This PDF file contains the front matter associated with SPIE Proceedings Volume 7355, including the Title Page, Copyright information, Tabe of Contents, Introduction (if any), and the Conference Committee listing.

When rewritten in an appropriate manner, the microscopic Maxwell-Lorentz equations appear as a wave-mechanical theory for photons, and their quantum physical interaction with matter. A natural extension leads from photon wave mechanics to quantum electrodynamics (QED). In its modern formulation photon wave mechanics has given us valuable new insight in subjects such as spatial photon localization, near-field photon dynamics, transverse photon mass, photon eikonal theory, photon tunneling, and rim-zone electrodynamics. The present review is based on my plenary lecture at the SPIE-Europe 2009 Optics and Optoelectronics International Symposium in Prague.

The orbital angular momentum carried by single photons represents a promising resource in the quantum information field. In this paper we report the characterization in the quantum regime of a recently introduced optical device, known as q-plate. Exploiting the spin-orbit coupling that takes place in the q-plate, it is possible to transfer coherently the information from the polarization to the orbital angular momentum degree of freedom, and viceversa. Hence the q-plate provides a reliable bi-directional interface between polarization and orbital angular momentum. As a first paradigmatic demonstration of the q-plate properties, we have carried out the first experimental Hong-Ou-mandel effect purely observed in the orbital angular momentum degree of freedom.

In this work we present the realization of multiphoton quantum states, obtained by optical parametric amplification, and we investigate their perspectives and possible applications. The multiphoton quantum states are generated by a quantum-injected optical parametric amplifier (QI-OPA) seeded by a single-photon belonging to an EPR entangled pair. The entanglement between the micro-macroscopic photon system is experimentally demonstrated, and the possible applications of the macro-qubits states are presented and discussed.

We investigate the spatio-temporal structure of the biphoton entanglement in Parametric Down Conversion (PDC). In particular we study the biphoton amplitude at the output face of the nonlinear crystal (near-field) and we demonstrate its X-shaped geometry in the space-time dimensions, i.e. the non-factorability of the state with respect to spatial and temporal variables. Our analysis provides a precise and quantitative characterization of this structure in various regimes and types of phase matching of PDC. The key elements of novelty emerging from our analysis are the non-factorability of the state with respect to spatial and temporal variables, and the extreme relative localization of the entangled photons, both in space (few microns) and time (few femtoseconds). This extreme localization is connected to our ability to resolve the photon positions in the source near-field. The non factorability opens the possibility of tailoring the temporal entanglement by acting on the spatial degrees of freedom of twin photons.

We report the first complete experimental reconstruction of the covariance matrix (CM) relative to a bi-partite continuous variable (CV) entangled state outing a non degenerate optical parametric oscillator (OPO) below threshold. The covariance matrix CM has been reconstructed following the method reported in V. D'Auria et al., J. Opt. B 7, S750 (2005). The two entangled beams (signal (a) and idler (b)) are produced by a by a continuous wave (CW) optical parametric oscillator (OPO) via type-II (same frequency but with orthogonal polarizations), phase matching and working below threshold. Our experimental setup makes use of a single homodyne detector and of a compact source of entangled beams. The quadratures values and other relevant quantities are reconstructed by quantum tomography, without making any a priori assumption on the state under evalutation.

A wafer fusing was applied to integrate an InP-based active medium and a GaAs/AlGaAs distributed Bragg reflector in an optically pumped semiconductor disk laser. Over 50 mW of output power at room temperature in 1570-1585 nm spectral range was demonstrated. The results of this study reveal an important finding: the wafer fusion can be used in emitters with high power. This approach would allow for monolithic integration of lattice-mismatched compounds, quantum-well and quantum-dot based media and promises substantial wavelength tailoring of semiconductor disk lasers.

Deep level transient spectroscopy (DLTS) and capacitance-voltage measurements (C-V) have been performed on AlGaAs/GaAs diode structures containing quantum wells (QWs) with graded or stepped barriers content and compared with structures without QWs. DLTS peaks have been observed only for the structures containing the QWs under reduced voltage pulse excitation. A mechanism of carrier capture into and escape from the quantum wells has been discussed.

We are presenting the results of the study of various Single Photon Avalanche Diodes (SPADs) for the detection of optical signal consisting of single up to several thousands of photons. We were investigating the correlation between the avalanche buildup time and the photon number involved in the avalanche trigger. Three different detection chips made by three manufacturers were tested. The detection chips were operated in a passive quenching circuit with active gating. This setup enabled us to monitor both the diode reverse current using an electrometer and an avalanche buildup time using a fast digitizing oscilloscope. The electrometer reading enabled to estimate the photon number per detection event, the avalanche build up was recorded on the oscilloscope and processed by custom designed waveform analysis package. The correlation of avalanche build up to the photon number, bias above break, photon absorption location and optical pulse length were investigated in detail. The experimental results are presented.

We present the discrete amplification approach used for development of a very high gain and low excess noise factor in the near infrared wavelength region. The devices have the following performance characteristics: gain > 2X10⁵, excess noise factor < 1.05, rise time < 350ps, fall time < 500ps and operating voltage < 60V. In the photon counting mode, the devices can be operated in the non-gated mode under a constant DC bias and do not require any external quenching circuit. These devices are ideal for researchers in the fields of deep space optical communication, spectroscopy, industrial and scientific instrumentation, Ladar/Lidar, quantum cryptography, night vision and other military, defense and aerospace applications.

This paper describes a simulation model (implemented in MATLAB) of a typical setup used for time-resolved fluorescence measurements, including: a laser source, basic fluorescence sample, optics, single-photon avalanche diode and read-out electronics. The correctness of the model has been verified by setting up a simple time-resolved fluorescence measurement using a CMOS SPAD-based detector. The solution of fluorophore (CdSe/ZnS quantum dots in toluene) in a glass capillary was placed above the detecting surface and excited by laser pulses. We have used a time-gating technique with 10-ns observation window shifted at 60-ps time steps across the appropriate time interval. The observed curve corresponds to the convolution of the fluorescence emission and the 10-ns observation window. Simulation accuracy has been verified by comparing the experimental fluorescence decay with the simulated one using chi-square test. The proposed model allows researchers to simulate the behaviour of SPAD detectors with a good accuracy and demonstrates how imperfections in the experimental system can affect the result. The model enables the design of SPAD-based detectors with the best performance for a specific application area.

Signal processing method was developed for simultaneous particle counting, sizing and flow velocity measurements with photon correlation laser Doppler anemometers. The high sensitivity of avalanche photodiodes in photon counting mode assures the ability to catch the individual particles in the submicron/nanometer size range. A detailed discussion is given about the optimal set up parameters (wavelength, detector position and refractive index) and calibration measurements are shown to determine system parameters in a particular arrangement and simulations to estimate the lower size limit of the particle characterization. Estimations are given for the required laser power to detect 20 photon counts in average for a single particle transit as a lower limit of the particle sizing procedure. In the calibration measurement the most sensitive size region was below 300nm down to the sizing limit (20 photons in average) at 514nm illumination wavelength. As a numerical example we conclude that the size estimation of a polystyrene sphere particle of 50nm diameter requires at least 123 kW/cm² laser power density at 350nm while 587 kW/cm² at 514nm in the studied system.

Almost all astronomical instruments detect and analyze the first order spatial and/or temporal coherence properties of the photon stream coming from celestial sources. Additional information might be hidden in the second and higher order coherence terms, as shown long ago by Hanbury-Brown and Twiss with the Narrabri Intensity Interferometer. The future Extremely Large Telescopes and in particular the 42 m telescope of the European Southern Observatory (ESO) could provide the high photon flux needed to extract this additional information. To put these expectations (which we had already developed at the conceptual level in the QuantEYE study for the 100 m OverWhelmingly Large Telescope to experimental test in the real astronomical environment, we realized a small prototype (Aqueye) for the Asiago 182 cm telescope. This instrument is the fastest photon counting photometer ever built. It has 4 parallel channels operating simultaneously, feeding 4 Single Photon-Avalanche Diodes (SPADs), with the ability to push the time tagging capabilities below the nano-second region for hours of continuous operation. Aqueye has been extensively used to acquire photons from a variety of variable stars, in particular from the pulsar in the Crab Nebula. Following this successful realization, a larger version, named Iqueye, has been built for the 3.5 m New Technology Telescope (NTT) of ESO. Iqueye follows the same optical solution of dividing the telescope pupil in 4 sub-pupils, imaged on new generation SPADs having useful diameters of 100 micrometers, time jitter less than 50 picoseconds and dark-count noise less than 50 counts/second. The spectral efficiency of the system peaks in the visible region of the spectrum. Iqueye operated very successfully at the NTT in January 2009. The present paper describes the main features of the two photometers and present some of the astronomical results already obtained.

Multilayers clouds layer's horizons have been detected in strong snowing condition by using the micro-Joule eye-safe lidar. Lidar is based on the 1 μJ (30 ns length) pulsed diode laser, which operates with high repetition rate (up to 10 kHz) and silica (Si) photon counting receiver (Single Photon Avalanche Diode, SPAD) from Czech Technical University. Note that the unique low avalanche voltage of Czech SPAD (~ 26-28 Volts), low power consumption (~ 0.2 Watts), the wide (-100 to 20 °C) temperature operation and low weight (~ 0.94 kg) were the main arguments to involve this lidar version into the NASA Mars Polar Lander mission a decade ago in 1999. The Geiger (photon counting) mode of SPAD operation and laser high repetition rate allow us to apply the specifically statistical approach to the development of the remote sensing return, which is scattered by aerosol and other inhomogeneous along the sounding trace. To get of reliable signal-to-noise ratio (SNR) we have to use a few hundred or thousand laser pulses because the probability of the photon scattered by sounding object is smaller than unit. As a role a Poison statistics is used to development of the remote sensing return.

Using our Satellite Laser Ranging (SLR) facility, our experience and our available equipment for Single Photon detection, we installed a Single Photon Counting Module (SPCM) to measure the photon flux of variable stars, and of stars with transiting exoplanets; these observations are intended as a complementary application to our standard SLR activities, to contribute observations to already known - and also to candidate - variable stars and stars with transiting exoplanets. While it is relatively easy to detect the large - in some cases up to 50% - variations of some stars, it is a challenge to detect the transiting exoplanets with this method; the decrease in photon flux here is only in the order of a few percent. In this paper, we present first results.

The Satellite Laser Ranging (SLR) Station Graz is measuring routinely distances to satellites with a 2 kHz laser, achieving an accuracy of 2-3 mm. Using this available equipment, we developed - and added as a byproduct - a kHz SLR LIDAR for the Graz station: Photons of each transmitted laser pulse are backscattered from clouds, atmospheric layers, aircraft vapor trails etc. An additional 10 cm diameter telescope - installed on our main telescope mount - and a Single- Photon Counting Module (SPCM) detect these photons. Using an ISA-Bus based FPGA card - developed in Graz for the kHz SLR operation - these detection times are stored with 100 ns resolution (15 m slots in distance). Event times of any number of laser shots can be accumulated in up to 4096 counters (according to > 60 km distance). The LIDAR distances are stored together with epoch time and telescope pointing information; any reflection point is therefore determined with 3D coordinates, with 15 m resolution in distance, and with the angular precision of the laser telescope pointing. First test results to clouds in full daylight conditions - accumulating up to several 100 laser shots per measurement - yielded high LIDAR data rates (> 100 points per second) and excellent detection of clouds (up to 10 km distance at the moment). Our ultimate goal is to operate the LIDAR automatically and in parallel with the standard SLR measurements, during day and night, collecting LIDAR data as a byproduct, and without any additional expenses.

In the last years Time-Correlated Single-Photon Counting (TCSPC) has increasingly been used in many different scientific applications (e.g.: single molecule spectroscopy, fluorescence lifetime imaging, diffuse optical tomography). Many of these applications are calling for new requests on the development of instrumentation that operates at higher and higher conversion rates and that is able to resolve optical signals not only in the time domain, but also in wavelength, polarization and position. To exploit the potential of parallel analysis over multiple acquisition channels, a new generation of TCSPC devices is needed that is characterized by low size and costs. The core block of TCSPC instrumentation is the time-interval measurement section, which can be implemented with a Time-to-Amplitude Converter (TAC); the converter can be integrated on a single chip in order to reduce the overall size and cost of the system. This paper presents a monolithic TAC that has been designed to achieve the high resolution, good differential linearity and fast counting rate required in modern applications. The TAC here described is built on a commercial 0.35 μm CMOS technology, and is characterized by resolution better than 60 ps, differential nonlinearity limited to 0.5% rms and short dead-time of 80 ns. The low area occupation (1.4x1.8 mm) and minimal need for external components allow the realization of very compact instruments with multiple acquisition channels operating simultaneously at very high count rates.

We are presenting novel active quenching circuit for Single Photon Avalanche Diodes (SPADs). It was designed and optimized for satellite laser ranging applications, where the specific requirements are put on the gating performance. The goal of this work was to be able to detect the photons in short time after gate on with constant detection delay and sensitivity to minimize the measurement errors on one hand and background photon flux induced false count on the other hand. The detector sensitivity and especially the detection delay must be stabilized few nanoseconds after the gate activation. In the new circuit the SPAD can be pulse operated up to 5 volts above its breakdown voltage, the gate is opened by the incoming external pulse and is closed by the first photon detection. The new circuit was built and tested, the detector package for the field operation at the satellite laser ranging station was completed. The device performance: detection sensitivity, detection delay and timing resolution was measured and will be presented.

In this paper we present a physically-based model aimed at calculating the Photon Detection Efficiency (PDE) and the temporal response of a Single-Photon Avalanche Diode (SPAD) with a given structure. In order to calculate these quantities, it is necessary to evaluate both the probability and the delay with which a photon impinging on the detector area triggers an avalanche. Three tasks are sequentially performed: as a first step, the electron-hole generation profile along the device is calculated according to the silicon absorption coefficient at the considered wavelength; successively, temporal evolution of the carriers distribution along the device is calculated by solving drift diffusion equations; finally, the avalanche triggering probability is calculated as a function of the photon absorption point. Validation of the model has been carried out by comparing simulation and experimental results of a few generations of detectors previously realized in our laboratory. Photon detection efficiency has been measured and calculated for wavelengths ranging from 400nm to 1000nm and for excess bias voltages ranging from 2 to 8V. Similarly, temporal response has been investigated at two different wavelengths (520 and 820nm). A remarkable agreement between experimental and simulation results has been obtained in the entire characterization domain simply starting from the measured doping profile and without the need of any fitting parameter. Consequently, we think that this model will be a valuable tool for the development of new detectors with improved performances.

In this work we report on InAs avalanche photodiodes (APDs) that exhibit high gain with extremely low excess avalanche noise. Our measurements showed that InAs has significantly larger electron ionization coefficient than most compound III-V semiconductors and extremely small hole ionization coefficient. This large electron to hole ionization coefficient ratio leads to excess noise factor, F~2 when electrons initiated the multiplication process in our APDs. Significantly larger excess noise factors were measured when both electrons and holes were injected into the avalanche region to initiate the multiplication process. Our InAs APDs demonstrated ionization characteristics similar to those observed in Cadmium Mercury Telluride (CMT) in the short wave infrared (SWIR). Measurements of temperature dependence of leakage current provided early indications of potentially higher operating temperature than CMT. The low excess noise behaviour and higher operating temperatures, demonstrate that InAs APDs have potential to be developed into low cost high performance photon counting APD arrays to rival CMT.

Low- noise avalanche photodiodes for the spectral range of 1.6-2.4 μm were created using the GaInAsSb solid solution in the absorption region and the wide-gap GaAl_X(As)Sb alloy of resonant composition (x=0.04) in the multiplication region. This APD has a very high ratio of ionization coefficients, β/α>30 and low excess noise factor, F~1.6 (M=10). The sensitivity of a receiver for longwavelength communication (λ=1.6-2.5 μm) based on GaInAsSb/AlGa(As)Sb SAM APD is reported. The sensitivity for a direct detection receiver using the SAM APD was calculated according to the treatment of Personick at bit rate B=500 Mbit/s. The dependence of minimum detectable power η<P_APD> on multiplication M for the SAM APD for the wavelength λ=2.1 μm was calculated and compared with one for a standard Ge APD operating at λ=1.55 μm. A minimum detectable power level η<P_APD> = -42.3 dBm at M_opt=34-39 and η<P_APD>=-41.8 dBm at M_opt=10 of the receivers with the GaInAsSb/GaAl(As)Sb SAM APD and the Ge APD, respectively were obtained. These results demonstrate the potential of an optical receiver with the GaInAsSb/GaAl(As)Sb SAM APD for use in mid-IR wavelength optical communication system as well as of great interest for their potential applications in laser range-finding system.