Photonic Integrated Chaotic Semiconductor Laser Utilizing Distributed Grating

With the rapid development of semiconductor technology,researchers have developed a variety of small and stable photonically integrated chaotic semiconductor lasers based on optical feedback and mutual injection,which can be reduced to the μm scale in length and have a power spectrum bandwidth of several GHz.These researches have promoted the application of chaotic lasers in scientific research and engineering application.However,there are still some problems in the research of photonically integrated chaotic semiconductor lasers:Firstly,the central wavelength of the chaotic laser is single and cannot be tuned.Currently,most of the photonically integrated chaotic semiconductor lasers are of Distributed Feedback(DFB)structure,and the central wavelength of the generated chaotic laser cannot be tuned in a wide range,which limits its application in wavelength division multiplexing optical communication systems.Secondly,the chaotic laser bandwidth is narrow and the power spectrum is not flat.Restricted by the relaxation oscillation of semiconductor lasers,the chaotic laser power spectrum is not flat,and the energy is concentrated near the relaxation oscillation frequency.Therefore,the bandwidth of chaotic laser can hardly exceed 10 GHz.Narrow bandwidth severely affects the spatial resolution of chaotic optical time domain reflectometer,chaotic distributed fiber sensing and chaotic lidar,and limits the transmission rate of chaos optical communications and the bit rate of random numbers generation.Thirdly,the chaotic laser has a time delay signature,which indicates weak periodicity.The optical feedback structure has a fixed external cavity length,which leads to the weak periodicity of the chaotic laser and obvious time delay signature.Time delay signature of chaotic laser can reduce the randomness of random numbers;lead to security vulnerabilities in chaos optical communications;and introduce false alarms or misjudgments to chaotic lidars and optical time domain reflectometers.Focusing on the above problems,two photonically integrated chaotic semiconductor lasers based on distributed grating are proposed in this thesis to generate wavelength-tunable,broadband,time-delay-signature-suppressed chaotic lasers to satisfy the different application requirements of chaotic lasers.The major works of the thesis are as follows:(1)The photonically integrated chaotic semiconductor laser with distributed Bragg reflector(DBR-PICSL)has been designed and developed,which achieved the wavelength of chaotic laser tuning from 1551.4 nm to 1564.8 nm in the photonically integrated laser,its wavelength tuning range is 13.4 nm.Firstly,a four-segment DBR-PICSL chip is designed based on the DBR laser mode selection and chaotic laser generation mechanism.Secondly,the feasibility of the chip for chaotic laser generation and wavelength tuning is verified by simulation.Finally,the DBR-PICSL chip is fabricated and the wavelength tuning of the chaotic laser are experimentally studied,and the influence of the phase and feedback intensity in the external cavity on the chaotic laser,as well as the distribution of the bandwidth and dynamics in the space of different current parameters are explored.(2)The nonlinear dynamics of the DBR-PICSL with multi-parameter modulation is studied,and a prototype of photonically integrated chaotic signal generator is developed.Firstly,the evolution path of the laser from periodic state,intermittent chaotic state,chaotic state,steady state,to optical square wave when the gain of the external cavity gradually increases is investigated.Secondly,the beat frequency between two optical frequencies in the singleperiodic state is investigated,and the tunable high-frequency microwave with frequencies from23.94 GHz to 25.26 GHz is obtained;the periodic and nonperiodic optical square wave is obtained,and the effects of the SOA section current on the periodicity and duty cycle of the optical square wave are explored.Finally,a packaged DBR-PICSL,a temperature control and multiple current drive system,as well as a host computer master control system,are designed to develop a prototype of the photonically integrated broadband chaotic signal generator.(3)The methods of mutual injection and optical feedback based on the DBR-PICSL are proposed to realize the bandwidth enhancement of wavelength-tunable chaotic lasers.Firstly,the method of mutual injection based on the DBR-PICSL is proposed to widen the bandwidth of the chaotic laser by exciting the nonlinear optical frequency,and a chaotic laser with a wavelength tuning range of 6.2 nm and a bandwidth up to 36.7 GHz is generated experimentally.Further,the method of ring optical feedback based on the DBR-PICSL is proposed to widen the bandwidth of the chaotic laser by exciting the nonlinear frequency components,and a chaotic laser with a tuning range of 10.0 nm and a bandwidth up to 33.6 GHz is generated by adjusting the DBR section current.The effect of feedback intensity on the bandwidth of the chaotic laser at different wavelengths are investigated.(4)The photonically integrated chaotic semiconductor laser with random grating and mutual injection(RG-MI-PICSL)has been proposed and designed.A chaotic laser with bandwidth of 13.1 GHz and time delay signature value of 0.06 is generated by simulation.Firstly,the semiconductor rate equation theoretical model of the RG-MI-PICSL is developed.Secondly,the suppression effect of the random grating on the time delay signature and the enhancement effect of the mutual injection on the bandwidth are investigated.The mechanism of time delay signature suppression and bandwidth enhancement is investigated.Finally,the variation of chaotic laser bandwidth and time delay signature value in the parameter space of injection strength,feedback strength and detuning frequency are investigated,and the twodimensional parameter space map of chaotic laser with time delay signature suppression and bandwidth enhancement is obtained.