Study On Optical Frequency Comb Generation With Switchable Frequency Spacing Based On Nonlinear Effect

Optical Frequency Comb(OFC)relates to a spectrum consisting of a series of discrete,equal-spaced frequencies in the frequency domain,with a stable phase relationship between the spectrum lines.In time domain,OFC is regarded as a regular ultra-short pulse with fixed repetition frequency,which can reach GHz level as a time-frequency standard based on Microwave atomic clock.The optical frequency standard can reach THz magnitude.Therefore,OFC can be used as a bridge between microwave frequency and optical frequency to further improve the precision and accuracy of time measurement.With the continuous development of the times and optical communication technology,optical frequency comb has attracted worldwide attention because of its great application prospects.Moreover,it is a rising star in the field of laser after the emergence of ultra-short pulse laser.Regarding the goal of my research,I have studied and designed two schemes,both of which are closely related to the non-linearity of optical fibers.My major work and research contents are as follows:1.Optical Frequency Comb Generation Scheme based on Mach Zendel Modulator(MZM).This scheme uses a Mach-Zehnder Modulator(MZM),a High Nonlinear Optical Fiber(HNLF)and a Polarization Detector(POL).The signal modulated by MZM is amplified by High Power Erbium Doped Amplifier(HP-EDFA)and injected into High Nonlinear Optical Fiber(HNLF).After four-wave mixing,an Optical Frequency Combs(OFC)is obtained.Under the action of polarization controller(PC)and polarizer,the polarization state of optical signal transmission is changed,and the Pedestal of the output OFC spectrum line can be eliminated,so that the distribution of the output OFC power spectrum line is more uniform.2.Frequency Interval Switchable Optical Frequency Comb Generation Scheme based on Nonlinear Effect.The scheme mainly uses a 1:99 polarization-maintaining coupler and a High Nonlinear Optical Fiber(HNLF).The optical signal is affected by the nonlinear effect(stimulated Brillouin effect,cascaded four-wave mixing effect)of HNLF in transmission,which results in equal spacing optical frequency combs.OFC with switchable output spacing is due to Rayleigh scattering effect in optical fibers and the influence of polarization change of optical signal after PC adjustment.