Key Update using Y-00 Quantum Noise Stream Cipher with 20-bit Intensity Levels in a 1,000-km Optical Fiber Link

We demonstrate simultaneous intensity-modulated Y-00 cipher transmission of a private key at 200 kb/s and 1.5-Gb/s data over 1,000 km fiber. Highly secure key transmission with 1,048,576 (=220) intensity levels and key update are achieved.