Research On The Generation Of Microwave Waveforms Based On A Dual Parallel Phase Modulator

Arbitrary microwave waveform signals are widely used in radar communication,all-optical network communication,medical imaging and modern instrument systems,and the performance of the system is largely determined by the waveform quality.Compared with the waveform signal generated in the electronic field,the microwave photonic waveform signal breaks through the bottleneck of bandwidth limitation below20 GHz,and has the advantages of high bandwidth,large frequency adjustable range,small loss and anti-electromagnetic interference.Using external modulation technology to generate high frequency millimeter wave signal by frequency doubling of low frequency signal can avoid using expensive high frequency signal source to reduce production cost.In order to solve the problems of small repetition frequency range,low bandwidth and poor system stability of waveform signal generated in the electronic field,this thesis focuses on multi-frequency and multi-waveform microwave signal technology.The research contents are as follows :(1)Firstly,the background and significance of microwave photonic waveform generation technology are expounded.The research status of microwave photonic waveform generation technology at home and abroad is introduced.The advantages of microwave photonic waveform generation technology based on external modulation technology are summarized.The theoretical derivation and principle analysis of the sideband modulation method of the dual parallel phase modulator are carried out,and the characteristics and advantages of the external modulation technology scheme based on dual parallel phase modulators are summarized.(2)In order to improve the frequency doubling factor of the generated signal,two frequency doubling schemes based on cascaded and parallel dual parallel phase modulators are analyzed.The output of frequency-sextuple,frequency-octupled and frequency-quadrupled signals can be generated by the two schemes without any photoelectric filter.The influence of modulation index on the quality of frequency doubling signal and system performance is further analyzed,and the applicable scenarios of cascaded and parallel dual parallel phase modulator frequency doubling scheme are summarized.a 10-tupling millimeter wave signal generation scheme based on a single double parallel phase modulator and stimulated Brillouin scattering effect is proposed.Without using photoelectric filters,the RFSSR of the generated signal is 23.2d B,and the spectrum purity is high.It has certain reference value for millimeter wave generation with high frequency doubling factor.(3)In order to solve the problems of single waveform,a triangular wave,trapezoidal wave and square wave signal generation scheme based on dual parallel phase modulator is proposed.The amplitude of the input signal is the same and the phase difference is 90 ° by adjusting the RF signal of the two sub-phase modulators,which can suppress the ±2 order sideband.In the simulation experiment,by adjusting the RF driving voltage and frequency,a series of continuous triangular wave,square wave and trapezoidal wave microwave signals can be output at 5 ? 12.5GHz,and the root mean square error is less than 0.37.(4)In order to solve the problems of low frequency doubling factor and small repetition frequency range of microwave signal generation,an improved scheme of arbitrary microwave photonic waveform generation based on dual parallel phase modulator is proposed.After laser input dual parallel polarization modulator modulation,two optical signals are obtained by fiber Bragg grating,and the optical signal is balanced to output square wave and trapezoidal microwave signals.Meanwhile,triangular and sawtooth microwave signals can be obtained by using an additional 90°phase shifter.The simulation results show that by adjusting the amplitude and frequency of the RF drive signal,the output microwave photonic signal frequency can achieve 10 to 25 GHz continuous output,and the root mean square error of the signal is less than 0.33.In addition,the effects of modulation index and 90° bridge phase balance on the microwave photonic waveform quality are experimentally analyzed,which verifies that the system has good stability.