Abstract

The necessary condition for a uniform index-guided phase-locked laser array to operate in the fundamental supermode is to have high gain in the regions of low refractive index and vice versa. This condition is fulfilled by a self-focused laser filament. Therefore, if filamentation could be controlled to form stripes uniformly spaced and phase locked, the expected emission would be in the fundamental supermode. Filamentation control was achieved experimentally by etching one of the mirrors of a broad area laser in a sinusoidal form. The alternating converging and diverging regions of the mirror efficiently stabilized the filament array. Since the device relies on self-focusing, it is sensitive neither to the laser length nor to the exact shape of the etched mirror. We observed emission in the fundamental supermode, with a stable near-field intensity distribution. Devices fabricated so that the filament spacing was comparable to the filament width emitted in a single lobe, nearly diffraction-limited far field. In addition to the potential applications, the device provides a powerful tool for studying self-focusing due to the nonlinear response in semiconductor lasers. As an illustration of that, measurements of the filament width and phase front curvature as a function of injection current are presented.

© 1985 Optical Society of America