Research On Time Lens And Its Applications Based On Four-wave-mixing In Silicon-based Waveguides

The time lens has the similar function as the space lens,which can perform the broadening,compression,and fourier transform of the optical pulse.The ultrashort pulse could be magnified by a time lens to achieve the real-time analysis in the time domain.This greatly reduces the requirements of measurement accuracy and response rate of detection equipment.In addition,the fourier transform of ultrashort pulses can be performed with a time lens,which can realize the mutual conversion between the frequency domain information and time domain information.Thus the frequency domain information could be characterized and measured in real-time using photodetectors.Therefore,time lens has great potential and practical value in time microscopy,time domain imaging and optical signal processing.In this paper,the time lens and its applications based on four-wave mixing in the silicon-based waveguide are investigated.The temporal magnification,fourier transform and real-time sampling of high-speed optical signal could be realized.The main research work includes:1.The research background and significance of time lens are analyzed in detail.The different implementation methods,their advantages and disadvantages are compared.The research status of time lens and its applications at home and abroad is also summarized.2.Based on the principle of space-time duality,the basic theory of time lens is expounded by comparing the diffraction characteristics of near-axial monochromatic light in space domain with the dispersion transmission characteristics of narrow band light pulse in time domain.The generation conditions of temporal magnification and fourier transform are analyzed.3.A low transmission loss silicon-germanium micro-nano waveguide for the midinfrared is optimally designed.The transmission theory of light in waveguides and the influence of structure parameters on waveguide dispersion and nonlinearity are investigated.A mid-infrared silicon-germanium micro-nano waveguide with wide band,low flat dispersion and high nonlinearity is designed.The coupling mode equation of mid-infrared ultrashort pulse transmission in the waveguide is established,and the influence of pump light power,signal light power and waveguide length on the fourwave mixing process is studied.An efficient and wide-band four-wave mixing process is realized by optimizing these parameters.4.The time lens technique based on four-wave mixing on a chip is studied.Influences of the high order dispersion,three photon absorption,free carrier effect,phase modulation and cross phase modulation on the time imaging are analyzed.It is found that the third-order dispersion can lead to the output waveform distortion and broadening,fourth-order dispersion will cause the compression of output waveform,three photon absorption and the free carrier effect will cause the output waveform distortion and conversion efficiency decrease.Self-phase modulation effect and crossphase modulation effect also distort the output waveform.By optimally designing the input dispersion,four-wave mixing and output dispersion,the temporal magnification of an ultrashort mid-infrared pulse could be performed with magnification greater than 500 times.High-speed optical pulse sampling and fourier transform are also realized.These results provide new technical approach for real-time measurement of ultrafast pulse and ultrafast optical signal processing.