Secure optical communications using wavelength tunable optical filters

This report presents several conceptual designs for all-optical implementations to enhance the security of optical communications links. The method takes advantage of technology which uses the wavelength selective filtering properties of electronically tunable high finesse Fabry-Perot interferometers (FPIs). For the application under consideration the FPI would physically separate from a broad band (e.g., >20 nm) optical source, such as superluminescent LED, a narrow band (e.g., <0.1 nm) of wavelengths and the latter would be modulated with the information signal of interest. The modulated optical signal is combined with the unmodulated part of the broadband signal prior to transmission. The decoding process at the receiver would require an identical FPI tuned to the same narrow band of wavelengths in order to selectively extract the modulated narrowband signal carrying the information transmitted. Robustness of the security is enhanced by the electronic tunability of the FPIs which could potentially lead to a wavelength-hopped transmission and tracking communication system.