Generation Of White Chaos And Its Applications In Physical Random Number Generation And Radar Detection

Chaotic laser has great potentials in the applications of physical random number generation and high-resolution anti-jamming radar.The key to these applications is a compact and broadband chaotic light source.And a semiconductor laser with external optical feedback is usually the common choice owing to its simple and integratable setup.However,some defects of chaotic laser induced by the external-cavity feedback restrict its practical applications.(1)External-cavity semiconductor laser(ECL)has obvious relaxation oscillation.Observed from the power spectrum,the power amplitude of relaxation oscillation is much higher than that of the lowest spectral component and dominates the whole spectrum.It greatly limits the effective bandwidth and flatness of power spectrum.(2)External-cavity resonance causes obvious correlation peaks at the external-cavity period and its multiples in the autocorrelation function of chaotic laser,which is referred to as time-delay signautre.This signature makes ECL correlated with its previous states periodically.(3)Temporal waveforms of ECL oscillate asymmetrically whichs results in an asymmetric amplitude distribution.For physical random number generation,the relaxation oscillation limits the effective bandwidth only to a few GHz and thus restricts the entropy rate of random numbers.Moreover,the time-delay signature and asymmetric amplitude distribution deteriorate random numbers' randomness and ratios,respectively.To surmount this deterioration,complex and offline processing operations are required,which degrades the capability of real-time generation of random numbers limiting the practical applications.For the radar detection,the relaxation oscillation limits the detection bandwidth of chaotic laser hindering the improvement of range resolution in target identification.Morevover,the time-delay signature exposes ECL's key parameter of external-cavity length,with which the radar system can be reconstructed.As a result,the security and anti-jamming capability are degraded.To solve the aforementioned problems,we proposed to utilize the optical heterodyne of two ECLs to generate the noise-like wideband chaotic signals,which is referred to as white chaos.The white chaos not only has no time-delay signature but also has a flat spectrum and a symmetric amplitude distribution.Using the white chaos as entropy source,applications of chaotic laser in physical random number generation and high-resolution anti-jamming radar are both greatly optimized.For random number generation,the entropy rate is greatly improved.In addition,the post-processing operaions in random number generation are minimized while improving the randomness of random numbers.For radar detection,the range resolution and anti-jamming capabilities are both enhanced.The main works and results of this paper are summarized as follows.(1)In chapter 1,a brief overview of chaotic laser's applications is first given.Then,two typical generation methods of chaotic laser are introduced.Finally,the defects of chaotic laser induced by external-cavity feedback and its restrictions in physical random number generation and radar detection are discussed.(2)In chapter 2,an optial heterodyne method to surmount the defects of chaotic laser is demonstrated theoretically and experimentally.With non-resonant beatings of two ECLs,the phase dynamics of ECL are converted into intensity dynamics and resultantly the noise-like wiedeband chaotic signal(white chaos)is generated.To extract the white chaos,the heterodyne detection of a balanced photodetector is used.Experimental results indicate that the white chaos has a wide and flat power spectrum with a 3-dB bandwid th of 16.7 GHz.Moreover,it not only has a symmetric amplitude distribution with a small skewness of 0.072 but also has no time-delay signature.Using this method,the defects of ECL above mentioned are overcome simultaneously.(3)In chapter 3,the physical randomness of white chaos is analyzed theoretically and experimentally including correlation dimension,permutation entropy as well as bit entropy.Results show that white chaos is a high-deimensional and complex signal with wide bandwidth and excellent randomness.(4)In chapter 4,experimental results indicate that the white chaos can not only improve the generation rates of random numbers but also can minimize the post-processing operations in random number generation.For single-bit extraction,the theoretical generation rate is estimated to be 16Gb/s,and real-time 14Gb/s random number generation is achieved in the confirmatory experiment.For multi-bit extraction,a theoretical generation rate of 320Gb/s can be achieved using only least-significant-bit(LSB)retention without other post-processing operations.Confirmatory experiment obtains 112Gb/s generation rate by extracting 4LSBs at the sampling rate of 28GS/s.Having not rechaed the theoretical generation rates in the confirmatory experiments of single-bit and multi-bit extractions is due to the bandwidth limitation of ADC.(5)In chapter 5,by harnessing the white chaos as source signal,we theoretically propose a white-chaos radar and investigate its performances in range resolution and anti-jamming capability.Results of calculating auto-ambiguity functions show that the white-chaos radar not only has a marvelous unambiguous detection performance with subcentimeter range resolution but also has an excellent anti-jamming capability.