Polarization Bistability Characteristic Of Vertical Cavity Surface Emitting Lasers Subject To Optoelectronic Feedback

Vertical-cavity surface-emitting lasers(VCSELs)have attracted considerable attention due to its unique advantages such as small active region,lower threshold current,easy-integration into two-dimensional laser array,low cost and easy coupling with the fiber,and so on.Specially,the circular symmetry structure of active region and anisotropy of gain medium make its polarization mode unstable.When the parameters such as bias current or temperature changes,the switching between two orthogonal polarization components(X-PC and Y-PC)can happen,which is named as polarization switching(PS).In addition,PS of VCSELs subject to optical feedback or optical injection has also been demonstrated.Moreover,when these parameters such as bias current,feedback strength are continuously varied along different paths,the output powers of two orthogonal polarization components can be different even if the same parameters are set,which denotes that polarization bistability(PB)phenomenon happens.PB in VCSELs has a huge application prospect in these fields of optical logic switch,optical interconnect,optical storage and optical communication.At present,most of researches on the PB characteristics of VCSELs focus on the cases of optical feedback and optical injection.However,related researches on that of optoelectronic feedback are relatively scarce.In this paper,the polarization bistability characteristics of 1550 nm-VCSEL subject to optoelectronic positive feedback or optoelectronic negative feedback are experimentally investigated,and the influence of feedback strength on PS point and PB width has also been discussed.The experimental results show that,type I PS or type II PS can happen in a free-running 1550 nm-VCSEL through gradually increasing or decreasing the bias current,and their PS points have different bias current values.After introducing positive optoelectronic feedback,the bias currents for type I PS and type II PS points are accordingly varied for different feedback strengths.As for relatively weak feedback strength,the bias currents of type I PS and type II PS points are almost same to that of free-running laser.With increasing the feedback strength,the bias currents of two types of PS points are varied and the width of bistability loop shows a gradually decreasing trend.After introducing negative optoelectronic feedback,with increasing the feedback strength,the bias currents of two types of PS points almost shift towards lower values and the width of the bistability loop shows a generally decreasing trend with obvious fluctuation.