0.75 Gbit/s high-speed classical key distribution with mode-shift keying chaos synchronization of Fabry-Perot lasers

Abstract

High-speed physical key distribution is diligently pursued for secure communication. In this paper, we propose and experimentally demonstrate a scheme of high-speed key distribution using mode-shift keying chaos synchronization between two multi-longitudinal-mode Fabry-Perot lasers commonly driven by a super-luminescent diode. Legitimate users dynamically select one of the longitudinal modes according to private control codes to achieve mode-shift keying chaos synchronization. The two remote chaotic light waveforms are quantized to generate two raw random bit streams, and then those bits corresponding to chaos synchronization are sifted as shared keys by comparing the control codes. In this method, the transition time, i.e., the chaos synchronization recovery time is determined by the rising time of the control codes rather than the laser transition response time, so the key distribution rate is improved greatly. Our experiment achieved a 0.75-Gbit/s key distribution rate with a bit error rate of 3.8 × 10^-3 over 160-km fiber transmission with dispersion compensation. The entropy rate of the laser chaos is evaluated as 16 Gbit/s, which determines the ultimate final key rate together with the key generation ratio. It is therefore believed that the method pays a way for Gbit/s physical key distribution.

Fig. 1. Overview of the key distribution scheme using mode-shift keying chaos synchronization.

a Principle and b experimental system configuration. Common-light-driven multi-mode Fabry–Perot (FP) lasers with dynamic filtering achieve the mode-shift keying chaos synchronization. The red bits obtained by quantizing synchronized chaos in the mode-matching time intervals are sifted as the final keys. In the experimental configuration, dynamic filtering consists of a wavelength division multiplexer (WDM) followed by parallel on/off modulation by random binary control codes C_A (C_B) and corresponding inverse codes.

Fig. 2. Chaos synchronization of single longitudinal modes between FP lasers.

a–d The same mode λ₀ = 1546.408 nm, e–h different modes λ₀ and λ₁ = 1547.768 nm: optical spectra, temporal waveforms, scatter plot, and histogram of short-term cross-correlation. Bias currents I_A = 11.2 mA, I_B = 11.0 mA and injection power P_jA = P_jB = 400 μW. The inset of Fig. 2b shows the electrical spectrum of chaotic light which indicates a bandwidth of 21.5 GHz.

Fig. 3. Effects of parameters mismatch on chaos synchronization of the λ₀ modes.

a Center wavelength mismatch, b injection power mismatch, and c bias current mismatch. Original settings: center wavelength λ_A = λ_B = λ₀ = 1546.408 nm, bias currents I_A = 11.2 mA, I_B = 11.0 mA, injection power P_jA = P_jB = 400 μW.

Fig. 4. Experimental mode-shift keying chaos synchronization.

a Temporal waveforms of the mode-shift keying chaos as well as the corresponding control sequences of Alice (upper) and Bob (middle), and their sliding short-term cross-correlation (bottom). b The enlarged view of the transition process of synchronization recovery. The correlation length is 1 ns.

Fig. 5. BER and rate of the final keys as a function of the upper comparison threshold V_u.

a Same-frequency extraction at 200 Mbit/s and b frequency-multiplication extraction at 3.2 Gbit/s. m and σ are the mean value and standard deviation of chaotic series.