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Impact of noise on current-driven polarization switching of vertical-cavity surface-emitting lasers

Vertical-cavity surface-emitting lasers (VCSELs) are widely used as low-cost coherent sources in optical communication systems because they offer many advantages over edge-emitting lasers. However, because of their circular transverse geometry, they often present polarization instabilities. When VCSELs start to lase they emit a linear polarization, and as the injection current is increased, a switching to the orthogonal polarization often occurs. Here I study the influence of spontaneous emission noise on the value of the injection current at which the polarization switching (PS) occurs, when the injection current is sweep in time, starting below the lasing threshold and brought above the PS point and back. I analyze the cases of type I PS, from the high-frequency to the low-frequency polarization, and of type II PS, and from the low-frequency to the high-frequency polarization, and discuss the dependence of the PS point on the noise strength and on the injection current sweep rate.