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(5) Applications of fast physical random number generation
Another practical application using complex photonics is the process of fast random number generation. By using chaos in lasers, it is possible to generate fast chaotic oscillations with large spectral bandwidth. Typical frequency bandwidths in semiconductor lasers reach some GHz. This order is determined by the relaxation oscillation frequency. Lasers having this range of oscillation speed are suitable for applications oriented to physical random number generation. Moreover, the micro-noise existing in the laser internal cavity gets amplified by the chaos, allowing for producing high-amplitude irregular oscillations. By the united actions of chaos complexity and laser speed, novel engineering applications like fast physical random number generation have emerged.
Figure 1 illustrates the process of random number generation from a chaotic optical waveform. The chaotic output signal is acquired by a photodiode and electrically converted by an analog-to-digital converter (AD) into a binary digital signal. The AD converter operates the comparison of an input signal voltage with a given threshold voltage and converts it into a digital binary signal. The resulting output signal is constituted of random sequences of zeros and ones, called binary random sequences.
Figure 1: Fast physical random number generation using laser chaos
The world’s first fast physical random number generator using laser chaos was experimentally demonstrated in 2008 in our laboratory, and we have then improved it into a real-time fast physical random number generator at the rate of 1.7 Gb/s. Since then, intense research activity has been carried out throughout the world, with recent results showing generation speeds exceeding the Tb/s order. Besides, research projects aiming at reducing the spatial extension of physical random number generators by using photonic integrated circuits are also very active.