Abstract

Phased-locked arrays of diode lasers have been reported as early as 1978.⁽¹⁾ However, very rarely have the beam patterns of arrays displayed the desired result: a single, diffraction-limited beam in both cw and pulsed operation. Initially, the problem has been that arrays were made of gain-guided devices, that is, devices for which lateral optical-mode confinement is solely provided by the injected-carrier profile. Gain-guided devices are thus intrinsically vulnerable to gain-profile changes due to drive condition changes (i. e. cw or pulsed), spatial hole-burning at high drive levels above threshold, and/or temperature variations across the laser chip. Revealingly, recent studies of arrays of gain-guided lasers⁽²⁾ show that such devices are more appropriately modeled as broad-area devices with gain perturbations rather than coupled waveguides. Thus, even though output powers as high as 5W have been reported from gain-guided arrays, their beam quality has generally been poor, which removes them as candidates for applications requiring beam-forming optics. While harder to make, arrays of index-guided lasers,⁽³⁾ that is devices with "built-in" dielectric waveguides, have demonstrated both stable-beam operation under cw and pulsed drive conditions as well as single-longitudinal mode operation. Most recent work has concentrated on the fabrication and mode control of index-guided devices.

© 1987 Optical Society of America