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Sensing displacements at the nanoscale is the basis for many metrology applications, in particular atomic-force microscopy. Displacement sensing with nano-optomechanical structures provides interesting opportunities for integration, but it typically features a small dynamic range due to the near-field nature of the sensor-sample interaction. Here, a far-field sensing approach based on a grating coupler is considered and an analytical model used to tune its performance is introduced. The proposed model allows exploiting the full range of design parameters and thereby optimizing resolution and dynamic range. The compact size of the sensor and the possibility of integrating it with an on-chip laser and detector make it very promising for fully-integrated optical sensing systems.

We present an efficient and flexible method to realize micro- and nano-optical structures on the tip of optical fibers. We demonstrate this approach for a fiber-tip sensor consisting of a photonic crystal (PhC) structure in a semiconductor membrane on the cleaved facet of a telecom fiber. The PhC structure is fabricated on a wafer by lithography and etching and then transferred to the fiber facet by a simple mechanical pickup process through an opening in the substrate, without the need for adhesives or a micromanipulator. Due to its reliability, scalability, and the use of wafer-scale fabrication methods, this process increases the possibilities for fiber-tip applications at the industrial level. With the fabricated fiber tip sensors, we demonstrate sensing of the refractive index and temperature, with resonance wavelength shifts of 120 nm/RIU and 95 pm/K, respectively.

Optical read-out of motion is widely used in sensing applications. Recent developments in micro- and nano-optomechanical systems have given rise to on-chip mechanical sensing platforms, potentially leading to compact and integrated optical motion sensors. However, these systems typically exploit narrow spectral resonances and therefore require tuneable lasers with narrow linewidth and low spectral noise, which makes the integration of the read-out extremely challenging. Here, we report a step towards the practical application of nanomechanical sensors, by presenting a sensor with ultrawide (∼80 nm) optical bandwidth. It is based on a nanomechanical, three-dimensional directional coupler with integrated dual-channel waveguide photodiodes, and displays small displacement imprecision of only 45 fm/Hz1/2 as well as large dynamic range (>30 nm). The broad optical bandwidth releases the need for a tuneable laser and the on-chip photocurrent read-out replaces the external detector, opening the way to fully-integrated nanomechanical sensors., On-chip mechanical sensing platforms require tuneable lasers with narrow linewidth and low spectral noise, making read-out challenging. Here, the authors report a nanomechanical sensor with 80nm bandwidth, displacement imprecision of 45 fm/Hz1/2 as well as a dynamic range greater than 30 nm with integrated photodetectors.

Photonic integration in a micrometer-thick indium phosphide (InP) membrane on silicon (IMOS) offers intrinsic and high-performance optoelectronic functions together with high-index-contrast nanophotonic circuitries. Recently demonstrated devices have shown competitive performances, including high side-mode-suppression ratio (SMSR) lasers, ultrafast photodiodes, and significant improvement in critical dimensions. Applications of the IMOS devices and circuits in optical wireless, quantum photonics, and optical cross-connects have proven their performances and high potential.

Spectrometry is widely used for the characterization of materials, tissues, and gases, and the need for size and cost scaling is driving the development of mini and microspectrometers. While nanophotonic devices provide narrowband filtering that can be used for spectrometry, their practical application has been hampered by the difficulty of integrating tuning and read-out structures. Here, a nano-opto-electro-mechanical system is presented where the three functionalities of transduction, actuation, and detection are integrated, resulting in a high-resolution spectrometer with a micrometer-scale footprint. The system consists of an electromechanically tunable double-membrane photonic crystal cavity with an integrated quantum dot photodiode. Using this structure, we demonstrate a resonance modulation spectroscopy technique that provides subpicometer wavelength resolution. We show its application in the measurement of narrow gas absorption lines and in the interrogation of fiber Bragg gratings. We also explore its operation as displacement-to-photocurrent transducer, demonstrating optomechanical displacement sensing with integrated photocurrent read-out., Fully integratable spectrometers have trade-offs between size and resolution. Here, the authors present a nano-opto-electro-mechanical system where the functionalities of transduction, actuation and detection are fully integrated, resulting in an ultra-compact high-resolution spectrometer with a micrometer-scale footprint.

Nanoscale light sources using metal cavities have been proposed to enable high integration density, efficient operation at low energy per bit and ultra-fast modulation, which would make them attractive for future low-power optical interconnects. For this application, such devices are required to be efficient, waveguide-coupled and integrated on a silicon substrate. We demonstrate a metal-cavity light-emitting diode coupled to a waveguide on silicon. The cavity consists of a metal-coated III–V semiconductor nanopillar which funnels a large fraction of spontaneous emission into the fundamental mode of an InP waveguide bonded to a silicon wafer showing full compatibility with membrane-on-Si photonic integration platforms. The device was characterized through a grating coupler and shows on-chip external quantum efficiency in the 10−4–10−2 range at tens of microamp current injection levels, which greatly exceeds the performance of any waveguide-coupled nanoscale light source integrated on silicon in this current range. Furthermore, direct modulation experiments reveal sub-nanosecond electro-optical response with the potential for multi gigabit per second modulation speeds., Despite much progress, nanoscale light sources suitable for photonic integration are lacking. Here, the authors present a metal-cavity nanopillar LED on a silicon substrate working at telecommunications wavelengths, which demonstrates compatibility with membrane-on-Si photonic integration platforms.

Nanoscale light sources are being intensively investigated for their potential to enable low-energy, high-density optical communication and sensing systems. Both nano-light-emitting diodes (nanoLEDs) and nanolasers have been considered, based on advanced nanophotonic concepts such as photonic crystals and plasmonic structures, with dimensions well into the sub-micrometer domain. With decreasing dimensions, light-matter interaction becomes stronger, potentially leading to efficient and ultrafast radiative emission, both in the spontaneous and stimulated regime. These features have created wide expectations for the practical prospects of such nanoscale light sources, in particular for optical interconnects. In this article we examine the limits to the downscaling of LEDs and lasers, and ask ourselves which type of source is most suited to ultralow-power optical communications. Based on simple physical considerations on the scaling of spontaneous and stimulated emission rates for semiconductor active regions at room temperature, we analyze the speed and energy limits for nanoLEDs and nanolasers as a function of their size. The role of spontaneous emission enhancement (Purcell effect) in practical nanophotonic sources is also revisited. The main conclusion is that nanoLEDs reach a fundamental energy/speed limit for data rates exceeding a few Gb/s, whereas nanolasers with active dimensions in the range of few 100s nm may enable direct modulation rates larger than 40 Gb/s at power levels adequate for short-distance and low-energy optical interconnects., 13 pages, 8 figures

The recent progress in integrated quantum optics has set the stage for the development of an integrated platform for quantum information processing with photons, with potential applications in quantum simulation. Among the different material platforms being investigated, direct-bandgap semiconductors and particularly gallium arsenide (GaAs) offer the widest range of functionalities, including single- and entangled-photon generation by radiative recombination, low-loss routing, electro-optic modulation and single-photon detection. This paper reviews the recent progress in the development of the key building blocks for GaAs quantum photonics and the perspectives for their full integration in a fully-functional and densely integrated quantum photonic circuit.

Miniaturization of displacement sensors for nanoscale metrology is a key requirement in many applications such as accelerometry, mass sensing, and atomic force microscopy. While optics provides high resolution and bandwidth, integration of sensor readout is required to achieve low-cost, compact, and parallelizable devices. Here, we present a novel integrated opto-electro-mechanical device for displacement sensing that has sub-nanometer resolution. The proposed sensor is a micron-sized double-membrane photonic crystal cavity with integrated electro-optical readout, directly addressed via an on-chip waveguide. This sensor displays a noise floor down to 7 fm/Hz and is suitable for the realization of integrated arrays.

Nanophotonic structures with narrow optical resonances, such as high-quality factor photonic crystal cavities, in principle enable spectral sensing with high resolution. This can also result in high-sensitivity displacement and/or acceleration sensing if a part of the cavity is compliant. However, the control of the resonance and its optical read-out are complex and usually not integrated with the sensing part. In this talk we will introduce a novel nano-opto-electromechanical system (NOEMS), where actuation, sensing and read-out are integrated in the same device. It consists of a double-membrane photonic crystal cavity, where the resonant wavelength is tuned by electrostatically controlling the separation between the membranes. The output current signal provides direct information about either the wavelength of the incident light or the cavity resonance. This nanophotonic sensing system can be employed to measure the spectrum of incident light, to determine the wavelength of a laser line with pm-range resolution, or equivalently to measure tiny displacements.

In the last few years, the real-time monitoring of civil infrastructures has become an essential tool for the safety inspection, the design and planning of maintenance. In this context, the implementation of optic fiber sensors embedded in the structural elements is particularly useful to check strains and displacements and assess the structural safety level. In this paper, a methodology aimed at the control of the safety and serviceability level of a Prestressed Reinforced Concrete Viaduct located in the city of Bari (Italy) is presented. The procedure is based on information acquired by fiber optic monitoring system implemented during the construction of the bridge. The processing of the data provided by the sensors at different times of the execution has allowed the appraisal of the strain variations related to the load increments and to the stress losses in the different phases and the comparison with the theoretical values. This comparison enables a double check: control in the construction phases, safety in the service life.

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.

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 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 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 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

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.

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.

Solid-state cavity quantum electrodynamics systems will form scalable nodes of future quantum networks, allowing the storage, processing and retrieval of quantum bits, where a real-time control of the radiative interaction in the cavity is required to achieve high efficiency. We demonstrate here the dynamic molding of the vacuum field in a coupled-cavity system to achieve the ultrafast nonlocal modulation of spontaneous emission of quantum dots in photonic crystal cavities, on a timescale of ~200 ps, much faster than their natural radiative lifetimes. This opens the way to the ultrafast control of semiconductor-based cavity quantum electrodynamics systems for application in quantum interfaces and to a new class of ultrafast lasers based on nano-photonic cavities., Comment: 15 pages, 4 figures

Aims: The objective of this study was to determine the presence of infectious hepatitis A virus (HAV) in molluscs naturally contaminated with viral HAV-RNA. Methods and Results: One hundred and forty-two mollusc samples were analysed for the presence of viral HAV-RNA using RT-nested-PCR; positive samples were then analysed with an integrated method, cell-culture RT-PCR, to detect infectious virus. Viral HAV-RNA was detected in 34·5% of the samples while 12·7% of the total samples were positive for the presence of infectious virus. Conclusions: The results demonstrate the validity of the screening method (RT-nested-PCR) and the necessity of applying a method that is capable of detecting the presence of infectious HAV. Significance and Impact of the Study: The study demonstrates that in any case, to determine the safety for human consumption, the results of RT-nested-PCR must be confirmed with an integrated cell-culture PCR method.

We report direct evidence of enhanced spontaneous emission in a photonic crystal light-emitting diode (LED) at telecom wavelength (lambda similar to 1300 nm). This result is crucial to obtain an electrically driven single photon source with high extraction efficiency. This kind of devices can be used for different types of applications in emerging fields like quantum key distribution, quantum information technology as well as in fundamental studies on quantum electrodynamics. In this work we present a device which combines a photonic crystal nanocavity with InAs quantum dots (QDs) and an LED, leading to cavity-enhanced emission at telecom wavelengths under electrical injection. The fabrication process, based on e-beam lithography and additive and subtractive processes, is described in detail. A well-isolated emission peak at about 1300 nm from the PhC mode electrically pumped is obtained (Q similar to 4000), and the enhancement of the spontaneous emission rate (similar to 1.5 fold) is clearly evidenced by time-resolved electroluminescence measurements. (C) 2008 Elsevier B.V. All rights reserved.

Coupling the emitted light from single quantum dots into an optic fiber has been demonstrated as a. plug and play' single-photon Source. In this work, lifetime dynamics measurements were performed with two time-delayed femtosecond optical pulses at different wavelengths. When the energy of the Pumping light is less than the energy of the wetting layer (i.e. quasi-resonant excitation), the single-photon sources can be operated at a speed of 1 GHz. (C) 2008 Elsevier Ltd. All rights reserved.

We directly investigate, by means of near-field spectroscopy, the spatial distribution of the optical cavity modes of 2D photonic crystal microcavities. Numerical simulations confirm that the photoluminescence maps of quantum dots embedded in the photonic structure qualitatively match the spatial modulation of the electric field intensity. (C) 2007 Elsevier B.V. All rights reserved.

A method for the detection of HAV in shellfish, based on the use of guanidinium isothiocyanate-containing solution for RNA extraction and purification steps, followed by nested PCR, is hereby proposed. Tests were carried out on mollusc samples spiked with HAV strain FG. Results showed that in samples subjected only to one round of PCR it was possible to detect HAV at concentrations of 10 3 –10 4 TCID 50 /10 g of mollusc. The use of the nested PCR renders the system more sensitive and specific enabling the identification of HAV concentrations as low as 1 TCID 50 /10 g of mollusc. Furthermore thus method, in addition to allowing the avoidance of confirming tests, such as hybridization, proved to be inexpensive and simple to perform.

Combined lateral-vertical oxidation of AlGaAs is investigated as a means of tuning the resonant wavelength of a semiconductor microcavity after the epitaxial growth. It is shown that this technique can provide arrays with a wavelength spread equal to the cavity's free spectral range with a single postgrowth processing step. Design issues for multiple-wavelength vertical-cavity laser arrays using this postgrowth tuning technique are discussed, comparing the performance of devices with all-semiconductor and partially or totally oxidized Bragg mirrors. Experimental results are presented on arrays with a 48-nm lasing span around 970 nm, using partially and totally oxidized mirrors.

We analyze the scaling characteristics of the optical and current confinement for three different vertical-cavity surface-emitting laser (VCSEL) structures with tapered apertures. The improvements in scaling have allowed devices with apertures

Frequency conversion in nonlinear optical crystals is an effective means of generating coherent light at frequencies where lasers perform poorly or are unavailable. For efficient conversion, it is necessary to compensate for optical dispersion, which results in different phase velocities for light of different frequencies. In anisotropic birefringent crystals such as LiNbO3 or KH2PO4 ('KDP'), phase matching can be achieved between electromagnetic waves having different polarizations. But this is not possible for optically isotropic materials, and as a result, cubic materials such as GaAs (which otherwise have attractive nonlinear optical properties) were little exploited for frequency conversion applications. Quasi-phase-matching schemes, which have achieved considerable success in LiNbO3, provide a route to circumventing this problem, but the difficulty of producing the required pattern of nonlinear properties in isotropic materials, particularly semiconductors, has limited the practical utility of such approaches. Here we demonstrate a different route to phase matching-based on a concept proposed by Van der Ziel 22 yr ago (Appl. Phys. Lett., 1975) which exploits the artificial birefringence of multilayer composites of GaAs and oxidized AlAs. As GaAs is the material of choice for semiconductor lasers, such optical sources could be integrated in the core of frequency converters based on these composite structures. [on SciFinder (R)]

Densely integrated light sources are essential for centimeter scale data communication. In this paper we examine the factors and challenges influencing the efficiency of such devices. We then focus on studying the performance of reflector and out-coupling concepts using finite different time domain simulations. Keywords: integrated photonics, nanolasers, reflectors, waveguide-coupling.

The experimental demonstration of a superconducting photon-number-resolving detector, based on the series connection of N superconducting nanowires, is presented. An integrated resistor is connected in parallel to each section of the device that provides in this way a single voltage-readout, proportional to the number of photons detected in distinct nanowires. As a proof of principle a four element detector has been fabricated from an NbN film on a GaAs substrate and fully characterized. Clearly separated output levels corresponding to the detection of n = 1-4 photons are observed achieving a single-photon system quantum efficiency of 2.6% at ?=1.3 ?m. In order to demonstrate the potential scalability of the series-nanowire detector to a larger number of photons, we report our preliminary results in the characterization of detectors fabricated with 8 and 12 pixels. Clear evidence of n= 1-8 photon absorption in the 8-pixel detector has been achieved. © Published under licence by IOP Publishing Ltd.

We discuss relevant design considerations for the fabrication of electromechanically tunable photonic crystal cavities based on double semiconductor slabs. A simple optical and electromechanical model of the device based on coupled-mode theory and electrostatics is discussed and used jointly with 3-D finite-element calculations of optical cavity modes to extract the tuning-range dependence on geometrical parameters. A design rule, which avoids the sticking of membranes due to capillary forces and keeps a large tunability, is defined. The details of the fabrication process and a summary of the experimental results on GaAs and InGaAsP/InP material systems are given. We also address the problem of nonsymmetric devices, where the thicknesses of the membranes are not exactly the same, resulting in an imbalanced power emission of coupled modes.

We demonstrate a superconducting photon-number-resolving detector capable of resolving up to twelve photons at telecommunication wavelengths. It is based on a series array of twelve superconducting NbN nanowire elements, each connected in parallel with an integrated resistor. The photon-induced voltage signals from the twelve elements are summed up into a single readout pulse with a height proportional to the detected photon number. Thirteen distinct output levels corresponding to the detection of n=0-12 photons are observed experimentally. A detailed analysis of the excess noise shows the potential of scaling to an even larger dynamic range., 13 pages

We report a study of single quantum dots inside photonic crystal cavities with a low-temperature scanning near-field optical microscope. The spatial maps of single excitonic lines from the quantum dot show the clear signature of coupling to the cavity modes for small detunings. We also show that the near-field tip can be used to control the exciton-photon coupling at the nanoscale. A general framework for the interpretation of near-field maps of single emitters in cavities is proposed.

The generation, manipulation and detection of single photons enable quantum communication, simulation and potentially computing protocols. However scaling to several qubits requires the integration of these functionalities in a single chip. A promising approach to the integration of single-photon sources in a chip is the use of single quantum dots embedded in photonic crystal waveguides or cavities. To this aim, efficient coupling of the emission from single quantum dots in photonic crystal cavities to low-loss ridge-waveguide (RWG) circuits is needed. This is usually hampered by the large mode mismatch between the two systems. In this work the emission of a photonic crystal (PhC) cavity realized on a GaAs/AlGaAs membrane and pumped by quantum dots has been effectively coupled and transferred through a long RWG (~1mm). By continuous tapering in both horizontal and vertical direction, transmission values (fiber-in, fiber-out) around 0.16 and 0.08% for RWG and coupled PhC waveguide-RWG have been achieved, respectively. This corresponds to about 2.8% coupling efficiency between the center of the PhC waveguide and the single-mode output fiber, a value much higher than what is achieved by top collection. It further shows that around 70% of the light in the PhC waveguide is coupled to the RWG. The emission from quantum dots in the cavity has been clearly identified by exciting from the top and collecting the photoluminescence from the cleaved facet of the device 1mm away from the cavity which enables the efficient coupling of single photons to RWG and detector circuits.

We present our progress in the development of an integrated technology suitable for the photonic quantum information processing, showing the first autocorrelator based on two separated detectors integrated on top of the same ridge waveguide. An efficiency of ~1% at 1300 nm for both detectors and independent of the polarization of the incoming photons, is reported. This ultracompact device enables the on-chip measurement of the second-order correlation function g (2) (τ) . We will further discuss ongoing work on the integration of detectors with single-photon sources.

A plasmonic laser structure coupled to a dielectric waveguide is proposed and investigated by rigorous simulations. Modal characteristics, such as propagation loss and confinement factor were obtained for a wavelength of 1.55 µm. In addition, FDTD (Finite-Difference Time-Domain) simulations were used to calculate the reflectivity from the end facets of the laser structure and also to calculate the coupling between the laser and a dielectric waveguide. Simulations show that a threshold gain of 1796 cm-1 is required to compensate the total loss in a 200 nm wide and 50 µm long laser, which can be achievable at room temperature.

Photonic crystal (PhC) cavities made in broadband luminescent material offer attractive possibilities for flexible active devices. The luminescence enables the cavity to operate as an autonomous entity. New applications of this property are demonstrated for cavities made in the InGaAsP underetched semiconductor membrane with embedded InAs Quantum Dots that emit in the range of 1400-1600 nm. Planar photonic crystal membrane nanocavities were released from the parent chip by mechanical nanomanipulation. The released cavity particle could be bonded on an arbitrary surface, which was exploited to make a novel fiber-optic tip sensor with a PhC cavity attached to the tip. A single mode from a short cavity is shown to couple simultaneously to at least three cavity modes of a long cavity, as concluded from level anticrossing data when the small cavity was photothermally tuned. Reconfigurable and movable cavities were created by locally varying the infiltration status by liquid oil near a PhC waveguide or defect cavity. Liquid was displaced locally on a micron scale using capillary force effects or laser-induced evaporation and condensation phenomena.

We present the experimental demonstration of a superconducting photon number resolving detector. It is based on the series connection of N superconducting nanowires, each connected in parallel to an integrated resistor. The device provides a single voltage readout, proportional to the number of photons absorbed in distinct nanowires. Clearly separated output levels corresponding to the detection of n=1-4 photons are observed in a 4-element detector fabricated from an NbN film on GaAs substrate, with a single-photon system quantum efficiency of 2.6% at the wavelength of 1300nm. The series-nanowire structure is promising in view of its scalability to large photon numbers and high efficiencies., Comment: 12 pages, 6 figures

We introduce a device structure and a fabrication technique that allow the realization of efficient light-emitting diodes (LEDs) with dimensions of the active area in the 100 nm range. Using optical lithography, selective oxidation, and an active region consisting of InAs quantum dots (QDs), we fabricated LEDs with light–current–voltage characteristics which scale well with nominal device area down to 600 nm diam at room temperature. The scaling behavior provides evidence for strong carrier confinement in the QDs and shows the potential for the realization of high-efficiency single-photon LEDs operating at room temperature. ©2002 American Institute of Physics.

The implementation of single-photon detectors in waveguide photonic circuits will open the possibility of experiments in quantum regime that would otherwise be impossible to be implemented using bulk optics. Nanowire superconducting single-photon detectors (SSPDs) are good candidates for integration due to their relative ease of fabrication on top of GaAs heterostructures. In this paper we show the experimental demonstration of single-photon detectors, based on superconducting nanowires, fully integrated with GaAs/AlGaAs ridge waveguides. We will discuss all the major challenges surmounted and all the steps necessary to achieve these results.

Nanowire superconducting single photon detectors (SSPDs) are superior detectors of choice for many applications particularly in quantum information and communication technology. SSPD's excellent sensitivity and time resolution are brought about by the ultrafast transition of the very thin and narrow NbN nanowire meander from superconducting to normal state upon absorption of a single photon at near-infrared wavelengths [1]. However, low optical absorption in the ultrathin nanowire structures, puts a limit on the detection efficiency of these devices. A promising approach to improve the photon absorption in SSPDs is integrating them with advanced optical structures [2]. In this work, we report on the successful integration of SSPDs with optical cavity based on GaAs/AlAs distributed Bragg reflector (DBR) to enhance their detection efficiency.

We report on efficient nanowire NbN superconducting single photon detectors (SSPDs), integrated with an optical cavity based GaAs/AlAs distributed Bragg reflectors, showing a detection efficiency of 18.3% at 4.2K at 1.3 μm wavelength.

InAs quantum dots (QDs) have been grown by molecular-beam epitaxy on different InGaAs or GaAs surface layers to investigate the effect of the matrix on the structural and optical properties of the QDs. The density of QDs directly grown on GaAs is 1.1×1010 cm-2, and increases to 2.3×1010 cm-2 for dots grown on a 1 nm InGaAs layer. Single-mirror light-emitting-diode (SMLED) structures with InAs QDs capped by InGaAs and grown on GaAs and InGaAs layers were fabricated to compare the electroluminescence efficiency between the two structures. The maximum external quantum efficiency for QDs on a GaAs structure is 1.1% while that for QDs on InGaAs is 1.3%. The corresponding radiative efficiency could be deduced to be 17.5% for QDs on GaAs and 21.5% for QDs on InGaAs, respectively.

In this work we report on our recent studies on Silicon-Nitride PhC single-defect nanocavity membranes embedding colloidal nanocrystals. A novel structure consisting of a layer of nanocrystals sandwiched between two layers of Silicon-Nitride has been used. Photoluminescence measurements prove the efficient coupling among the nanoemitters and the optical modes localized in the Si"3N"4 photonic crystal nanocavities, showing enhancement of the spontaneous emission in resonant conditions. This technology enables the realization of NC-based ultra-small lasers and non-classical light sources operating at visible wavelengths on silicon substrates.