The Optimization Of Chaotic Laser Characteristics By Dispersion And Self-phase Modulation In Fibers

Chaotic laser contains the characteristics of wide frequency spectrum and noise-like,and possesses important applications in the fields of chaotic secure communication,chaotic radar,physical random number generation,optical time domain reflectometer and distributed optical fiber sensing.The generation of chaotic lasers usually uses optical feedback semiconductor lasers with simple structures.There are problems such as the chaotic time-delay signature(TDS)caused by the feedback external cavity,the relaxation of the oscillation frequency result in uneven spectrum of the chaotic spectrum,and the narrow bandwidth(BW),which limit the application of chaotic lasers.Therefore,it is urgent to carry out research on the optimization of chaotic characteristics such as suppression of chaotic TDS and enhancement of chaotic spectrum BW.This paper proposes to use the dispersion and self-phase modulation effects in a single-mode fiber to suppress the chaotic TDS and enhance the chaotic spectrum BW.This simulation model can adjust various parameters in the fiber in detail to intuitively control the strength of dispersion and self-phase modulation effects,which saves experimental cost and can provide theoretical guidance for follow-up research.The research work of this paper is specifically carried out as follows:(1)The Lang-Kobayashi single-mode rate equation and the nonlinear Schr?dinger equation are used to establish a theoretical model that uses fiber dispersion and self-phase modulation to suppress the chaotic TDS and enhance the chaotic spectrum BW.In the simulation,the second-order dispersion coefficient and the average input optical power in fibers are adjusted to control dispersion and self-phase modulation.Numerical analysis results show:When the fiber length reaches the chaotic laser dispersion length,the chaotic TDS starts to be suppressed due to the significant enhancement of dispersion,then the value of the autocorrelation at the chaotic TDS will descent at the fastest rate of 0.5 d B/km.When chaos transfer to a certain length in the fibers,the self-phase modulation also accumulates to the significant range of action.At this time,the chaotic TDS will achieve a best and stable suppression state,and the suppression effect can reach 11.6 d B.(2)We carry out the study of fiber dispersion and self-phase modulation effect to achieve chaotic spectrum BW enhancement.The numerical analysis results show:when the average fiber input power of the chaotic laser reaches 14.9 m W,the selection is different according to the different fiber length.which can make chaos spectrum BW enhancement over 40%.Especially,when fiber length is 10 km and second-order dispersion coefficient is 4 ps~2/km,the BW is increased from 6.51 GHz to 9.46 GHz,which can be enhanced about 45.3%.And on this basis,the simultaneous optimization of chaotic TDS suppression and spectrum BW enhancement is realized.