Optical steganography of code-shift-keying OCDMA signal based on incoherent light source

A method to enhance the security of the optical stealth channel is proposed. The proposed method uses the techniques of polarization modulator based code-shift-keying (CSK) data modulation and optical code-division multiple-access (OCDMA) en/decoding, where an incoherent light source is needed. Our analysis and experimental results show that the CSK-OCDMA signal, where a wavelength selective switch is used for optical en/decoding, has been stealthily transmitted over a 40-km wavelength-division multiplexing optical fiber link. In addition, the stealth channel only causes a power penalty less than 0.48 dB to the public channel, whereas both of these two channels can achieve error-free transmission (with bit error rate less than 10^-9.