Observation of laser pulse propagation in optical fibers with a SPAD camera

Abstract

Recording processes and events that occur on sub-nanosecond timescales poses a difficult challenge. Conventional ultrafast imaging techniques often rely on long data collection times, which can be due to limited device sensitivity and/or the requirement of scanning the detection system to form an image. In this work, we use a single-photon avalanche detector array camera with pico-second timing accuracy to detect photons scattered by the cladding in optical fibers. We use this method to film supercontinuum generation and track a GHz pulse train in optical fibers. We also show how the limited spatial resolution of the array can be improved with computational imaging. The single-photon sensitivity of the camera and the absence of scanning the detection system results in short total acquisition times, as low as a few seconds depending on light levels. Our results allow us to calculate the group index of different wavelength bands within the supercontinuum generation process. This technology can be applied to a range of applications, e.g., the characterization of ultrafast processes, time-resolved fluorescence imaging, three-dimensional depth imaging, and tracking hidden objects around a corner.

Ballistic and snake photon imaging for locating optical endomicroscopy fibres

“…2(c)) to aid understanding of image reconstruction and later results. A pulse of 785 nm light travelling along an optical fibre undergoes scattering, a limited number of the scattered photons are detected by the camera and can be used to observe the passage of the pulse along the fibre length [20]. A series of images were reconstructed such that the time axis of the data becomes the time axis of a video with photon count intensity as the z-axis.…”

“…A variety of related low photon number imaging techniques use advanced computation to improve image quality [20,[23][24][25]. Expected temporal correlations between photon arrivals at neighbouring image pixels can be exploited to improve image quality [23] or overcome detector array timing limitations [24].…”

Quantum-inspired computational imaging

“…More recent measurements based on SPAD arrays have allowed the first capture of light pulses propagating in free space with total acquisitions times on the order of seconds or less (44). SPAD array cameras have also been used to directly image laser pulse propagation through optical fibers: Beyond their direct applications (e.g., estimation of physical parameters of optical fibers), these measurements combined a fusion of single-photon data with hyperspectral imaging over several different wavelengths (discussed below) and computational processing through which the 32-pixelby-32-pixel resolution was successfully up-sampled by using the temporal axis to re-interpolate the pulse trajectory in the (x, y) spatial plane (49).…”

Intensity-corrected 4D light-in-flight imaging

“…The type of scattering that is observed is dependent on the medium that the light propagates through. For example, light has been captured propagating through fibre optics [11] and heated rubidium vapor [12]. When light travels through air, Rayleigh scattering is the dominant effect, and this was captured by Gariepy el al.…”