A1GaAs /GaAs Diode Lasers

Stable diffraction limited high order array mode operation has been achieved to high drive current levels above threshold. Data is presented from two different array struc­ tures, both of which incorporate the wide-waveguide-interferometric array pattern together with strong transverse antiguiding between array elements in order to select L=8 array mode operation. Evidence supporting recent theoretical predictions that higher-order modes of evanescently coupled arrays are stable against spatial hole burning is also presented. Phase-locked diode-laser arrays are desirable from the standpoint of providing high optical output powers into narrow single-lobed beams. Most research efforts have pri­ marily focused on achieving single, diffraction-limited-beam operation to high power levels (>100 mW).'1"'' Many methods to obtain single-lobed beam operation rely on modal- gain discrimination that favors fundamental-array-mode operation. However, even if com­ plete higher-order mode discrimination were possible, beam broadening invariably occurs (typically at drive levels in excess of 50% above threshold) due to self-focusing of the fundamental array mode as a result of gain-spatial hole burning.'°'9) Stable beam-pattern operation has been demonstrated in Y-coupled arrays to high drive currents, with lobe- widths »4 times the diffraction limit, apparently a result of weak overall interelement coupling.^' u,ll; It thus appears that to obtain narrow, single-lobe beam operation it is essential to have strong evanescent coupling between the array elements. In contrast with the fundamental-array-mode operation in evanescently coupled devices, higher-order array modes have been shown theoretically to be significantly less vulnerable to spatial hole burning, thereby offering the oossibi1ity of stable, diffraction-limited- beam operation to high drive current levels.' ' In this article, a novel array structure is presented which selects a high-order array mode, and maintains virtually diffraction- limited beam operation to high drive current levels above threshold. Single-beam opera­ tion is then possible by selectively placing IT phase-shifters in close proximity to the emitting facet.^ 3~15; Data is presented for two different 10/11-element array struc­ tures; (1) an MOCVD/LPE-grown channeled-substrate-pianar (CSP)-like array structure and (2) an entirely MOCVD-grown complementary self-aligned (CSA) laser array. ^1°»' ''