Spectro-temporal Analyzer Based On Time Lens And Its Application

With the rapid development of ultrafast measurement technology,the fast dynamic process research extends to explore some rapid transient phenomena,which occur in the time scale of microsecond to nanosecond.As an important carrier of information,optical spectrum is essential for the dynamic process research.Since the spectro-temporal analysis technology is able to overcome the acquisition speed limitation of traditional spectrometers,it has become one of the most powerful tools that investigate the rapid dynamic processes.Among them,the spectro-temporal analysis technology based on time lens focusing mechanism,analogous to the Fourier transform at the focal plane of the space lens,can obtain the spectral information in the time domain.Combined with the advantage of fast detection respond speed,the fast dynamic spectrum can be presented in real time,which greatly enhanced the acquisition speed of spectrum.In this dissertation,the spectro-temporal analyzer based on the time lens focusing mechanism is analyzed in detail,and two kinds of spectro-temporal analyzer with enhanced temporal stability or large temporal numerical aperture are proposed and demonstrated.Moreover,the spectro-temporal analysis technology is applied to the research of the thermo-optic dynamics in optical microspheres.Research achievements and contributions are summarized as following:(1)Basic theory of the spectro-temporal analysis technique is investigated.Firstly,the basic principle of the space-time duality is provided.Then the principle and theoretical model of the spectral analysis based on dispersive time-stretch is analyzed.Meanwhile,the principle and theoretical model of the spectral analysis based on time lens focusing is also analyzed.By contrast with the dispersive time-stretch,the spectro-temporal analyzer based on time lens focusing achieves improved observation window and spectral resolution.(2)A temporal stability enhanced spectro-temporal analyzer is designed and experimentally investigated.The stability mechanism of the time lens focusing process is theoretically analyzed,and it pointed out that the sources of the temporal instability are the temperature-induced frequency jitter of time lens and timing jitter of output dispersion,which result in the degraded spectral accuracy.By introducing the phase-locked loop for the mode-locked fiber laser and the temperature feedback control for the long fiber links,the temporal instability of the spectro-temporal analyzer has been resolved,and the spectral accuracy is improved from 1.6nm to 0.04nm.(3)An integrated spectro-temporal analyzer with large temporal numerical aperture,which utilizes the silicon based four-wave-mixing time lens,is also designed and experimentally demonstrated.Firstly,the dispersion requirement of the four-wave-mixing time lens for nonlinear waveguide is analyzed in detail.Simulation design and fabrication of the silicon waveguide are also carried out.By using the time lens based on silicon waveguide,an integrated spectro-temporal analyzer with large temporal numerical aperture is realized.It is able to achieve non-degraded four-wave-mixing conversion with 2.5-nm pump bandwidth,1.4-pm spectral resolution,as well as 21-nm spectral bandwidth.Finally,considering the limited electrical resolution,which hinders the characterization of the actual resolution performance of the spectro-temporal analyzer,a dual-comb asynchronous optical sampling scheme has been proposed.Leveraging this measurement scheme,the time resolution is improved to 2-ps pulsewidth limit,which corresponds to 1.4-pm spectral resolution.(4)The spectro-temporal analysis technique is combined with the research of the thermo-optic dynamics in optical microspheres,which was monitored by spectro-temporal variation.For the application of lasers and filters based on optical microspheres,the nonlinear thermo-optic effect induces the resonance wavelength shift,and results in the variation of operating wavelength.However,the conventional scheme,such as recording transmission spectral line,cannot monitor the thermo-optic dynamics in real time.To solve this problem,a scheme for monitoring the thermo-optic dynamics of optical microspheres based on spectro-temporal analysis is proposed.The thermo-optic dynamics that captured under different pump power and swept rate,revealing a complete thermo-optic dynamic process in the time scale of millisecond.