Field transmission test of 2.5 Gb/s Y-00 cipher in 160-km (40 km × 4 spans) installed optical fiber for secure optical fiber communications

Field transmission test of 2.5-Gb/s Y-00 cipher in 160-km (40 km × 4 spans) is demonstrated in the installed optical fiber for secure optical fiber communications. A long term investigation of an intensity modulated Y-00 transmitter and receiver with signal intensity levels of 4096 is conducted and the bit error rate of < 10−9 for a month is successfully achieved.