Spectral Detection And Application Based On Optical Fourier Transform

Spectrum analysis is a fundamental tool in many areas today.With the increase of radio frequency,the development of frequency hopping communication and the emergence of various new radar technologies,the spectrum detection based entirely on electronic devices is restricted by electronic bottlenecks and cannot meet the everincreasing demand.The spectrum detection based on optical Fourier transform realizes a wide variety of detection schemes with the help of the high precision of microwave technology and the rapidity of photon technology.However,the disadvantage of this solution is that the required dispersion is too large to achieve sufficient spectral resolution.In order to overcome the limitations of low resolution and small bandwidth,the microwave signal to be measured needs to be broadened in spectrum and then subjected to Fourier transform.Compared with other spectrum analysis schemes based on Fourier transform,this system has the advantages of bandwidth and resolution,and has wide application prospects.In this paper,the time compression system is used to broaden the spectrum of microwave signal to be measured and zoom in the internal details of the spectrum,and then the signal is modulated by a nonlinear light intensity spectrum analysis(LISA)system to achieve spectrum extraction and Fourier transform,and finally observed by an oscilloscope.This scheme improves the resolution,and realizes large bandwidth and rapidity.The main research contents are as follows:(1)We propose and experimentally demonstrate a time compression scheme based on single-sideband modulation.Mathematical derivation compares the output waveforms under double-sideband and single-sideband modulation,and proves that single-sideband can effectively eliminate the frequency attenuation factor.The output of the system is simulated under single-sideband modulation when the microwave signal is 25 GHz and the compression factor are 10 and 20.The results show that the frequencies of 250 GHz and 500 GHz are obtained in the spectrum,respectively,the spectra have a good signalto-noise ratio.In addition,the simulation shows that increasing the bandwidth of the optical source will reduce the amplitude-decreasing of the system.(2)Completed experiment of time compression scheme.The output waveform of the experiment is obtained when the compression ratio is 2.7,8,and 11.The results show that as the compression factor increases,the signal-to-noise ratio of the system decreases,it is indicated that the maximum compression factor of the experimental system is 11.Finally,the advantages of this system,such as no time-aperture limitation and high linearity,are introduced.(3)The light intensity spectrum analysis system based on nonlinear cross-phase modulation is simulated and analyzed.Using the time domain light intensity spectrum analysis system to extract the compressed spectrum,using the frequency domain light intensity spectrum analysis system to achieve frequency-time conversion.The results show that the frequency difference of the output waveform is 250 GHz in the time domain light intensity spectrum analysis system,which is the value of the compressed microwave signal.The output waveform of the time domain light intensity spectrum analysis system is filtered and shaped to realize frequency time conversion through the frequency domain light intensity spectrum analysis system.The simulation result is 6.94 ns,and the theoretical value is 6.95 ns,it is indicated that the system has realized the Fourier transform.Combining time compression and nonlinearity,this paper implements a detection system with a resolution of 400 MHz and a bandwidth of 840 GHz.