This PDF file contains the front matter associated with SPIE Proceedings Volume 7608, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

While the short term and mid-term archiving of digital data and information can be handled reasonably well with modern techniques, the long term aspects of the problem (several decades or even centuries) are much more difficult to manage. The heart of the problem is the longevity of storage media, which presently does not go beyond a few years, maybe one or two decades in the best cases. In this article, we review the various strategies for long term archiving, with two main categories: active and passive. We evaluate the various recording media in terms of their longevity. We then discuss the recordable optical digital disks (RODDs) and the state of the art in this domain; the present situation is that, with the techniques that are implemented commercially, good prospects for long term archiving are not available. Nevertheless, the conceptual simplicity of RODDs could be exploited to create new recordable digital media; the improvements that are needed seem to be reachable with reasonable development effort. Since RODDs are now in strong competition with other systems (hard disks or flash memory for instance) that constantly make enormous progress, there seems to be little hope to see RODDs win the race of capacity; nevertheless, longevity could provide them with a new market, since the need for long term archiving is so pressing everywhere in the world.

Modal optical linewidths of a passively mode-locked and optical injection locked quantum dot laser are studied. For the free-running case the modal linewidth is in the order of tens of MHz and demonstrates a parabolic dependence on the mode optical frequency. The slope of the parabola, as was predicted theoretically, is proportional to the radio-frequency (RF) linewidth, which provides a direct measurement of the timing jitter. With optical injection the slave laser optical spectrum becomes narrowed and tunable via the master wavelength. Frequency resolved Mach-Zehnder gating measurements performed to characterize slave laser pulses showed significantly improved pulse time-bandwidth product with optical injection. Measurements of the modal optical linewidths of the injected laser have shown phase locking of the slave laser modes to the master laser in the vicinity of the injection wavelength. However, far from this wavelength modal linewidth of the slave laser increases to greater than that of the free running case, leading to increase of the RF linewidth and timing jitter with single-tone injection.

Quantum light emitters have great application potential in quantum key distribution, precision metrology and quantum imaging. We present triggered electrically driven single photon sources based on semiconductor quantum dots in GaAs/AlAs micropillar cavities with on demand single photon rates of 35 MHz while a record outcoupling efficiency up to 34 % is obtained. Photon autocorrelation measurements reveal g⁽²⁾(0) down to 0.13. The high efficiency is achieved due to an optimized contact scheme which allows for the injection of electrical current into micropillar cavities which are characterized by low absorption losses and diameters down to 1 μm. By exploiting the established fabrication procedure, micropillar cavities exhibiting pronounced cavity quantum electrodynamics effects have been realized. Furthermore, by applying a reverse bias to the micropillar cavities, photocurrent measurements allow for wavelength selective sensing of light at powers down to 20 nW and further design changes promise photon detection sensitivities approaching the quantum limit.

The detection and quantification of trace gases is of great interest in a wide range of applications such as environmental monitoring, industrial process control and medical diagnostics. In combination with quantum cascade lasers, photoacoustic spectroscopy offers the advantage of high sensitivity (parts per billion detection limits), compact set-up, fast time-response and simple optical alignment. We will report here on the design and fabrication of optoacoustic sensors based on two different cell configurations to detect nitric oxide and formaldehyde.

Quantum cascade lasers possess very small linewidth enhancement factor, which makes them very prominent candidates for realization of high power, nearly diffraction limited and single mode photonic crystal distributed feedback broad area lasers in the mid-infrared frequencies. In this paper, we present room temperature operation of a two dimensional photonic crystal distributed feedback quantum cascade laser emitting at 4.5 μm. peak power up to ~0.9 W per facet is obtained from a 2 mm long laser with 100 μm cavity width at room temperature. The observed spectrum is single mode with a very narrow linewidth. Far-field profile has nearly diffraction limited single lobe with full width at half maximum of 3.5^o normal to the facet. The mode selection and power output relationships are experimentally established with respect to different cavity lengths for photonic crystal distributed feedback quantum cascade lasers.

Laser-spectroscopic applications in medicine increase in importance. We present two medical applications of laser-based analyses of trace gases. The analysis of exhaled breath concerns the determination of the D/H isotope ratio after intake of a small amount of heavy water. The D/H isotope ratio can be used to deduce the total body water weight and lays the foundation for many other laser-based clinical applications. An elevated D/H ratio could be monitored in breath samples up to 30 days after ingestion of only 5 ml of D₂O. A second example concerns the analysis of surgical smoke produced in minimally invasive laparoscopic surgery with electroknives. The quantitative determination of harmless and hazardous compounds down to the ppm level is demonstrated. A specific example is the presence of sevoflurane at concentrations of 80 to 300 ppm, an anesthetic, which to our knowledge is measured for the first time in an abdominal cavity.

Results on the detection of traces of trinitrotoluene (TNT) on different substrate-materials like Aluminum and standard car paint are presented. We investigated different samples with a movable imaging standoff detection system at angles of incidence far away from specular reflection. The samples were illuminated with a tunable mid-infrared external-cavity quantum cascade laser. For collection of the diffusely backscattered light a highperformance infrared imager was used. Trace concentrations of TNT corresponding to fingerprints on realworld- substrates were detected, while false alarms of cross-contaminations were successfully suppressed.

An amplifier design for broadband Mid-IR buried-hetero (BH) structure epitaxial laser is presented, and external cavity design based on this amplifier is described. Spectroscopy results characterizing such single frequency lasers are demonstrated with whispering gallery mode CaF₂ disc/ball, saturated absorption in hollow waveguide and direct chemical analysis in water.

Some of the recent advances in high power quantum cascade laser development will be reviewed in this paper. Research areas explored include short wavelength (λ<4 μm) lasers, high performance strain-balanced heterostructures, and high power long wavelength (7< λ< 16 μm) lasers. Near λ=4.5 μm, highlights include demonstration of 18% continuous wave wallplug efficiency at room temperature, 53% pulsed wallplug efficiency at 40 K, and 120 W of peak power output from a single device at room temperature. Near λ~10 μm, up to 0.6 W of continuous output power at room temperature has also been demonstrated, with pulsed efficiencies up to 9%.

With the anticipated retirement of Space Shuttles in the next few years, the re-supplying of short-lifetime sensors on the International Space Station (ISS) will be logistically more difficult. Carbon Monoxide (CO) is a well-known combustion product and its absence in a fire and post-fire environment is a reliable indicator for mission specialists that the air quality is at a safe to breathe level. We report on the development and performance of a prototype compact CO sensor, based on the PHOTONS platform [1], developed for the ISS based on tunable diode laser absorption spectroscopy (TDLAS). A CO absorption line at ~4285 cm^-1 is targeted using a distributed-feedback (DFB) laser diode operating at room temperature. A custom designed Herriott multipass cell 16cm long, with an effective path length of 3.7 m is employed. Mechanical, optical and electronics systems are integrated into a compact package of dimensions measuring 12.4"x 3.4"x 5". Power consumption is less than 1 W, enabling prolonged battery life. A detection limit of 3 ppm is achieved when performing 40 second long temperature scans. A recent initial test at NASA-JSC was successful. Future improvements include the reduction of the sampling volume, scan time and an improved CO minimum detection limit.

We describe the performance of a sensor system designed for simultaneous detection of multiple chemicals with both broad and narrow absorption features. The sensor system consists of a broadly tunable external cavity quantum cascade laser (ECQCL), multi-pass Herriott cell, and custom low-noise electronics. The ECQCL features a fast wavelength tuning rate of 2265 cm^-1/s (15660 nm/s) over the range of 1150-1270 cm^-1 (7.87-8.70 μm), which permits detection of molecules with broad absorption features and dynamic concentrations, while the 0.2 cm^-1 spectral resolution of the ECQCL system allows measurement of small molecules with atmospherically broadened absorption lines. High-speed amplitude modulation and low-noise electronics are used to improve the ECQCL performance for direct absorption measurements. We demonstrate simultaneous detection of Freon-134a (1,1,1,2-tetrafluoroethane), ammonia (NH₃), and nitrous oxide (N₂O) at low-ppb concentrations in field measurements of atmospheric chemical releases from a point source.

The ν₁+ν₃ combination band of uranium hexafluoride (UF₆) is targeted to perform analytical enrichment measurements using laser absorption spectroscopy. A high performance widely tunable EC-QCL sources emitting radiation at 7.74 μm (1291 cm^-1) is employed as an UF₆-LAS optical source to measure the unresolved rotational-vibrational spectral structure of several tens of wavenumbers (cm^-1). A preliminary spectroscopic measurement based on a direct laser absorption spectroscopy of methane (CH₄) as an appropriate UF₆ analyte simulant, was demonstrated.

We demonstrate very high wall plug efficiency (WPE) of mid-infrared quantum cascade lasers (QCLs) in low temperature pulsed mode operation (53%), room temperature pulsed mode operation (23%), and room temperature continuous wave operation (18%). All of these values are the highest to date for any QCLs. The optimization of WPE takes the route of understanding the limiting factors of each sub-efficiency, exploring new designs to overcome the limiting factor, and constantly improving the material quality.

Molecular Beam epitaxy (MBE) of cubic group III-nitrides is a direct way to eliminate polarization effects which inherently limit the performance of optoelectronic devices containing quantum well or quantum dot active regions. In this contribution the latest achievement in the MBE of phase-pure cubic GaN, InN, AlN and their alloys will be reviewed. A new RHEED control technique enables to carefully adjust stoichiometry and to severely reduce the surface roughness, which is important for any hetero-interface. The structural, optical and electrical properties of cubic nitrides and AlGaN/GaN will be presented. We show that no polarization field exists in cubic nitrides and demonstrate intersubband absorption at 1.55 μm in cubic AlN/GaN superlattices. Further the progress towards the fabrication of cubic GaN/AlGaN superlattices for terahertz applications will be discussed.

GaN/AlN multiple quantum wells (MQWs), designed for intersubband (ISB) absorption in the telecommunication range, are grown by molecular beam epitaxy. We demonstrate that the use of both AlN template and optimized growth temperature allows to reach ISB transition energy in the telecom range, i.e. above 0.8 eV (λ = 1.55 μm). Absorption spectra exhibit narrow linewidth (< 50 meV) with a relative energy broadening of 8%. An electro-optical modulator based on electron tunnelling in coupled QWs is then fabricated. A modulation bandwidth of 2 GHz at -3 dB cut off frequency is achieved for 15x15 μm² mesas. We show that the modulation rate is limited by the device geometry rather than by the material quality, which makes this technology a good candidate for THz regime.

We present a review of Resonant Tunneling Diode (RTD) OptoElectronic Integrated Circuits (OEICs). Resonant tunneling diodes (RTDs) can be relatively easily integrated on the same chip as optoelectronic components and in this paper we discuss the integration of RTDs with laser diodes, electroabsorption modulators and photodiodes. The RTD provides the OEIC with negative differential resistance over a wide bandwidth. RTDs are highly nonlinear devices and by applying nonlinear dynamics we have recently gained considerable insight into the operation of the RTD OEICS and that has allowed us to design, fabricate and characterize OEICs for wireless/photonic interfaces.

Silicon Photonics has the potential to revolutionise a whole raft of application areas. Currently, the main focus is on various forms of optical interconnects as this is a near term bottleneck for the computing industry, and hence a number of companies have also released products onto the market place. The adoption of silicon photonics for mass production will significantly benefit a range of other application areas. One of the key components that will enable silicon photonics to flourish in all of the potential application areas is a high performance optical modulator. An overview is given of the major Si photonics modulator research that has been pursued at the University of Surrey to date as well as a worldwide state of the art showing the trend and technology available. We will show the trend taken toward integration of optical and electronic components with the difficulties that are inherent in such a technology.

The discrete states resulting from three-dimensional confinement in semiconductor quantum dots retain much of the character of their bulk-band origins, for example their angular momentum and effective mass. In addition they have many features of discrete atomic-like single particle states. Strong optical field interactions and reasonable dephasing rates make this system attractive for basic quantum optics experiments, as well as applications in quantum information sciences. However, semiconductor quantum dots have large inhomogeneous state broadens due to variations in size and shape. In addition, epitaxial semiconductor quantum dots, one of the classes in common use, rarely have ideal symmetry. Here we show how an optical technique can be used to fine-tune the transition energies of semiconductor quantum dots states and if desired restore targeted symmetry elements. This approach can be applied to establish degeneracies in biexciton-exciton decays to form discrete entangled photon pairs or to establish indistinguishability between different quantum dots.

In this paper we introduce a coupled system of two quantum bits residing at the interface of a heterostructure device. The structure encompasses a reference quantum bit, a photonic/plasmonic crystal waveguide and an obedient quantum bit. Each quantum bit is an electronic device which is designed based on an anti-dot lattice of two-dimensional electron gas in heterostructures. By applying a potential gate in the aforementioned structure it is possible to control electronic tunneling rate and hence quantum bits' swapping frequency. Coupling through the plasmonic waveguide may be employed to entangle quantum bits. The waveguide has been designed by exploiting conducting islands of two-dimensional electron gas in a host of layered semiconductor heterostructure, behaving effectively as a patterned metallic thin film. The plasmonic characteristic is here modeled by Drude dispersion which obviates the required frequency dependency of our case. Employment of a plasmonic crystal waveguide benefited from plasmonic nature instead of regular dielectrics decreases the dimensions ten-fold, which helps the structure's size to come within the range of practical fabrication technologies. In order to estimate the evolution of the entangled state of the pair of quantum bits, it is necessary to estimate the coupling coefficient between electronic and optical subsystems. This parameter can be regarded as a design goal of matched electronic and optical structures, and has been discussed in detail for the optimization purposes. In the present work, both plasmonic and electronic properties are investigated. For simulating different sections, revised guided mode expansion (RGME) and finite difference time domain (FDTD) methods are employed.

Nitride semiconductor quantum structures feature some unique properties for intersubband device development, including a record large conduction-band offset that allows extending the operating wavelength to the near-infrared spectral region, and large optical phonon energies that are advantageous for the development of THz devices. In this paper we review our recent work aimed at the demonstration of novel intersubband device functionalities using these materials. In particular, we have developed ultrafast all-optical switching devices operating at fiber-optic communication wavelengths, based on intersubband cross-absorption saturation in GaN/AlN quantum-well waveguides. Strong self-phase modulation of ultrafast optical pulses has also been measured in these waveguides, revealing a large intersubband refractive-index nonlinearity which is also promising for all-optical switching applications. Furthermore, we have demonstrated optically pumped intersubband light emission from GaN/AlN quantum wells at the record short wavelength of about 2 μm. Finally, we have used a rigorous Monte Carlo model to show that GaN/AlGaN quantum wells are promising for the development of THz quantum cascade lasers capable in principle of operation without cryogenic cooling.

In light of the growing interest in spin-related phenomena and devices, there is now a renewed interest in the science and engineering of narrow gap semiconductors. They offer several scientifically unique electronic features such as a small effective mass, a large g-factor, a high intrinsic mobility, and large spin-orbit coupling effects. Our studies have been focused on probing and controlling the coherent and quantum states in InSb quantum wells and InMnAs ferromagnetic semiconductors. Our observations are providing new information regarding the optical control of carriers and spins in these material systems. We demonstrated the generation of spin polarized photo-current in an InSb QW where a non-equilibrium spin population has been achieved by using circularly polarized radiation. In addition, the differential transmission measurements in InSb QWs demonstrated that the initial distribution function strongly influences the carrier relaxation dynamics. We employed the polarization-resolved differential transmission as well as the MOKE measurements to provide information on the spin relaxation dynamics in MOVPE grown InMnAs. Our measured T₁ is comparable to the reported measurements in MBE grown InMnAs and several time resolved measurements on InAs.

Entanglement between quantum objects can be used to enhance the sensitivity of measurements. We demonstrate this effect by using entangled multi-photon states to go beyond the shot noise limit when observing polarization rotations.

As they are compatible with on-chip integration, photonic-crystal (PhC) devices operating with slow light represent a promising solution for time-domain processing of optical signals. However, the slow-light transport is strongly impacted by random fabrication fluctuations, such as variations in hole sizes, shapes or locations, and since disorder is regarded as critical in practice, there has been significant effort to determine the induced extrinsic losses. Our current understanding of how does light actually propagate in real photonic-crystal waveguides (PhCWs) relies on perturbation approaches. Although intuitively sound, the latter are only valid in the weak-scattering regime, where the structural imperfections hardly affect the light propagation. Here we introduce a new Bloch mode scattering formalism that overcomes the present limitations of perturbation approaches, since it takes into account the inevitable multiple-scattering that leads to Anderson's localization in such waveguides.

In high finesse semiconductor microcavities containing quantum wells, photons emitted by the quantum well excitons can oscillate long enough inside the cavity to be reabsorbed reemitted again and so forth. The system enters the so-called strong coupling regime, with the formation of entangled exciton-photon eigenstates, named cavity polaritons, which governs all the physics of the system. After an introduction to cavity polaritons, we will review in this paper some of their original physical properties and discuss their potential in terms of new photonic devices. In a first part, we will show how polaritons can massively occupy a single quantum state, thus acquiring spatial and temporal coherence reflected in the emitted light. Such polariton laser could provide a low threshold source of coherent light. Then the properties of polariton diodes will be addressed and in particular we will describe a new optical bistability based on the control of the light matter coupling via the intra cavity electric field.

In this paper we present our recent developments in control and manipulation of individual spins and photons in a single nanowire quantum dot. Specific examples include demonstration of optical excitation of single spin states, charge tunable quantum devices and single photon sources. We will also discuss our recent discovery of a new type of charge confinement - crystal phase quantum dots. They are formed from the same material with different crystal structure, and today can only be realized in nanowires.

Active plasmonic devices are much promising for optical devices and circuits at the nanoscale. We show that single nanoparticles coupled to metallic surfaces are good candidates for integrated components with nanometric dimensions. The localized plasmon of the nanoparticle launches propagating surface plasmons in the metallic thin film. Direct particle observation using leaky wave microscope geometry permits easy detection through the interference of the direct transmitted excitation light and the surface plasmon leaky mode. Investigations of the optical response of a nanoparticle deposited on metallic thin metal films reveals unexpectedly high transmission of light associated to contrast inversion in the images.

By Scanning Near-field Optical Microscopy (SNOM), we study the propagation of surface waves created by nanostructures on a thin gold film. The nanostructures are slits and ridges fabricated by electron or ion beam lithography techniques. We will first show that the light scattered by a slit made in a gold film illuminated in transmission is composed of two components: a diffracted field and a surface plasmon polariton that propagates on the gold surface over several tens of nanometers. When two slits are illuminated, the created waves encounter and form an interference pattern which involves both the surface plasmon polariton and the diffracted waves. The situation is more complicated when the nanostructures are illuminated in a reflection mode at oblique incidence. In that case, the created waves are superimposed to the incident and reflected fields. Despite a larger number of waves, the analysis of the interference pattern provides several informations on the nature of the scattered waves and their generation rate. In this article, we provide a qualitative analysis of the waves created by slits, and by linear and curved ridges located on a gold surface.

Bloch Surface Waves (BSWs) are propagation modes that exist at the interface between a homogeneous medium and a photonic crystal (PhC). The confinement at the interface of the media relies on total internal reflection in the homogeneous medium and on the photonic band gap in the PhC. The dispersion relation of BSWs can be easily tailored through the design of the PhC. This makes BSWs extremely flexible and suitable for applications in the field of optical sensors, light emitters, and photovoltaic devices, where the capability to confine and amplify the electromagnetic field in micro- and nano-structures allows for the enhancement of the light-matter interaction. In particular, we present two different configurations for the detection of Bloch surface waves in silicon nitride multilayers: attenuated total reflectance and photoluminescence measurements. In the first, we measured a 50-fold enhancement of the diffraction signal by a protein grating printed on the multilayer when the incident light beam is coupled to the surface waves. In the second, we observe a significant modification of the spontaneous emission by a monolayer of rhodamine molecules bonded to the photonic crystal surface. These results may found application in the field of optical sensors, particularly for biosensing.

At Terahertz (THz) frequencies metals are still excellent materials to guide and confine electromagnetic radiation with relatively low losses. Therefore the concepts developed in the microwave range to design efficient waveguides and resonators can be successfully transferred up to this frequency region. A successful example of such "technology transfer" is the so-called metal-metal resonator, effectively used as a waveguide for THz Quantum Cascade Lasers (QCLs). This type of resonator is essentially a downscaled version of a microstrip waveguide, widely used at microwave frequencies. In this work we report on microwave impedance measurements of metal-metal ridge-waveguide THz QCLs. Experimental data, recorded at 4K in the 100MHz-55GHz range, are well reproduced by distributed-parameter transmission-line simulations, showing that the modulation cutoff is limited by the propagation losses that increase for higher microwave frequencies, yielding a 3dB modulation bandwidth of ~70GHz for a 1mm-long ridge. By using a shunt-stub matching we demonstrate amplitude modulation of a 2.3THz QCL up to 24GHz. In the last part of this work we discuss the experimental evidence of a feedback-coupling between the intracavity THz field and the microwave field generated by the beating of the Fabry-Perot longitudinal modes above the lasing threshold.

Recently we proposed a new approach which potentially has single spin sensitivity, sub-nanometer spatial resolution, and ability to operate at room temperature (J. Appl. Phys. 97, 014903 (2005); U.S. Patent No. 7,305,869, 2007). In our approach a nanoscale photoluminescent center exhibits optically detected magnetic resonance (ODMR) in the vicinity of magnetic moment in the sample related with unpaired individual electron or nuclear spins, or ensemble of spins. We consider as a sensor material that exhibit ODMR properties nitrogen-vacancy (N-V) centers in diamond. N-V centers in diamond has serious advantage having extraordinary chemical and photostability, very long spin lifetimes, and ability single-spin detection at room temperature. The variety of possible scanning schemes has been considered. The potential application to 3D imaging of biological structure has been analyzed.

In this invited paper, we first discuss different submicron- and nanoscale structures that have been introduced over the past few years to enhance the Raman scattering efficiency in two important materials, namely silicon and hydrogen gas. Next, we explain how the heat dissipation in silicon- and hydrogen-based Raman lasers and amplifiers could be intrinsically reduced by the use of coherent anti-Stokes Raman scattering (CARS). We conclude by numerically demonstrating that with this CARS-based heat mitigation technique the heat generation in these Raman devices could be suppressed with at least 30%.

We demonstrate the rolling process of strained III-V compound semiconductor films upon epitaxial liftoff from the substrate. The formed tubular structures with diameters in the micron range, embedded with quantum confined GaAs light emitters in the ultra-thin tube walls (< 100 nm) show dramatic enhancement in intensity and reduction of bandgap as a function of tube curvature. Emission characteristics and implications are analyzed.

Thermal-induced index variations are experimentally observed with Schottky diodes; they are opposite to the carrier induced ones, with an increase of optical index as high as 0.1, and a 1μs response time. It turns out that the thermal effect can be an important limiting factor to the optical index change. In this paper we evaluate each phenomenon separately (lifetime and thermal effects) and the influence of the thermal effects on the carrier induced index variations.

We report the subwavelength antireflection structures in various semiconductor materials such as Si, ZnO, and GaP/light emitting diode (LED) structure for LED and solar cell applications in the visible and near-infrared wavelength region, together with the rigorous coupled wave analysis simulation. Subwavelength structures are fabricated by holographic lithography and dry etching, effectively suppressing the surface reflection. To enhance the absorption efficiency over a wide-angle broadband range of incident light, the thin-film crystalline Si solar cells with subwavelength structure, which reduce the surface reflection, are studied. The improvement of light intensity is achieved for the fabricated LEDs with a subwavelength structure compared to the conventional LEDs due to a strongly reduced internal reflection at the semiconductor/air interface.

The fundamentals of the near-field interaction between a subwavelength tip and a photonic-crystal nanocavity are investigated experimentally and theoretically. It is shown experimentally that the cavity resonance is tuned without any degradation by the presence of the tip and that the reported near-field interaction is strongly related to the field distribution within the nanostructure. From the interaction between the probe and the cavity, we will show a new kind of microscopy.

The near-field distribution of plasmonic coupling effect in gold nanoparticle pairs was directly investigated by a nearfield scanning optical microscope (NSOM) in the fiber-collection mode. NOSM images show that the localized plasmonic coupling and the electromagnetic field distribution of nanoparticle pairs are systematically influenced by the interparticle space and axial direction of incident polarization. This observation can facilitate the understanding of localized hot spots in surface-enhanced Raman spectroscopy in the near field and can be used as a guideline for fabricating specific nanostructures in controlling the spatial distribution of surface plasmon (SP) modes for ultrasensitive sensors or photonic devices.

Compactness, massive integration of multiple functions on a single chip and power consumption are crucial for transmission of large aggregated bit rates at short distance. Efficient implementation of data processing at the optical level are very attractive. Here we present a technology for implementing ultra-fast switching with recordlow energy·recovery time product. We developed high-quality photonic crystal micro-resonators based on III-V semiconductors. The very short carrier lifetime of nano-pattened Gallium Arsenide enabled us to achieve 6 ps recovery time, thus enabling operations beyond the 100Gb/s rate. For broadband operation, highly nonlinear waveguides with low insertion loss have been demonstrated.

Two-dimensional (2D) plasma waves in field effect transistors are well known since the pioneer work of Dyakonov and Shur. The application to terahertz (THz) detection was proven recently both at cryogenic and room temperatures. Aside from these experiments, we used the interband photoexcitation brought by the difference-frequency component of a photomixed laser beam to excite very efficiently plasma waves in HEMT channel at room temperature. Owing to a specific experimental setup avoiding unwanted high-frequency electrical oscillations of the HEMTs, we obtained the spectral profiles of THz 2D plasma waves resonances of InGaAs HEMTs for many experimental conditions. The effect of geometrical HEMTs parameters (lengths of the gate and surrounding regions) as well as biasing conditions (drain and gate voltages) was evaluated on both plasma oscillations frequencies and amplitudes. Simultaneously, a numerical approach, based on hydrodynamic equations coupled to a pseudo-2D Poisson solver, was developed that compares well with experiments. Using this unique combination of experiments and numerical simulations, a comprehensive spectroscopy of plasma waves in HEMTs is thus obtained. It provides a deeper insight into the physical processes involved in plasma wave excitation and allows predicting for mixer operation at THz frequency only using the plasma wave nonlinearity. Mixing experiments are under progress.

We investigate quantum interference and classical interference effects when a three-level system interacts with both a cavity field mode and an external driving field mode, within the confines of a photonic crystal material. In freespace, we found that under certain circumstances the cavity field evolves to be equal in magnitude to, but 180° out-of- phase with the external pump field when the pump field frequency equals the cavity frequency. The better the cavity, the quicker this build-up occurs. When the cavity field reaches this out-of-phase condition, the resonance fluorescence from the atom in the cavity goes to zero. This is a purely classical interference effect between the two out-of-phase fields, with the resonance fluorescence going to zero at the same time as the two excited state populations go to zero. This is quite different from the quantum interference that occurs under the right circumstances, when the state populations are coherently driven into a linear combination that is decoupled from any applied field - and population is trapped in the excited states, thus allowing for a population inversion and an amplification of incoming optical signals. In this paper, we investigate the additional effects due to the presence of the altered photon density of states in a photonic crystal.

FDTD simulations are performed on two-dimensional clusters of plasmonic metal nanoparticles in response to incident planewave irradiation. Using an iterative optimization algorithm, we determine the spatial configuration of the nanoparticles that gives the maximum electric field intensity at the center of the cluster. The optimum configurations of these clusters have mirror symmetry about the axis of planewave propagation, but are otherwise non-symmetric and non-intuitive. The optimized electric field intensity increases monotonically with the number of nanoparticles in the cluster, producing surface enhanced Raman spectroscopy (SERS) enhancements that are 25 times larger than linear chains of nanoparticles and 6 million times larger than the incident electromagnetic field.

We discuss recent advances in light-matter coupling in quantum dots with a point-defect nanocavity in a woodpile three-dimensional (3D) photonic crystal with the highest quality (Q) factor among those for 3D photonic crystal cavities. The Q factor over 10,000 was so far achieved by optimizing the size of the defect cavity, in which the defect was not so large that power loss into the in-plane direction limited the Q factor.

InAs nanostructures formed on InP substrates allow the realization of devices working in telecommunication wavelength range between 1.4 and 1.65 μm. However due to the low lattice mismatch existing between InAs and InP, the self assembling process in InP is more complex than on GaAs substrates. First high density quantum wires obtained on InP(001) have been integrated in laser. Lasers emitting at room temperature have been achieved. For an infinite length cavity, a threshold current density per QD plane as low as 45 A/cm² is deduced. This result compares favourably with those obtained on quantum wells lasers. However, the stability of the threshold current with temperature, predicted for quantum dots laser is not observed. Thus, growth on non standard substrates such as miscut substrates or high index substrates have been investigated in order to achieve QDs on InP. On (113) B substrates, quantum dots in high density and with size comparable with those achieved on GaAs(001) have been obtained. Lasers with record threshold current have been obtained. However the modulation properties of the laser are not as good as predicted for ideal quantum dots lasers. Finally we present the attempts to extend the QD emission wavelength in the 2-3 μm region.

We report the results on the growth, structural and optical characterization of single wurtzite (WZ) GaAs nanowires as well as WZ GaAs/AlGaAs core-shell nanowires with ZB GaAsSb inserts. For the GaAs/GaAsSb heterojunction both the crystal material and crystal phase change plays a critical role in the exact band alignment. We show that ZB GaAsSb inserts with both WZ and ZB GaAs barriers can be grown and hence both type I and type II band alignment can be achieved which has large effects on the optical properties of the nanowires. We thus demonstrate that it is possible to engineer the band-structure at a semiconductor heterojunction by modulating the crystal material as well as the crystal phase.

Nanowire photodetectors of a variety of materials have been attracting increased attention due to their potential for very high sensitivity detection. Silicon photodetectors are of particular interest for detection in the visible spectrum, having many benefits including cost of substrate, ease of processing, and ability for integration with conventional fabrication techniques. Using top-down fabrication techniques results in additional benefits of precise control of number, geometry, and placement of these wires. To demonstrate the potential of these devices, top-down, vertical silicon nanowire phototransistor arrays have been fabricated using ebeam lithography and deep reactive ion and inductively coupled plasma etching. These devices show a much higher phototransistive gain over nanowire photodiodes with similar geometry under illumination from a 635nm laser. Low temperature measurements also show the dependence of dark current and sensitivity on temperature. The mechanism responsible for this gain is shown to be dominated by the large surface-to-volume ratio of nanowires where charge capture and recombination at the surface creates a radial gate bias which is modulated with light intensity. 3D numerical simulations validate this mechanism and further show the dependence of device behavior on nanowire doping, geometry, and surface state density. This will allow for the precise engineering of these devices to achieve the maximum sensitivity obtainable as we strive for the ultimate goal of single photon resolution.

Dipole and quadrupole surface plasmon polariton (LSPP) resonances of gold nanoparticle array were directly investigated by a near-field scanning optical microscope (NSOM) in the fiber-collection mode. Separated gold nanoparticles on the quartz substrate were fabricated by nanosphere lithography. Results demonstrate that controlling the incident polarization and angle of oblique incidence enables to excite dipolar and quadrupolar LSPP at 633- and 488-nm excitations. This observation facilitates the understanding of LSPP and interactions with nanostructures in the near field that can be used as a guideline for fabricating nanostructures in controlling spatial distributions of LSPP for ultra sensitive bio-/chemo-detectors or plasmonic metamaterials.

Here is presented a review of radiation damage studies of detectors used primarily in astronomy focused space missions. Covered are effects on devices used for the wavelengths from the IR all the way through to X rays.

Extending the intersubband transitions in III-nitride nanostructures from near-infrared to longer wavelengths might have significant consequences for critical applications like imaging, remote sensing and mine detection. In this work, we analyze the potential of polar and semipolar AlGaN/GaN technologies for this relevant spectral range.

We proposed the grating coupled surface plasmon resonance (GC-SPR) sensors using ZnO and metallic nanograting structures to enhance the sensitivity of an SPR sensor. The GC-SPR sensors were analyzed using the finitedifference time-domain method. The optimum resonance angles of 49 and 55.5 degrees are obtained in the 150 nm wide grating structure with a period of 300 nm for the ZnO thickness of 30 and 50 nm, respectively. Here, an enhanced evanescent field is obtained due to the surface plasmon on the edge of the bandgap when the ZnO and metallic grating structures are used to excite the surface plasmon.

Recent developments of III-nitride materials and devices for energy applications such as photovoltaic, thermoelectric, and hydrogen generation are discussed. Although there are only few reports on InGaN based solar cells, some superior properties of this material including radiation tolerance and tunable band gap overlapping with solar spectrum considered it as a suitable candidate for space based and multijuction solar cell. Design and characterization, of InGaN based efficient p-MQW-n solar cells are presented. For the thermopower generation, we discuss the potential of InGaN alloys as thermoelectric material. Good thermoelectric materials possess low thermal conductivity and high Seebeck coefficient with high electrical conductivity. The thermal conductivity about two orders less than that of GaN and thermoelectric figure of merit as good as that of SiGe alloys are measured in In_0.36Ga_0.64N alloy. Our results indicate that InGaN alloys can be used to convert heat energy directly into electrical energy. Generation of hydrogen by splitting of water using InGaN alloy electrodes and solar energy via photoeletrochemical effect is also discussed.

Recent theoretical studies on exciton absorption in carbon nanotubes in an effective-mass approximation are reviewed. It is clarified that one-dimensional character plays important roles in optical properties of carbon nanotubes. For semiconducting tubes, exciton effects for polarization perpendicular to the tube axis cause prominent peaks in optical absorption spectra in spite of the depolarization effect. Calculated excited exciton energies for parallel polarization well reproduce measured energies for one- and two-photon absorption. Excitons can also exist in metallic carbon nanotubes.

Inducing a large electric field enhancement is very important to have good signals in surface-enhanced Raman scattering (SERS) experiments. In this study, the nano-scale sliver annular structures have been introduced to design the substrate for SERS experiment because of its localized surface plasmon (LSP) resonances phenomena. The excited electric field has been simulated by FDTD (finite-difference time-domain) and the design parameters, such as the thickness of the metallic film, the inner diameter, and the outer diameter, were changed. The largest electric field happens when the metallic film thickness is 5 nm and the inner and outer diameters are 0.1 μm and 0.4 μm, respectively. The results are in good agreement with the theoretical predictions. In addition, the dimer geometry of the annular structures has also been examined by FDTD to observe the field enhancement. The coupled plasmons effects appear obviously when two annular structures are very close. It indeed makes the excited electric field in the dimer structure larger than in the single one for 40 times. In conclusion, a design of dimer constituted with two annular structures which have 0.1 μm and 0.4 μm inner and outer diameters with 0 nm overlap owns the best electric field enhancement property and has great potential for SERS applications.

InAS/GaSb-based Type-II Strained-Layer Superlattice detectors (T2SLS) attract increasing interest for the development of high sensitivity large format mid- and long-wavelength infrared focal plane arrays. This paper will discuss the T2SLS detector performance requirements and readout integrated circuit (ROIC) noise levels for several staring array long-wavelength infrared (LWIR) imaging applications at various background levels. It will show a calculation of the dark current originated by various mechanisms and dependence on the minority carrier lifetime. Advanced heterojunction-based designs in T2SLS detector material have already demonstrated LWIR detectors with sufficient performance for tactical applications and potential for strategic applications. However, significant research is needed to suppress surface leakage current in order to reproduce performances at pixel levels of T2SLS focal plane arrays.

An overview of quantum cascade detector technology for the near- and mid-infrared wavelength range will be given. Thanks to photovoltaic instead of photoconductive operation, quantum cascade detectors offer great opportunities in terms of detection speed, room temperature operation, and detectivity. Besides some crucial issues dealing with fabrication and general characteristics, some possibilities for performance improvement will also be briefly presented. In a theory section, some basic considerations adopted from photoconductive detectors confirm the necessity of various trade-offs for the optimization of such devices. Nevertheless, we will show several possible measures to push the key performance figures of these detectors closer to their physical and technological limits.

The High Operating Temperature Auger suppressed infrared detector concept is being pursued using the high density vertically integrated photodiode (HDVIP®) architecture and an n⁺-p device structure. Dark current densities as low as 2.5 mA/cm² normalized to a 5 μm cutoff at 250K have been demonstrated on these diodes. These dark currents imply minority carrier lifetimes in excess of 300μsec. 1/f noise in these devices arises from the tunneling of charge into the passivation interface, giving rise to a modulation in the surface positive charge and hence to the width of the depletion region in the p-side of the device and a modulation in the total dark current. The measured 1/f noise is in agreement with the predictions of this model, with very low noise being observed when the lifetimes are high.

We have fabricated mid-wave infrared photodetectors containing InAsSb absorber regions and AlAsSb barriers in n-barrier-n (nBn) and n-barrier-p (nBp) configurations, and characterized them by current-voltage, photocurrent, and capacitance-voltage measurements in the 100-200 K temperature range. Efficient collection of photocurrent in the nBn structure requires application of a small reverse bias resulting in a minimum dark current, while the nBp devices have high responsivity at zero bias. When biasing both types of devices for equal dark currents, the nBn structure exhibits a differential resistance significantly higher than the nBp, although the nBp device may be biased for arbitrarily low dark current at the expense of much lower dynamic resistance. Capacitance-voltage measurements allow determination of the electron concentration in the unintentionally-doped absorber material, and demonstrate the existence of an electron accumulation layer at the absorber/barrier interface in the nBn device. Numerical simulations of idealized nBn devices demonstrate that photocurrent collection is possible under conditions of minimal absorber region depletion, thereby strongly suppressing depletion region Shockley-Read-Hall generation.

Recent efforts have been paid to elevate the operating temperature of Type II InAs/GaSb superlattice Mid Infrared photon detectors. Optimized growth parameters and interface engineering technique enable high quality material with a quantum efficiency above 50%. Intensive study on device architecture and doping profile has resulted in almost one order of magnitude of improvement to the electrical performance and lifted up the 300K-background BLIP operation temperature to 166K. At 77K, the ~4.2 μm cut-off devices exhibit a differential resistance area product in excess of the measurement system limit (10⁶ Ohm.cm²) and a detectivity of 3x10¹³cm.Hz^1/2/W. High quality focal plane arrays were demonstrated with a noise equivalent temperature of 10mK at 77K. Uncooled camera is capable to capture hot objects such as soldering iron.

We report on study of electrical and optical properties of type II heterostructures with InSb quantum dots (QDs) inserter into the InAs-based p-n junction made by LPE-MOVPE combine method. InSb QDs were grown on an InAs(100) substrate by LPE. Overgrowth on the surface with the self-assembled InSb QD arrays was performed by MOVPE using capping layers based on binary InAs and quaternary InAsSb solid solutions. High-resolution cross-sectional image of the InSb QDs buried into the InAs(Sb,P) matrix was obtained for the first time by transmission electron microscopy. Structural parameters of the InSb QDs such as size, shape and internal strain were demonstrated and discussed. The uniform small QDs with high density (>10¹⁰ cm^-2) with dimensions of 3 nm in height and 14 nm in diameter were found to be self-assembled and dislocation-free without any extended defects, whereas the low-density large QDs (10⁸ cm^-2) with dimensions of 10 nm in height and 50 nm in diameter were relaxed and demonstrated interface strain with the InAs substrate. I-V characteristics of the mesa-diode heterostructures with the InSb QDs inserted into InAs p-n junction were studied at the wide temperature range T=77-300 K. Intense positive and negative electroluminescence for both n-InAs/p- InAs and n-InAs/InSb-QDs/p-InAs heterostructures was found in the spectral range 3-4 μm. Evolution of the spectra in dependence on applied external bias (forward and reverse) were observed at 77 K and 300 K.

The past decade has witnessed rapid progress in the development of techniques for correcting lens aberrations in high-resolution transmission electron microscopy (HRTEM), resulting in significant enhancement in the directly interpretable spatial resolution in HRTEM images. Furthermore, in combination with advanced image processing and analysis, it is now possible to employ HRTEM as a quantitative technique for structural and chemical analysis at the atomic scale. In this paper we have applied these developments to investigate interfaces in InAs/GaSb superlattices, the main objectives being the mapping of changes in chemical composition and strain at each interface. For examining changes in composition we use the focal series reconstruction technique, which retrieves the quantum-mechanical electron wave function at the exit surface of the sample. The phase images of the electron wave function are then analyzed by linear multivariate statistical analysis to independently quantify change in the In/Ga and As/Sb contents across each interface. The strain profiles across interfaces are determined from HRTEM images, obtained from a TEM equipped with a spherical aberration corrector, employing the "peak-pair analysis" (PPA) algorithm. Finally, the high-angle annular dark-field imaging technique (HAADF), using a monochromated and probe corrected TEM, is also employed to examine interfaces.

Infrared detectors based on InAs/GaSb superlattices (SL) have recently emerged as a promising technology for high performance infrared (IR) imaging systems. In this paper, we present the results of dark current and noise measurements realized on MWIR superlattice single detectors. The SL structure was made of 8 InAs monolayers (MLs) and 8 GaSb MLs, for a total thickness of 2μm. This structure exhibits a cut-off wavelength of 4.8μm at 77K. An original chemical etching solution was designed to obtain smooth mesa sidewalls, followed by a simple passivation technique. Dark current measurements were carried out to prove the good quality of both the etching and the passivation steps. The measured R0A product reaches the state-of-the-art values at 80K. Noise measurements were also performed under dark conditions. The detectors under test proved to be Schottky-limited on a range of bias voltage of 200mV typically, which confirms the very good quality of the technological process.

Electrical properties of non-intentionally doped (nid) InAs/GaSb Superlattice (SL) structures and p-nid-n detectors grown by Molecular Beam Epitaxy on GaSb substrate are reported. The SL structures were made of 600 periods of 8 InAs monolayers (MLs) and 8 GaSb MLs, for a total thickness of 3ìm. This structure exhibited a cutoff wavelength in the midwave infrared (MWIR) domain, near 4.7μm at 80K. Electrical transport measurements, based on resistivity and Hall Effect measurements, were performed on SL structure after removing the conducting GaSb substrate with an appropriate technological process. Carrier concentrations and mobilities carried out as a function of temperature (77- 300K) for magnetic fields in the 0-1 Tesla range are analyzed. A change in type of conductivity is observed. The nid SL layers is p-type at liquid Nitrogen temperature while is n-type at room temperature. These results are completed with diode characterizations based on current-voltage (I-V) and capacitance-voltage (C-V) measurements performed on p-nidn devices with identical InAs/GaSb SL active zone.

Recently, a new "XBn" device architecture, based on heterostructures, has been proposed as an alternative to a homojunction photodiode. The main difference is that no depletion layer exists in any narrow bandgap region of the device. Instead, the depletion layer is confined to a wide bandgap barrier material. The Generation-Recombination (G-R) contribution to the dark current is then almost totally suppressed and the dark current becomes diffusion limited. This lowering of the dark current allows the device operating temperature to be raised relative to that of a standard photodiode made from the same photon absorbing material, with essentially no loss of performance. At SCD we have been developing XBn devices grown on GaSb substrates with an InAsSb photon absorbing layer and an AlSbAs barrier layer. The results of optical and electrical measurements are presented on devices with a bandgap wavelength of about 4.1μm. Strong suppression of the G-R current is demonstrated over a range of almost two orders of magnitude in the doping of the photon absorbing active layer (AL), while at the same time very high internal quantum efficiencies are achieved. A model of the spectral response is developed which can reproduce the observed behaviour very well at 88K and 150K over the whole AL doping range. In properly optimized devices, the BLIP temperature is shown to be in the region of 160K at f/3.

Interband cascade (IC) infrared (IR) photodetectors (ICIPs) are a new type of detector that combines features of conventional interband photodiodes with the discrete nature of quantum-well IR photodetectors (QWIPs) and IC lasers. The operation of ICIPs takes advantage of fast intersubband relaxation and interband tunneling for carrier transport, and relatively slow interband transitions (long lifetime) for photon generation. As such, ICIPs can be tailored to optimize device performance for specific application requirements. We report our initial efforts in the development of ICIPs. We have observed the photocurrent from an InAs-based IC laser with a cutoff wavelength near 8 μm at 80 K, and significant photocurrent from GaSb-based ICIPs with cutoff wavelengths near 5 μm at 80 K and 7 μm at above room temperature.

In this paper, we report some of our recent results on improving the operating temperature of dots-in-a-well (DWELL) infrared photodetectors. This was achieved by engineering the dot geometry and the interrelated quantum confinement by varying the growth conditions and composition of the subsequent capping of the quantum dots (QDs). The influence of these conditions was determined by examining the optical properties of the QDs directly and indirectly with their function in a DWELL IR photodetector. Spectral response was observed until 250K with spectral response peak at 3.2μm, and the peak detectivity is 1×10⁹ cmHz^1/2/W at 77K and ~ 1e8 cmHz^1/2/W at 250K. By varying the external bias, the DWELL heterostructure allows for the manipulation of the operating wavelength. This tunability is a critical stepping stone towards creating multicolor imaging systems that can be used to take images at multiple wavelengths from each pixel in a focal plane array.

InAs/GaSb short-period superlattices (SL) based on GaSb, InAs and AlSb have proven their great potential for high performance infrared detectors. Lots of interest is currently focused on the development of short-period InAs/GaSb SLs for advanced 2nd and 3rd generation infrared detectors between 3 - 30 μm. For the fabrication of mono- and bispectral thermal imaging systems in the mid-wavelength infrared region (MWIR) a manufacturable technology for high responsivity thermal imaging systems has been developed. InAs/GaSb short-period superlattices can be fabricated with up to 1000 periods in the intrinsic region without revealing diffusion limited behavior. This enables the fabrication of InAs/GaSb SL camera systems with high responsivity comparable to state of the art CdHgTe and InSb detectors. The material system is also ideally suited for the fabrication of dual-color MWIR/MWIR InAs/GaSb SL camera systems with high quantum efficiency for missile approach warning systems with simultaneous and spatially coincident detection in both spectral channels.

High sensitivity HgCdTe infrared detector arrays operating at 77 K can be tailored for response across the infrared spectrum (1 to 14 μm and beyond), and are commonly utilized for high performance infrared imaging applications. However, the cooling system required to achieve the desired sensitivity makes them costly, heavy and limits their applicability. Reducing cooling requirements and eventually operating at temperatures that could be reached with thermoelectric coolers can lead to lighter and more compact systems. However, at these elevated temperatures, the absorber layer becomes intrinsic, carrier concentrations are high and Auger processes typically dominate the dark current and noise characteristics. Auger processes can be suppressed by placing the absorber layer between an exclusion junction and an extraction junction at reverse bias. This reduces the minority carrier concentration in the absorber by several orders of magnitude below thermal equilibrium. The majority carrier concentration also drops significantly below thermal equilibrium to maintain charge neutrality, eventually reaching the extrinsic doping level. This device architecture produces a lower dark current density and lower noise at non-cryogenic temperatures than standard p-n junction photodiodes. Due to the precise control of the layer's thicknesses and compositions that could be achieved with molecular beam epitaxy (MBE), this technique is the method of choice for implementing these novel non-equilibrium devices. In this work, we analyze Auger suppression in HgCdTe alloy-based device structures and determine the operation temperature improvements expected when Auger suppression occurs. We identified critical material (absorber dopant concentration and minority carrier lifetime) requirements that must be satisfied for optimal performance characteristics. Experimental dark current-voltage characteristics between 120 and 300 K are fitted using numerical simulations. Based on this, the negative differential resistance (NDR) observed in experimental data is attributed to the full suppression of Auger-1 processes and the partial suppression of Auger-7 processes. We will also present an analysis and comparison of our theoretical and experimental device results in structures where Auger suppression was realized.

We report a longwave infrared quantum dot infrared photodetector working at room temperature (RT) (298K). A high photoresponsivity and photodetectivity of 0.02A/W and 9.0x10⁶ cmHz^1/2/W were achieved at 298K with a low bias voltage of -0.1V. The RT QDIP avoids bulk and heavy cryogenic cooling systems and thus enables the development of ultra-compact IR sensing and imaging systems.

Excessive surface leakage currents, and their associated noise, deteriorate the performance of infrared photodetectors. The conventional approach to suppress surface leakage is post-epitaxy deposition of polycrystalline or amorphous passivation layers. Disadvantages of such passivation layers are the cost and complexity of the required additional processing steps, and the fact that they do not always work well. An alternative approach, presented here, is to design the photodetectors' epitaxial structures so that surface leakage currents are suppressed without the need for ex-situ deposition of passivation layers. Two examples of such epitaxial designs are the nBn detector and the unipolar barrier photodiode.

Recently developed high operating temperature (up to 330 K) GaAs/AlGaAs detectors responding in the 3-5 μm wavelength range and based on split-off (SO) transitions followed by escape by scattering to the light/heavy hole(LH/HH) band or by direct quantum mixing of the states offer a viable alternative to present day detectors operating at cryogenic temperatures. This paper presents a theoretical model to predict the response of SO detectors. The model calculates the dark current and illuminated currents from the photoabsorption, carrier escape, and transport, explaining the experimental response. Using this model, different strategies to improve the performance of the GaAs based SO detectors are presented. A graded barrier improves the performance by reducing the space charge build up, and the double barrier resonant structure by enhanced escape of holes from the SO to the light/heavy hole bands by bringing the two bands into resonance. A detailed analysis of the effect of detector parameters on responsivity and D* is made. The change of material system to GaN/AlGaN should extend the response to longer wavelengths (THz) as its zinc blende and wurtzite crystal structures have SO transition energies of 20meV and 8meV respectively. Experimental measurement of SO absorption in GaN and potential THz detector designs are discussed.

The electronic structure of isoelectronic defects, donors and acceptors is calculated within a full superlattice picture for InAs/GaSb and InAs/GaInSb superlattices. The wavefunctions associated with these states extend beyond a typical layer width for the superlattices. Thus band alignments between the layers as well as interface properties are predicted to dramatically change these defects' binding energy as well as their influence on superlattice electronic, optical and transport properties. Defect properties are also substantially modified by their location within a superlattice layer.

The bandstructure tunability of Type II antimonide-based superlattices has been significantly enhanced since the introduction of the M-structure superlattice, resulting in significant improvements of Type II superlattice infrared detectors. By using M-structure, we developed the pMp design, a novel infrared photodetector architecture that inherits the advantages of traditional photoconductive and photovoltaic devices. This minority electron unipolar device consists of an M-structure barrier layer blocking the transport of majority holes in a p-type semiconductor, resulting in an electrical transport due to minority carriers with low current density. Applied for the very long wavelength detection, at 77K, a 14μm cutoff detector exhibits a dark current 3.3 mA/cm², a photoresponsivity of 1.4 A/W at 50mV bias and the associated shot-noise detectivity of 4x10¹⁰ Jones.

It is known that major restrictions of room-temperature semiconductor photodetectors and some other optoelectronic devices are caused by short photoelectron lifetime, which strongly reduces the photoresponse. Here we report our research on advanced optoelectronic materials, which combine manageable photoelectron lifetime, high mobility, and quantum tuning of localized and conducting states. These structures integrate quantum dot (QD) layers and correlated QD clusters with quantum wells (QWs) and heterointerfaces. The integrated structures provide many possibilities for engineering of electron states as well as specific kinetic and transport properties. Thus, these structures have the strong potential to overcome the limitations of traditional QD and QW structures. The main distinctive characteristic of the QD structures with collective potential barriers is an effective control of photoelectron capture due to separation of highly mobile electrons transferring the photocurrent along heterointerfaces from the localized electron states in the QD blocks (rows, planes, and various clusters). Besides manageable photoelectron kinetics, the advanced QD structures will also provide high coupling to radiation, low generation-recombination noise, and high scalability.

Photon-counting detectors are required for numerous NASA future space-based laser receivers including science instruments and free-space optical communication terminals. Silicon avalanche photodiode (APD) single photon counting modules (SPCMs) are used in the Geoscience Laser Altimeter System (GLAS) on Ice, Cloud, and land Elevation Satellite (ICESat) launched in 2003, currently in orbit measuring the Earth surface elevation and atmosphere backscattering. To measure cloud and aerosol backscattering, the SPCMs detect the GLAS laser light at 532-nm wavelength, with quantum efficiencies of 60 to 70% and maximum count rates greater than 13 million per second. The performance of the SPCMs has been monitored since ICESat launch on January 12, 2003. There has been no measurable change in the quantum efficiency, linearity or after-pulsing. The detector dark counts rates monitored while the spacecraft was in the dark side of the Earth have increased linearly at about 60 counts/s per day due to space radiation damage. As the ICESat mission nears completion, we have proposed ground-to-space optical and quantum communication experiments to utilize the on-orbit 1-meter optical receiver telescope with multiple SPCMs in the focal plane. NASA is preparing a follow-on mission to ICESat, called ICESat-2, with a launch date of late 2014. The major candidate photon-counting detectors under evaluation for ICESat-2 include 532 nm and 1064 nm wavelength-sensitive photomultiplier tubes and Geiger-mode avalanche photodiode arrays. Key specifications are high maximum count rate, detection efficiency, photon number resolution, radiation tolerance, power consumption, operating temperature and reliability. Future NASA science instruments and free-space laser communication terminals share a number of these requirements.

NASA considers Flash Lidar a critical technology for enabling autonomous safe landing of future large robotic and crewed vehicles on the surface of the Moon and Mars. Flash Lidar can generate 3-Dimensional images of the terrain to identify hazardous features such as craters, rocks, and steep slopes during the final stages of descent and landing. The onboard flight comptuer can use the 3-D map of terain to guide the vehicle to a safe site. The capabilities of Flash Lidar technology were evaluated through a series of static tests using a calibrated target and through dynamic tests aboard a helicopter and a fixed wing airctarft. The aircraft flight tests were perfomed over Moonlike terrain in the California and Nevada deserts. This paper briefly describes the Flash Lidar static and aircraft flight test results. These test results are analyzed against the landing application requirements to identify the areas of technology improvement. The ongoing technology advancement activities are then explained and their goals are described.

The operation of InP-based single photon avalanche diodes (SPADs) in Geiger mode provides great utility for the detection of single photons at near-infrared wavelengths between 1.0 and 1.6 μm. However, SPADs have performance limitations with respect to photon counting rate and the absence of photon number resolution that, at the most fundamental level, can be traced back to the positive feedback inherent in the impact ionization-driven avalanche process. In this paper, we describe the inclusion of negative feedback with best-in-class InP-based single photon avalanche diode (SPAD) structures to form negative feedback avalanche diodes (NFADs) in which many of the present limitations of SPAD operation can be overcome. The use of thin film resistors as monolithic passive negative feedback elements ensures rapid self-quenching with very low parasitic effects. We demonstrate a qualitative difference in the performance of NFADs in the two regimes of small and large negative feedback. With small feedback, we have studied the behavior of the persistent current prior to quenching, for which we have found oscillatory behavior as well as an exponentially distributed duration. For large feedback, we find rapid quenching, accompanied by evidence for a partial discharge of the detector capacitance, leading to charge flows as low as ~3 ×10⁵ carriers associated with each avalanche event.

Infrared single-photon avalanche photodiodes (SPADs) are used in a number of sensing applications such as satellite laser ranging, deep-space laser communication, time-resolved photon counting, quantum key distribution and quantum cryptography. A passively quenched SPAD circuit consists of a DC source connected to the SPAD, to provide the reverse bias, and a series load resistor. Upon a photon-generated electron-hole pair triggering an avalanche breakdown, current through the diode and the load resistor rises quickly reaching a steady state value, after which it can collapse (quench) at a stochastic time. In this paper we review three recent analytical and Monte-Carlo based models for the quenching time. In the first model, the applied bias after the trigger of an avalanche is assumed to be constant at the breakdown bias while the avalanche current is allowed to be stochastic. In the second model, the dynamic negative feedback, which is due to the dynamic voltage drop across the load resistor, is taken into account, albeit without considering the stochastic fluctuations in the avalanche pulse. In the third model, Monte-Carlo simulation is used to generate impact ionizations with the inclusion of the effects of negative feedback. The latter model is based on simulating the impact ionizations inside the multiplication region according to a dynamic bias voltage that is a function of the avalanche current it indices. In particular, it uses the time evolution of the bias across the diode to set the coefficients for impact ionization. As such, this latter model includes both the negative feedback and the stochastic nature of the avalanche current.

Aim of the paper is to discuss design, fabrication and performances of Single-Photon Avalanche Diode (SPAD) arrays developed at the SPADLab of Politecnico di Milano, in both custom and fully-CMOS technologies. Applications span from 2D imagers for high sensitivity fast frame-rate (close to Mframe/s) video acquisitions, to molecular imaging, to functional time-resolved Near-Infrared Spectroscopy (fNIRS) of organs and tissues, to Fluorescence Correlation Spectroscopy (FCS), Fluorescence Lifetime Imaging (FLIM) with 30psFWHM photon timing resolution. Various microelectronic single-chip detection modules and monolithic SPAD arrays will be presented and discussed.

Solution-based single-molecule fluorescence spectroscopy is a powerful new experimental approach with applications in all fields of natural sciences. The basic concept of this technique is to excite and collect light from a very small volume (typically femtoliter) and work in a concentration regime resulting in rare burst-like events corresponding to the transit of a single-molecule. Those events are accumulated over time to achieve proper statistical accuracy. Therefore the advantage of extreme sensitivity is somewhat counterbalanced by a very long acquisition time. One way to speed up data acquisition is parallelization. Here we will discuss a general approach to address this issue, using a multispot excitation and detection geometry that can accommodate different types of novel highly-parallel detector arrays. We will illustrate the potential of this approach with fluorescence correlation spectroscopy (FCS) and single-molecule fluorescence measurements obtained with different novel multipixel single-photon counting detectors.

Microphotoluminescence experiment has been performed on InAsP/InP epitaxial quantum dots, emitting in the telecommunication wavelength range. The exciton emission from a single quantum dot has been detected via the excitation power dependence of the microphotoluminescence spectra. Two photon entanglement schemes are proposed in order to produce entangled photons out of the excitonic and bexcitonic transitions in such dot. Both schemes require the implementation of Purcell effect, in order to collect efficiently the emitted photons and to restore entanglement.

Vertical silicon nanowire detectors with high phototransistive gain have been demonstrated and the principles responsible for the high gain have been reported in recent publications. The emphasis of this paper is (a) the fabrication technology of silicon nanowire array detectors that can be integrated with Si VLSI and (b) the ability of sub-bandgap detection to achieve ultrawide band (from UV to IR) responsivity. We have demonstrated responsivity of greater than 100 A/W at 1550 nm for single crystal silicon nanowires to detect picowatts of IR light, the highest record ever reported for single crystal silicon detectors.

Optoelectronic devices based on single, self-assembled semiconductor quantum dots are attractive for applications in secure optical communications, quantum computation and sensing. In this paper we show how it is possible to dictate the nucleation site of individual InAs/InP quantum dots using a directed self-assembly process, to control the electronic structure of the nucleated dots and also how to control their coupling to the optical field by locating them within the high field region of a photonic crystal nanocavity. For application within fiber networks, these quantum dots are targeted to emit in the spectral region around 1550 nm.

Since 2006, MIT Lincoln Laboratory has been developing Digital-pixel Focal Plane Array (DFPA) readout integrated circuits (ROICs). To date, four 256 × 256 30 μm pitch DFPA designs with in-pixel analog to digital conversion have been fabricated using IBM 90 nm CMOS processes. The DFPA ROICs are compatible with a wide range of detector materials and cutoff wavelengths; HgCdTe, QWIP, and InGaAs photo-detectors with cutoff wavelengths ranging from 1.6 to 14.5 μm have been hybridized to the same digital-pixel readout. The digital-pixel readout architecture offers high dynamic range, A/C or D/C coupled integration, and on-chip image processing with low power orthogonal transfer operations. The newest ROIC designs support two-color operation with a single Indium bump connection. Development and characterization of the two-color DFPA designs is presented along with applications for this new digital readout technology.

We report here our study on suppression of fluorescence blinking of colloidal CdSe/ZnS quantum dots (QDs) for potential applications as high performance single-photon sources. Blinking is an interesting property for single QDs, but it is undesirable for their applications. We have demonstrated that by coupling these QDs to adjacent silver nanoprisms, we could not only completely suppress the blinking but also enhance the fluorescence quantum yield, and also increase the fluorescence decay rates. These single QDs also exhibit anti-bunching behavior which is a signature for a single-photon emitter. In addition, we have also achieved blinking suppression by embedded the QDs in agarose gel. The electrostatic environment around QDs due to negatively charged fibers of gel might strongly affect the extent of blinking suppression. The mechanisms of blinking suppression will be discussed in the frame work of diffusion-controlled electron transfer model.

Surface emission from distributed feedback terahertz quantum cascade lasers operating in double-metal waveguides is investigated. After analyzing the origin of vertical out-coupling in linear second-order gratings, the enhancement of radiative efficiency achieved with quasi-periodic and circular gratings is presented. Linear Fibonacci resonators and microdisk lasers have been realized allowing great flexibility in tailoring the surface emission intensity and profile. Finally, ring lasers showing high power collimated emission in the vertical direction by employing a double-slit grating configuration will be discussed.