Depolarization of the lasing emission from CW double-heterostructure junction lasers

Measurements of the polarization characteristics of the optical emission from CW AlzGa1-zAs-AlxGa1-xAs double-hetero-structure (DH) junction lasers are reported. Spectral observations demonstrate that in many lasers the lasing emission is not linearly polarized as expected from the conventional electromagnetic (EM) theory of the laser. A small but measurable field component is observed orthogonal to the main emission. In some lasers, the optical field is shown to be elliptically polarized, while in other devices the polarization state is more complex. The observed depolarization of the lasing modes is attributed to a strain-induced anisotropy in the dielectric properties of the laser waveguide. The anisotropic configuration which leads to elliptically polarized light is analyzed in detail and is shown to be equal to a pure shear in a plane parallel to the junction.