We have developed superconducting nanowire single-photon detectors (SSPDs) with system detection efficiency (SDE) over 80% at a 1,550 nm wavelength, which is improved by a factor of around 3 compared to that in our previous SSPD. This significant increase in SDE has been achieved by employing a double-side cavity structure for enhancing an optical absorptance and by changing substrate material of the nanowire for improving the current uniformity in the nanowire (Fig. 1). In addition to the high SDE, we also have achieved a low dark count rate (DCR) of 40 cps and a low timing jitter of 68 ps simultaneously, all of which are preferable features in quantum communication systems.
We also have found that the optical absorptance in the SSPDs with double-side cavity structures does not rapidly decrease even for low filling factors (FFs). A lower FF enables a faster optical response, and the resulting maximum counting rate (MCR) of our SSPD reached 70 MHz for FF=0.18, while keeping a high SDE of 65%. The MCR of 70 MHz is 2.8 times better than that in our previous SSPD with the conventional FF of around 0.5. Our SSPDs are operational in a compact Gifford-McMahon (GM) cryocooler, allowing us a long-term continuous run without using costly liquid helium (Fig. 2). The total performance factor given by SDE x MCR / DCR is 1,440 times better than that in the InGaAs avalanche photo diode (APD) (Table 1).
By optimizing the cavity structure, the SDE of the SSPD will exceed those in the photomultiplier tube and the Si APD even at the wavelength below 1 μm. Then, use of the SSPD will widely spread not only in quantum communication systems but also in various fields such as quantum optics, free-space optical link, laser ranging, and fluorescence measurement.
The details of this study have been published in Optics Express on Nov. 4, 2013 (http://www.opticsinfobase.org/oe/issue.cfm).
