Polarization switching in VCSEL's due to thermal lensing

We demonstrate a new mechanism for polarization switching in slightly anisotropic vertical-cavity surface-emitting lasers (VCSEL's) based on index guiding due to the effect of thermal lensing. This polarization switching takes place when the laser operates on the short-wavelength side of the gain maximum. The two orthogonal linear polarizations correspond to slightly different wavelengths and switching occurs from shorter toward longer laser wavelength as the drive current increases. Polarization modulation has been observed up to 50 MHz with a polarization contrast ratio of 20:1.