Study On The Mode-locked Characteistic For The974nm Fiber Grating External Cavity Semiconductor Laser

The fiber grating external-cavity semiconductor laser(FGESL) has the advantages ofsingle wavelength,narrow linewidth and high temperature stability.With the devel-Opment of informations,the FGSEL has been widely used.Therefore the mode-locked ofFGSEL has become a hot issue.The article introduces the composition and development of FGSEL.It discussed indetail the advantage of FGSEL,a brief introduction to the research direction at home and atabroad.The article describes the theoretical model of FGSEL.By the coupled mode theorydeduces the expression of FBG reflectivity formulas,by theoretical calculation shows FBGmode selection principle.Through the transfer matrix theory derived theoretical model of adual grating;using the equivalent cavity mode,the equivalent reflectivity isdeduced,discusses the FBG caused the change of the threshold value;the characteristics ofFGSEL is analsyed by multimode rate equation.The experiment shows the sizes of the front facet reflectivity (R2),the fiber gratingreflectivity(Rg) and the wedge coupling fiber reflectivity(R3)discusses the mode locked,thecoupling efficiency and temperature changes on the characteristics of mode-locked.The results showed that the R2and R3is a key factor in the mode-locked.With the R2and R3decreases,the output is the single wavelength,the side mode suppressionratio(SMSR) is larger than30dB, the R2and R3is more smaller,the SMSR is more larger.There is an optimum value on the Rg,with the Rgincreases,the SMSR is larger,but when theRgincreases to a certain extent,the SMSR will be decreases.This is because thetransmissivity is decrease when the Rgincrease,the output power is decreases.The couplingefficiency is more larger,the Reffis more bigger,the threshold current decreases,the power isincreased,the SMSR is increased,the coupling efficiency can effectively increase the outputpower.By optimizing the various parameters,the output wavelength is a single,thewavelength range is974±0.1nm,the linewidth<0.6nm,the SMSR>45dB,the injectioncurrent of100mA,the output power can reach more than50mW.