  Chaotic semiconductor lasers have been widely investigated for high-speed
random bit generation, which is applied for the generation of cryptographic
keys for classical and quantum cryptography systems. Here, we propose and
demonstrate a self-chaotic microlaser with enhanced chaotic bandwidth for
high-speed random bit generation. By designing tri-mode interaction in a
deformed square microcavity laser, we realize a self-chaotic laser caused by
two-mode internal interaction, and achieve an enhanced chaotic standard
bandwidth due to the photon-photon resonance effect by introducing the third
mode. Moreover, 500 Gb/s random bit generation is realized and the randomness
is verified by the NIST SP 800-22 statistics test. Our demonstration promises
the applications of microlasers in secure communication, chaos radar, and
optical reservoir computing, and also provides a platform for the
investigations of multimode nonlinear laser dynamics.
