Ryan E. Warburton

Design and performance of an InGaAs-InP single-photon avalanche diode detector

This paper describes the design, fabrication, and performance of planar-geometry InGaAs-InP devices which were specifically developed for single-photon detection at a wavelength of 1550 nm. General performance issues such as dark count rate, single-photon detection efficiency, afterpulsing, and jitter are described.

Imaging high-dimensional spatial entanglement with a camera

The light produced by parametric down-conversion shows strong spatial entanglement that leads to violations of EPR criteria for separability. Historically, such studies have been performed by scanning a single-element, single-photon detector across a detection plane. Here we show that modern electron-multiplying charge-coupled device cameras can measure correlations in both position and momentum across a multi-pixel field of view. This capability allows us to observe entanglement of around 2,500 spatial states and demonstrate Einstein–Podolsky–Rosen type correlations by more than two orders of magnitude. More generally, our work shows that cameras can lead to important new capabilities in quantum optics and quantum information science.

Subcentimeter depth resolution using a single-photon counting time-of-flight laser ranging system at 1550 nm wavelength

We demonstrate subcentimeter depth profiling at a stand off distance of 330 m using a time-of-flight approach based on time-correlated single-photon counting. For the first time to our knowledge, the photon-counting time-of-flight technique was demonstrated at a wavelength of 1550 nm using a superconducting nanowire single-photon detector. The performance achieved suggests that a system using superconducting detectors has the potential for low-light-level and eye-safe operation. The systems instrumental response was 70 ps full width at half-maximum, which meant that 1 cm surface-to-surface resolution could be achieved by locating the centroids of each return signal. A depth resolution of 4 mm was achieved by employing an optimized signal-processing algorithm based on a reversible jump Markov chain Monte Carlo method.

Free-running, room temperature operation of an InGaAs/InP single-photon avalanche diode

Passive quenching operation of an InGaAs/InP single-photon avalanche diode detector at low excess bias is reported in terms of the key figures of merit including afterpulsing analysis. The reduced charge required to measure individual photon events meant that room temperature single-photon counting at 1550 nm wavelength was achievable without the requirement of electrical gating and with negligible afterpulsing effects evident.

Ge-on-Si Single-Photon Avalanche Diode Detectors: Design, Modeling, Fabrication, and Characterization at Wavelengths 1310 and 1550 nm

The design, modeling, fabrication, and characterization of single-photon avalanche diode detectors with an epitaxial Ge absorption region grown directly on Si are presented. At 100 K, a single-photon detection efficiency of 4% at 1310 nm wavelength was measured with a dark count rate of ~ 6 megacounts/s, resulting in the lowest reported noise-equivalent power for a Ge-on-Si single-photon avalanche diode detector (1×10-14 WHz-1/2). The first report of 1550 nm wavelength detection efficiency measurements with such a device is presented. A jitter of 300 ps was measured, and preliminary tests on after-pulsing showed only a small increase (a factor of 2) in the normalized dark count rate when the gating frequency was increased from 1 kHz to 1 MHz. These initial results suggest that optimized devices integrated on Si substrates could potentially provide performance comparable to or better than that of many commercially available discrete technologies.

SINGLE PHOTON SOURCES BASED UPON SINGLE QUANTUM DOTS IN SEMICONDUCTOR MICROCAVITY PILLARS

Semiconductor microcavity pillars with both circular and elliptical cross-section containing semiconductor quantum dots are shown to be good candidates for efficient single photon sources. Pillars with small diameters are shown to have exceptionally high quality factors and the reduction in the measured quality factor as the pillar diameter is reduced is shown to agree well with finite difference time domain simulation. These pillars exhibit a Purcell enhancement of the quantum dot emission when the dots are on-resonance with the cavity mode and strong photon antibunching. The use of the polarized modes of an elliptical micropillar allows the polarization of the emitted single photons to be selected.

Underwater depth imaging using time-correlated single photon counting

We investigate the potential of a depth imaging system for underwater environments. This system is based on the timeof- flight approach and the time correlated single-photon counting (TCSPC) technique. We report laboratory-based measurements and explore the potential of achieving sub-centimeter xyz resolution at 10’s meters stand-off distances. Initial laboratory-based experiments demonstrate depth imaging performed over distances of up to 1.8 meters and under a variety of scattering conditions. The system comprised a monostatic transceiver unit, a fiber-coupled supercontinuum laser with a wavelength tunable acousto-optic filter, and a fiber-coupled individual silicon single-photon avalanche diode (SPAD). The scanning in xy was performed using a pair of galvonometer mirrors directing both illumination and scattered returns via a coaxial optical configuration. Target objects were placed in a 110 liter capacity tank and depth images were acquired through approximately 1.7 meters of water containing different concentrations of scattering agent. Depth images were acquired in clear and highly scattering water using per-pixel acquisition times in the range 0.5-100 ms at average optical powers in the range 0.8 nW to 120 μW. Based on the laboratory measurements, estimations of potential performance, including maximum range possible, were performed with a model based on the LIDAR equation. These predictions will be presented for different levels of scattering agent concentration, optical powers, wavelengths and comparisons made with naturally occurring environments. The experimental and theoretical results indicate that the TCSPC technique has potential for highresolution underwater depth profile measurements.

Enhanced performance photon-counting time-of-flight sensor

We describe improvements to a time-of-flight sensor utilising the time-correlated single-photon counting technique employing a commercially-available silicon-based photon-counting module. By making modifications to the single-photon detection circuitry and the data analysis techniques, we experimentally demonstrate improved resolution between multiple scattering surfaces with a minimum resolvable separation of 1.7 cm at ranges in excess of several hundred metres.

Non-line-of-sight tracking of people at long range

A remote-sensing system that can determine the position of hidden objects has applications in many critical real-life scenarios, such as search and rescue missions and safe autonomous driving. Previous work has shown the ability to range and image objects hidden from the direct line of sight, employing advanced optical imaging technologies aimed at small objects at short range. In this work we demonstrate a long-range tracking system based on single laser illumination and single-pixel single-photon detection. This enables us to track one or more people hidden from view at a stand-off distance of over 50 m. These results pave the way towards next generation LiDAR systems that will reconstruct not only the direct-view scene but also the main elements hidden behind walls or corners.

Observation of laser pulse propagation in optical fibers with a SPAD camera

Recording processes and events that occur on sub-nanosecond timescales poses a difficult challenge. Conventional ultrafast imaging techniques often rely on long data collection times, which can be due to limited device sensitivity and/or the requirement of scanning the detection system to form an image. In this work, we use a single-photon avalanche detector array camera with pico-second timing accuracy to detect photons scattered by the cladding in optical fibers. We use this method to film supercontinuum generation and track a GHz pulse train in optical fibers. We also show how the limited spatial resolution of the array can be improved with computational imaging. The single-photon sensitivity of the camera and the absence of scanning the detection system results in short total acquisition times, as low as a few seconds depending on light levels. Our results allow us to calculate the group index of different wavelength bands within the supercontinuum generation process. This technology can be applied to a range of applications, e.g., the characterization of ultrafast processes, time-resolved fluorescence imaging, three-dimensional depth imaging, and tracking hidden objects around a corner.