Polarization Modes Response of VCSEL Below the Threshold Under External Optical Feedback

Abstract:

Although it is well known that vertical-cavity surface-emitting lasers (VCSELs) are very sensitive to internal optical feedback (OF), dominated by internal cavity mirrors, and external OF, dominated by an external cavity mirror. Consequently, their dynamics under such effects have been intensively studied. However, the external OF effects below the threshold on the lasers’ polarization modes and the light-current (L-I) characteristics have not yet been studied to the best of our knowledge. In this paper, we show experimentally that polarization modes behaviors of VCSEL below the threshold follow its behaviors above the threshold with the existence of an external OF. OF can enhance or suppress the polarization modes below the threshold, depending on two parameters: OF strength and the polarization state of the feedback light. Moreover, abrupt polarization switching occurs between low- and high-power polarization modes of the VCSEL beneath the threshold when the bias current is increased from zero to the threshold value of the laser with and without OF.

Key words:VCSEL, Polarization, Optical feedback, Threshold