Computational photonics

Pao-Lo Liu

Dr. Liu works on computational photonics for device and system simulations. Recent projects include simulations of optical chaotic communications systems and the improvement of modulation speed using detuned loading.

              Today, security of communications systems is a primary concern. Encryption is very effective for file streaming. For real time applications, it is limited to moderate data rate. For high data rate, optical communications, one can operate the semiconductor laser in the chaotic regime. The high frequency chaotic events very effectively mask off the real data. On the receiving side, using an identical laser, the received signal is decrypted to obtain the actual data. His student, Jaya Rao, performed extensive simulations on the effectiveness of chaotic encryption under conditions of various degrees of synchronization, data rate, and multiple modes.

           The external feedback can modify the behavior of lasers. In addition to the linewidth and chirp reduction, the feedback can also lead to an increased modulation bandwidth. His student, Shubhrangshu Senguptauses rate equations to simulate the dynamics of composite-cavity lasers. A variety of cavity configurations are evaluated. Optimal feedback conditions which lead to a substantial increase in modulation bandwidth are identified. Detuning of the main mode alone may not be sufficient to reach the optimal point. However, it is possible to bring a side mode to the optimal point. The side mode provides the initial response before the main mode builds up. With properly controlled feedback, the bandwidth of direct intensity modulation can increase well beyond what is available from a solitary semiconductor laser.