Theoretical Investigation On The Polarization Characteristics Of VCSEL With Negative Optoelectronic Feedback

Since the vertical cavity surface emitting lasers (VCSEL) appear, VCSEL have been concerned by related fields scholars at home and abroad for their advantages as low threshold current, wide modulation bandwidth, single longitudinal mode outputs, easily produced as laser array in process, and have broad application values in the domain as optical communication, optical Interconnect and optical storage.As experiments show, VCSEL have obvious linear polarization of transverse mode, which could be well described by spin-flip model (SFM). Furthermore,the the polarization mode of VCSEL is unstable, the polarization mode of a single polarization mode VCSEL could be abruptly hop when some parameters of lasers are changed, then the suppressed mode turns to be dominant mode and the original dominant mode turns to be suppressed mode, which is named as polarization switching(PS). Investigations show that the positions of polarization switching could be changed with the route of parameter changing, which is named as polarization bistability(PB). And polarization characteristics and polarization bistability characteristics could be affected when changing the bias current of a VCSEL or some parameters of exterior perturbation like light injection, light feedback and optoelectronic feedback.Based on the theoretical model of VCSEL with optoelectronic negative feedback, this paper will stressed on the influences of the polarization bistability characteristic of VCSEL under optoelectronic negative feedback from the feedback strength and the scan period of injection time-varying. The results show that, with the increase of the feedback index, the width of the bistability region tends to become bigger totally, and fluctuates in the region of bigger feedback index. And this is because the VCSEL appear complicated nonlinear dynamics for the feedback index in the region and edge of the bistability region is in chaos state, then, the width of the bistability region varies randomly, In the region where the feedback index is small, the width of the bistability region of VCSEL tends to become increase linearly with the increase of feedback index, and the bigger the scan period is, the slower the increase is. And, the width of the bistability region of VCSEL will become insensitive to the variety of the feedback index with great scan period. So, smaller photoelectric feedback index should be chosen to control the bistability region more effectively, and the period of the time-varying injection current should be small. On the other side, the width of the bistability region will decrease obviously with the increase of scan period for the memery effect of VCSEL with time-varying current injection, and the faster the injection current vary, the more remarkable the memery effect is, then the bigger the bistability region is. The bistability region moves towards bigger current and the width of bistability region increases; with the increase of the scan period of injection time-varying current, the width of bistability region decreases. As a result, the polarization bistability characteristics can be controlled through adjusting the strength of optoelectronic feedback and the scan period of injection time-varying current.