Quantum-inspired computational imaging

Computational imaging combines measurement and computational methods with the aim of forming images even when the measurement conditions are weak, few in number, or highly indirect. The recent surge in quantum-inspired imaging sensors, together with a new wave of algorithms allowing on-chip, scalable and robust data processing, has induced an increase of activity with notable results in the domain of low-light flux imaging and sensing. We provide an overview of the major challenges encountered in low-illumination (e.g., ultrafast) imaging and how these problems have recently been addressed for imaging applications in extreme conditions. These methods provide examples of the future imaging solutions to be developed, for which the best results are expected to arise from an efficient codesign of the sensors and data analysis tools.Y.A. acknowledges support from the UK Royal Academy of Engineering under the Research Fellowship Scheme (RF201617/16/31). S.McL. acknowledges financial support from the UK Engineering and Physical Sciences Research Council (grant EP/J015180/1). V.G. acknowledges support from the U.S. Defense Advanced Research Projects Agency (DARPA) InPho program through U.S. Army Research Office award W911NF-10-1-0404, the U.S. DARPA REVEAL program through contract HR0011-16-C-0030, and U.S. National Science Foundation through grants 1161413 and 1422034. A.H. acknowledges support from U.S. Army Research Office award W911NF-15-1-0479, U.S. Department of the Air Force grant FA8650-15-D-1845, and U.S. Department of Energy National Nuclear Security Administration grant DE-NA0002534. D.F. acknowledges financial support from the UK Engineering and Physical Sciences Research Council (grants EP/M006514/1 and EP/M01326X/1). (RF201617/16/31 - UK Royal Academy of Engineering; EP/J015180/1 - UK Engineering and Physical Sciences Research Council; EP/M006514/1 - UK Engineering and Physical Sciences Research Council; EP/M01326X/1 - UK Engineering and Physical Sciences Research Council; W911NF-10-1-0404 - U.S. Defense Advanced Research Projects Agency (DARPA) InPho program through U.S. Army Research Office; HR0011-16-C-0030 - U.S. DARPA REVEAL program; 1161413 - U.S. National Science Foundation; 1422034 - U.S. National Science Foundation; W911NF-15-1-0479 - U.S. Army Research Office; FA8650-15-D-1845 - U.S. Department of the Air Force; DE-NA0002534 - U.S. Department of Energy National Nuclear Security Administration)Accepted manuscrip

Single-photon detection techniques for underwater imaging

This Thesis investigates the potential of a single-photon depth profiling system for imaging in highly scattering underwater environments. This scanning system measured depth using the time-of-flight and the time-correlated single-photon counting (TCSPC) technique. The system comprised a pulsed laser source, a monostatic scanning transceiver, with a silicon single-photon avalanche diode (SPAD) used for detection of the returned optical signal. Spectral transmittance measurements were performed on a number of different water samples in order to characterize the water types used in the experiments. This identified an optimum operational wavelength for each environment selected, which was in the wavelength region of 525 - 690 nm. Then, depth profiles measurements were performed in different scattering conditions, demonstrating high-resolution image re-construction for targets placed at stand-off distances up to nine attenuation lengths, using average optical power in the sub-milliwatt range. Depth and spatial resolution were investigated in several environments, demonstrating a depth resolution in the range of 500 μm to a few millimetres depending on the attenuation level of the medium. The angular resolution of the system was approximately 60 μrad in water with different levels of attenuation, illustrating that the narrow field of view helped preserve spatial resolution in the presence of high levels of forward scattering. Bespoke algorithms were developed for image reconstruction in order to recover depth, intensity and reflectivity information, and to investigate shorter acquisition times, illustrating the practicality of the approach for rapid frame rates. In addition, advanced signal processing approaches were used to investigate the potential of multispectral single-photon depth imaging in target discrimination and recognition, in free-space and underwater environments. Finally, a LiDAR model was developed and validated using experimental data. The model was used to estimate the performance of the system under a variety of scattering conditions and system parameters