Fiber transmission of antisqueezed light for secure communications

Secure communications are a prospective application of the technologies originating from quantum information physics. Antisqueezed light, which is not necessarily in a quantum state, is a candidate for secure optical communications because it is tolerant to loss and amplification. We transmitted antisqueezed light, generated with a reflection-type fiber interferometer, through 100 km dispersion-shifted fibers including two erbium-doped fiber amplifiers for the first time. The coding was pseudo-randomized phase-shift keying, and the combination of the pseudo-randomization and antisqueezed fluctuations increased the bit-error rate of eavesdroppers, suggesting that our system is a technological candidate for future secure optical communications.