Research On Microwave Generation Based On Optically Injected Semiconductor Lasers

Microwave signal source is the“engine”of the RF information system(wireless communication,radar,electronic warfare,deep space exploration),which determines the upper limit of system performance.Photonic generation of microwave signals can overcome various limitations of electronic technology in carrier frequency,bandwidth,electromagnetic interference and noise.However,the existing schemes of microwave photonic signal generation suffer from large volume,complicated system and poor tuning ability,which limits its application in practical systems.Therefore,it is urgent to develop a new microwave photonic signal generation technique that can overcome the above disadvantages.Semiconductor laser is a potential candidate for microwave signal generation due to compactness and potential for integration.In this thesis,optical injection technology is used to break through the limitation of the intrinsic relaxation oscillation frequency of the semiconductor laser to realize the generation of the tunable single-frequency microwave signal.In addition,multi-dimensional dynamic parameter manipulation is used to generate wideband microwave waveform.Three key problems of the microwave signal generation method,such as small tuning range,poor signal quality and poor reconfigurability,are studied.Firstly,nonlinear dynamic characteristics of the optically injected semiconductor laser aretheoretically analyzed.The characteristics and distribution of different dynamic states,evolution routing of the nonlinear dynamics,as well as the influence of system parameters on the nonlinear dynamic evolution are studied by analyzing the theoretical model.It is concluded that a larger linewidth enhancement factor can enhance the period-one(P1)oscillation state,which laid the foundation of enlarging frequency range in the microwave generation.A theoretical model of microwave signal generation is established.Simulation and experimental results show that the generated microwave signal can be tuned from several GHz to hundreds of GHz.To address the problem of poor signal quality,an approach to enhance the performance of the P1 oscillation signals based on subharmonic modulation and optoelectronic feedback is proposed,and the side-mode suppression ratio,phase noise as well as frequency stability are significantly improved.Secondly,pulsed signal generation technology based on optically injected semiconductor lasers is also studied.We propose a modulator-free triangular pulse generator based on time-domain synthesis.The effects of delay error and amplitude error on the synthesized triangle waveform are analyzed.In the experiment,triangular pulse trains with tunable repetition rates are successfully generated.Assisted by optical pulse compression technique,a frequency tunable short optical pulse generation scheme based on an optically injected semiconductor laser is proposed and investigated.In the experiment,optical pulse trains with repetition rates tunable from 6.5 to 15 GHz are generated.To achieve reconfigurable wideband waveform generation,the high-speed frequency switching characteristic of P1 oscillation state is numerically and experimentally studied.Based on modulated optical injection,dynamical control of injection parameters is proposed to manipulate the instantaneous frequency of the generated microwave,various wideband waveforms like microwave frequency-hopping(FH)sequence and linear frequency-modulated(LFM)waveform are then generated with a time-bandwidth product(TBWP)over 1.2×10~5,and the main parameters are reconfigurable.Signal quality of the generated waveform can be significantly enhanced by Fourier Domain Mode Locking(FDML).Based on this system,an improved scheme for extending the frequency and bandwidth of the generated LFM signal is proposed by employing a polarization modulator to implement microwave photonic frequency multiplication.In addition,when applied to radar system,the range resolution can be improved effectively.In the experiment,a ranging resolution of 2.46 cm is obtained.In summary,the proposed microwave signal generator features low cost,simple structure and high performance,which can find applications in future multi-functional,multi-tasking and integrated RF systems.