Near-Infrared Single-Photon Detection

Abstract

With the rapid increase of research interest in quantum information (BennettB Gisin et al., 2002; Knill et al., 2001), the near-infrared single-photon detection received a great boost not only in inventing (or improving) basic devices, but also in improving operation techniques on the conventional devices. Especially, in the application of quantum key distribution (BennettB Gisin et al., 2002), practical single-photon detectors (SPDs) with small size, operating at room-temperature are in great need. Avalanche photodiodes (APDs) are usually used to build SPDs. Avalanche photodiodes (APDs) have internal gain due to a process of impact ionization that leads to multiple electron-hole pairs per input photon. Applying a large reverse voltage to the APD will result in a large multiplication gain, until the breakdown voltage (Vbr) is reached. Usually, the output photocurrent of the APDs is linearly proportional to the intensity of the optical input when the bias voltage is below Vbr, and this mode is called as “linear mode”. When the bias voltage is larger than Vbr, the electron-hole generation process can become self-sustaining and result in a runaway avalanche, then a single photoexicited carrier can induce a runaway avalanche that gives rise to a detectable macroscopic current, and this mode is called as “Geiger mode”. Si-APD SPD exhibits excellent performance with the spectral range from 400 to 1000 nm. Si APD is typically operated in free-running mode. Its detection efficiency is as high as 70% around 700 nm with the dark count rate (DCR) of 10-100 counts per second (Stipcevic et al., 2010). InGaAs/InP APD has a spectrum response range from 1200 to 1700 nm, covering the fiber optical communication window at 1310 and 1550 nm. However, InGaAs/InP-APD SPD has a large dark count (e.g. DCR~105 per second) and afterpulsing effect. Especially, the serious afterpulsing effect of the InGaAs/InP APD limits the application of high-speed detection. In order to improve its performance, an InGaAs/InP APD is usually operated in gated Geiger mode to suppress dark counts and afterpulsing effect. Recently, (Yuan et al., 2007; Namekata et al., 2006) reported self-cancellation and sinewave techniques, which exhibited great improvements on the InGaAs/InP-APD SPD. The single-photon detection speed was increased significantly from megahertz to gigahertz. Previously, it was thought that APDs are unable to resolve the number of photons in a short time interval. (Kardynal et al., 2008) first found that by suppressing the capacitive response down to a sufficiently low level, the weak avalanche current of an InGaAs/InP APD can be discriminated in its early development before saturated. In this mode, the variation in