Mode deformation due to self-focusing in injection lasers and its connection with nonlinearity of the output characteristic

The effect of the pump current on the mode configuration of an injection laser with an external selective resonator was studied. It was found that in a single-mode regime, controlled by the external resonator, a number of regularly spaced filamentary channels appear as the pump current is increased. Interference effects give rise to side lobes in the far-field radiation-pattern polar diagram, which are interpreted as being due to self-focusing of the radiation in the active medium, arising from the relationship of the refractive index of the inverted semiconductor with the electron density and the electromagnetic field intensity. The appearance of channels is accompanied by a kink in the energy characteristic of the laser.