Investigation On Ultra-broadband Tunable Microwave Frequency Comb Generation Using A Semiconductor Laser Under Regular Pulse Injection

Microwave frequency comb(MFC)is a set of frequency components with equal frequency interval.MFCs can provide multi-band microwave signals,and therefore they can be utilized in all-optical frequency conversion,frequency and distance metrology,radio-over-fiber communication,sensors,and so on.Therefore,it is very meaningful to explore the generation of ultra-broadband tunable microwave frequency comb both the academic and application field.Microwave frequency comb can be generated by electronic or photonic technology.The traditional electronic technology is to use the special performance of nonlinear devices such as varistor diodes,step recovery diodes,and transistors,which are generated by frequency doubling.However,due to the limitation of the electronic bandwidth of the devices used,the bandwidth of the generated MFC is very narrow and the harmonic frequency components are drastically reduced.There are three method to obtain MFC by photonic technology: one is obtained by tunnel junction method using a laser scanning tunneling microscope;the other is to use the photodetector(PD)to convert the optical frequency comb;the third is to use the nonlinear dynamic state of semiconductor laser(SL)under suitable external disturbances.Due to the MFC obtained in the first two methods has the disadvantages of narrow bandwidth and the comb space is difficult to adjust,therefore,the third method has obtained much more attention based on its great advantages of generating ultra-bandwidth optimized MFC.Among them,the MFC comb line signal generated by the subharmonic locking exhibited by the photoelectric feedback SL is unbalanced,the bandwidth is small,and the comb distance cannot be flexibly adjusted.Among them,the power of MFC generated by the subharmonic locking of optoelectronic feedback semiconductor laser is unbalanced,and the bandwidth is narrow,also the comb distance cannot be flexibly adjusted.Therefore,in order to better meet the needs of the development of modern communication technology,it is necessary to explore a method for obtaining ultra-wideband high-quality MFC signals with power balance,uniform comb space and stable frequency.In particular,The MFC obtained by the nonlinear dynamic state exhibited by the current modulating semiconductor laser can well solve the problems of bandwidth and tunability.A system scheme for generating ultra-broadband microwave frequency comb based on a semiconductor laser under optical injection of regular pulse from a current-modulated laser is proposed,and the performances of the generated MFC are numerically investigated.In such a scheme,a distributed feedback semiconductor laser(DFB-SL1)under current modulation with suitable modulated parameters can be driven into regular pulsing state,which is utilized as a seed MFC with tunable frequency interval to inject into another distributed feedback semiconductor laser(DFB-SL2)for producing optimal MFC with ultra-broadband and tunable frequency interval.The simulated results demonstrate that,for a seed MFC with a bandwidth of 26.4 GHz and frequency interval of 3.3 GHz,the bandwidth of the optimized MFC generated by DFB-SL2 can arrive at 72.6 GHz through selecting appropriate injection parameters.Also,the variations of optimized MFC bandwidth with the frequency detuning and injection coefficient are analyzed.