Investigation On The Characteristics Of Polarization Switching In VCSELs Under Optical Injection

As a new type of semiconductor laser, vertical cavity surface emitting lasers (VCSELs) possess many advantages such as small divergence angle, low threshold current, single longitudinal mode outputs, easy to integrate into two-dimensional arrays, and high modulating frequency, and then they have a broad application prospect in optical communications, optical interconnects, optical storage and optical switch etc. The researches have demonstrated that the output of a VCSEL generally includes two perpendicular linear polarized modes due to the weak cavity and material anisotropy, which leads to unstable linear polarization mode in VCSELs. For a VCSEL with determined polarization direction, its polarization direction could be abruptly hop when some parameters of lasers are changed, then the suppressed mode turns to be dominant model, and the original dominant mode is suppressed at the same time, which is named as polarization switching(PS). The polarization switching characteristic of VCSELs could be affected by adjusting the exterior perturbation of VCSELs such as optical injection, optical feedback, etc. Recently, research about polarization switching of VCSELs is mostly limited to linearly polarized injection, and research on polarization switching characteristics of VCSELs under elliptically optical injection are still relatively scarce.In this paper, the basic structure and theory of VCSELs are introduced mainly, Based on the framework of the spin-flip model (SFM), the polarization switching performance of vertical-cavity surface-emitting lasers (VCSELs) subject to elliptical optical injection have been investigated theoretically, illustrate the effects of injection polarization angle and frequency detuning. The results show that, for a VCSEL in which x-LP mode is dominant, the minimum injection strength (ηinmm) demanded for occurring polarization switching decreases with the increase of injection polarization angle θ when the VCSEL is injected by elliptical optical injection. With the increase ofAv (△v=Vin-v0, where vin and v0are the frequencies of the injection light and the central frequency of the VCSELs, respectively) from negative to positive value, ηinmm decreases firstly, and after passing through a minimum value, increases finally. The minimum value emerges when the frequency of the injection light is located at near the frequency of y-LP in VCSEL. Therefore, turning the injection polarization angle and the injection frequency detuning can both regulate effectively the polarization switching of VCSELs.