optical response via the magnetic field components. © 2010 The American Physical Society.

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Polarization selectors, especially, those involving quantum dots (QDs) in photonic crystals (PCs) are interesting as they offer scalability for planar architectures. Three-dimensional finite difference time domain simulations were used to design PC structures suitable for polarization-selective transmission of QD emission into different regions as well as polarization beam splitters with different splitting ratios. Different waveguide out couplers were also designed for these coupled waveguide PC structures. As the transmitted intensity is the net result of superposition of all scattered beams, QD position defines the coupling efficiency to different paths. A detailed study showed that the transmission efficiency has intermediate maxima when the QD is shifted in either x- or z-directions. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)

We report on photocurrent and photoconductance processes in a freely suspended p-doped single GaAs nanowire. The nanowires are grown by molecular beam epitaxy (MBE), and they are electrically contacted by a focused ion beam (FIB) deposition technique. The observed photocurrent is generated at the Schottky contacts between the nanowire and metal source-drain electrodes, while the observed photoconductance signal can be explained by a photogating effect induced by optically generated charge carriers located at the surface of the nanowire. Both optoelectronic effects are sensitive to the polarization of the exciting laser field, enabling polarization dependent photodetectors.

In this invited paper of the 28th International Conference of the Physics of Semiconductors (ICPS-28), we discuss the peculiar quantum electrodynamical properties of a semiconductor microcavity system, in which a cavity photon mode is strongly coupled to an intersubband transition of a doped quantum well system. In this kind of semiconductor system, it is possible to achieve an unprecedented ultrastrong coupling regime, in which the vacuum Rabi frequency is comparable to the electronic transition frequency. We discuss the anomalous quantum properties of the quantum ground state (a squeezed vacuum) and of the intersubband cavity polariton excitations. We address the role of dissipation and point out some future perspectives concerning the investigation of quantum vacuum radiation effects induced by an ultrafast time modulation of the quantum vacuum.

We report on a set of experimental measurements aimed to fully characterize both the spatial and angular pattern of the optical modes of photonic crystal microcavities. By using a confocal microscope we resolve the spatial distribution of the mode on the sample surface. With the same setup, by introducing an iris placed on a translational stage within the collimated beam region of the confocal microscope, we are able to measure the far field angular pattern of the microcavity modes. The experimental data are compared with theoretical predictions obtained by finite difference in time domain calculations and a very good agreement is found. (c) 2009 Elsevier B.V. All rights reserved.

We present a novel semiconductor structure in which 0D polaritons coexist with 2D microcavity polaritons. Spatial trapping of the 2D microcavity polaritons results from the confinement of their photonic part in a potential well, consisting of an adjustable thickness variation of the spacer layer. This original technique allows to create polaritonic boxes of any size and shape. Strong coupling regime is evidenced by the typical energy level anticrossing, in real space and in momentum space, and supported by a theoretical model.

A method to achieve photoinduced tuning of PhC nanocavity modes is discussed and implemented. It is based on light induced oxidation in air atmosphere with very low thermal budget which produces a local reduction of the GaAs membrane effective thickness and a large blueshift of the nanocavity modes. It is also shown that green light is much more efficient in inducing the micro-oxidation with respect to near infrared light. The observed behaviour is attributed to oxide growth promoted by photoenhanced reactivity. (C) 2012 American Institute of Physics. [doi:10.1063/1.3678036]

The growth of highly-reflective nitride-based distributed Bragg reflectors (DBRs) and their use in vertical cavity structures is reviewed. We discuss the various nitride material systems employed to design Bragg mirrors and microcavities, namely the Al-x(Ga)(1-x)N/(Al)(y)Ga1-yN and the lattice-matched Al1-xInxN/GaN (x(ln) similar to 18%)-based systems. An emphasis on particular issues such as strain management, internal absorption, alloy morphology and contribution of leaky modes is carried out. Specific properties of the poorly known AlInN alloy such as the bandgap variation with In content close to lattice-matched conditions to GaN are reported. The superior optical quality of the lattice-matched AlInN/GaN system for the realization of nitride-based DBRs is demonstrated. The properties of nitride-based vertical cavity devices are also described. Forthcoming challenges such as the realization of electrically pumped vertical cavity surface emitting lasers and strongly coupled quantum microcavities are discussed as well, and in particular critical issues such as vertical current injection.

A fine control of a photonic molecule is obtained by nanofluidic techniques. The coupling condition between the modes of two photonic crystal nanocavities is modified by spectrally tuning each single resonator. Clear mode anticrossing and transition from localized to delocalized states are observed. The detuning induced by disorder, always present in real device, is experimentally compensated by locally modifying the photonic environment of the cavity.

We demonstrate three-dimensional spatial confinement of exciton-polaritons in a semiconductor microcavity. Polaritons are confined within a micron-sized region of slightly larger cavity thickness, called mesa, through lateral trapping of their photon component. This results in a shallow potential well that allows the simultaneous existence of extended states above the barrier. Photoluminescence spectra were measured as a function of either the emission angle or the position on the sample. Striking signatures of confined states of lower and upper polaritons, together with the corresponding extended states at higher energy, were found. In particular, the confined states appear only within the mesa region, and are characterized by a discrete energy spectrum and a broad angular pattern. A theoretical model of polariton states, based on a realistic description of the confined photon modes, supports our observations.