Using Wavelength/Time Signatures Scrambling to Realize Cryptographic Coded-WDM Data Networks

To combat with multiple-users interference and malicious eavesdropping, this paper proposes a double scrambling scheme over time/wavelength for a cryptographic optical CDMA (OCDMA) data transmission. By using wavelength-spreading/time-hopping, data reliability in OCDMA network can be highly improved. On the transmitter side, data bits are sliced into spectral chips, coded into M-sequence codes, and conducted with different units of time-delay. In the receiver side, fiber-delay lines (FDLs) reverse the spectral chips back to the same time basis, and optical switches (OSWs) turn on-off spectral chips into balanced detector for the final data decoding. By changing signature code frequently, the eavesdroppers cannot catch on the changing code speed and have little chance to detect the channel waveform to solve the code. To against eavesdropping, we take advantages of linear cyclic, periodic, and nearly-orthogonal characteristics of M-sequence codes. OSWs and FDLs are added into the arrayed-waveguide grating (AWG) codecs. The spectral codes and the time-delay units will follow cell states of a controlling shift register. Different shift register states will reconfigure AWG light spectra into different coding sequences. After pass through the associated OSWs and FDLs, user signature code appears to be a two-dimensional code matrix. In perspective of eavesdropper, smooth eavesdropping presents difficulties due to signature codes’ frequent changing. The system can therefore achieve a high level of network confidentiality.