Single Photon Communication with Avalanche Diodes and the General Basics of Photon Counting

Abstract

Single photon communication (SPC) already exists in several applications in laboratory and even outdoor conditions. In the field of quantum cryptography SPC experiments are part of military applications too. There are several methods to detect every single impacting photon in such an experiment. Mostly photomultiplier tubes (PMT) are used. In some cases single photon avalanche diodes (SPAD) are more suitable for photon detection. Both the SPADs and PMTs have advantages and disadvantages. Usually PMTs have much larger detection areas than SPADs, but most of the PMTs detection efficiency peaks at 400 nm wavelength compared to the SPADs, where it peaks at 600–700 nm wavelength. For long distance laser measurements the higher wavelength is more suitable due to the Rayleigh scattering, but the detection hole of SPAD is very tight, which is why it is really hard to target the laser punctually without an optical gyroscope.