Polarization bistability in tuned, external-grating diode lasers

Spectral domains showing polarization-wavelength hysteresis regions up to 0.3 nm wide were observed when the emission frequency of a diode laser having a nearly polarization-independent confinement factor was tuned in a simple external cavity with grating. In these regions the laser emits in a stable single mode with either TE or TM polarization, depending on whether the region was entered from lower or higher wavelengths. We explain the observed phenomenon on the basis of nonlinear gain saturation between TE and TM polarization