Two-Dimensional Laser Array Technology Comparison: "Stack-And-Rack" Vs. Monolithic

Two-dimensional laser diode arrays can be divided into two basic types: (1) "stack-and-rack" and (2) monolithic. The first approach involves stacking linear arrays of edge emitters, which emit light parallel to the epitaxial layers, into 2-D arrays. These devices have been used primarily to side pump (in single device form) or surface pump (in 2-D arrays) solid state lasers. Monolithic arrays are a collection of devices which emit light normal to the epitaxial layers. Three designs currently under development can be divided into two categories: 1) conventional laser diodes which use either etched turning mirrors, or a Bragg grating to couple the light out of the epitaxial layers and 2) laser diodes with their optical cavity perpendicular to the epitaxial layers. This paper reviews the current status of each of these devices and compares the characteristics of each approach. These parameters include: packing density, electrical contact techniques, pulsed optical power density, CW optical power density, and processing and assembly issues. The results of this comparison clearly shows that the technology for the stacked array design approach is more mature than it is for the monolithic surface emitters and is the dominant approach for achieving high optical fluences.