Highly Directional Semiconductor Lasers

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© Eliza Grinnell.

While semiconductor lasers are widely used in everyday products, they suffer from poor directionality. Divergent beams from semiconductor lasers are focused or collimated with lenses that typically require meticulous optical alignment. To get around such conventional limitations, researchers sculpted a metallic structure (shown in the background), dubbed a plasmonic collimator, consisting of an aperture and a periodic pattern of sub-wavelength grooves. The aperture couples part of the emitted light into surface electromagnetic waves (so-called surface plasmons) on the laser facet. As the surface waves propagate on the facet, they are progressively scattered by the grooves and are reemitted into the far field. The laser maintains a high output optical power and could be used for long range chemical sensing, without requiring bulky collimating optics. Harvard School of Engineering and Applied Sciences' researchers Federico Capasso (right) and Nanfang Yu (left) working at the far-field measurement setup. (Unit: 8)