Research On Microwave Waveform Control Technology Based On Time-frequency Synthesis Method

Generation and control of microwave arbitrary waveform have attracted much attention due to their applications in radar,sensors,and signal processing.Usually,microwave arbitrary waveform is generated in the electrical domain,but due to the existence of electronic bottleneck,the generated waveform bandwidth is very limited and can not meet the needs of modern communication system.Fortunately,photonic technology is a good way to solve this problem,and also has the advantages of large bandwidth,low loss,electromagnetic immunity.Based on this,optical arbitrary waveform generation technology came into being.In this paper,several main optical arbitrary waveform generation techniques are introduced,focusing on the analysis of time domain synthesis and frequency domain synthesis and their advantages and disadvantages.The advantages of time domain and frequency domain are combined and comprehensively utilized.Based on these two methods,simple and convenient methods to generate high-quality microwave arbitrary waveforms by combining with external modulation technology are studied,especially the generation of more complex sawtooth pulse and parabolic pulse.The following works have been accomplished.A sawtooth waveform generation based on time-frequency synthesis method is proposed.In this work,depended on the polarization-sensitive characteristic of the Mach-Zehnder modulator,the modulation sidebands and optical carrier can independently exist on two orthogonal polarization directions.Therefore,the required Fourier components can be obtained on two polarization dimensions separately,and the superposition of the orthogonal optical envelopes synthesize a sawtooth waveform in time domain.The feasibility of the scheme is theoretically analyzed.In this scheme,great sawtooth pulses with full duty cycle at 3,5,and 8 GHz are obtained by only use a modulator and a laser.A parabolic pulses generation based on the transmissivity characteristics of Mach-Zehnder modulator is proposed.In this work,the transmission and modulation characteristics of Mach-Zehnder modulator are fully used.Mathematically,a small region in the center of a peak or valley of a sine-squared function can be considered as a parabola.Fortunately,the power transfer function of Mach-Zehnder modulator is a sine-squared function.When MZM is driven by a linearly signal,the transmissivity curve can be mapped to the time domain,and the location and span of the mapping are controlled by the bias voltage and the driven voltage respectively.Therefore,parabolic pulses with the same frequency as the drive signal can be obtained by using a triangular signal to drive the modulator,which the modulator is biased at the point closing to maximum transmission point or minimum transmission point and the driven voltage is small enough.Moreover,the frequency-doubled parabolic pulses are generated when the bias is accurately set at maximum transmission point or minimum transmission point.