Asymmetric modes in oxide stripe heterojunction lasers

The region between the pair of heterojunctions of an oxide stripe laser is modeled by a step profile in the lateral distribution (parallel to the heterojunctions) of the gain and of the refractive index, in an attempt to gain insight about the interpretation of the asymmetric radiation patterns frequently observed. A region of width Waconcentric with the stripe contact is subdivided into three sections, in each of which the gain and index are uniform. The step heights for the gain distribution and for the index distribution are given complementary symmetry, with the gain maximum superimposed on the index minimum. Asymmetry is introduced by lateral shift of the extrema at fixed Wa. With values of gain, index step, and Wathat seem reasonable for the laser studied, the near and far fields reproduce the measured profiles of a representative 10 μm stripe laser. The offset of the spontaneous profile is about 3 μm from the center of the stripe, and the beam has a single lobe for all low-order modes with offset of order 5° from the facet normal. Because of the near cancellation of gain guiding by index antiguiding which is required to give the observed asymmetries, the propagation constant becomes very sensitive to injection level; this may explain the observed nonmonotonic change of modal power and the very rapid shift of modal wavelength with current.