Investigations On The Polarization Switching And Bistability In A 1550nm Vertical Cavity Surface Emitting Laser Under Variable-polarization Optical Injection

As a new generation of semiconductor lasers,1550 nm vertical cavity surface emitting lasers(1550 nm-VCSELs)not only have great application prospect in ultra-high speed and long distance optical fiber communication network,but also become the core devices of optical storage system,optical logic system and parallel optical computing system.Since the active region of 1550 nm-VCSELs is a circular symmetrical structure with weak anisotropy,its output is usually one of the two orthogonal polarization modes.When the bias current or temperature conditions change,the two polarization modes are prone to occur polarization switching(PS).In addition,1550 nm-VCSELs under external disturbances such as optical injection,optical feedback,optoelectronic feedback can also show PS.In particular,when the external parameters which induce the PS change along different paths,the corresponding parameter conditions of the PS will may change,and then the polarization bistability(PB)appears.In recent years,the PS and PB characteristics in 1550 nm-VCSELs under optical injection have been reported extensively,but mainly concentrated in the case of orthogonal optical injection,while the study of PS and PB in a variable polarization optical injection 1550 nm-VCSELs is still relatively lacking.In this paper,based on the spin-flip model(SFM),the characteristics of polarization switching(PS)and bistability(PB)in a variable polarization optical injection 1550 nm vertical cavity surface emitting laser(VPOI 1550 nm-VCSEL)have been investigated numerically.The results show that,when the injection light polarization angle ?p(defined as the angle difference between the polarization direction of injection light and Y polarization-mode of the 1550 nm-VCSEL)is greater than a certain value,continuously scanning of the optical power can induce PS in VPOI 1550 nm-VCSEL,different scanning paths will lead to changing the switching point,that presents the PB effect;for a given frequency detuning Av(defined as the frequency difference between the injection light and the X polarization-mode),type ? PS occurs during increasing the injection power and type ? PS occurs during inverse process if the polarization-angle of the injection light ?p is large enough.Moreover,the injection power required for generating type ? PS is different from that for generating type ? PS,namely PB is observed.For a determined ?v,with the increase of ?p,the injection power for switching point of two types PS and the width of PB are decreased.For a larger value of |?v|,the injection power for the switching point of type ? PS is higher but the width of the PB is wider.Additionally,for a given injection power,PS and PB can also be observed through scanning ?p forward and backward under different ?v.Under a relative small |Av|,the values of ?p required for type ? and type ? PS are similar,and therefore the width of the PB is very small.On the other hand,for a relative large |?v|,the values of ?p required for two types of PS and the width of PB severely fluctuate with the variation of Av.Therefore,under the case that the operation parameters of a 1550 nm-VCSEL is fixed,through adjusting the injection parameters,the performances of the PS and PB can be optimized.