On-chip tunable SOI interferometer for quantum random number generation based on phase diffusion in lasers

Quantum random number generators (QRNG) derive randomness from quantum mechanical processes and therefore are considered a reliable source of randomness. However large size, high cost and instability issues due to conventional bulk, fiber or free space implementations restrict widespread use into complex systems and significantly affect the scalability and reliability of such solutions. Recently there has been a huge interest in photonic integration technologies for quantum optics in order to overcome aforementioned issues. We report demonstration of a QRNG based on phase diffusion in gain switched (GS) lasers. It produces random numbers by translating random phases of GS pulses (generated at 2.5 GHz rate) into amplitude fluctuations using a packaged on-chip silicon on insulator (SOI) tunable unbalanced Mach–Zehnder interferometer (uMZI). The 400 ps delay line in uMZI has been specially designed by using the combination of multi-mode and single mode waveguides to reduce the losses. The combination of tunable loss control (balancing), low waveguide losses and shorter delay improve interference quality and increase random number generation rates to gigabit scale. The mid-way and output monitoring ports on the chip can potentially be used for health checks to improve the long-term stability and reliability of QRNG in line with NIST recommendations for entropy source. True random numbers are extracted by offline post processing of the raw data. The extracted random numbers show low correlation coefficients and passed all NIST randomness tests achieving 10 Gb/s generation rate.