| Optical frequency comb(OFC)is represented as a series of discrete frequency components with equal interval and stable phase relationship in the frequency domain.As a hub connecting microwave and light waves,OFC is widely used in the fields of optical communication systems,precision optical measurement and optical arbitrary waveform generation.Among the existing OFC generation methods,the external modulator method is easy to implement,and the generated OFC has the advantages of spectral stability and tunable comb-line spacing.Electro-absorption modulation(EAM)has the advantages of easy integration,low modulation voltage and high modulation rate.Compared with the traditional lithium niobate electro-optic modulators,EAM is less expensive.This paper focuses on the research on the generation technology of OFC based on single EAM,and the specific work is as follows.An OFC generation device based on RF coupled signal driving single EAM is proposed.RF coupled signal is generated by a low-cost multiplier coupler,and the RF coupled signal is used to drive the modulator to increase the number of comb-lines of the OFC.The scheme is simple in structure and low in cost.The working principle of the scheme is expounded,and a complete theoretical model is established.The effects of frequency and amplitude of the RF signal,the n-th power of the RF coupled signal,the chirp factor and modulation index of the EAM on the performance of OFC are investigated by using Opti System 13.0 software.The research results show that the OFC generated by the scheme has the characteristics of large number of comb-lines,wide spectrum width and tunable frequency interval,which solves the problem of the complex structure of the OFC generator,the small number of generated comb-lines and the dependence on high-frequency RF signal sources in the traditional scheme.In order to obtain an OFC with better flatness,an OFC generation device based on Gaussian pulse signal driven the single EAM is proposed.The working principle of the scheme is expounded,and a complete theoretical model is established.The effects of the full width at half maximum of the Gaussian pulse signal,the output bit rate of the BSG,the chirp factor and modulation index of the EAM on the performance of the OFC are analyzed by using Opti System 13.0 software.The research results show that by properly reducing the full width at half maximum of the periodic Gaussian pulse signal,a higher quality OFC can be generated.The frequency interval of OFC can be tunable by adjusting the bit rate of BSG,and the frequency interval of OFC is tunable between1.25 GHz and 10 GHz.By adjusting the chirp factor and modulation index of the EAM,an OFC with a considerable number of comb-lines and good flatness can be obtained.By optimizing the parameters of the device,a tunable OFC with 25 comb lines and 4.3d B flatness can be generated. |
