A photonic lantern is an adiabatic guided-wave transition between a multimode waveguide and a set of single-mode cores. As such, photonic lanterns facilitate the efficient coupling of multimode light to single-mode devices, examples of which include fibre Bragg gratings and arrayed waveguide gratings. In this work, we demonstrate that photonic lanterns based on tapered multicore fibres (MCFs) provide a potentially powerful new route to efficiently couple multimode states of light to a two-dimensional array of Single Photon Avalanche Detectors (SPADs). The SPAD array consists of a 32×32 square array of pixels, each of which has its own time to digital converter (TDC) for Time Correlated Single Photon Counting (TCSPC) with a timing resolution of 55 ps. For our application, the geometry of the MCF used to fabricate the photonic lantern was chosen such that each single mode in the MCF can be mapped onto an individual SPAD pixel. Upon injecting a broad supercontinuum signal into a 290 m long MCF via a photonic lantern, wavelength-to-time mapped spectra were obtained from all modes. We believe that the techniques we report here may find applications in areas such as Raman spectroscopy, coherent LIDAR, and quantum optics.
Using an electron multiplying CCD camera we observe both image plane (position) and far field (momentum) correlations between photon pairs produced from spontaneous parametric down-conversion when using a 201 x 201 bi-dimensional array of pixels and a flux of around 0.02 photons/pixel. After background subtraction we characterize the strength of signal and idler correlations in both transverse dimensions by applying entanglement and EPR criteria, showing good agreement with the theoretical predictions. The application of such devices in quantum optics could have a wide range, including quantum computation with spatial degrees of freedom of single photons.
We have developed a new approach to measuring the spatial position of a single photon. Using fibers of different
length, all connected to a single detector allows us to use the high timing precision of single photon avalanche diodes
(SPAD) to spatially locate the photon. We have built two 8-element detector arrays to measure the full-field quantum
correlations in position, momentum and intermediate bases for photon pairs produced in parametric down conversion.
The strength of the position-momentum correlations is found to be an order of magnitude below the classical limit.
Single-photon detectors play an increasing role in emerging application areas in quantum communication and low-light
level depth imaging. The single-photon detector characteristics have a telling impact in system performance, and this
presentation will examine the role of single-photon detectors in these important application areas. We will discuss the
experimental system performance of GHz-clocked quantum key distribution systems focusing on issues of quantum bit
error rate, net bit rate and transmission distance with different detector structures, concentrating on single-photon
avalanche diode detectors, but also examining superconducting nanowire-based structures. The quantum key
distribution system is designed to be environmentally robust and an examination of long-term system operation will be
presented. The role of detector performance in photon-counting time-of-flight three-dimensional imaging will also be
discussed. We will describe an existing experimental test bed system designed for kilometer ranging, and recent
experimental results from field trials. The presentation will investigate the key trade-offs in data acquisition time, optical
power levels and maximum range. In both examples, experimental demonstrations will be presented to explore future
perspectives and design goals.