This PDF file contains the front matter associated with SPIE Proceedings Volume 9114, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

There is a growing interest in developing systems employing large arrays of SNSPDs. To make such instruments practical, it is desirable to perform signal processing before transporting the detector outputs to room temperature. We present a cryogenic eight-channel pixel combiner circuit designed to amplify, digitize, edge detect, and combine the output signals of an array of eight SNSPDs. The circuit has been fabricated and measurement results agree well with expectation. The paper will conclude with a summary of ongoing work and future directions.

We gate a InGaAs/InP single-photon avalanche diode with a narrow periodic gate obtained by summing a 1.25 GHz sinusoid with its second and third harmonic. The temporal full-width at half maximum (FWHM) of the gate is kept below 200 ps by adjusting relative weight of the harmonic components. Measurements of detection efficiency and afterpulse probability as the gate pulse duration is reduced show that it is possible to reach the same detection efficiency obtainable with wider gates with the advantage of significantly reducing afterpulse probability.

How many photons does it take to form an image? Although a single photon can be spatially encoded to carry large amounts of information, real images are not fully orthogonal to each other and hence, realistically, require many detected photons to distinguish between them. Even if one has access to a pixelated imaging detector with high quantum efficiency, the fidelity of a recorded, or inferred, image depends critically upon the dark counts from the detector. Here we present imaging using heralded single-photons and a time-gated intensified camera to all but eliminate noise-events, and record images of a standard test-target. The images are formed from only a few thousand photons and are therefore subject to a noise inherent within the Poissonian distribution of single-photon events. We apply techniques of compressive sensing and image regularization to obtain good estimates of the object, obtained for ultra-low optical exposures.

We present our latest results concerning CMOS Single-Photon Avalanche Diode (SPAD) arrays for high-throughput parallel single-photon counting. We exploited a high-voltage 0.35 μm CMOS technology in order to develop low-noise CMOS SPADs. The Dark Count Rate is 30 cps at room temperature for 30 μm devices, increases to 2 kcps for 100 μm SPADs and just to 100 kcps for 500 μm ones. Afterpulsing is less than 1% for hold-off time longer than 50 ns, thus allowing to reach high count rates. Photon Detection Efficiency is > 50% at 420 nm, > 40% below 500 nm and is still 5% at 850 nm. Timing jitter is less than 100 ps (FWHM) in SPADs with active area diameter up to 50 μm.
We developed CMOS SPAD imagers with 150 μm pixel pitch and 30 μm SPADs. A 64×32 SPAD array is based on pixels including three 9-bit counters for smart phase-resolved photon counting up to 100 kfps. A 32x32 SPAD array includes 1024 10-bit Time-to-Digital Converters (TDC) with 300 ps resolution and 450 ps single-shot precision, for 3D ranging and FLIM. We developed also linear arrays with up to 60 pixels (with 100 μm SPAD, 150 μm pitch and in-pixel 250 ps TDC) for time-resolved parallel spectroscopy with high fill factor.

The ability to count single photons is necessary to achieve many important science objectives in the near future. This paper presents the lab-tested performance of a photon-counting array-based Geiger-mode avalanche photodiode (GMAPD) device in the context of low-light-level imaging. Testing results include dark count rate, afterpulsing probability, intra-pixel sensitivity, and photon detection efficiency, and the effects of radiation damage on detector performance. The GM-APD detector is compared to the state-of-the-art performance of other established detectors using Signal-to-noise ratio as the overall evaluation metric.

The operation of avalanche photodiodes in Geiger mode by arming these detectors above their breakdown voltage provides high-performance single photon detection in a robust solid-state device platform. Moreover, these devices are ideally suited for integration into large format focal plane arrays enabling single photon imaging. We describe the design and performance of short-wave infrared 3D imaging cameras with focal plane arrays (FPAs) based on Geigermode avalanche photodiodes (GmAPDs) with single photon sensitivity for laser radar imaging applications. The FPA pixels incorporate InP/InGaAs(P) GmAPDs for the detection of single photons with high efficiency and low dark count rates. We present results and attributes of fully integrated camera sub-systems with 32 × 32 and 128 × 32 formats, which have 100 μm pitch and 50 μm pitch, respectively. We also address the sensitivity of the fundamental GmAPD detectors to radiation exposure, including recent results that correlate detector active region volume to sustainable radiation tolerance levels.

Recent developments in 3D imaging lidar are presented. Long range 3D imaging using photon counting is now a possibility, offering a low-cost approach to integrated remote sensing with step changing advantages in size, weight and power compared to conventional analogue active imaging technology. We report results using a Geiger-mode array for time-of-flight, single photon counting lidar for depth profiling and determination of the shape and size of tree canopies and distributed surface reflections at a range of 9km, with 4μJ pulses with a frame rate of 100kHz using a low-cost fibre laser operating at a wavelength of λ=1.5 μm. The range resolution is less than 4cm providing very high depth resolution for target identification. This specification opens up several additional functionalities for advanced lidar, for example: absolute rangefinding and depth profiling for long range identification, optical communications, turbulence sensing and time-of-flight spectroscopy. Future concepts for 3D time-of-flight polarimetric and multispectral imaging lidar, with optical communications in a single integrated system are also proposed.

Single photon sensitive 3D imaging lidars have multiple advantages relative to conventional multiphoton lidars. They are the most efficient 3D imagers possible since each range measurement requires only one detected photon as opposed to hundreds or thousands in conventional laser pulse time of flight (TOF) or waveform altimeters. Their high efficiency enables orders of magnitude more imaging capability (e.g. higher spatial resolution, larger swaths and greater areal coverage). In our Single Photon Lidars (SPLs), single photon sensitivity is combined with nanosecond recovery times and a multistop timing capability, This enables our lidars to penetrate semiporous obscurations such as vegetation, ground fog, thin clouds, etc. Furthermore, the 532 nm operating wavelength is highly transmissive in water, thereby permitting shallow water bathymetry and 3D underwater imaging. Publisher’s Note: This paper, originally published on 5/28/14, was replaced with a corrected/revised version on 8/7/14. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.

This paper reports the performance of a long range 3D imaging system operating at a wavelength of 1550nm incorporating a Geiger mode 32x32 array InGaAs/InP camera. A cross-correlation technique were used to mitigate range aliasing and therefore enable the measurement of the absolute range to single or multiple surfaces within the instantaneous field of view of each pixel in the 2D array. The system uses a fibre amplified laser source operating at an average pulse repetition rate of 125kHz with pulse energies of 2.4μJ per pulse. Measurements of the absolute range to remote manmade Lambertian surfaces and foliage at ranges up to 10km with range accuracy of better than 4cm are reported. The simultaneous imaging and measurement of the absolute range of two remote manmade Lambertian surfaces separated by >1km is also presented.

A multi-element HgCdTe electron initiated avalanche photodiode (e-APD) array has been developed for space lidar. The detector array was fabricated with 4.3μm cutoff HgCdTe with a spectral response from 0.4 to 4.3 μm. We have demonstrated a 4x4 e-APD array with 80 μm square elements followed by a custom cryogenic CMOS read-out integrated circuit (ROIC). The device operates at 77K inside a small closed-cycle cooler-Dewar with the support electronics integrated in a field programmable gate array. Measurements showed a unity gain quantum efficiency of about 90% at 1.5-1.6 μm wavelength. The bulk dark current of the HgCdTe e-APD at 77K was less than 50,000 input referred electrons/s at 12 V APD bias where the APD gain was 620 and the measured noise equivalent power (NEP) was 0.4 fW/Hz^1/2. The electrical bandwidth of the device was about 6 MHz, mostly limited by the ROIC, but sufficient for the lidar application. Although the devices were designed for low bandwidth pulse detections, the high gain and low dark current enabled them to be used for single photon detections. Because the APD was biased below the break-down voltage, the output is linear to the input signal and there were no nonlinear effect such as dead-time and afterpulsing, and no need for gated operation. A new series of HgCdTe e-APDs have also been developed with a much wider bandwidth ROIC and higher APD gain, which is expected to give a much better performance in single photon detections.

The Silicon Photomultiplier (SiPM) represents a new step in the development of the modern silicon based detection structures in the area of low photon flux detection. The high intrinsic gain obtained in the detecting structure is responsible of the digital signal nature of the SiPM at the elementary cell level. In this paper the study and development of SiPM detection structures is shown, for the specific application to the read out of scintillation light in high energy physics and Nuclear Medicine.

Free-running single photon detectors at telecom wavelengths are attractive for many tasks in quantum optics. However, until recently, the convenient and compact InGaAs/InP avalanche photodiodes did not operate with satisfactory performance in this regime due to high dark count rates and afterpulsing effects. Recent development of negative feedback avalanche diodes (NFADs) enabled very fast passive quenching of the avalanche current, effectively reducing the afterpulse probability and subsequently allowing free-running operation. Here, we present analysis of NFAD operation at low temperatures, down to 163 K, which reveals a significant reduction of the dark count rate. We succeeded in developing a compact single photon detection system with a dark count rate of ~1 cps at 10% detection efficiency. To ensure that the NFAD is in a well-defined initial condition during the characterization of the detection efficiency and afterpulsing, we use a recently developed FPGA based test procedure suitable for free-running detectors. To demonstrate the performance of the detector in a real-world application we integrate it into a 1.25 GHz clocked quantum key distribution system. An optimization of the detector temperature allowed secret key distribution in the presence of more than 30 dB of loss in the quantum channel.

This paper discusses the system engineering challenges involved with the transmission of optically encoded data through water. The scenarios of data transmission from an airborne platform to a submerged platform and data transmission from a submerged platform to another submerged platform will be discussed. A photon-counting experimental system was constructed to investigate the transmission of optical data through a 1m long tank of water. This test system incorporated a laser diode operating at a wavelength of 450nm and an optical receiver containing a shallow junction, silicon single photon avalanche diode. The optical data was transmitted through the tank containing ~100 litres of water at transmission rates equivalent to 40Mb/s. The attenuation of the optical path was increased by increasing the level of scattering of the photons using Maalox. The effects on the temporal distribution of photons in the optical pulse from adding Maalox are also discussed. The synchronisation of the transmitter and receiver clocks was investigated using reference headers appended to the encoded message signal which the receiver used to correct for timing drift. The performance of this experimental system and experimental results are discussed.

Advances in ultraviolet (UV) source, detector, and solar-blind filtering technologies have recently spurred significant research interest in non-line-of-sight (NLOS) UV communications. Although this research has primarily focused on short-range applications, the achievable range of a NLOS UV system can be extended (e.g., up to a few kilometers) with the use of a pulsed UV laser transmitter. However, the short-duration high-intensity pulses of such a laser have the potential to overwhelm the response time of photomultiplier detectors, which are often employed by a receiver to implement high-sensitivity photon-counting detection. In particular, after the detection of a photon, there exists a period of time, called dead time, during which the detector is unable to detect subsequently impinging photons, resulting in missed photon detections and, hence, altered received signal statistics relative to an ideal photon counter. In this paper, we examine the effect of receiver dead time on a NLOS UV system. We extend an existing UV NLOS channel model to account for nonzero dead time at the receiver and then use this extended model to examine the significance of dead-time effects for various representative system configurations. The results suggest the importance of accounting for dead time when designing practical UV communication systems.