Free space-coupled superconducting nanowire single photon detectors for infrared optical communications

TL;DR

This paper presents a cryostat and optical system achieving over 56% free-space coupling efficiency to superconducting nanowire single-photon detectors for infrared communication, with detailed performance metrics and pathways for improvement.

Contribution

It introduces a novel cryostat and optical setup that significantly enhances free-space coupling efficiency to SNSPDs for infrared quantum communication.

Findings

Coupling efficiency of 56.5% achieved

Dark count rate of 95 kcps measured

System detection efficiency of 1.64% reported

Abstract

This paper describes the construction of a cryostat and an optical system with a free-space coupling efficiency of 56.5% +/- 3.4% to a superconducting nanowire single-photon detector (SNSPD) for infrared quantum communication and spectrum analysis. A 1K pot decreases the base temperature to T = 1.7 K from the 2.9 K reached by the cold head cooled by a pulse-tube cryocooler. The minimum spot size coupled to the detector chip was 6.6 +/- 0.11 {\mu}m starting from a fiber source at wavelength, {\lambda} = 1.55 {\mu}m. We demonstrated efficient photon counting on a detector with an 8 x 7.3 {\mu}m^2 area. We measured a dark count rate of 95 +/- 3.35 kcps and a system detection efficiency of 1.64% +/- 0.13%. We explain the key steps that are required to further improve the coupling efficiency.