Fast and compact VCSEL-based quantum random number generator

Random number generators (RNGs) are an essential ingredient of modern cryptographic systems. Particular attention is paid today to a special class of RNGs – quantum RNGs, which are attracting close attention of researchers due to the explosive development of quantum key distribution systems, where the use of quantum randomness is a necessary security requirement. A large number of various quantum entropy sources have been proposed over the last 10-15 years. Most of them are based on the use of different quantum optics phenomena, particularly, on the effects occurring in semiconductor lasers. This choice is due to the relatively low cost and ease of use of such devices and the high random bit generation rate available with optical QRNGs. Motivated by these reasons, we study in the present research the QRNG based on variations of light polarization in a vertical-cavity surface-emitting laser (VCSEL). The scheme we propose allows creating an extremely compact and fast optical QRNG, consisting essentially of only a laser and a polarizing beam splitter. We revealed that it is possible to ensure the pulsed operation of a VCSEL in a bistable regime, which is characterized by random switch of light polarization. We show, however, that probabilistic properties of such laser pulses significantly depend on the internal laser parameters as well as on its operating mode. Understanding these properties is fundamentally important for the correct assessment of the quantum noise contribution and, consequently, for the subsequent post-processing of digitized random sequences.