Investigating On The Influence Of Optical Feedback On The Polarization Switching Characteristics Of Multi-transverse-mode In VCSEL Subject To Orthogonal Optical Injection

As a new kind of semiconductor laser, vertical-cavity surface-emitting lasers (VCSELs) have a significant implication prospect in optical communication, optical interconnection, image signal processing, etc. due to their merits such as low threshold, working in single longitudinal mode, small angle of divergence, high dynamic modulating frequency, easily implemented two-dimension integration. Based on the structure characteristics of VCSELs, the output contain commonly two vertical linearly polarized modes. Polarization switching can be happened through adjusting the biased current or change the parameters value of outside distribution. Orthogonal optical injection as a convenient way to control polarization switching is obtained great attentions. Though the output of VCSEL is single-longitudinal-mode commonly, it exist high-order transverse modes for the large transverse size of active region. Under contain condition, the influences of high-order transverse modes on the performance of VCSEL can not be neglected. After taking the multi-transverse-modes into account, the characteristics of polarization switching in VCSELs subject to orthogonal optical injection have been investigated.Considering the realistic application, optical feedback can not be avoided. So the influences of optical feedback on the polarization switching of multi-transverse-mode in VCSELs subject to orthogonal optical injection are investigated in this paper. The results show that, for the case of horizontal optical feedback, the polarization switching can be happened through adjusting the injection power and frequency detuning. With the varying of the frequency detuning, there exit two minimum injected powers needed for polarization switching, and the corresponding frequency detuning for obtaining two minimum injected powers are OGHz and 220GHz, respectively. For frequency detuning is OGHz, the polarization switches between the fundamental x-and y-polarized mode (LP_01,x and LP_01,y). However, for frequency detuning is 220GHz, the polarization switches between the fundamental x-polarized mode and the first-order transverse y-polarized mode (LP_11,y). With the increase of the horizontal feedback rate, the competition among the multi-transverse-modes becomes more seriously, but the influences of the horizontal feedback on the polarization switching are not obvious. At the condition of orthogonal optical feedback, for frequency detuning is OGHz, polarization switch still between LP_01,x and LP_01,y. But for frequency detuning is 220GHz, LP_01,x and LP_01,y modes can be coexisted at first. With increase of injection power, LP_11,y mode lase and switch with LP_01,x and LP_01,y modes. Then LP_11,y become the dominate mode, LP_01,x and LP_01,y modes are suppressed. At the condition of orthogonal optical feedback, the injection power needed for polarization switching is smaller than the case of horizontal optical feedback. With the increase of the orthogonal feedback rate, the injection power needed for polarization switching is decreased.