Abstract

High speed fiber and free-space optical transmission systems are the backbone of many critical data networks that require encryption. The traditional method of securing such communications is to electronically encipher the data stream. Electronic encryption technology is a mature and well-known technique, however, electronic encryption methods become very expensive as bit rates exceed 2.5 Gbps due to the limitations of the electronic-optical interfaces and accommodation of the various communication protocols. At high bit rates these methods can introduce a delay and there is also a general physical vulnerability at every optical-electrical-optical (OEO) conversion point. A need exists for a cost-effective method to adequately protect optical networks operating at any bit rate without introducing delays or alterating the native WDM transmission, i.e., one that is protocol agnostic. This paper describes such a system using an all-optical method of encryption with the recently patented Optical Tapped Delay Line (OTDL) channelizer. Using the OTDL technology, a band of information-carrying light is channelized into many narrow subbands and the phase of each band is randomly offset. The temporal waveform of this signal is therefore “encrypted.” This encrypted signal is transmitted across the link without significant optical side effects. At the authorized point of destination, the original signal is recovered by inverting the phase offsets and returned to its original temporal waveform. A transmission using this technique is protected from an attack. Any attack would require coherent detection of a large bandwidth of analog data at a high precision digitization rate. Even if coherently intercepted, the signal's properties are encrypted to the extent that recovery is virtually impossible. To make decrypting even less likely, the encrypting scheme could be periodically changed.

© 2005 Optical Society of America