All-optical cryptography through spectral amplitude and delay encoding

All-optical data encryption is a promising technology that could lead communication systems to an unprecedented degree of security. In this paper we use computer simulations to systematically investigate a new all-optical cryptography technique that is bit-rate independent and transparent to modulation formats. Encryption encompasses signal spectral slicing followed by two encoding stages that impose different attenuations and delays to each of the spectral slices. We analyze the quality of the encoded signal by evaluating its bit error rate (BER) performance. Results indicate that such BER may achieve 45 and 28%, respectively, for input non-return-to-zero on-off keying (NRZ-OOK) and differential quadrature phase-shift keying (DQPSK) signals. At the receiver side, results suggest that signals may be properly decoded after propagation distances that are compatible with those utilized in metropolitan area networks. The robustness of the technique against waveform analysis and brute force attacks is also approached.