Beam steering in narrow-stripe high-power 980-nm laser diodes

We used near-field scanning optical microscopy to measure the optical beam characteristics of weakly-guided narrow-stripe high-power laser diodes. For both facets of the device, we correlate changes in the near-field optical characteristics with beam steering and the kink in the light output versus operating current curve. Our measurements demonstrate that: 1) frequency-locking of lateral modes exists for operating currents below the kink in the L-I curve; 2) beam steering is a result of a shift of in the beat-length pattern inside the laser cavity of the frequency-locked lateral modes; and 3) the kink in the L-I curve results from a sudden increase in the beam waist of the guided-modes.