Transverse magnetic emissions of GaAs unstrained quantum-well microcavity lasers

We investigated the polarization characteristics of emissions from two-dimensional microcavity laser diodes. For an unstrained single-quantum-well active layer structure, an argument based on the interband optical transition usually leads to the lasing of transverse electric (TE) rather than transverse magnetic (TM) modes. Indeed, we observed TE-polarized emissions for the excitation of modes quantized along a one-dimensional (Fabry-Perot) orbit. However, when selectively pumping modes quantized along a diamond-shaped ray orbit, we observed TM-polarized emissions. These unusual TM-polarized emissions can be explained by the fact that the incident angles of the diamond-shaped orbit are very close to the Brewster angle, making corresponding TE modes too leaky to be excited. This mode-dependent polarization leads us to propose a microcavity laser diode with the function of polarization switching.