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

High-power, 980 nm laser diodes are currently used to optically pump erbium-doped fiber-amplifiers for telecommunication systems. In this capacity, the laser diode must reliably provide high output power in a stable optical beam with efficient power coupling to the waveguide-mode of the fiber amplifier. To this end, narrow-stripe devices capable of single spatial mode operation are utilized. These devices typically employ weak lateral guiding to ensure single mode operation while maximizing the spatial size of the fundamental mode to reduce the peak power density and thus prevent catastrophic optical damage on the output facet. We employed near-field scanning optical microscopy (NSOM) to image the output of a 980 nm, graded-index, separate-confinement, heterostructure (GRINSCH) laser diode that exhibits a kink in the light versus current (L-I) curve and lateral beam steering. Measurements were performed on the output of both the antireflection and high-reflection coated facets. We correlate the NSOM images of the laser near-field with far-field measurements of beam-steering as a function of the laser diode operating current with an emphasis on the behavior at around the L-I kink.