Model & Results
Modelling & external cooling
The filtering of the optical stack was modeled by assuming a black-body emitter at 298 K and a field of view defined by the 18.75 mm focal length of the cryogenic lens and the 8 mm diameter of the apertures. The resulting spectrum was multiplied by the transmission of the filters and detector optical stack (see the filter transmission spectrums). The model showed that two each of the
While the bandpass filter (FWHM = 7 nm) was found to blue-shift by about 2 nm at cryogenic temperatures, the passband was wide enough such that significant attenuation was not observed at the original target wavelength of 1550 nm. This filter is also sufficiently wide to avoid Fourier-limited broadening of ultra-short laser pulses.
Also evident in Fig. 1 a is the strong dependence of DCR on the temperature of the final surface outside the cryostat emitting thermal radiation. This motivated the exterior cooling apparatus sketched in the previous full-system figure and shown in Fig. 2 b and c. The bulkhead holding the fiber connector is cooled to around
This work used a low-jitter SNSPD of the tapered differential design [1], with an active area of
Results
As also shown in Fig. 3 a, the free-space coupling system achieves up to
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Colangelo, M., Korzh, B., Allmaras, J. P., Beyer, A. D., Mueller, A. S., Briggs, R. M., Bumble, B., et al. (2023). Impedance-matched differential superconducting nanowire detectors. Physical Review Applied, 19(4), 044093. doi:10.1103/PhysRevApplied.19.044093 ↩
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Shibata, H., Shimizu, K., Takesue, H., & Tokura, Y. (2015). Ultimate low system dark-count rate for superconducting nanowire single-photon detector. Optics Letters, 40(14), 3428–3431. Retrieved from http://ol.osa.org/abstract.cfm?URI=ol-40-14-3428 ↩
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Boaron, A., Boso, G., Rusca, D., Vulliez, C., Autebert, C., Caloz, M., Perrenoud, M., et al. (2018). Secure quantum key distribution over 421 km of optical fiber. Physical Review Letters, 121(19), 190502. doi:10.1103/PhysRevLetters121.190502 ↩
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Taylor, G. G., Morozov, D., Gemmell, N. R., Erotokritou, K., Miki, S., Terai, H., & Hadfield, R. H. (n.d.). Photon counting lidar at 2.3 m wavelength with superconducting nanowires. Optics Express, 27(26), 38147–38158. doi:10.1364/OE.27.038147 ↩
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Wollman, E. E., Verma, V. B., Lita, A. E., Farr, W. H., Shaw, M. D., Mirin, R. P., & Nam, S. W. (2019). Kilopixel array of superconducting nanowire single-photon detectors. Optics Express, 27(24), 35279–35289. doi:10.1364/OE.27.035279 ↩