| In recent years,chaotic lasers have been widely used in many fields,including modern secure communications,high-speed random number generation,and high-precision radar ranging.In the above applications,the preferred light source is generally a semiconductor laser.This is because semiconductor lasers have the advantages of being lightweight and compact,having a wide wavelength range and rich dynamic characteristics.However,the chaotic signal output by the traditional optical feedback semiconductor laser system has two disadvantages: first,the path length information of the output light of the semiconductor laser entering the external cavity and returning to the laser will cause the chaotic signal output by the system to contain obvious time delay signature,it will bring great drawbacks to the application of chaotic lasers.For example,in modern confidential communication,it will destroy communication security and cause information leakage;in the application of random number generation,it will lead to statistical performance degradation.Reduced;in radar ranging,it will affect the accuracy of detection,and even lead to misjudgment of detected objects.Secondly,the main energy of the output signal is concentrated near the relaxation oscillation frequency,and the energy in the low frequency part and high frequency part of the spectrum is insufficient.This will limit the speed of information transmission and random number generation in the process of chaotic optical communication and random number generation;in the process of circuit design and information processing of the actual system,the lack of low-frequency energy will affect the collection of signals.inconvenience.Based on the above reasons,this paper deeply studies the chaotic signal generation method with wide spectrum and low TDS.The main research contents are as follows:(1)Theoretical research on the output characteristics of optical feedback semiconductor lasers.Research the process of the optical feedback semiconductor laser output signal entering the chaotic state;establish the rate equation model of the fiber Bragg grating(FBG)feedback semiconductor laser,and study the influencing factors of the TDS of the chaotic signal generated by the FBG feedback;establish the FBG array feedback semiconductor laser rate The equation model simulates the suppression of the TDS of the chaotic signal by the enhanced distributed feedback of the FBG array,and studies the influence of the structure of the FBG array on the TDS in theory.(2)Experimental verification of the output characteristics of the optical feedback semiconductor laser.Complete the construction of the experimental platform of the traditional optical feedback,FBG feedback and FBG array feedback semiconductor laser system,analyze the dynamic characteristics of the semiconductor laser and the conditions for entering chaos;complete the device selection by testing the core optical components in the system;use FBG The distributed feedback is used to realize the output of low TDS chaotic signal.The time domain,frequency domain and autocorrelation function characteristics of the system output signal are calculated,and the influence of optical feedback intensity and detuning frequency on the TDS peak is analyzed.The chaotic light characteristics of the enhanced distributed feedback output of the FBG array as a reflective element,and the effects of the feedback light intensity and detuning frequency on the TDS suppression effect are studied.(3)Research on spectrum broadening method of chaotic signal.A structure of FBG array ring oscillator is proposed,which can not only strengthen the high-frequency components in the chaotic signal,but also strengthen the low-frequency components in the chaotic signal,and the spectral shape of the chaotic signal spectrum is more flat.The effects of the detuning frequency of the laser and FBG and the gain of the semiconductor optical amplifier on the chaotic bandwidth are studied,and the TDS value of the output chaotic signal is also tested. |
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