36 research outputs found
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
3D LIDAR imaging using Ge-on-Si single–photon avalanche diode detectors
We present a scanning light detection and ranging (LIDAR) system incorporating an individual Ge-on-Si single-photon avalanche diode (SPAD) detector for depth and intensity imaging in the short-wavelength infrared region. The time-correlated single-photon counting technique was used to determine the return photon time-of-flight for target depth information. In laboratory demonstrations, depth and intensity reconstructions were made of targets at short range, using advanced image processing algorithms tailored for the analysis of single–photon time-of-flight data. These laboratory measurements were used to predict the performance of the single-photon LIDAR system at longer ranges, providing estimations that sub-milliwatt average power levels would be required for kilometer range depth measurements
Ge-on-Si Single Photon Avalanche Diode Detectors for LIDAR in the Short Wave Infrared
Ge-on-Si single photon avalanche diodes are used to demonstrate LIDAR in laboratory conditions. Modelling demonstrates that eye-safe kilometre range-finding is achievable at 1450nm wavelength. Afterpulsing is found to be considerably lower than commercial InGaAs/InP devices
Custom-Technology Single-Photon Avalanche Diode Linear Detector Array for Underwater Depth Imaging
We present an optical depth imaging system suitable for highly scattering underwater environments. The system used the time-correlated single-photon counting (TCSPC) technique and the time-of-flight approach to obtain depth profiles. The single-photon detection was provided by a linear array of single-photon avalanche diode (SPAD) detectors fabricated in a customized silicon fabrication technology for optimized efficiency, dark count rate, and jitter performance. The bi-static transceiver comprised a pulsed laser diode source with central wavelength 670 nm, a linear array of 16 × 1 Si-SPAD detectors, with a dedicated TCSPC acquisition module. Cylindrical lenses were used to collect the light scattered by the target and image it onto the sensor. These laboratory-based experiments demonstrated single-photon depth imaging at a range of 1.65 m in highly scattering conditions, equivalent up to 8.3 attenuation lengths between the system and the target, using average optical powers of up to 15 mW. The depth and spatial resolution of this sensor were investigated in different scattering conditions