Longsheng Wang

Minimal-post-processing 320-Gbps true random bit generation using physical white chaos

Chaotic external-cavity semiconductor laser (ECL) is a promising entropy source for generation of high-speed physical random bits or digital keys. The rate and randomness is unfortunately limited by laser relaxation oscillation and external-cavity resonance, and is usually improved by complicated post processing. Here, we propose using a physical broadband white chaos generated by optical heterodyning of two ECLs as entropy source to construct high-speed random bit generation (RBG) with minimal post processing. The optical heterodyne chaos not only has a white spectrum without signature of relaxation oscillation and external-cavity resonance but also has a symmetric amplitude distribution. Thus, after quantization with a multi-bit analog-digital-convertor (ADC), random bits can be obtained by extracting several least significant bits (LSBs) without any other processing. In experiments, a white chaos with a 3-dB bandwidth of 16.7 GHz is generated. Its entropy rate is estimated as 16 Gbps by single-bit quantization which means a spectrum efficiency of 96%. With quantization using an 8-bit ADC, 320-Gbps physical RBG is achieved by directly extracting 4 LSBs at 80-GHz sampling rate.

Time delay signature elimination of chaos in a semiconductor laser by dispersive feedback from a chirped FBG

Time delay signature (TDS) of a semiconductor laser subject to dispersive optical feedback from a chirped fibre Bragg grating (CFBG) is investigated experimentally and numerically. Different from mirror, CFBG provides additional frequency-dependent delay caused by dispersion, and thus induces external-cavity modes with irregular mode separation rather than a fixed separation induced by mirror feedback. Compared with mirror feedback, the CFBG feedback can greatly depress and even eliminate the TDS, although it leads to a similar quasi-period route to chaos with increases of feedback. In experiments, by using a CFBG with dispersion of 2000ps/nm, the TDS is decreased by 90% to about 0.04 compared with mirror feedback. Furthermore, both numerical and experimental results show that the TDS evolution is quite different: the TDS decreases more quickly down to a lower plateau (even background noise level of autocorrelation function) and never rises again. This evolution tendency is also different from that of FBG feedback, of which the TDS first decreases to a minimal value and then increases again as feedback strength increases. In addition, the CFBG feedback has no filtering effects and does not require amplification for feedback light.

Synchronization-Based Key Distribution Utilizing Information Reconciliation

We propose a scheme to realize a synchronization-based key distribution utilizing the information reconciliation method of lower triangular error-bits detection. The proposed method can solve the problem of error bits caused by parameter mismatches of two synchronized semiconductor lasers in the scheme of synchronization-based key distribution. Theoretical analysis shows that this method can detect error bits with high probability through one-time information transmission of public keys. Moreover, reconciliation efficiency of this method is also studied theoretically. Finally, we demonstrate the feasibility of this method and investigate the security against leakage of information in the reconciliation procedure.

Post-processing-free 400 Gb/s true random number generation using optical heterodyne chaos

True or physical random number generation (RNG) is vital to supply keys for information security. Chaotic laser has proven to be a promising physical entropy source for high-speed RNG. Unfortunately, some defects of laser chaos such as sharp spectrum, time-delay signature and asymmetrical amplitude distribution, limit the generation speed and lead to requirement of complicated post processing. Here, we report a RNG method by using the optical heterodyne of two chaotic optical-feedback semiconductor lasers as entropy source. The optical heterodyne chaos has a flat spectrum, symmetric amplitude distribution, and has no time-delay signature; these merits can improve the RNG speed and reduce post-processing requirements. In experiments, we generate a flat-spectrum chaos with a 3-dB bandwidth of 16GHz. Using 8-bit analog-digital conversion at a sampling rate of 80Gb/s, we experimentally find that the random numbers directly extracted from the 5 least significant bits (LSBs) can pass the NIST randomness test without help of any post-processing method. That is, 400-Gb/s (5×80Gb/s) physical random number generation is achieved without post processing.

Random Bit Generator Using Delayed Self-Difference of Filtered Amplified Spontaneous Emission

We propose a scheme for random bit generation with filtered amplified spontaneous emission (ASE). Using the filtered ASE, we can get larger signal fluctuations than when using directly detected ASE with a photodetector. Utilizing the delayed self-difference technique to improve the symmetry of filtered ASE, we experimentally achieve real-time 2.5-Gbit/s random sequence generation, which matches with the speeds of fiber communication for one-time pad encryption. Experimental results show that the generated random sequences can pass NIST tests as long as the delay time is beyond a threshold value, which is called the minimum delay time (MDT). Further simulation results indicate that there is a certain relationship between the MDT and bandwidth of the ASE signal.

Ultra-Wideband Chaos Life-Detection Radar with Sinusoidal Wave Modulation

We propose and experimentally demonstrate an ultra-wideband (UWB) chaos life-detection radar. The proposed radar transmits a wideband chaotic-pulse-position modulation (CPPM) signal modulated by a single-tone sinusoidal wave. A narrow-band split ring sensor is used to collect the reflected sinusoidal wave, and a lock-in amplifier is utilized to identify frequencies of respiration and heartbeat by detecting the phase change of the sinusoidal echo signal. Meanwhile, human location is realized by correlating the CPPM echo signal with its delayed duplicate and combining the synthetic aperture technology. Experimental results demonstrate that the human target can be located accurately and his vital signs can be detected in a large dynamic range through a 20-cm-thick wall using our radar system. The down-range resolution is 15cm, benefiting from the 1-GHz bandwidth of the CPPM signal. The dynamic range for human location is 50dB, and the dynamic ranges for heartbeat and respiration detection respectively are 20...

White-Chaos Radar With Enhanced Range Resolution and Anti-Jamming Capability

Laser chaos is promising for constructing high range-resolution and anti-jamming radars, whereas the range resolution and anti-jamming capability are unfortunately limited by laser relaxation oscillation and external-cavity resonance, respectively. Here, we theoretically propose using a broadband white chaos generated by optical heterodyne of two chaotic external-cavity semiconductor lasers as source signal to construct a radar system with enhanced range resolution and anti-jamming capability. The white chaos not only has a white-noise-like wide spectrum without relaxation oscillation, but also has no signature of external-cavity resonance. Benefitting from these merits, the proposed white-chaos radar shows a marvelous unambiguous detection performance with subcentimeter range resolution. Moreover, the elimination of external-cavity resonance enables the randomness improvement of source signal, and resultantly, the anti-jamming capability is enhanced as well.

Applications of chaotic laser in optical communications

Laser chaos has wide applications in field of optical communication. Besides optical chaos communication, laser chaos can be used in random bit generation, lidar and optical time-domain reflectometer. This paper reviews our recent results of chaos-based optical time-domain reflectometer and random number generation in our group. In addition, we present that chaotic laser can be utilized to generate white noise with a 3-dB bandwidth of 14GHz.

Improving intergroup synchronization in a ring topology structure of semiconductor lasers by asymmetric coupling

We numerically demonstrate the enhancement of intergroup synchronization in a ring topology structure consisting of four semiconductor lasers (SLs) by asymmetric coupling. The lasers are divided into two groups, each of which consists of two non-adjacent lasers with the same optical frequency. We study the intergroup synchronization performance of symmetric coupling and asymmetric coupling. The results indicate that the synchronization coefficient (SC) of intergroup synchronization has a saturation value which displays a plateau ranging only from 0.8 to 0.9 in symmetric coupling ring structure. Through asymmetric coupling, the SC of intergroup synchronization above 0.9 can be obtained, and its maximum value can be enhanced up to 0.98 as coupling strength increases. Besides, the intragroup isochronal identical synchronization is kept. Our results also indicate that the enhancement of the intergroup synchronization is physically attributed to the injection-locking effects caused by asymmetric coupling between groups.