Non-invasive WDM channel scrambling for secure high data rate optical transmissions

This paper proposes a non-invasive optical scrambling technique to secure optical transmissions at high data rates (>10Gb/s). The proposed method belongs to the optical code-division multiple access (OCDMA) technique, using spectral phase encoding, based on overlapping of adjacent scrambled/spread pulses to encrypt transmitted data. In our system, data confidentiality is directly related to scrambled/spread pulse interference, avoiding direct detection by a power detector, in contrast to network access application (OCDMA), where this overlapping should be avoided. Our goal is to secure data transmission without impacting the physical layer, by guaranteeing the optical transparency of the encryption technique with respect to conventional transmission equipments. Therefore, we simulated the system penalty as a function of the transmission distance for a bit error rate (BER) target of 10-9 to estimate the impact of the linear and non-linear transmission effects on our encryption technique. We consider a point-to-point span for mono-channel and multi-channel setups where self-phase modulation (SPM) and cross-phase modulation (XPM) become significant. In the last section, we discuss the resilience of our encryption technique to some realistic attack scenarios. The eavesdropper can use the linear optical sampling (LOS) technique, which with coherence conditions on the waveform under test, permits to extract the amplitude and the phase of each spectral compound, enabling, to determinate the phase filter used to encrypt. Determining the necessary time to crack the mask allows us to establish the mask refreshment to guarantee data confidentiality.