Investigations On Polarization Switching And Bistability Of Optically Pumped Spin Vertical-Cavity Surface-Emitting Lasers

The polarization characteristics of the semiconductor laser outputs mainly depends on the gain medium of the active region and the polarization characteristics of the optical cavity,and thus the polarization characteristics of edge emitting semiconductor lasers(EELs)have some essential difference with that of vertical-cavity surface-emitting lasers(VCSELs).VCSELs are quasi-symmetrical devices,which have almost no selectivity for polarization and therefore can only select one of the polarization states of their output through a suitable optimization mechanism.Based on the correlation between the electron spin and the optical polarization,the control to the electron spin can select the polarization state of the laser output.Compared with conventional VCSELs,spin vertical-cavity surface-emitting lasers(spin VCSELs)have some unique advantages such as polarization stability,easy polarization control,and low threshold.Therefore,the polarization characteristics of spin-VCSEL have attracted extensive attentions.Considering that the optically pumped method enable the laser to obtain polarized carriers and then control the polarization performance of the laser output.Therefore,investigations on the polarization switching(PS)and polarization bistability(PB)characteristics of optically pumped spin VCSEL,especially the long wavelength spin VCSEL,have some academic and applied significance.In this paper,based on the spin-flip model(SFM),the circular polarization switching(PS)and polarization bistability(PB)characteristics of a 1300 nm spin vertical-cavity surface-emitting laser(spin VCSEL)subject to optical pump are investigated numerically.The results show that,for a certain polarization ellipticity P_P of pump light,pump power can control the polarization ellipticity Pout of the laser outputs at a certain extent.For a certain normalized pump power ?,the PS can occur between the left circularly polarized light and the right circularly polarized light of the spin VCSEL output and PB phenomenon can also be observed when forward scanning(gradually increasing)or backward scanning(gradually decreasing)the polarization ellipticity P_P of pump light.The PS positions are different for these two cases,which denotes PB phenomenon happens.For the smaller pump power ?,the hysteresis loop width first increases to a maximum and then decreases to 0 with the increase of?.For a relatively larger?,the hysteresis loop width shows a decreasing trend with the increase of?on the whole.Moreover,the internal parameters?and?_p of the laser have a great influence on the PS and PB characteristics induced through changing the polarization ellipticity P_P of pump light.In addition,the distribution of the hysteresis loop width is also given in the parameter space of some key internal parameters of the laser and normalized pump power ?.