Characterization of the polarization fluctuations in gain-switched VCSELs for quantum random number generation

Abstract

We report a characterization of the polarization fluctuations observed when gain-switching vertical-cavity surface-emitting lasers (VCSELs) for quantum random number generation (QRNG) applications. We compare our experimental measurements with the results obtained from a stochastic rate equations model that incorporates the intrinsic parameters of the VCSEL found using the state-of-the-art experimental techniques. The good agreement obtained between our experiments and simulations can be used to establish a validation process that permits to monitor the device behaviour to detect malicious intrusion or malfunctioning of the QRNG. Simulations of the model are used to look for parameters that maximize the QRNG performance. Along this direction we consider the performance when considering a VCSEL with vanishing values of the amplitude and phase anisotropies. We show that in this system the obtained raw bits have a low bias value that is independent on the sampling time chosen to obtain the random bit and on the parameters of the modulation. We also use the simulations of the model to predict the QRNG performance at high modulation frequencies. We show that random bits obtained at several Gbps rates, after appropriate post-processing, fully pass the NIST statistical test.