Error free secure key distribution with decoy mechanism via spectral encoding in Raman fiber laser

Secure key distribution is a vital yet challenging task for most secure communication systems. Here, we demonstrate an error-free secure key distribution scheme with a decoy mechanism by establishing Raman lasing between the parties. At the transmitter port, true keys mixed with fakes keys are spectrally encoded into Raman signals at different wavelengths. A spectral manipulable feedback ring is adopted to provide week feedback for the true signal and strong feedback for the fake one. Over the transmission link, true Raman signals are suppressed and eavesdropper could only detect the fake ones. At the receiver port, the user can reveal the hidden true signals and identify the fake signals by turning on a magic switch. Moreover, the distributed Raman gain along the fiber could compensate for the fiber loss, thereby enabling error-free secure key distribution over 50 km. The structure simplicity, error-free property, and the novel decoy mechanism renders this scheme a promising alternative for long distance secure key distribution.