Bifurcation bridges between external-cavity modes lead to polarization self-modulation in vertical-cavity surface-emitting lasers

Abstract

We analyze the bifurcation mechanism responsible for the experimentally observed polarization self-modulation (PSM) in a vertical-cavity surface-emitting laser subject to optical feedback. We show that closed branches of time-periodic intensity solutions connecting distinct external-cavity modes (ECMs) exhibit PSM. Along these bridges, the linearly polarized components of the optical field oscillate in antiphase and with a frequency close to the difference between two ECM frequencies. A beating mechanism between stable ECMs then explains the PSM phenomenon. Our results also substantiate recent theoretical studies of edge-emitting lasers subject to optical feedback.