Research On Optical Frequency Comb Generation Technology Based On RF Coupled Signal And Mach-Zehnder Modulator

Optical frequency comb(OFC)is a spectrum composed of a series of uniformly spaced discrete frequency components with stable coherent phase relationship,which is widely used in metrology,microwave photonics,astronomy and other fields.The commonly used OFC generation methods are mainly based on mode-locked laser,fiber nonlinear effect,micro ring resonator and electro-optic modulator.Among them,the OFC generation based on electro-optic modulator has the advantages of high flatness and adjustable comb spacing.However,the OFC generated by this method has some shortcomings,such as unprogrammable comb line number and complex device structure.In order to solve these problems,the purpose of this paper is to study the OFC generation technology with programmable comb line number,tunable comb line spacing,high flatness and high side mode rejection ratio(SMSR).Firstly,an OFC generation method based on in-phase Mach-Zehnder modulator(MZM)driven by radio frequency(RF)coupled signal is proposed,which includes two progressive structures:single MZM and cascaded MZMs.The device structure and working principle of this method are introduced,the theoretical model is established and simulation experiments are carried out.Using the simulation software Optisystem,the parameters such as coupling operation circuit,RF source frequency,reference modulation voltage,modulation voltage difference,bias voltage difference between upper and lower branches are discussed,and the effects of these parameters on the comb spacing,comb line number and flatness of OFC are analyzed.This method is easy to implement,with low modulation voltage,high flatness and programmable comb line number;The low frequency RF signal is transformed into a multi-frequency RF signal by using the coupling operation circuit,which broadens the comb line interval and bandwidth of the OFC and reduces the cost of the OFC generator.Then,an OFC generation method based on push-pull mode MZM driven by RF coupled signal is proposed,which includes two progressive structures:single MZM and cascaded MZMs.The device structure and working principle of the method are introduced,the theoretical model is established,the corresponding working parameters of the flat OFC are analyzed,and the simulation experiments are carried out.Using Optisystem,the parameters such as coupling operation circuit,RF source frequency,modulation voltage and bias voltage are discussed,and the effects of these parameters on the comb spacing,comb line number,flatness and SMSR of OFC are analyzed.This method is easy to implement,with high flatness,high SMSR and programmable comb line number;The low frequency RF signal is transformed into a multi-frequency RF signal by using the coupling operation circuit,which broadens the comb line interval and bandwidth of the OFC.