Ultrafast Imaging using Arrayed Quantum Detection Technologies (ULTRA-IMAGE)

Vision is arguably the most important of our senses and our most direct channel of interaction with the surrounding world. It is no surprise therefore that so much of the technology that affects our everyday lives relies on light in one form or the other. The continuous strive to improve our light sources, ranging from lasers for research purposed to ambient lighting technologies is paralleled by a continuous increase in efforts to improve our imaging capabilities, ranging from artificial vision implants to hyperspectral imaging.
An exciting and emerging imaging technology relies on the ability to detect remarkably low light signals, i.e. even single photons. This same technology, based for example of Single-Photon-Avalanche-Detectors (SPADs) comes hand in hand with another rather unexpected and also remarkable feature: incredibly high temporal resolution and the ability to distinguish events that are separated in time by picoseconds or less. This temporal resolution is obtained by operating the SPAD in so-called Time-Correlated-Single-Photon-Counting (TCSPC) mode, where the single photons are detected in coincidence with an external trigger and then electronically stored with a precise time-tag that, after accumulating over many events, allows to precisely identify the photon arrival time.
These technologies are now relatively well established and are routinely employed in research activities, mainly associated to quantum optics measurements and time of flight measurements. However, these detectors are all single pixel detectors and thus do not allow to directly reconstruct an image in much the same way that a digital camera with a single pixel will not create an image. Workaround solutions have been adopted; for example a laser may be scanned across an object and the single pixel records intensity levels for each position of the laser beam.
However, our obsession with the pixel-count in our latest digital camera clearly explains the paradigm shift in going from a single pixel detector to a multi-pixel detector and eventually to high resolution imaging.
ULTRA-IMAGE aims at demonstrating a series of applications of very novel SPAD technology: for the first time these detectors are available in imaging arrays. This is an emerging technology that will represent the next revolution in imaging and we will have first hand access to each technological breakthrough in SPAD array design, as they occur over the next few years.
We are currently employing 32x32 SPAD arrays and will be using the first ever (at the time of writing) 320x240 pixel array, which is able to deliver the first high quality spatially resolved images. The remarkable aspect of these detectors is that they still retain their picosecond temporal resolution therefore enabling a series of game-changing and remarkable technological applications that are not even conceivable with traditional cameras.
As examples of the potential of this new imaging technology, we will utilise our SPAD cameras to visualise the propagation of light and perform time-of-flight detection of remote objects in harsh environments (the FEMTO-camera), to enable of the real-time tracking of objects hidden from view (the CORNER-camera), and to perform the first quantum measurements using low-rep rate, high-power lasers (the QUANTUM-camera). The solutions we will develop are enabled by four key features: first, the single-photon sensitivity of silicon detectors; second, the spatial resolution provided by the arrayed nature of the detectors; third, the precise picosecond and femtosecond timing resolution; and fourth, the ultra low-noise performance of gated detection.

Imaging technologies are at the forefront of a wide range of applications in numerous fields. Our most obvious and direct interaction with the surrounding is world is through vision; hence, advances in imaging technologies are possibly the most valuable in terms of broadband impact. Our goal is to develop and demonstrate imaging technologies with significantly better temporal resolution and better sensitivity than the current state of the art. Our program builds upon the UK's existing worldwide-recognised excellence in the areas of SPAD detector development (including technologies developed at ST Microelectronics), time-of-flight depth imaging, and low-light level imaging. This will put the UK at the forefront in terms of challenging and exciting engineering problems, such as imaging around corners, through turbid, scattering media, and in situations where low-noise single-photon sensitivity and arrayed detectors (a combination that is a unique aspect of CMOS SPADs) is required. SPAD arrays are already on the verge of commercial impact in some areas (notably positron emission tomography - PET) and we will help consolidate the UK's leadership position in the field by establishing strong foundations in other fields, for example in security and defence. Letters of support from DSTL and SELEX illustrate the potential impact of this work in this field.
Our work will prove the potential for emerging SPAD technology thus lending support for the case for future commercialisation of these arrays. Our work will also push the limits broaden the vision of what can be done with modern imaging technologies and thus potentially seed future developments.
Finally, the translational nature of this proposal means that it is positioned in both quantum information processing and general photonics. Quantum Information Processing is highlighted as a New and Emerging Area in EPSRC's ICT Theme. Quantum Optics and Information is also a growth area highlighted in EPSRC's Physical Sciences Theme and thus translates some work previously considered within EPSRC's Physical Sciences Theme to the ICT Theme where we expect improved interaction with the image processing and computer vision communities.