Breakdown flash at telecom wavelengths in InGaAs avalanche photodiodes

Abstract

Quantum key distribution (QKD) at telecom wavelengths (1260 - 1625 nm) has the potential for fast deployment due to existing optical fibre infrastructure and mature telecom technologies. At these wavelengths, Indium Gallium Arsenide (InGaAs) avalanche photodiode (APD) based detectors are the preferred choice for photon detection. Similar to their Silicon counterparts used at shorter wavelengths, they exhibit fluorescence from recombination of electron-hole pairs generated in the avalanche breakdown process. This fluorescence may open side channels for attacks on QKD systems. Here, we characterize the breakdown fluorescence from two commercial InGaAs single photon counting modules, and find a spectral distribution between 1000 nm and 1600 nm. We also show that by spectral filtering, this side channel can be efficiently suppressed.

Backflash Light as a Security Vulnerability in Quantum Key Distribution Systems

“…The presence of a significant backflash radiation has been experimentally demonstrated in both commercially available InGaAs/InP [36] and Si-based [28] SPADs. In the case of an InGaAs-based SPAD with a nominal detection efficiency of about 10%, the backflash emission can be a source of significant information leakage, thus compromising the security of the entire QKD system [37], [38]. An experiment with a silicon-based detector also revealed a considerable rate of backflash emission.…”

“…This explains why different SPAD models operating in different regimes exhibit different backflash spectral distribution, temporal profile, and intensity. Although there exists an analytical theory of backflash radiation, this effect has been mainly investigated experimentally for QKD applications, and the reported results are tied to the properties of the concrete SPADs used [28], [35], [37], [38].…”

“…Of course, the non-unit detection efficiency of the second SPAD, as well as optical losses in the channel, should be taken into account during the estimation. The spectral distribution of the backflash light with this setup could be analyzed by plugging different narrow-band filters between the two SPADs or by using diffraction gratings [35], [37]. Recent reports have shown that commercial SPADs have unique temporal profiles depending on the detector material and the manufacturer.…”

Backflashes from fast-gated avalanche photodiodes in quantum key distribution

“…We note, however, that characterizing the spectrum of the backflashes is also important for enforcing this point in order to more accurately determine the information leakage. While this has been partially explored in previous studies, [18][19][20] these have not corrected for the spectral response of the measurement apparatus. We believe that this is an important avenue for future work, not only from a security perspective but also to shed light on the precise origin of backflashes within APDs.…”

“…It has been shown that APDs are susceptible to emitting light after detection, known as backflashes. [17][18][19][20][21] Backflashes can then allow Eve to act in a more passive way and thus ascertain which of Bob's detectors has clicked without having to interact with any components in the QKD system. However, no studies have yet been performed on fast-gated detectors that are used in stateof-the-art QKD systems.…”