MTL Annual Report

In order to improve the sensitivity of superconducting nanowire single-photon-detectors (SNSPDs ^[1] ) at telecom wavelengths and extend it to the middle infrared range, we fabricated SNSPDs based on 30-nm-wide nanowires (see Figure 1).

To make the photodetection pulse detectable with standard room-temperature electronics, N nanowires were arranged in a parallel architecture such that when one section fired, the current flowing through the whole device was redirected to the read-out circuitry (Superconducting Nanowire Avalanche Photodetector: SNAP) ^[2]. The signal-to-noise ratio was then N times higher than with a series design.

The single-photon detection efficiency (DE) of 30-nm-wide nanowire SNSPDs and of 2-, 3- and 4-section SNAPs was measured for 1550-nm wavelength at a temperature of 4.7 K. The DE exhibited a reduced dependence on the bias current (I_B) compared with 100-nm-wide SNSPDs. This reduced dependence allowed operating narrow SNSPDs at an I_B (~ 50 % of the critical current I_C) far lower than with wide SNSPDs (typically ~ 95 % of I_C) for the same DE. This reduction in the operating bias current would in principle improve the detector sensitivity, as the dark count rate (DK) of SNSPDs decreases exponentially with I_B. However, the highest DE measured at 0.5 I_C was 7% for a DK = 100 Hz, which does not represent an improvement to the sensitivity of wide SNSPDs. This performance occurred in part due to the low fill factor (f = 30 %) of the device’s active area, due to the high operating temperature, and due to the background-radiation-induced dark counts.

The work at Lincoln Lab was sponsored by the United States Air Force under Air Force Contract #FA8721-05-C-0002. Opinions, interpretations, recommendations and conclusions are those of the authors and are not necessarily endorsed by the United States Government.

1. G.N. Gol’tsman et al., “Picosecond superconducting single-photon optical detector,” Appl. Phys. Lett., vol. 79, pp. 705, 2001. [↩]
2. M. Ejrnaes et al., “A cascade switching superconducting single photon detector,” Appl. Phys. Lett., vol. 91, pp. 262509, 2007. [↩]