Polarization asymmetry and optical modal gain saturation via carrier-photon interaction in ZnO

The polarization dependence of modal gain was examined in ZnO using a variable stripe length method, where the transverse electric (TE) mode gain was dominant over the transverse magnetic (TM) mode gain due to the polarization asymmetry of the wurtzite structure. Modal gain saturation was also investigated using a modal gain contour map for the wavelength and stripe length. The TE modal gain and degree of polarization increased with increasing stripe length up to a threshold length (∼100 μm). At longer stripe lengths, rapid reduction in the carrier density along the stripe resulted in gain saturation and a spectral redshift.