Research On All-optical Measurement Technology Of Transient Optical Signals Based On Four-wave Mixing And Time Stretching

Ultrashort laser pulse provides a strong means for the study of ultrafast phenomena. Using ultrashort pulse pump/detection system, people can study physics, chemistry, biology and many of the basic process. Researching of high-speed optical pulse amplitude and phase measurement method has important practical significance on the development and application of ultrashort pulse laser technology. Especially in the field of the transient optical signal measurement which can solve the key issues in national defense and economic development.This paper proposes an all-optical real-time measurement technology based on a wide spectrum four-wave mixing and time stretching. Time-wavelength mapping four-wave mixing converts a single wavelength signal to a time-wavelength-mapped idle light, which achieves a super-resolution all-optical sampling. Time-stretching can greatly compress the bandwidth of the signal and can be easily measured by the photoelectric detection system. The combination of the two techniques achieves the real-time measurement of the transient optical signal.This paper focused on the following topics:1. The significance of the transient optical signal measurement technology has been introduced.It describes the current methods for the measurement of transient optical signals, including direct measurement photoelectric streak camera, fast pulse sampling and other indirect measurement methods SHG, FROG and SPIDER, etc. The advantages and disadvantages of these methods are given. We introduced the applications of Photonics in transient optical signal measurement and proposed a transient optical signal measurement method applying Photonics-Dispersive Fourier Transform time stretching techniques.2. Explained the theory of a broad spectrum four-wave mixing and dispersion Fourier transform time-stretching.According to Maxwell's equations it derives the coupled wave equations, and gives its analytical solution. We introduced the phase matching condition and give three methods to achieve single-mode fiber approximate phase matching. We value coupled wave equation solving, analysis of the factors influencing the efficiency of four-wave mixing. Including: the frequency of the signal light, pump power and fiber dispersion characteristics. We give the wavelength range of four-wave mixing gain wide pump light of 1530-1550nm simulation calculations.Simply analyzed the nonlinear Schrodinger equation used to describe the dispersive Fourier transform, introduced the basic parameters of the dispersive Fourier Transform: spatial resolution, scanning frequency, time domain sampling point, and give their relationship. Analyzed the derivation of time-stretching factor and analog to digital conversion and the effect of time-stretching on SNR. It introduces the realization method of time-stretching using SM fiber structure.3. It describes the transient optical measuring method of the research.It introduced its composition, comprising:a pump light source, time-wavelength mapping module, four-wave mixing wavelength conversion module, a filter structure, time-stretch module, signal processing. It gives the working principle of four-wave mixing and time-stretch module, introduces the key technical parameters of time stretching and signal gain.4. Verified the feasibility of the four wave mixing and time stretching.Carried out experiment on single-frequency pump four-wave mixing and wide spectrum pump four-wave mixing. Measured the optical power of idler light using different lengths of high non-linear fiber. Compared the four-wave mixing efficiency of different pump light wavelength ranges. Build a dispersive Fourier transform module having a stretch factor of 5.8 with an optical SNR of 27dB. A 50GHz beat signal is measured, and the experimental results are analyzed.5. The results of the experiment and the limitations of the measurement are analyzed, and suggestions for improvement are put forward.