Multilongitudinal mode operation in angled stripe buried heterostructure lasers

The various index-guided lasers have superior device performance over gain-guided lasers but operate in single longitudinal mode rendering them unsuitable for use as optical sources in multimode optical fiber transmission systems because of the increased modal noise produced. In this experiment we show that multilongitudinal mode operation can be obtained in buried-heterostructure (BH) lasers throughout the entire output power range from threshold to catastrophic damage by angling the buried active stripes so that they are nonorthogonal to the cleaved facets by angles, θ≳5°. These lasers also exhibit the various desirable characteristics of BH lasers with θ=0° such as linearity in light-current, low spontaneous emission level, and abrupt turnon of lasing. The angles buried stripe caused no noticeable degradation of threshold current, Ith, or external differential quantum efficiency, ηD. The averaged Ith ranged between 16 to 20 mA in all lasers and ηD increased with θ. In all cases, the lasers operated stably in the lowest order transverse mode.