Polarization Mode Switching and Bistability in Semiconductor Lasers

Generally, TE-mode emission (the transverse electric field is polarized parallel to the active-layer plane) is favored in unstrained semiconductor lasers in comparison with TM-mode emission (the magnetic field is polarized parallel to the active-layer plane) due to a larger reflectivity for the TE wave at the cleaved facets forming the laser cavity. The optical gain delivered from the active medium is the same for both modes, i. e., gTE = gTM = g given by g = A (N - N0) where A is the gain coefficient, N is the carrier density, and N0 denotes the carrier density required to achieve transparency, g = 0.