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Using a semi-analytic guided-mode expansion technique, we present theory and analysis of intrinsic propagation losses for topological photonic crystal slab waveguide structures with modified honeycomb lattices of circular or triangular holes. Although conventional photonic crystal waveguide structures, such as the W1 waveguide, have been designed to have lossless propagation modes, they are prone to disorder-induced losses and backscattering. Topological structures have been proposed to help mitigate this effect as their photonic edge states may allow for topological protection. However, the intrinsic propagation losses of these structures are not well understood and the concept of the light line can become blurred. For four example topological edge state structures, photonic band diagrams, loss parameters, and electromagnetic fields of the guided modes are computed. Two of these structures, based on armchair edge states, are found to have significant intrinsic losses for modes inside the photonic band gap, more than 100 dB/cm, which is comparable to or larger than typical disorder-induced losses using slow-light modes in conventional photonic crystal waveguides, while the other two structures, using the valley Hall effect and inversion symmetry, are found to have a good bandwidth for exploiting lossless propagation modes below the light line., 10 pages, 9 figures

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.

We report on the observation of optical Stark effects in J-aggregate-metal hybrid nanostructures exhibiting strong exciton-surface-plasmon-polariton coupling. For redshifted nonresonant excitation, pump-probe spectra show short-lived dispersive line shapes of the exciton-surface-plasmon-polariton coupled modes caused by a pump-induced Stark shift of the polariton resonances. For larger coupling strengths, the sign of the Stark shift is reversed by a transient reduction in normal mode splitting. Our studies demonstrate an approach to coherently control and largely enhance optical Stark effects in strongly coupled hybrid systems. This may be useful for applications in ultrafast all-optical switching.

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

ON-OFF intermittency or blinking is a phenomenon observed in single quantum emitters, which reduces their overall light emission. Even though it seems to be a fundamental property of quantum dots (QDs), substantial differences can be found in the blinking statistics of different nanocrystals. This work compares the blinking of numerous single, oxide-capped Si nanocrystals with that of CdSe/ZnS core-shell nanocrystals, measured under the same conditions in the same experimental system and over a broad range of excitation power densities. We find that ON- and OFF-times can be described by exponential statistics in Si QDs, as opposed to power-law statistics for the CdSe nanocrystals. The type of blinking (power-law or monoexponential) does not depend on excitation but seems to be an intrinsic property of the material system. Upon increasing excitation power, the duty cycle of Si quantum dots remains constant, whereas it decreases for CdSe nanocrystals, which is readily explained by blinking statistics. Both ON-OFF and OFF-ON transitions can be regarded as light-induced in Si/SiO2 QDs, while the OFF-ON transition in CdSe/ZnS nanocrystals is not stimulated by photons. The differences in blinking behavior in these systems will be discussed. QC 20140307

The absorption properties of a resonator can be tuned by varying the phase between incoming coherent light beams. Such control is now shown under strong coupling conditions, allowing all incoming energy to be converted into polaritons. The ability to drive a system with an external input is a fundamental aspect of light–matter interaction. The key concept in many photonic applications is the ‘critical coupling’ condition1,2: at criticality, all the energy fed to the system is dissipated within the system itself. Although this idea was crucial to enhance the efficiency of many devices, it was never considered in the context of systems operating in a non-perturbative regime. In this so-called strong-coupling regime, the matter and light degrees of freedom are mixed into dressed states, leading to new eigenstates called polaritons3,4,5,6,7,8,9,10. Here we demonstrate that the strong-coupling regime and the critical coupling condition can coexist; in such a strong critical coupling situation, all the incoming energy is converted into polaritons. A general semiclassical theory reveals that such a situation corresponds to a special curve in the phase diagram of the coupled light–matter oscillators. In the case of a system with two radiating ports, the phenomenology shown is that of coherent perfect absorption (CPA; refs 11, 12), which is then naturally understood in the framework of critical coupling. Most importantly, we experimentally verify polaritonic CPA in a semiconductor-based intersubband-polariton photonic crystal resonator. This result opens new avenues in polariton physics, making it possible to control the pumping efficiency of a system independent of the energy exchange rate between the electromagnetic field and the material transition.

Surface plasmon polaritons (SPPs), optical excitations at the interface between a metal and a dielectric, carry significant potential for guiding and manipulating light on the nanoscale(1-3). However, their weak optical nonlinearities hinder active device fabrication, for example, for all-optical switching(4-7) or information processing(8,9). Recently, strong optical dipole coupling has been demonstrated between SPPs and nonlinear quantum emitters with normal mode splittings of up to 700 meV (refs 10-15). The predicted ultrafast energy transfer between quantum emitters and SPP fields could be a crucial microscopic mechanism for switching light by light on the nanoscale. Here, we present the first real-time observation of ultrafast Rabi oscillations in a J-aggregate/metal nanostructure, indicating coherent energy transfer between excitonic quantum emitters and SPP fields. We demonstrate coherent manipulation of the coupling energy by controlling the exciton density on a 10 fs timescale, which represents a step towards coherent, all-optical ultrafast plasmonic circuits and devices.

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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Recent experimental progress in cavity optomechanics has allowed cooling of mesoscopic mechanical oscillators via dynamic backaction provided by the parametric coupling to either an optical or an electrical resonator. Here we analyze the occurrence of normal-mode splitting in backaction cooling at high input power. We find that a hybridization of the oscillator's motion with the fluctuations of the driving field occurs and leads to a splitting of the mechanical and optical fluctuation spectra. Moreover, we find that cooling experiences a classical limitation through the cavity lifetime., 4 pages, 3 figures

Here we report the growth and the characterization of pillar microcavities, constituted by Bragg mirrors, which are composed by alternate layers of GaAs and aluminum oxide. The selective oxidation of the AlAs layers allowed to increase the refraction index mismatch between the GaAs and AlAs. As a consequence we obtained high reflectivity Bragg mirrors even with only three layers, a factor three less than usually necessary in the more common GaAs/AlAs Bragg reflectors. This not only simplifies the growth process, but also gives a reduction of the cavity mode volume. We have examined several MESAs with pillar diameter ranging from 1 to 10 mm, containing a system of InAs quantum dots. The quality factors of the cavities range from Q = 600–2000. Enhancement of the spontaneous emission rate of QDs was observed when the emission is on resonance with cavity modes. Purcell factors up to 2 were measured. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We experimentally observe a sizable and reversible spectral tuning of the resonances of a two-dimensional photonic crystal microcavity induced by the introduction of a subwavelength size glass tip. The comparison between experimental near-field data, collected with lambda/6 spatial resolution, and results of numerical calculations shows that the spectral shift induced by the tip is proportional to the local electric field intensity of the cavity mode. This observation proves that the electromagnetic local density of states in a microcavity can be directly measured by mapping the tip-induced spectral shift with a scanning near-field optical microscope.

The authors demonstrate more than 9 nm tunability of the whispering gallery modes (WGMs) of rhodamine B doped water microdroplets resting on a superhydrophobic surface. Tunability was achieved by controlling the size of the microdroplets in a current controlled mini humidity chamber. WGMs were observed with quality factors of more than 8000 when kept stable. The sensitivity of the resonances to the size and shape of the microdroplet reveals opportunities for the use of this technique as a probe to characterize superhydrophobic surfaces and investigate liquid-solid surfaces., NA

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.