Long-haul Stealth Communication Based on Different State Bases Unidirectional Loopback in Optical Fiber Link

This paper describe a long-haul stealth communication based on different state bases unidirectional loopback (DSBUL) in optical fiber link. In order to prevent the optical signal in the optical fiber from being directly detected by the eavesdropping, our scheme combine the quantum noise stream cipher with a novel signal expension technology. We demonstrate digital signal processing (DSP) algorithm steps of transmitter and receiver in detail and experimentally implement a long-haul stealth communication based on DSBUL system, which can be compatible with existing coherent optical communication systems without changing any hardware structure. The stealth transmission distance (L) is 300 kilometers with free bit error rate. And transmission rate is over 550 kbps. In additional, we evaluate the security of this scheme with capability against various tapping attacks.