Simultaneous Coherent Detection With Baseband Enhancement in Chaotic Random Bit Generation by an Optically Injected Laser

Abstract

Optical injection into a semiconductor laser invokes chaos that is coherently detected without direct detection for fast random bit generation (RBG). Originating from the injection without any feedback, the chaos contains no undesirable time-delay signature. Although the injection dynamics only supports a low dimensionality of three, simultaneous coherent detection uses the two dimensions of intensity $I$ and phase $\varphi $ in yielding two signals $I_{\mathrm{H}}$ and $I_{\mathrm{B}}$ , which are from heterodyning and balanced delayed homodyning, respectively. Compared to $I$ from direct detection, the two coherently detected signals $I_{\mathrm{H}}$ and $I_{\mathrm{B}}$ are baseband-enhanced for effectively utilizing the low-frequency responses of the detectors. Experimentally, on a laser with a relaxation resonance of 5.2 GHz, $I_{\mathrm{H}}$ and $I_{\mathrm{B}}$ are baseband-enhanced by 8 dB and 12 dB, respectively. Through a basic postprocessing by discarding bits, they are digitized for RBG with an output bit rate reaching 280 Gbps. Through an extensive postprocessing by involving pseudo-random contributions, a boosted output bit rate of 1.28 Tbps is possible even when the detection bandwidth is reduced to 3 GHz. Both postprocessings satisfy a set of standardized randomness tests from the National Institute of Standards and Technology. Based on the simultaneous coherent detection, the potential of baseband enhancement is illustrated for the low-dimensional dynamics from injection.