Each photon can be used to start a tiny CMOS stopwatch, providing time-resolved data for use in fluorescence lifetime microscopy and time-of-flight detection applications.
Photons having different colours can be spread over a region in space by optical diffraction gratings, yielding the wavelength spectrum of the light. Once directed onto a SPAD array, the relative time of arrival of each photon of any given colour can then be measured. The RAI and RAII light sensors used in the Proteus project can be thought of therefore as arrays of wavelength-sensitive pixel-stopwatches.
Repeated triggering of these pixel-stopwatches enables the construction of time-resolved photon statistics at each wavelength. These statistics – in the form of wavelength-time histograms – can be calculated on-chip, leading to a tremendous advantage in terms of data compression and data acquisition rates.
This ‘system-on-a-chip’ design enables the rapid construction and analysis of time-resolved spectra arising from fluorescence, Raman scattering and other light scattering phenomena. The long-term objective is to combine the sensors with a confocal microscopy scanning system and lung endoscope capable of building time-resolved microscopic imagery of cells.