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We perform quantum state reconstruction of coherent and thermal states with a detector which has an enhanced multiphoton response. The detector is based on superconducting nanowires, where the bias current sets the dependence of the click probability on the photon number; this bias current is used as tuning parameter in the state reconstruction. The nonlinear response makes our nanowire-based detector superior to the linear detectors that are conventionally used for quantum state reconstruction., Comment: revision of intro compared to V1

A photonic crystal three missing holes nanocavity, having only a few modes, is coupled to a 60 missing holes long multimode cavity, both fabricated in the same InGaAsP membrane. The coupling was studied in detail by the photothermal tuning of the small cavity over about three free spectral ranges of the large cavity. Strong coupling effects, involving at least three large cavity modes simultaneously, were observed from level anticrossing data. The observations are excellently reproduced by a model of coupled Fabry Perot resonators.

We propose a novel photon number resolving detector structure with large dynamic range. It consists of the series connection of N superconducting nanowires, each connected in parallel to an integrated resistor. Photon absorption in a wire switches its current to the parallel resistor producing a voltage pulse and the sum of these voltages is measured at the output. The combination of this structure and a high input impedance preamplifier result in linear, high fidelity, and fast photon detection in the range from one to several tens of photons.

A local tuning of the modes of photonic crystal systems both to blue and to red sides of the resonance is implemented by nano-infiltration/evaporation of water and laser micro-oxidation. This technology is used to completely control coupled photonic nanocavities (photonic crystal molecules). Beside the standard condition of zero detuning between identical modes of the two cavities (homoatomic molecule), we are also able to produce coupling between two modes of different polarization and spatial distribution (heteroatomic molecule). (C) 2011 Elsevier B.V. All rights reserved.

The insertion of a metal-coated tip on the surface of a photonic crystal microcavity is used for simultaneous near field imaging of electric and magnetic fields in photonic crystal nanocavities, via the radiative emission of embedded semiconductor quantum dots (QD). The photoluminescence intensity map directly gives the electric field distribution, to which the electric dipole of the QD is coupled. The magnetic field generates, via Faraday's law, a circular current in the apex of the metallized probe that can be schematized as a ring. The resulting magnetic perturbation of the photonic modes induces a blue shift, which can be used to map the magnetic field, within a single near-field scan. (C) 2011 Elsevier B.V. All rights reserved.

We present the first nanoscale (down to approximate to 50 x 50 nm(2)) detector displaying single-photon sensitivity and a nanosecond response. This type of nanodetector can also be operated in multiphoton mode, where the detection threshold can be set at N = 1, 2, 3, or 4 photons, thus allowing the mapping of photon number statistics on the nanoscale. Its operation principle based on that of hot-spot formation in superconducting nanowires allies the temporal resolution and sensitivity of superconducting single-photon detectors with subwavelength resolution and photon number discrimination. Such detectors can be of great interest for the study of nanophotonic devices at low temperature.

A method to avoid the stiction failure in nano-electro-opto-mechanical systems has been demonstrated by coating the system with an anti-stiction layer of Al2O3 grown by atomic layer deposition techniques. The device based on a double-membrane photonic crystal cavity can be reversibly operated from the pull-in back to its release status. This enables to electrically switch the wavelength of a mode over ~50 nm with a potential modulation frequency above 2 MHz. These results pave the way to reliable nano-mechanical sensors and optical switches.

We report a systematic theoretical and experimental investigation of the polarization properties of columnar quantum dots (CQDs) with extremely large aspect ratio and high compositional contrast. A strong variation of the polarization of the dominant interband transitions as a function of the CQD composition and aspect ratio is predicted by the theory and observed experimentally. In optimized InAs CQDs grown on GaAs, dominant emission and lasing is obtained in the transverse-magnetic polarization, which shows the potential of this approach for polarization-independent amplifiers on GaAs.

The progress in nanofabrication has made possible the realization of optic nanodevices able to handle single photons and to exploit the quantum nature of single-photon states. In particular, quantum cryptography (or more precisely quantum key distribution, QKD) allows unconditionally secure exchange of cryptographic keys by the transmission of optical pulses each containing no more than one photon. Additionally, the coherent control of excitonic and photonic qubits is a major step forward in the field of solid-state cavity quantum electrodynamics, with potential applications in quantum computing. Here, we describe devices for realization of single photon generation and detection based on high resolution technologies and their physical properties. Particular attention will be devoted to the description of single-quantum dot sources based on photonic crystal microcavites optically and electrically driven: the electrically driven devices is an important result towards the realization of single photon source “on demand”. A new class of single photon detectors, based on superconducting nanowires, the superconducting single-photon detectors (SSPDs) are also introduced: the fabrication techniques and the design proposed to obtain large area coverage and photon number-resolving capability are described.

In this work we present a sizeable and reversible spectral tuning of the resonances of a two-dimensional photonic crystal nanocavity by exploiting the introduction of a sub-wavelength size glass tip. The comparison between experimental near-field data 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. Moreover, a non-linear control on the cavity resonance is obtained by exploiting the local heating induced by near-field laser excitation at different excitation powers. The temperature gradient due to the optical absorption results in an index of refraction gradient which modifies the dielectric surroundings of the cavity and shifts the optical modes. (C) 2009 Elsevier B.V. All rights reserved.

We present eight-band k.p calculations of the electronic and polarization properties of columnar Inz Ga1-z As quantum dots (CQD) with high aspect ratio embedded in an Inx Ga1-x As/GaAs quantum well. Our model accounts for the linear strain effects, linear piezoelectricity, and spin-orbit interaction. We calculate the relative intensities of transverse-magnetic (TM) and transverse-electric (TE) linear polarized light emitted from the edge of the semiconductor wafer as a function of the two main factors affecting the heavy hole-light hole valence band mixing and hence, the polarization dependent selection rules for the optical transitions, namely, (i) the composition contrast z/x between the dot material and the surrounding well and (ii) the dot aspect ratio. The numerical results show that the former is the main driving parameter for tuning the polarization properties. This is explained by analyzing the biaxial strain in the CQD, based on which it is possible to predict the TM to TE intensity ratio. The conclusions are supported by analytical considerations of the strain in the dots. Finally, we present the compositional and geometrical conditions to achieve polarization independent emission from InGaAs/GaAs CQDs. © 2010 American Institute of Physics. U7 - Export Date: 2 August 2010 U7 - Source: Scopus U7 - Art. No.: 073509

Using a pump-probe differential transmission experiment in heterodyne detection, we measured the refractive index dynamics at the ground-state excitonic transition in electrically pumped InAs/GaAs quantum-dot amplifiers emitting near 1.3 µm at room temperature. We compare three samples differing only in the level of p-doping, and interpret the measured index changes taking into account the gain dynamics in these devices. We find that in absorption, the excess hole density due to p-doping accelerates the recovery and reduces the refractive index change, since filling of the hole states by p-doping shifts the induced changes in the hole population toward high energy states. Conversely, in gain, the reduced electron reservoir in the excited states in p-doped devices results in slower gain recovery dynamics and in larger refractive index changes compared to undoped devices operating at the same modal gain. The linewidth enhancement factor inferred from these measurements shows that p-doping is effective in reducing this parameter mainly due to the larger differential gain in p-doped devices in the gain regime. © 2009 IEEE.

We report on the fabrication and characterization of high performance nanowire superconducting single photon detectors (SSPD) on MgO substrates. The deposition of the superconducting material (NbN) has been performed by magnetron sputtering at 400°C. This deposition temperature is low enough to be compatible with the fabrication on traditional optical materials like GaAs. First, SSPD meanders covering a surface of 5 × 5 µm2 were characterized. We measured quantum efficiencies up to 20% at 1300 nm. Then, we used a straight 250 µm-long NbN nanowire to perform a spatially resolved measurement of the efficiency. Both efficiency dips and peaks were observed. The dips were correlated to lithographic defects, as confirmed by scanning electron microscopy. Conversely, no evidence of a lithographic origin of efficiency peaks was found.

Optical-to-electrical conversion, which is the basis of the operation of optical detectors, can be linear or nonlinear. When high sensitivities are needed, single-photon detectors are used, which operate in a strongly nonlinear mode, their response being independent of the number of detected photons. However, photon-number-resolving detectors are needed, particularly in quantum optics, where n-photon states are routinely produced. In quantum communication and quantum information processing, the photon-numberre-solving functionality is key to many protocols, such as the implementation of quantum repeaters(1) and linear- optics quantum computing(2). A linear detector with single-photon sensitivity can also be used for measuring a temporal waveform at extremely low light levels, such as in long-distance optical communications, fluorescence spectroscopy and optical time-domain reflectometry. We demonstrate here a photon-number-resolving detector based on parallel superconducting nanowires and capable of counting up to four photons at telecommunication wavelengths, with an ultralow dark count rate and high counting frequency.

Electrical and optical characterization has been performed on several superconducting single photon detectors (SSPDs) consisting of meanders made of ultrathin NbN films. The NbN films, with thickness ranging from 150 nm to 3 nm, were deposited by dc magnetron sputtering on MgO substrates kept at temperature T = 400C. This deposition process carried out at low temperature opens the way of monolithic integration with other photonic devices. The superconducting properties of NbN films and the critical design parameters that affect the quantum efficiency (QE) have been optimized. In particular, by measuring the switching current distribution of each stripe of the meander the process uniformity has been studied. Optical measurements on the fabricated SSPDs showed a QE approximate to 20% at 4.2 K for photons with a wavelength of 1300 nm.

We unveil the role of bound-to-continuum photoexcitation of carriers as a relevant process that affects the performance of quantum dot (OD) lasers. We present the response of an InAs/InGaAs QD laser to a sub-band gap pump, showing an unexpected depletion of the emitted photons. We relate this observation with carrier photoexcitation through additional transmission and photocurrent measurements. We provide a theoretical support to the experimental data and highlight the important role of this process in the laser characteristics.

We demonstrate high-performance nanowire superconducting single photon detectors (SSPDs) on ultrathin NbN films grown at a temperature compatible with monolithic integration. NbN films ranging from 150nm to 3nm in thickness were deposited by dc magnetron sputtering on MgO substrates at 400C. The superconducting properties of NbN films were optimized studying the effects of deposition parameters on film properties. SSPDs were fabricated on high quality NbN films of different thickness (7 to 3nm) deposited under optimal conditions. Electrical and optical characterizations were performed on the SSPDs. The highest QE value measured at 4.2K is 20% at 1300nm.

Integrated quantum photonics offers three principal advantages over bulk optics—low loss, simplicity and scalability. Quantum photonic integrated circuits show promise for on-chip generation, manipulation and detection of tens of single photons for quantum information processing. For quantum photonic integration, gallium arsenide is one of the most promising material platforms as full integration of all active and passive circuit elements can be obtained.

Superconducting nanowire single photon detectors (SNSPDs) are the detectors of choice in quantum optics applications due to their leading performances. To exploit their performances, great care must be devoted to efficiently couple light from a single-mode fiber to their small area, ∼10 μm in size, at cryogenic temperature (∼3K). In addition, to further improve the SNSPDs functionality, implementing the photon number resolving capability, arrays of spatially multiplexed SNSPDs, must be realized. We will discuss our results obtained for these two approaches.

We investigated the passivation of III-V semiconductor nanostructures using wet-chemical ammonium sulfide treatment and SiOx encapsulation. We achieved an ultra-low surface recombination velocity value of ~530 cm/s enabling the future development of high-performance room-temperature nanolasers.

We use quantum detector tomography to investigate the detection mechanism in WSi nanowire superconducting single photon detectors (SSPDs). To this purpose, we fabricated a 250nm wide and 250nm long WSi nanowire and measured its response to impinging photons with wavelengths ranging from $\lambda$ = 900 nm to $\lambda$ = 1650 nm. Tomographic measurements show that the detector response depends on the total excitation energy only. Moreover, for energies Et > 0.8eV the current energy relation is linear, similar to what was observed in NbN nanowires, whereas the current-energy relation deviates from linear behaviour for total energies below 0.8eV.

Using a differential transmission pump-probe experiment in heterodyne detection, the ultrafast gain and refractive-index dynamics of the ground-state transition in InAs/GaAs quantum- dot amplifiers emitting near 1.3 mum at working condition, that is at room temperature and under electrical injection were measured. An ultrafast gain recovery on a subpicosecond time scale is observed at high electrical injection indicating fast carrier relaxation into the dot ground state, which is appealing for high-speed applications with these devices. Comparing p-doped and undoped devices of otherwise identical structure and operating at the same gain, a faster absorption recovery but a slower gain dynamics in p-doped amplifiers was observed. This finding should help in elucidating the role of p-doping in the design of QD-based devices with high-speed performances.

We reported the growth of asymmetric InAs bilayer quantum dots (QD) on GaAs substrate by molecular beam epitaxy. A combination of different InAs growth rates (GR) for the two QD layers was used, respectively, to increase QD density and extend photoluminescence (PL) emission wavelength. A high GR used for the first layer guarantees a high QD density; while a low GR used for the second layer helps to extend the PL emission wavelength due to the dot size increase, which was confirmed by transmission electron microscopy and PL measurements. It was found that this kind of QDs is very sensitive to post-growth annealing procedure due to the dot size increase. By appropriately choosing the growth parameters, InAs bilayer QD laser diodes embedded in a conventional AlGaAs/GaAs waveguide structure were demonstrated. The devices yielded the lowest ever reported threshold current density of 134 A/cm 2 in the range of 1.5 μm wavelength for GaAs-based lasers.

High-power broadband superluminescent diodes (SLDs) emitting in the 1.2-1.3-?m region are demonstrated using InAs-GaAs quantum dots (QDs). The highest output powers of ?30-50 mW are achieved using 18 QD layers with p-doped GaAs spacers. At these high powers the device operates in a regime of broad bandwidth (?100 nm) with a spectral dip of ?5 dB between two separate peaks originated by the QD ground and excited states. Spectral calculations performed with a traveling-wave rate equation model show excellent agreement with the experimental data and provide design rules for optimizing the output spectrum. SLD characteristics are presented for two different device structures consisting of tilted and bent waveguides. The latter allows the achievement of higher output powers at lower currents. The coherence properties and the temperature characteristics are also discussed in detail. © 2007 IEEE

We describe the design and characterization of a fiber-coupled double-channel single-photon detection system based on superconducting single-photon detectors (SSPD), and its application for quantum optics experiments on semiconductor nanostructures. When operated at 2-K temperature, the system shows 10% quantum efficiency at 1.3-¿m wavelength with dark count rate below 10 counts per second and timing resolution

The growth of InAs columnar quantum dots (CQDs) on GaAs substrates by MBE was studied. The CQDs were formed by depositing a 1.8 monolayer (ML) InAs seed dot layer and a short period GaAs/InAs superlattice (SL). The growth of the CQDs is very sensitive to growth interruption (GI) and growth temp. Both longer GI and higher growth temp. impact the size dispersion of the CQDs, which causes the broadening of photoluminescence (PL) spectrum and the presence of the addnl. PL peak tails. By properly choosing the GI and the growth temp., CQDs including GaAs (3 ML)/InAs (0.62 ML) SL with period no. up to 35 without plastic relaxation were grown. The corresponding equiv. thickness of the SL is 41 nm which is two times higher than the theor. crit. thickness of the strained InGaAs layer with the same av. In compn. of 16%. The increase of the crit. thickness is partially assocd. with the formation of the CQDs. Based on a five-stack CQD active region, laser diodes emitting around 1120 nm at room temp. were demonstrated, indicating a high material quality. CQDs with nearly isotropic cross section (20 nm*20 nm dimensions) were formed by depositing a 16-period GaAs (3 ML)/InAs (0.62 ML) SL on an InAs seed dot layer, indicating the feasibility of artificial shape engineering of QDs. Such a structure is expected to be very promising for polarization insensitive device applications, such as semiconductor optical amplifiers. [on SciFinder (R)]

We present the design, fabrication and characterization of double-membrane photonic crystal cavities electromechanically tunable over >10 nm, and their application in integrated quantum photonics.

We theoretically investigate the multipolar effects on the dipole-forbidden transitions of a semiconductor quantum dot. An approximated expression for the decay rate of these transitions is derived. Unlike the general theory of the spontaneous emission beyond the dipole approximation, the distinct roles of the emitter and the vacuum electric field in the transition rate are here clearly recognizable and can be separately optimized. We illustrate the potential of this formalism by calculating the spontaneous emission decay rate of an InAs/GaAs quantum dot embedded into two realistic nanostructures---an L3 photonic crystal cavity and a plasmonic dimer antenna. The obtained results show that, although the two structures provide an enhancement of the same order of magnitude, the plasmonic antenna constitutes a more promising candidate for the experimental observation of the dipole-forbidden transitions of a quantum dot.

Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. By exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions.

Arrays of photonic cavities are relevant structures for developing large-scale photonic integrated circuits and for investigating basic quantum electrodynamics phenomena due to the photon hopping between interacting nanoresonators. Here we investigate, by means of scanning near-field spectroscopy, numerical calculations and an analytical model, the role of different neighboring interactions that give rise to delocalized supermodes in different photonic crystal array configurations. The systems under investigation consist of three nominally identical two-dimensional photonic crystal nanocavities on membrane aligned along the two symmetry axes of the triangular photonic crystal lattice. We find that the nearest-neighbor and next-nearest-neighbor coupling terms can be of the same relevance. In this case, a nonintuitive picture describes the resonant modes, and the photon hopping between adjacent nanoresonators is strongly affected. Our findings prove that exotic configurations and even postfabrication engineering of coupled nanoresonators could directly tailor the mode spatial distribution and the group velocity in coupled resonator optical waveguides.

We probe the local detection efficiency in a nanowire superconducting single-photon detector along the cross-section of the wire with a far subwavelength resolution. We experimentally find a strong variation in the local detection efficiency of the device. We demonstrate that this effect explains previously observed variations in NbN detector efficiency as a function of device geometry.

We present time integrated and time resolved measurements on single In/As quantum dots (QD) emitting at 1300nm, at 10K, embedded in a planar microcavity. We clearly identify a standard spectroscopic signature from single QDs and compare the exciton line width and biexciton (BX) binding energy for several QDs. We present this data for QDs spatially selected by etched mesas and metallic apertures. Time resolved photoluminescence (PL) from single electron-hole recombination in the ground state of the QD is investigated as a function of excitation power and temperature. The measurements reveal the presence of a background emission that delays the PL of excitons in the ground state., Proceeding - 4th International Conference on Quantum Dots - will be published in Physica Status Solidi (c)

The size dispersion of InAs quantum dots (QD) was optimized to broaden the photoluminescence (PL) spectrum. A broad PL spectral width up to 96 nm is achieved from a single QD layer with InAs thickness smaller than 2.4 monolayers at a growth temperature of 510 °C. QD Superluminescent light emitting diodes with an ultrawide (115 nm), smooth output spectrum are obtained by incorporating this QD layer into chirped stacked structures.

A chirped multiple quantum dot (QD) structure is introduced as a means to controllably broaden the gain spectral width of InAs QDs. The In composition and thickness of InGaAs strain-reducing layers (SRLs) can be used as tuning parameters to adjust the emission wavelength of each layer in the chirped stack. The spectral linewidth depends on the span of the In composition and thickness of the InGaAs SRL. By varying the In composition of each InGaAs SRL, a ground-state photoluminescence spectral width of 78 nm was achieved. The spectral width can be further increased by Be modulation -doping. The chirped multi-layer QD structure was used as the active region of a laser diode, exhibiting a lasing spectrum as wide as 30 nm.

An understanding of the kinetics of the steam oxidation of AlAs and (AlGa)As layers is crucial to maintain good control of the process of manufacturing modern GaAs-based diode microresonator vertical-cavity surface-emitting lasers (VCSELs). Mathematically, the process has been described in our previous publications. Our theoretical equations contain, however, a few adjustable parameters, which should be found experimentally. Therefore, in this paper, an extensive analysis of existing experimental results (including ours) is performed. It enables us to extract the physical parameters describing oxidation kinetics for the AlAs and (AlGa)As oxidation process. While some scattering in the parameters is found from measurements reported by different groups, the same general trends are observed. These results support our physical understanding of the oxidation process. Nevertheless, the oxidation process still needs some experimental investigations to establish all conditions influencing its kinetics and to enable reproducible oxidation results obtained under assumed identical technological conditions. It has been confirmed that currently theoretical modelling cannot offer a reasonable a priori control of the oxidation process without a careful calibration of a given oxidation set-up and procedure. However, the simulation may enable determination of safe limits of the process, especially important in the fabrication of small-size microresonator VCSELs.

Theoretical analysis of carrier dynamics in quantum dot lasers is presented, particularly with regard to the effect of carrier relaxation. Two modeling approaches are applied, one is based on standard rate equations and the other on master equations of microstates, in order to consider random carrier capture. Both models show similar results and can be exploited to describe realistic devices quantitatively. In particular, a reliable estimation of the relaxation time can be obtained from comparison with experimental results. Finally, the modulation dynamics of real devices is modeled, which shows a suppression of relaxation oscillations on the ground state transition in dependence of the cavity length.

Measurements on 1.3-/spl mu/m quantum-dot lasers are presented that reveal a number of interesting effects. 1) At high bias, a second lasing line appears, corresponding to the excited state transition. 2) The linewidth enhancement factor increases dramatically above threshold. 3) The modulation performance is degraded when the second lasing line appears. A comprehensive numerical model is developed to explain this behavior. We attribute it to incomplete gain clamping above threshold. This is caused by a combination of the finite intraband relaxation time and the limited density of states.

We demonstrate the control of the spontaneous emission rate of single InAs quantum dots embedded in a double-membrane photonic crystal cavity by the electromechanical tuning of the cavity resonance. Controlling the separation between the two membranes with an electrostatic field we obtain the real-time spectral alignment of the cavity mode to the excitonic line and we observe an enhancement of the spontaneous emission rate at resonance. The cavity has been tuned over 13 nm without shifting the exciton energies. A spontaneous emission enhancement of 4.5 has been achieved with a coupling efficiency of the dot to the mode 92%., Comment: 4 pages, 3 figures

Monumental buildings are characterized by elements (such as columns, vaults, arches …) that can suffer significant damage even under moderate earthquakes. Unfortunately, the available modeling approaches require a huge amount of computing resources. The chapter presents a multi-level strategy that is able to overcome these difficulties by a rational adoption of different computational approaches. As a case study, the non-linear seismic assessment of the medieval “Maniace Castle”, in Syracuse (Sicily, Italy) is developed, by using different numerical models. First, the linear behavior of the building is studied by means of two 3D Finite Element models. Then, results are used to calibrate a 2D plane Rigid Body and Spring Model (RBSM), specifically formulated for approximating the macroscopic behavior of masonry texture with a small number of degrees of freedom. In order to account for the variability of the material characteristics, parametric non-linear analyses have been performed and compared.

During the seismic events occurred in the last decades, the existing reinforced concrete (RC) building stock has often exhibited a significant brittle collapse of joints and secondary elements such as infill walls. A quite common strategy, in the attempt of mitigating this vulnerability, is the generalised implementation of strengthening interventions on the structural elements, even in the absence of a complete seismic assessment procedure. This paper presents some considerations about the effects induced by strengthening interventions involving the tying of the infill panels to the RC frame. Within this context, an appraisal of the actual displacement capacity and the possible alteration induced on the global collapse mechanism is provided. The analyses and discussion of results are presented with reference to an actual case study concerning a school building, which was part of a wide vulnerability assessment investigation performed in the Province of Foggia, Italy. In particular, seismic analyses perfo...

We report the all-electrical control over cavity-emitter systems, consisting in Stark-tunable quantum dots embedded in mechanically reconfigurable photonic crystal membranes. Purcell-effect from a single dot is demonstrated at distinct wavelengths.

We use quantum detector tomography to identify photon assisted vortex entry as the photon detection mechanism in superconducting NbN nanowires. We exploit the polarization dependence to resolve the response of the nanowire with subwavelength resolution.

International audience; We experimentally investigate the effect of a magnetic field on photon detection in superconducting single-photon detectors (SSPDs). At low fields, the effect of a magnetic field is through the direct modification of the quasiparticle density of states of the superconductor, and magnetic field and bias current are interchangeable, as is expected for homogeneous dirty-limit superconductors. At the field where a first vortex enters the detector, the effect of the magnetic field is reduced, up until the point where the critical current of the detector starts to be determined by flux flow. From this field on, increasing the magnetic field does not alter the detection of photons anymore, whereas it does still change the rate of dark counts. This result points at an intrinsic difference in dark and photon counts, and also shows that no enhancement of the intrinsic detection efficiency of a straight SSPD wire is achievable in a magnetic field. (C) 2015 AIP Publishing LLC.

We report the full energy control over a semiconductor cavity-emitter system, consisting of single Stark-tunable quantum dots embedded in mechanically reconfigurable photonic crystal membranes. A reversible wavelength tuning of the emitter over 7.5 nm as well as an 8.5 nm mode shift are realized on the same device. Harnessing these two electrical tuning mechanisms, a single exciton transition is brought on resonance with the cavity mode at several wavelengths, demonstrating a ten-fold enhancement of its spontaneous emission. These results open the way to bring several cavity-enhanced emitters mutually into resonance and therefore represent a key step towards scalable quantum photonic circuits featuring multiple sources of indistinguishable single photons.

Photonic and plasmonic devices rely on nanoscale control of the local density of optical states (LDOS) in dielectric and metallic environments. The tremendous progress in designing and tailoring the electric LDOS of nano-resonators requires an investigation tool that is able to access the detailed features of the optical localized resonant modes with deep-subwavelength spatial resolution. This scenario has motivated the development of different nanoscale imaging techniques. Here, we prove that a technique involving the combination of scanning near-field optical microscopy with resonant scattering spectroscopy enables imaging the electric LDOS in nano-resonators with outstanding spatial resolution (λ/19) by means of a pure optical method based on light scattering. Using this technique, we investigate the properties of photonic crystal nanocavities, demonstrating that the resonant modes appear as characteristic Fano line shapes, which arise from interference. Therefore, by monitoring the spatial variation of the Fano line shape, we locally measure the phase modulation of the resonant modes without the need of external heterodyne detection. This novel, deep-subwavelength imaging method allows us to access both the intensity and the phase modulation of localized electric fields. Finally, this technique could be implemented on any type of platform, being particularly appealing for those based on non-optically active material, such as silicon, glass, polymers, or metals. A purely optical method for realizing ultra-subwavelength phase-sensitive imaging of localized photonic modes has been developed. The technique combines scanning near-field optical microscopy with resonance scattering spectroscopy and involves monitoring the spatial variation of the Fano resonance line shape in photonic-crystal nanocavities. Using the technique, Niccolo Caselli and co-workers in Italy, the USA, the UK, and the Netherlands realized a spatial resolution of λ/19 (where λ is the wavelength) for the electric local density of optical states (LDOS). The technique can be applied to resonators made from any kind of material and over a wide spectral range. Furthermore, it does not suffer from bleaching or tip-induced perturbation. This demonstration opens up new strategies for investigating the electric LDOS and phase distribution of modes in a wide range of nanophotonic and nanoplasmonic resonators.

In this paper, we present a systematic study of the effect of growth parameters on the structural and optical properties of InAs quantum dot (QD) grown under Stranski-Krastanov mode by molecular beam epitaxy. The dot density is significantly reduced from 1.9x10(10) to 0.6x10(10) cm(-2) as the growth rate decreases from 0.075 to 0.019 ML/s, while the island size becomes larger. Correspondingly, the emission wavelength shifts to the longer side. By increasing the indium fraction in the InGaAs capping layer, the emission wavelength increases further. At indium fraction of 0.3, a ground state transition wavelength as long as 1.4 mum with the excited state transition wavelength of around 1.3 mum has been achieved in our dots. The optical properties of QDs with a ground state transition wavelength of 1.3 mum but with different growth techniques were compared. The QDs grown with higher rate and embedded by InGaAs have a higher intensity saturation level from excitation dependent photoluminescence measurements and a smaller intensity decrease from temperature dependent measurements. Finally, single mirror light emitting diodes with a QD embedded in InGaAs have been fabricated. The quantum efficiency at room temperature is 1.3%, corresponding to a radiative efficiency of 21.5%. (C) 2002 American Institute of Physics.

Optical switches connect optical circuits, and route optical signals in networks. Nano-electromechanical systems can in principle enable compact and power-effective switches that can be integrated in photonic circuits. We proposed an optical switch based on four coupled waveguides arranged in three-dimensional configuration. The switching operation is controlled by a cantilever displacement of only 55 nm. Simulations show that our proposed device requires a low switching voltage down to 3V and can operate at frequencies in the MHz range. Our results also pave the way towards novel optical components that electromechanically manipulate light in both the horizontal and the vertical direction in photonic circuits.