Experimental And Simulation Research On Optical Frequency Comb Generation Based On Cascaded Modulators

Optical frequency comb is a multi-wavelength laser source with same frequency interval.In 1999,the team of Theodor W.H?nsch for the first time successfully generated the optical frequency comb using a mode-locked laser.In 2005,John L.Hall and Theodor W.H?nsch won the 2005 Nobel Prize in Physics for developing high-precision spectroscopic techniques based on optical frequency comb.Since then,the development of optical frequency comb has been accelerated.Except for using in high-precision spectral measurement,optical frequency comb has also been be utilized for multi-carrier communication,Gaussian filter,arbitrary waveform generation,optical clock and so on.However,it is still very challenging and important for the applications of optical frequency comb to produce combs with a large number of comb lines,good flatness,high carrier rejection ratio,and low RF power requirements.Under the development of optical frequency comb,a method of generating optical frequency comb by using linear modulation based on cascaded modulators is proposed.A 5-line comb with 0.06 dB flatness and 4.0 GHz spacing is first generated in an intensity modulator.And a 3-line comb with 0.02 dB flatness and 20.0 GHz spacing is generated in a phase modulator.By cascaded modulators,an ultra-flat OFC generation is demonstrated with 0.19 dB flatness,15 comb lines and 18.3 dBm total RF power consumption.It is proved that the interval is adjustable by obtaining a 15-line comb with 2.5 GHz spacing in the same scheme.We also find the solution of comb generation when the bandwidth of phase modulator is insufficient.The phase relation of the 15 flat comb lines has been deduced and analyzed.The mathematic model of optical frequency comb generation by cascaded modulators is established by MATLAB.And the factors affecting the flatness of the optical fiber comb have been analyzed by simulation.According to the theory of push-pull Mach-Zehnder interferometer(MZI)-based silicon modulator,an approximate simulation model is established,and five optical comb lines have been obtained by simulation,which may be a reference for the research of integrated optical frequency comb generation.Meanwhile,two schemes of optical frequency comb generation are proposed based on the principle of superposition by cascaded modulators,including optical frequency comb generated based on coupler and optical frequency comb generation based on multiple sources.And some preliminary experimental results are also given.Finally,we summarize the research work,and put forward our prospect for the future work for optical frequency comb.