Synchronization of bandwidth-enhanced chaos in semiconductor lasers with optical feedback and injection.

We experimentally investigate the generation and synchronization of bandwidth-enhanced chaos in a semiconductor laser (drive laser) that is subject to optical injection from another chaotic semiconductor laser (injection laser) with optical feedback. Effective bandwidth enhancement is achieved over 12 GHz, under the condition in which the optical wavelength of the drive laser is positively detuned with respect to that of the injection laser, outside the injection locking range. The bandwidth-enhanced chaotic signal of the drive laser is injected into a third semiconductor laser (response laser) for synchronization. Synchronization of chaos with a bandwidth greater than 12 GHz is observed between the drive and response lasers, under the condition in which the optical wavelength of the response laser is negatively detuned with respect to that of the drive laser, satisfying the injection locking condition. High-quality chaos synchronization is observed within the injection locking range between the drive and response lasers and under the condition of a low relaxation oscillation frequency of the response laser.

Differential-phase-shift quantum key distribution experiment using fast physical random bit generator with chaotic semiconductor lasers.

A high speed physical random bit generator is applied for the first time to a gigahertz clocked quantum key distribution system. Random phase-modulation in a differential-phase-shift quantum key distribution (DPS-QKD) system is performed using a 1-Gbps random bit signal which is generated by a physical random bit generator with chaotic semiconductor lasers. Stable operation is demonstrated for over one hour, and sifted keys are successfully generated at a rate of 9.0 kbps with a quantum bit error rate of 3.2% after 25-km fiber transmission.

Leader-laggard relationship of chaos synchronization in mutually coupled vertical-cavity surface-emitting lasers with time delay.

We experimentally and numerically observe synchronization of chaos in two mutually coupled vertical-cavity surface-emitting lasers (VCSELs) with time delay. We observe in-phase and antiphase synchronization of polarization-resolved chaotic temporal wave forms under the condition of wavelength matching. We investigate leader-laggard relationship between two chaotic wave forms of mutually coupled VCSELs and find that the laser with longer wavelength becomes the leader.