Polarization selection in birefringent vertical-cavity surface emitting lasers

An analysis has been undertaken of the effect of refractive index anisotropies or birefringence on the selection of polarization states in vertical-cavity surface emitting lasers. Attention is focused on the competition between the two orthogonal polarization states of the fundamental transverse mode. It is shown that refractive index differences of 0.005% are adequate for ensuring preferential excitation of a specific polarization state. It is found that at low injection currents both polarizations coexist with the same optical power. The dominant polarization state at higher injection currents is found to depend upon the geometry of the current injection in the active region.