Silicon-on-insulator electro-optics yields advanced random number generator

November 28, 2018 // By Bill Schweber
By using a laser diode's sporadic output, optically processing the resultant photons, and converting them to electrical pulses, researchers developed a tiny single-chip, quantum random number generator device.

The search for a better, smaller, faster “true” random number generator—increasingly needed for strong cryptography and security—has fascinated technologists for many years, as they seek genuine probabilistic sources rather than those with even a tiny hint of determinism. This endeavor generally begins with an all-natural, physics-based phenomenon that defies any possibility of prediction.

The chip, placed next to a penny coin, contains
nearly all of the optical components needed to generate
quantum-based random numbers at high speed.
(Image source: Francesco Raffaelli, University of Bristol)

In one of the most recent efforts, an international team of researchers, led by quantum-technology experts from the University of Bristol (U.K.), have developed a chip-based device that can be used to generate quantum-based random numbers at gigabit-per-second speeds.

They have demonstrated a silicon-on-insulator (SOI) quantum random number generator (QRNG) that uses phase fluctuations of the output a laser diode, where single photons are randomly emitted and thus generate an electrical signal that’s impossible to predict. All optical components (except the laser diode) and photodiodes are integrated onto a single monolithic device, fabricated by IMEC using industry-standard processing techniques. The laser diode is coupled to the circuit via an optical fiber.

The optical functions occupied less than 1 mm2 and were integrated onto a 2.5- × 2.5-mm SOI chip that was embedded and wirebonded to a 4- × 8-cm printed circuit board containing a transimpedance amplifier (TIA) and voltage supply for the photodiodes. Finally, the system was placed within a Faraday cage to reduce the RF noise pickup.

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