Abstract

Chaotic optical communication was originally proposed to provide high-level physical layer encryption. For high-speed and long-distance transmission, chaotic signal is very sensitive to channel impairments such as dispersion and Kerr fiber nonlinearity. In the traditional chaotic optical communications, these impairments must be compensated in optical domain before chaos synchronization. However completely compensating the high-order dispersion and fiber nonlinearity in the optical domain has great challenges, therefore limiting the transmission distance of high-speed chaotic optical communications less than 150 km. Here we propose a method aiming to break the limit. Thanks to coherent detection, channel impairments can be compensated in the digital domain using various algorithms. Digital back propagation algorithm is used for jointly compensating linear and nonlinear impairments of the chaotic signals, constant modulus algorithm is used for channel equalization and extended Kalman filter is adopted for carrier phase recovery. After digital processing, the recovered chaos signal is converted back to the optical domain for chaos synchronization. By this means, we demonstrate a 10 Gb/s phase-modulation signal encrypted by phase chaos transmission over record-breaking 1000 km single-mode fiber with bit-rate error less than 1.0 × 10⁻³ by simulation, and support the results with extensive numerical analysis.

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