Research On Linearly Chirped Pulse Generation Based On Optical Spectral Shaping And Fiber Dispersive

With the development of microwave technology in the fields of broadband wireless access network,wireless sensor network,radar system and radio astronomy and so on,the real-time generation of high frequency microwave signal becomes the major problem.Microwave photonics as a fusion of microwave and optical two major technical disciplines,it studies how to use optical advantages,such as inherent high speed,large bandwidth,low loss and anti-electromagnetic interference inherent,to solve the traditional microwave technology bandwidth and rate bottlenecks.Linear frequency modulation signal combined with pulse compression technology,can increase the pulse width to improve the detection range,but also can increase the receiver SNR to improve the radar range resolution.Which is widely used in high-performance radar.In this paper,the linearly chirped pulse microwave signal generation based on microwave photon technology is proposed as the research direction.A new method of photon-assisted is proposed on the linearly pulsed microwave signal generation.The main works are taken in the following aspects:1.The effect of group velocity dispersion and self-phase modulation on the spectrum of ultrashort optical pulse propagation in fiber is studied.Due to the dispersion effect,the different pulse frequencies have different speeds in the fiber,so that the pulse own the different time at the output and the pulse was widened.Due to the self-phase modulation effect,the optical pulse is introduced into a nonlinear phase shift related to the intensity of the input pulse,and the induced chirp is linear and positive in a large region of the Gaussian pulse.2.A chirped microwave signal generation method based on spectral filtering and unbalanced dispersion is proposed and studied.In this method,we adjust the two tunable optical filters to control the center frequency and bandwidth of the signal.The measured signal has ~11ns pulse duration and ~32GHz bandwidth,corresponding to a TBWP of ~352.3.A novel chirp microwave signal generation method using an unbalanced Sagnac loop is proposed and studied.Which solves the problem of linear chirp microwave signal instability from the previous study.In this method,a chirped microwave pulse generation scheme based on self-phase modulation effect in an unbalance Sagnac loop is proposed.The generation of chirped microwave pulse with a bandwidth as large as 23 GHz is experimentally demonstrated.