Fig. 4
a Experimental setup. For the optical system, the light is divided into two channels. The light in one arm is measured by the power meter (Thorlabs-PM100D), and the light in another arm is attenuated (EXFO FVA-3150) and illuminates the SPD through the fiber. The FSPD only includes fibers and nanowires. The blue lines represent fibers. For the readout circuit, the device is current biased with a voltage source (Keithley 2400 SourceMeter), while the RF port of the bias tee (ZFBT-6GW-FT+, Mini Circuit Inc.) is connected with a low-noise amplifier (MITEQAM-1309). The oscilloscope (KEYSIGHT infiniiVision DSOX6004A) shows the amplified voltage signal. This port is also chosen to connect with the counter (SR400 Gated Photon Counter) for SPD measurement. b Photograph of an FSPD transporting red-light source. c Oscilloscope persistence map of the electric output pulse at 0.9 Isw. d Histograms of the time-correlated photon counts measured at 405 nm. e Normalized photon count rate versus bias current ranging from 405 nm to 1550 nm. f Dark count rates versus bias current measured at 45 mK