Silicon Photomultipliers (SiPMs) are fabricated in two different configurations: p-on-n and n-on-p junctions. More particularly p-on-n SiPMs turn out to be more suitable in nuclear medical imaging applications like Positron Emission Tomography (PET), due to their higher sensitivity in blue wavelength range where common PET scintillators have their emission spectrum. Here we report on the preliminary results of the electro-optical characterization performed on the first STMicroelectronics p-on-n SiPMs with standard (45%) and enhanced (62%) fill factor. The performances of these devices are compared with standard n-on-p technology. The inversion of the junction results in a remarkable improvement of PDE in blue wavelength range. Moreover all the tested devices show very good single photoelectron resolution also for high overvoltage values confirming the excellent single photon detection capability of SiPM technology. In this work a comprehensive SiPM model integrating the electrical and statistical behavior of the device is also presented. We used a Monte Carlo model for statistical and a SPICE circuit model for the electrical behavior description of the SiPM.

Nowadays, many research fields like biology, chemistry, medicine and space technology rely on high sensitivity imaging instruments that allow to exploit modern measurement techniques; among these, Time-Correlated Single-Photon Counting (TCSPC) provides extremely high time resolution. Single-photon detectors play a key role in these advanced imaging systems, and in recent years Single-Photon Avalanche Diodes (SPADs) have become a valid alternative to Photo Multiplier Tubes (PMTs). Moreover scientific research has recently focused on single photon detector arrays, pushed by a growing demand for multichannel systems. In this scenario, we developed a compact, stand-alone, 32-channel system for time-resolved single-photon counting applications. The system core is represented by a 32×1 SPAD array built in custom technology, featuring high time resolution, high photon detection efficiency (> 45%) and low dark count rate. The SPAD avalanche signal is exported through an integrated inverter which is placed close to the photo detector, this way the avalanche event is detected with high time resolution while achieving negligible crosstalk between adjacent pixels. SPAD proper operation is guaranteed by a 32×1 mixed passive-active quenching circuit (AQC) array built in 0.18 μm HV-CMOS technology; its digital outputs are fed to an FPGA that performs on-board processing of photon counting information. On the contrary, photon timing information is directly extracted from the pixel array and exported in Current Mode Logic (CML) standard. Preliminary experiments have been carried out on the developed system, resulting in a high time resolution (< 60 ps FWHM) and mean dark count rate lower than 8500 counts/s at 25°C.

SPADs (Single Photon Avalanche Diodes) are emerging as most suitable photodetectors for both single-photon counting (Fluorescence Correlation Spectroscopy, Lock-in 3D Ranging) and single-photon timing (Lidar, Fluorescence Lifetime Imaging, Diffuse Optical Imaging) applications. Different complementary metal-oxide semiconductor (CMOS) implementations have been reported in literature. We present some figure of merit able to summarize the typical SPAD performances (i.e. Dark Counting Rate, Photo Detection Efficiency, afterpulsing probability, hold-off time, timing jitter) and to identify a proper metric for SPAD comparison, both as single detectors and also as imaging arrays. The goal is to define a practical framework within which it is possible to rank detectors based on their performances in specific experimental conditions, for either photon-counting or photon-timing applications. Furthermore we review the performances of some CMOS and custom-made SPADs. Results show that CMOS SPADs performances improve as the technology scales down; moreover, miniaturization of SPADs and new solutions adopted to counteract issues related with the SPAD design (electric field uniformity, premature edge breakdown, tunneling effects, defect-rich STI interface) along with advances in standard CMOS processes led to a general improvement in all fabricated photodetectors; therefore, CMOS SPADs can be suitable for very dense and cost-effective many-pixels imagers with high performances.

The design, simulation results and experimental characterization of a compact analog readout circuit for photon counting applications are presented in this paper. Two linear test arrays of 40 pixels with 25 μm pixel pitch have been fabricated in a 0.15 μm CMOS technology. Each pixel of the array consists of a Single-Photon Avalanche Diode (SPAD), a quenching circuit, a time-gating circuit and an analog counter. Each input pulse corresponding to a SPAD avalanche event is converted to a step in the output voltage. Along with compactness, the circuit was designed targeting low power consumption, good output linearity and sub-nanosecond timing resolution. The circuit features 8.6% pixel output nonuniformity and 1.1 % non-linearity. The gating circuit provides the sub-nanosecond window of 0.95 ns at FWHM. Consisting of a small number of transistors and occupying only 238μm2, this approach is suitable for the design of SPAD-based image sensors with high spatial resolution.

This paper proposes dual-mode buffer direct injection (BDI) and direct injection (DI) readout circuit design. The DI readout circuit has the advantage of being a simple circuit, requiring a small layout area, and low power consumption. The internal resistance of the photodetector will affect the photocurrent injection efficiency. We used a buffer amplifier to design the BDI readout circuit since it would reduce the input impedance and raise the injection efficiency. This paper will discuss and analyze the power consumption, injection efficiency, layout area, and circuit noise. The circuit is simulated using a TSMC 0.35 um Mixed Signal 2P4M CMOS 5 V process. The dimension of the pixel area is 30×30 μm. We have designed a 10×8 array for the readout circuit of the interlaced columns. The input current ranges from 1 nA to 10 nA, when the measurement current is 10 pA to 10 nA. The integration time was varied. The circuit output swing was 2 V. The total root mean square noise voltage was 4.84 mV. The signal to noise ratio was 52 dB, and the full chip circuit power consumption was 9.94 mW.

The concept and preliminary experimental results of photon counting based two-way optical time transfer are presented. It is based on free-space optical link delimited by a pair of SPAD-based single photon detectors and small reflectors injecting optical signals into the link alternately on two injection points. Several picosecond laser versions may be employed as signal source – laser diode 43 ps at 778 nm, fiber based laser 80 ps at 531 nm or both. Expected repetition rate of experiment is 5 kHz. The NPET timing devices are used to register detection events and custom software and algorithm are used to process measured data. The long term delay stability sub - -picosecond range and small temperature drifts of all elements of measuring chain are crucial to obtain useful data for final time scale comparison in picosecond range. The experimental results from measurement of long term stability of detector delays, delay independence on position in detector active area, and new achievements in quenching techniques will be presented.

The paper presents the concept and preliminary design of a single photon counting laser altimeter (lidar) dedicated for deep space rendezvous missions towards an asteroid. Overall estimated device weight and volume should not exceed 2 kg and 2 dm2 with the power consumption below 20 W. The altimeter range evaluation precision should be on the order of 5 cm. A complex software simulator of the entire laser ranging and photon counting link has been developed and verified. The simulator framework incorporates both the three-dimensional space-craft flight mechanics and topographical maps of the surface. Altimeter performance metrics are proposed and evaluated considering the topographical surface slope, environmental conditions, footprint coverage, gate range settings, and spacecraft-to-asteroid range and velocity. The asteroid topographical mapping and landing scenarios are discussed; specific spacecraft-to-asteroid approach phases are simulated and range reading maximum repetition rate is determined for each operation phase. Photon counting approach enables additional functions to laser altimetry, namely the one way laser ranging and laser time transfers over interplanetary distances and absolute radiometry at the laser wavelength.

Single photon avalanche diodes (SPADs), operated in Geiger mode, provide highest detection efficiency for time of flight measurements in the single photon regime. However, the risetime of the output signal shows time delays with changing number of generated photoelectrons. Therefore the measured time of arrival shows some drift with changing input light levels. Based on the continuity equations and the intrinsic resistance of SPADs, a simple model of the avalanche breakthrough was developed to analyze this behavior. By applying a suitable external gating circuit, e. g. implementing a decoupling resistor between the diode and the gating capacitor, this simulation shows a slight dependency of the diodes peak output current on the number of generated photoelectrons. Experimental observations performed with a passive quenching circuit and an InGaAs/InP-SPAD showed good agreement with the simulation. In time of flight measurements, e. g. in satellite laser ranging, this behavior can be used for compensating intensity dependent delays during the detection process.

Modern Time-Correlated Single-Photon Counting applications require to detect spectral and temporal fluorescence data simultaneously and from different areas of the analyzed sample. These rising quests have led the development of multichannel systems able to perform high count rate and high performance analysis. In this work we describe a new 32-channel TCSPC system designed to be used in modern setups. The presented module consists of four independent 8-channel TCSPC boards, each of them including two 4-channel Time-Amplitude Converter arrays. These TAC arrays are built-in 0.35 μm Si-Ge BiCMOS technology and are characterized by low crosstalk, high resolution, high conversion rate and variable full-scale range. The 8-channel TCSPC board implements an 8-channel ADC to sample the TAC outputs, an FPGA to record and organize the measurement results and a USB 2.0 interface to enable real-time data transmission to and from an external PC. Experimental results demonstrate that the acquisition system ensures high performance TCSPC measurements, in particular: high conversion rate (5 MHz), good time resolution (down to 30 psFWHM with the full scale range set to 11 ns) and low differential non-linearity (rms value lower than 0.15% of the time bin width). We design the module to be very compact and, thanks to the reduced dimensions of the 8-channel TCSPC board (95×40 mm), the whole system can be enclosed in a small aluminum case (160×125×30 mm).

The first Chinese mission of Laser Time Transfer (LTT) between ground and Chinese Navigation Satellites was successfully implemented by Shanghai Astronomical Observatory of Chinese Academy of Sciences. Because of LTT payloads onboard the High Earth Orbiting (HEO) satellites with orbit altitude of 21,500 to 36,000 km, the photon counting technology was adopted to increase the success rate of laser signal detection on satellites. The detection chip operates in a Geiger Mode with single photon sensitivity. It has a diameter of 40 um, it is produced by Czech Technical University. In order to reduce the background noise in space, the gated mode and two separated channels with different Field Of View (FOV) were used for the detector. The improvements for the next version of the LTT detector resulted in a lower background noise and better laser detection rate. It is also been demonstrated in the onboard experiments that the photon counting detector works well after sunlight directly entered into its optical window. Finally the LTT experiments result on Chinese Navigation Satellites are present in this paper. The clock and relative frequency difference were obtained with the single shot measuring resolution of about 300ps and 30 ps precision.

Transport properties of NbN/NiCu superconductor/ferromagnet (S/F) nanostripes fabricated in both in single-wire and series-parallel, meander-type configurations are presented down to T = 4.2 K. In particular, the enhancement of the superconducting critical current has been observed at smaller widths, apparently, due to an extra pinning mechanism, arising from clustering of ferromagnetic atoms inside the thin S layer. Moreover, we observed a number of characteristic voltage steps on the nanostripe current-voltage characteristics and their nature was investigated as a function of temperature. An explanation in terms of active phase-slip phenomena has been proposed based of the time-dependent Ginzburg-Landau theory and led to an estimation of the inelastic electron-phonon relaxation time τe-ph ~ 1 ps, in agreement with the τopt = 1.2±0.3 ps value, measured by the femtosecond transient optical reflectivity spectroscopy method on the same bilayer. Transient optical properties of our superconducting S/F nano-bilayers have been also investigated and compared to those obtained for pure NbN nanostripe reference samples. Finally, electrical photoresponse signals of S/F heterostructures exposed to ultraweak pulsed (width 400 ps, repetition rate ~100 MHz) laser radiation at 850 nm wavelength exhibited the falling time of voltage responses directly dependent on the NiCu overlayer. We have also noticed that the presence of the top F layer and the resulting proximity effect reduced frequency of dark counts in our samples.

The prospects for image recovery of space objects, observed in the visible range through the turbulent atmosphere by using large aperture telescope, were discussed and evaluated. A "dual" adaptation was introduced: at first - hardware adaptation, using reflected solar radiation from the space object or laser star, then algorithmic. We considered two scenarios for observation. The criterion of image quality was chosen to be potentially full compensation of phase distortion. The characteristics of photoreadout statistics for the various scenarios were analyzed.

We have collected and analyzed the values of thermoelectric parameters of thermoelectric materials and on this basis calculated the energy resolution and photon count rate of the Thermoelectric Nanowire Single-Photon Detector (TNSPD). It is concluded that the TNSPD can achieve higher specifications as compared with the best single-photon detectors. The lanthanum-cerium hexaboride sensors of TNSPD are expected to reach more than gigahertz count rates and will have a sensitivity of 0.1 eV. It means that the device is sensitive enough to register and spectrally characterize not only X-ray and UV, but also optical and infrared photons, as its major competitors, the superconducting and semiconducting single-photon detectors.

The paper presents design of a single photon lidar device suitable for space-borne applications. The device is composed of radiation tolerant components or components that have a radiation tolerant equivalent. The design is modular so that the same core can be utilized for several photon counting applications including laser altimeter, atmospheric lidar, laser transponder or one-way laser ranging receiver. The transmitter consists of a pulsed solid state diode pumped microchip Nd:YAG laser with second harmonic generator operating at 532 nm. Several laser versions may be employed { an externally triggered laser with repetition rate of up to 4 kHz or a free-running laser at 10 kHz. The receiver is equipped with a 1nm bandwidth optical band-pass interference filter and an active quenched SPAD detection module. A radiation tolerant K14 SPAD detector package developed at Czech Technical University with resolution of 20 ps rms is foreseen for space applications. Alternatively, commercial SPAD module lacking the radiation tolerance with higher detection efficiency can be used in air-borne or ground applications. The core module based on a radiation tolerant FPGA is reaching a timing precision of 30 ps. The overall ranging performance of the device is as good as 5 cm resolution for ranges of several kilometers. Besides the design and construction of the device, some performance test results will be presented.

Qudits, the d-dimensional extension of qubits, open new perspectives in several fields, from fundamental quantum mechanics to quantum cryptography. Although photon polarization is a privileged choice for qubits encoding, it is not suitable for the physical realization of qudits. However, in order to realize multidimensional quantum systems, other degrees of freedom of single photons such as path or orbital angular momentum are available. When two or more degrees of freedom are exploited simultaneously we refer to "hybrid encoding". It is possible for instance to encode information in a four dimensional (ququart) hybrid space spanned by polarization and a bidimensional orbital angular momentum subspace of a single photon. Here we present how high dimensional hybrid systems can be exploited to overcome a major limitation of quantum communication: the need of a shared reference frame. Indeed the joint action of polarization and orbital angular momentum of hybrid ququarts can be exploited to realize quantum communication without a shared reference frame. We experimentally showed that, by using a proper subspace of hybrid ququart space, it is possible to perform any quantum communication protocol and violate CHSH inequalities without any information about the reference frame orientation of the two parties (except the direction of propagation of the photons). Such feature could find application in satellite based communication schemes.

Recently, we experimentally proved that, even in presence of strong decoherence, the bi—partite continuous variable entangled state generated by a sub—threshold type—II optical parametric oscillator (OPO) never disentangles. It keeps breaking the limits for some of the entanglement criteria. In this contribution, we extend our previous analysis by focusing on the behaviour, under decohenrece, of two entanglement measures: Logarithmic Negativity (LN) and Entanglement of Formation (EOF).

With the recent progresses in quantum technologies, single photon sources have gained a primary relevance. Here we present a heralded single photon source characterized by an extremely low level of noise photons, realized by exploiting low-jitter electronics and detectors and fast custom-made electronics used to control an optical shutter (a LiNbO3 waveguide optical switch) at the output of the source. This single photon source showed a second-order autocorrelation function g(2)(0) = 0:005(7), and an Output Noise Factor (defined as the ratio of noise photons to total photons at the source output) of 0:25(1)%, among the best ever achieved.

It has recently been shown that multiphoton absorption in cavities containing an emitter and a nonlinear mirror or a two photon absorber can be used to create antibunched photons (i.e. nonclassical light). We investigate the generation of nonclassical photon states using nonlinear laser cavities where the excitation has been modified so that it consists of short current pulses. The light fields in the studied setups are ideally formed of superpositions of zero photon and one photon states. Our goal is to study and develop single photon sources which are needed e.g. in quantum information processing and quantum computing, and fundamental quantum optical experiments. We investigate the effect of exciting the photon emitter with time dependent current pulses to provide single-photon-on-demand sources. We maximize the probability of the single photon state by optimizing the strengths of linear losses, nonlinear absorption, photon emission, and the length of the current injection pulse into the amplifier. Furthermore, we analyze the output photon statistics and waiting times using Monte Carlo simulations. This type of a setup is technologically attractive since it potentially provides room temperature realization of photon antibunching with essentially standard optoelectronic materials and processing techniques.

We study the effects of continuous measurement of the field mode during the collapse and revival of spin Schr¨odinger cat states in the Tavis-Cummings model of N qubits (two-level quantum systems) coupled to a field mode. We show that a compromise between relatively weak and relatively strong continuous measurement will not completely destroy the collapse and revival dynamics while still providing enough signal-to-noise resolution to identify the signatures of the process in the measurement record. This type of measurement would in principle allow the verification of the occurrence of the collapse and revival of a spin Schr¨odinger cat state.

A quasi-transparent propagation phenomenon is presented for a pair of frequency-modulated laser pulses in an optically thick medium of cold atomic gas. The noninteracting, identical lambda-structured atoms are driven by two classical laser fields, which are frequency-chirped in the same way around the corresponding atomic transition frequencies, maintaining two-photon (Raman) resonance. It is shown by numerical analysis that after propagating over a relatively short distance (determined by the absorption length), the frequency-chirped pulse pair is affected by the atoms in such a way that instead of exciting the atoms (as it would happen in an optically dilute medium), they create a certain coherent superposition of the ground states (which can be varied by the parameters of the incoming fields), and they propagate in the remainder of the medium without significant further losses. This quasi-lossless propagation effect of the Raman-resonant frequency-chirped pulses, described above, is not only interesting in the point of view of the laser fields, but the on-demand creation of coherent superpositions among atomic states along the optically thick medium may also find applications in quantum optical experiments and quantum informatics.

In a recent experiment Shegai et al.1 have shown that a bimetallic particle dimer composed of gold and silver atoms may work as a directional frequency filter which scatters light of different frequencies in different directions. A phase difference between emitters required for the directional scattering of light was determined by the complex particle polarizabilities and therefore varies with the size, shape and material composition of the particles in accordance with their plasmon resonance characteristics. In this paper, we give a theoretical explanation of the experimental results in terms of interference between light fields emitted by nonidentical radiators.

According to the fundamental laws of quantum optics, noise is necessarily added to the system when one tries to clone or amplify a quantum state. However, it has recently been shown that the quantum noise related to the operation of a linear phase-insensitive amplifier can be avoided when the requirement of a deterministic operation is relaxed. Nondeterministic noiseless linear amplifiers are therefore realizable. Usually nondeterministic amplifiers rely on using single photon sources. We have, in contrast, recently proposed an amplification scheme in which no external energy is added to the signal, but the energy required to amplify the signal originates from the stochastic fluctuations in the field itself. Applying our amplification scheme, we examine the amplifier gain and the success rate as well as the properties of the output states after successful and failed amplification processes. We also optimize the setup to find the maximum success rates in terms of the reflectivities of the beam splitters used in the setup. In addition, we discuss the nonidealities related to the operation of our setup and the relation of our setup with the previous setups.

In this paper the electronic states and direct interband light absorption in the spherical quantum dot with modified Pöschl-Teller potential made of GaAs under influence of hydrostatic pressure and temperature effects are studied. For the regime of strong size quantization analytical expressions for the particle energy spectrum and dependencies of effective threshold frequencies of absorption on the geometrical sizes of quantum dot are obtained. The selection rules corresponding to different transitions between quantum levels are found. It has been demonstrated that the reduction of the half-width potential well leads to the “blue” shift of threshold frequencies, and the reduction of the depth of potential well leads to the ”red” shift of threshold frequency. Selection rules for quantum transitions have been obtained. It has been demonstrated that the reduction of the half-width potential well leads to the “blue” shift of threshold frequencies, and the reduction of the depth of potential well leads to the ”red” shift of threshold frequency. Selection rules for quantum transitions have been obtained.

I study the dimension-dependent (such as quantum well (QWs), quantum well wires (QWWs) and quantum dots (QDs)) transport in different nano-structures and the derivation of the expressions of many important transport coefficients are based on the temperature dependent electron concentration in nonlinear optical and optoelectronic nanostructure materials. The results for the corresponding emission and the electron statistics in the constituent materials have also been obtained. The thickness and the doping dependences of the field emission from all the aforementioned cases have been studied for the purpose of relative comparison, taking GaxAsyP1-y and AlAs lattice matched to InP quantum wire superlattice (QWSL) as an example.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews