Research On High Quality Optical Frequency Comb Generation And Its Application In Frequency Measurement

An optical frequency comb is a spectrum composed of a series of frequency components with equal frequency intervals and approximately equal power.It has a wide range of applications in the fields of frequency measurement,wavelength division multiplexing,and channelized reception.The common methods of generating optical frequency comb are as follows: mode-locked laser,recirculation frequency shifter,nonlinear effect of fiber and external modulator.This paper focuses on the generation of optical frequency comb based on external modulator and its application in frequency measurement.The main research contents of this paper are as follows:(1)Based on the analysis of the existing schemes of optical frequency comb generation,a new optical frequency comb generation scheme is proposed based on double-parallel Mach-Zehnder modulators cascaded an intensity modulator.In the scheme,the flatness of the optical frequency comb is effectively improved by power compensation,and different optical frequency combs can be obtained by controlling the parameters of the modulators.The results show that 80-line optical frequency comb with flatness of 0.32 d B and frequency interval of 8GHz can be obtained,and the frequency interval and center frequency of the optical frequency comb can be adjusted flexibly.(2)An optical frequency comb generation scheme based on intensity modulator cascaded with electro-absorption modulators is proposed.In the solution,by using an electro-absorption modulator with a higher integration level and a lower driving voltage,the integration level of the system is effectively improved,and the system cost is reduced.By adjusting the variable parameters of the modulators,different optical frequency combs can be obtained.The simulation results show that the optical frequency comb with flatness of 0.21 d B,frequency interval of 8GHz and comb number of 80 can be generated.The frequency interval and center frequency of the optical frequency comb can be adjusted easily.(3)A microwave instantaneous multi-frequency measurement scheme based on optical frequency comb is proposed.In the scheme,the microwave signals to be measured are loaded onto the optical carriers through a dual-parallel Mach-Zehnder modulator to realize carrier suppressed single sideband modulation,which can improve the modulation efficiency and sideband utilization of the system.Using the frequency optical power mapping method,the frequency measurement range is0.5GHz-39.5GHz,when the frequency measurement accuracy is ± 500 MHz.