| Optical frequency comb(OFC),as an ultra-short pulse source,presents a series of comb lines with equal frequency spacing in spectrum.Due to its large spectral range and strong coherence,OFC has been widely used in the fields of sensing,communication,radar,and high precision measurement.Microwave frequency comb(MFC)is like OFC in the frequency domain,showing equal spacing between neighbour comb lines.Because MFC can cover multiple bands,and has strong anti-interference ability and high propagation efficiency,it has been widely used in remote sensing,radar detection,communication and other fields.In recent years,with the development of microwave photonic(MWP)technology more and more mature,optically generated MFC has the advantages of large bandwidth,strong adjustable comb spacing and high carrier-to-noise ratio.It is of great significance to study the generation technology of OFC and MFC with high performance.This thesis aims to explore the generation technology of OFC and MFC based on a directly modulated laser(DML).It focuses on three parts,including studying dynamics of the semiconductor laser under direct modulation and external injection,analyzing their nonlinear behaviors,and using these characteristics to produce OFC and MFC.The main work of this thesis is as follows:1.This thesis briefly introduces the origin,development,and application of MWP technology,reviews typical generation methods for OFC and MFC and their characteristics,introduces the application fields of OFC and MFC,and summarizes the related research progress in recent years.2.Generation of OFC based on cascaded optical injection and subharmonic modulation.The theoretical and simulation analysis of the scheme has been carried out.In the experiment,OFCs have been demonstrated with comb spacing of 4.375 GHz and comb lines of 17,and with comb spacing of 5 GHz and comb lines of 15 within the range of 20 d B flatness.3.Generation of MFC based on the nonlinear modulation of a DML.The effect of relaxation oscillation frequency and the external injection on the performance of the generated MFC is simulated.MFC with bandwidth greater than 25 GHz is generated in the experiment,and the comb spacing can be continuously adjustable in the range of 0.5-3 GHz.4.Generation of MFC based on actively mode-locked optoelectronic oscillator(AMLOEO)with a DML.The theoretical analysis of AML-OEO based on a DML is carried out.In the experiment,when using a 30 MHz bandwidth filter,MFCs with the bandwidth of12.0-22.40 MHz are generated within the range of 10 d B flatness.When using a 2 GHz bandwidth filter,MFCs with the bandwidth of 21.2-53.68 MHz are experimentally demonstrated within the range of 10 d B flatness. |
