It has been demonstrated that time-correlated single-photon counting (TCSPC) has the potential to be the preferred choice of detection for high resolution three-dimensional profiling in several challenging scenarios, for example through obscurants and complex multiple surface targets. Over the last few years, the TCSPC technique has been used in highly scattering underwater environments, demonstrating submillimeter resolution in turbid environments with over 8 attenuation lengths between transceiver and target due to its excellent surface to surface resolution and high optical sensitivity. This presentation will describe several transceiver systems for underwater imaging based on a range of silicon single photon avalanche diode (Si-SPAD) detectors, either fabricated in custom planar fabrication technology and in complementary metal-oxide semiconductor (CMOS) technology. Laboratory based experiments and field trials were conducted in several scattering underwater environments, demonstrating imaging up to 9.2 attenuation lengths and ranging up to 14 attenuation lengths when using average optical power up to 50 mW.
Time-correlated single-photon counting (TCSPC) has been established as the preferred choice of detection for high resolution depth profiling in challenging scenarios due to its excellent surface to surface resolution and high optical sensitivity. This presentation will describe several transceiver systems for underwater imaging based on a range of CMOS silicon single photon avalanche diode (Si-SPAD) detector arrays. Laboratory based experiments and field trials were conducted in several scattering underwater environments, demonstrating imaging up to 7.5 attenuation lengths and ranging up to 14 attenuation lengths when using average optical power up to 50 mW.
Picosecond resolution time-correlated mode has emerged as a candidate technology for a variety of depth imaging applications in the visible, near-infrared and short-wave infrared regions. This presentation will examine this approach in a range of challenging sensing scenarios including: imaging though highly scattering underwater conditions; free-space imaging through obscurants such as smoke or fog; and depth imaging of complex scenes containing multiple surfaces.
This paper introduces the field of metamaterials, details various optical uses of metasurfaces and demonstrates their suitability for imaging with single-photon avalanche diode (SPAD) detector arrays as an integrated optical component. A design for a metasurface-based color filter array (CFA) is presented, the fabrication methodology detailed, and a sample is integrated with a SPAD array. Examples of imaging applications using the integrated assembly are demonstrated, including passive and fluorescence imaging microscopy. The limitations of current metasurface color filtering techniques are highlighted and directions for future advances and applications discussed.
Time-correlated single-photon counting (TCSPC) has been established as the preferred choice of detection for high resolution depth profiling due to its excellent surface to surface resolution and high optical sensitivity. This presentation will describe an underwater transceiver system based on a planar CMOS silicon single photon avalanche diode (Si-SPAD) detector array, and interfaced with a graphics processing unit (GPU) for real time processing capabilities with video rates up to 25 Hz. Depth and intensity profiles of stationary and moving targets were acquired with the transceiver fully submerged in scattering water, equivalent up to 7.5 attenuation lengths.
Time-correlated single-photon counting (TCSPC) has been established as the preferred detection approach for high performance lidar and depth profiling due to its excellent surface to surface resolution and high optical sensitivity. This presentation will show the results of laboratory-based experiments obtained using different optical transceiver configurations. Particular attention will be given to underwater depth imaging using silicon single photon avalanche diode (Si-SPAD) detector arrays fabricated in complementary metal-oxide semiconductor (CMOS) and Si SPAD detector arrays built in custom fabrication technology.
KEYWORDS: Scattering, 3D acquisition, 3D image processing, Picosecond phenomena, Temporal resolution, Transceivers, Single photon detectors, LIDAR, Profiling, 3D metrology
Time-correlated single-photon counting (TCSPC) has emerged as a key detection technology for lidar and depth profiling in a number of emerging application areas due to its high optical sensitivity and excellent surface to surface resolution. We have applied this technique to measure three-dimensional scenes of stationary and moving targets in several underwater environments. The presentation will show the results of laboratory-based experiments obtained using several different optical transceiver configurations. Particular attention will be given to underwater depth imaging using silicon single photon avalanche diode (Si-SPAD) arrays with in-pixel picosecond timing electronics.
This paper presents the Time-Correlated Single-Photon Counting (TCSPC) technique applied to underwater environments in order to reconstruct three-dimensional scenes. Two different transceiver systems approaches are described. The first transceiver comprised a single-pixel monostatic scanning unit, which used a fiber-coupled silicon single-photon avalanche diode (SPAD) detector, and a fiber-coupled supercontinuum laser source used in conjunction with an acousto-optic tunable filter (AOTF) for wavelength selection. The experiments were performed using the supercontinuum pulsed laser source operating at a repetition rate of 19.5 MHz, fiber coupled to the AOTF in order to select one operational wavelength, tuned for best performance for the level of scattering of the particular underwater environment. Laboratory-based experiments were performed using average optical powers of less than 1 mW and depth profiles were acquired at up to 8 attenuation lengths between the transceiver and target. The second transceiver system was based on a complementary metal-oxide semiconductor (CMOS) SPAD detector array in a bistatic configuration. It comprised an array of 192 × 128 SPAD detectors, with each detector having an integrated time to digital converter, and a laser diode operating at a wavelength of 670 nm, a repetition rate of 40 MHz, and average optical power up to 9 mW. The experiments demonstrated the recovery of intensity and depth profiles associated with moving targets at up to 4 attenuation lengths. Using data from both systems, various image processing techniques were investigated to reconstruct target depth and intensity profiles in highly scattering underwater environments.
Light detection and ranging (Lidar) systems based on single-photon detection can be used to obtain range and reflectivity information from 3D scenes with high range resolution. However, reconstructing the 3D surfaces from the raw single-photon waveforms is challenging, in particular when a limited number of photons is detected and when the ratio of spurious background detection events is large. This paper reviews a set of fast detection algorithms, which can be used to assess the presence of objects/surfaces in each waveform, allowing only the histograms where the imaged surfaces are present to be further processed. The original method we recently proposed is extended here using a multiscale approach to further reduce the computational complexity of the detection process. The proposed methods are compared to state-of-the-art 3D reconstruction methods using synthetic and real single-photon data and the results illustrate their benefits for fast and robust target detection.
Fibre-bundle endomicroscopy is an emerging medical imaging tool. Inter-core coupling within coherent fibre bundles limits the technology's imaging capabilities. We introduce a novel approach for quantifying and modelling cross coupling, optimising image reconstruction.
This paper investigates a new computational method for reconstruction and analysis of complex 3D scenes. In the presence of targets, Lidar waveforms usually consist of a series of peaks, whose positions and amplitudes depend on the distances of the targets and on their reflectivities, respectively. Inferring the number of surfaces or peaks, as well as their geometric and colorimetric properties becomes extremely difficult when the number of detected photons is low (e.g., short acquisition time) and the ambient illumination is high. In this work, we adopt a Bayesian approach to account for the intrinsic spatial organization of natural scenes and regularise the 3D reconstruction problem. The proposed model is combined with an efficient Markov chain Monte Carlo (MCMC) method to reconstruct the 3D scene, while providing measures of uncertainty (e.g., about target range and reflectivity) which can be used for subsequent decision making processes, such as object detection and recognition. Despite being an MCMC method, the proposed approach presents a competitive computational cost when compared to state-of-the-art optimization-based reconstruction methods, while being more robust to the lack of detected photons (empty or non-observed pixels). Moreover, it includes a multi-scale strategy which allows a quick recovery of coarse approximations of the 3D structures, while is often sufficient for object detection/recognition. We assess the performance of our approach via extensive experiments conducted with real, long-range (hundreds of meters) single-photon Lidar data. The results clearly demonstrate its benefits to infer complex scene content from extremely sparse photon counts.
A scanning depth imaging system is used for the investigation of three-dimensional image reconstruction and classification of targets in underwater environments. The system uses the Time-Correlated Single-Photon Counting (TCSPC) technique to measure single-photon time-of-flight. In this paper, we use both single and multiple wavelengths to interrogate underwater targets. This presentation will show laboratory measurements on several target scenarios, including targets in clutter. We demonstrate high resolution depth and intensity image reconstruction in highly scattering underwater scenarios, and show image reconstruction at up to nine attenuation lengths between transceiver and target.
The system comprised a scanning transceiver unit, fiber coupled to a silicon single-photon avalanche diode (Si SPAD) and a supercontinuum laser system operating at the repetition rate of 19.5 MHz. An acousto-optic tunable filter (AOTF) is used to select an individual operational wavelength in the range 500 nm to 725 nm. The measurements used a range of system configurations, including both single wavelength and multiple wavelength measurements. Generally, the measurements used sub-milliwatt average optical power levels.
Bespoke algorithms were developed to identify man-made objects hidden by marine vegetation in the scanned scene. Advanced statistical image processing methods were used to improve target discrimination and to reconstruct the target under different conditions, including reduced number of wavelengths and number of pixels, and reduced acquisition time. Particular attention will be given to the photon starved regime, which will be typical of data acquired at long distances in open ocean waters or in highly scattering environments.
Advances in LIDAR-based methods have enabled the detection and reconstruction of images of static objects hidden from the direct line-of-sight [1, 2]. One of the drawbacks to the technology used in these demonstrations is the requirement for long acquisition times. More recently, Gariepy et al. have shown that it is possible to detect and track a moving hidden object, albeit with no information of the object’s form [3]. Applications of this include, but are not limited to, search and rescue, and hazard detection.
We present a real-time tracking system that enables the detection of moving objects that are outside the direct line-of-sight. Our active imaging system is a single-pixel variant of the technology reported by Gariepy et al. It replaces the single-photon avalanche diode (SPAD) camera of 1024 pixels with a number of SPAD detectors to detect light back-scattered from the hidden object. The flexibility of the single-pixel detectors provides an increased field of view, allowing us to detect and simultaneously track with better precision with respect to a SPAD array. The use of single-pixel detectors also has the advantage of a high detection efficiency.
We perform two proof-of-concept experiments using three pixels and a single pulsed laser to interrogate a “room” for a hidden object. In the first experiment, we demonstrate that we can accurately locate the position of a hidden object. In the second experiment, we use the same system and demonstrate that we can accurately track the motion of a hidden object in real time.
The “room” is a purpose-built box measuring 102×102×77 cm. Optical access is provided by a 28×12 cm window. The target object is a 15×15 cm textured viewing screen that we move along a designated ground track outside the line-of- sight of our system. In our experiments, we send a train of light pulses through the window to the back of the room. The pulses scatter off the wall as a spherical wavefront that propagates in all directions. Some of this light reaches our hidden object and is scattered back again towards the rear wall where we image our three SPAD pixels. The SPAD detectors are capable of picosecond temporal resolutions. Our time-correlated single-photon counting system measures the photon arrival times (64 ps resolution) for the signal returning to each detector. A histogram is built up in one second of acquisition time over 80 million pulses. We use this temporal information in our target position retrieval of the hidden object.
We place the object at 11 positions in turn in a seven minute experiment, and localise its position. We then perform real-time tracking and move the object around the hidden scene for approximately one minute, processing the target position retrieval every 1.5 s.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.