Abstract

Phase-locked arrays of index-guided diode lasers are of considerable interest as monolithic sources of high powers (≥100 mW) in single diffraction-limited beams. With one exception, all index-guided arrays to date have been made of positive-index waveguides that are evanescently-coupled or Y-junction coupled. The fundamental mode of evanescently-coupled devices is vulnerable to gain spatial hole burning,² which causes the beam to invariably broaden at drive currents in excess of ~50% above threshold. Thus the highest reported power in a nearly diffraction- limited beam (i.e. lobewidth <1.5 times the diffraction limit) from ≥-element arrays is ~40 mW.³ Y-junction-coupled devices⁴ have strong (positive)-index guiding, which provides stable beams to high powers; but, due to weak interelement coupling,⁵ the beamwidths are 3.5-4.0 times wider than the diffraction limit. For systems employing beam-forming optics, such as free-space optical communications, it is imperative for the beam to be as close to the diffraction limit as possible. We present here a novel array structure: an array of closely spaced and strongly coupled negative-index guides (antiguides). As opposed to all previous arrays, the device has both strong optical-mode confinement as well as strong interelement coupling.

© 1988 Optical Society of America