Optical Steganography Over a Public DPSK Channel With Asynchronous Detection

We propose to apply optical steganography to public differential phase-shift keying (DPSK) transmission by transmitting a stealth amplitude-modulated signal through a DPSK link. The secretly transmitted signal is temporally stretched with chirped fiber-Bragg gratings (CFBGs), and therefore, can be hidden under public DPSK signals. The stealth signal is successfully recovered and detected asynchronously, without clock synchronization with the transmitter.