Randomness extraction from a chaotic laser diode with dispersive self-injection

High-speed generation of random bits has attracted much attention recently using chaotic dynamics in laser diodes subject to different perturbations. Extraction of randomness has been investigated from a chaotic laser using selfinjection from a grating with dispersion. While the optical feedback invokes chaos, the dispersion induces different delays to different frequency components to conceal the information of the feedback delay time. Experimentally, random bits were extracted using a laser under feedback from a grating. The undesirable time-delay signature (TDS) was reduced by about 10 times. So a continuously tunable sampling rate was allowed for random bit generation (RBG), where the overall output rate tunable across 3 orders of magnitude up to 100 Gbps was demonstrated. Numerically, the concealment of TDS is further investigated using a rate-equation model incorporating self-injection through an all-pass filter (APF), which is realized by coupling the feedback path to a lossless ring cavity. While the APF provides dispersion to suppress the TDS, the APF provides no frequency selectivity so that a large chaotic bandwidth is attained. For minimal TDS, the coupling ratio to the ring is optimized at 0.5. The round-trip time of the ring also needs to be sufficiently long for inducing dispersion in the chaotic light. With comparable performance in TDS suppression, the APF feedback can generate chaos with broader bandwidth than grating feedback. The results are applicable to generating random bits for digital systems with widely tunable rates.