Alladi Ramakrishnan Hall

Chaos synchronization in Semiconductor diode lasers

E. Jayaprasath

Department of Physics, Pondicherry University, Pondicherry

Chaos synchronization of semiconductor diode lasers has been a topic of interest in the recent decades due its direct application in secure optical communication. Secure optical communication involves encoding of a message in the chaotic output of a transmitter laser (TL) which is to be recovered at a receiver laser (RL). The encoded message can be decoded at receiver by synchronizing RL's chaotic output with that of the TL. Of the two major types of synchronization regimes that had been identified so far, injection-locked synchronization (RL will synchronize with TL with a delay equal to the time of flight ($\tau_f$)) is most commonly used for message encoding and decoding scheme and we use the same for our investigations. The cross-correlation analysis between TL and RL allows the estimation of this time delay. The maximum correlation for injection-locked synchronization should therefore occur with a time delay (inter-cavity delay) equal to $\tau_f$. This time delay needs to be corrected in the process of analyzing synchronization. However, due to the intra-cavity propagation of transmitter laser output within the receiver laser's cavity, the maximum correlation does not occur at $\tau_f$ or zero (if $\tau_f$= 0), but at an incrementally higher delay than zero which is noted at as intra-cavity propagation delay ($\tau_{pd}$). The transmitter laser acquires this $\tau_{pd}$, as it travels within the receiver’s cavity. We show in our investigations, the dependency of $\tau_{pd}$ on the actual chaotic nature of the lasers involved. Understanding of complex network systems, bridging the photonics system with complex biological systems and analyzing the synchronization phenomenon and chaotic time series analysis can form the future extensions of our present investigations