As the injection current is increased the laser heats up and there is an alteration in the topography of the laser which alters the light distribution. 

AFM & Light Distribution

Illustrated below: Distributed feedback laser structure, light distribution and collage of structure and light distribution at a low injection current.

Near-field optics provides the capability to predict the near-field from far-field methods. 

Far-Field
Near-Field

The Distributed Feedback Laser AFM & NSOM Image at Higher Injection Currents (22.5 mA)

As the injection current is increased the laser heats up and there is an alteration in the topography of the laser which alters the light distribution.