The Research Of Optical Fourier Transform Based On Time Lens

Traditional electronic technology is limited by its instantaneous bandwidth and response rate,so how to realize rapid broadband radio frequency(RF)spectrum detection is a hot topic in recent years.Photonic technology came into being.Optical Fourier Transform(OFT)can realize time-frequency conversion of signals in microseconds or nanoseconds,which provides a new method for real-time spectral measurement.Among various OFT schemes,the optical Fourier transform system based on time lens has simple structure and stable performance,so it attracts more attention.However,the spectrum resolution of the OFT system based on time lens merely is low,which cannot meet the spectrum analysis needs.In order to achieve high resolution spectrum analysis,this paper proposes a time compression technique to preprocess the signal.Inspired by the time stretch technique,first the RF signal is modulated onto the chirped optical pulse,then the dispersion compensation optical fiber is used to compress the RF signal in the time domain,thus the corresponding spectrum is broadened.Finally the compressed signal passes through the time lens system to perform spectrum detection.Thus a system with the same accuracy of spectrum detection can obtain a higher spectrum resolution.The main work of this paper is as follows:(1)Based on space-time correspondence,the principles of time lens are deeply analyzed.Based on the principle of Fourier transform,a time compression technique is proposed to compress the RF signal to obtain broadened spectrum,which equivalently improves the spectral resolution of the optical Fourier transform(2)In order to avoid the interference of the original chirped pulse on the signal,the compressed signal needs to be reloaded onto the optical carrier to perform OFT.But the compressed signal has a broad bandwidth,which exceeds the bandwidth of the existing photodetectors and modulators.Based on the cross-phase modulation effect of the highly nonlinear photonic crystal fiber,the compressed RF signal is loaded onto the target optical carrier.The all-optical modulation system of the high-speed signal is simulated.(3)The spectrum detection system based on time compression and time lens is simulated.The compressed RF signal is loaded onto the time lens system through the cross-phase modulation effect.The time lens system is a two-dispersion model,the RF spectrum is directly obtained in the time domain of the output signal.The system improved the spectral resolution effectively.The research results show that the scheme can realize the RF spectrum detection in the period of one optical pulse with the resolution of 44 megahertz,the performance are improved greatly compared with the existing optical Fourier transform system,therefore it has broad application prospects.