Secure optical communications utilizing PSK modulation, polarization multiplexing and coherent digital homodyne detection with wavelength and polarization agility

Data encryption and user authentication are the major communications security (ComSec) approaches used in today´s communications networks. While these methods provide an efficient means to secure the sensitive information, they do not prevent a hostile opponent from jamming the signal or tapping the link. We present here an analysis of a coherent optical communications system providing secure communications in free-space or over fiber. After reviewing the basic principles of coherent optical communications we present a system using polarization/frequency agility to secure the data link at the optical layer. The key building blocks are presented, including a QPSK transmitter, and an optical hybrid combined with a coherent digital receiver. A description of CeLight´s LiNbO₃ integrated implementation of the transmitter and the receiver is detailed. Next, a theoretical analysis demonstrating the capabilities of such a secure communications system to send data over fiber and in free space eliminating the need for optical filtering and lambda-based de-multiplexing. Finally, we present an experiment demonstrating the ability of the proposed frequency hopping solution to avoid an eavesdropper from intercepting the data channel.