Epitaxially-stacked multiple-active-regions for high differential efficiency monolithic 1.55 /spl mu/m VCSELs

The development of monolithic 1.55 /spl mu/m VCSELs has been hampered by the lack of readily available highly reflective DBRs. However, it is possible to achieve lasing with less reflective DBRs by epitaxially stacking multiple active regions and increasing the gain. For example, 30.5-period AlGaInAs/AlInAs DBRs can be mated to a three-stage active region to achieve lasing. Epitaxy of such VCSEL can be short enough to maintain source stability in an MBE system. The other benefit is greater differential efficiency, which can actually exceed unity, for greater signal to noise ratio. We have investigated the properties of such active regions. We have created edge-emitters with external differential efficiencies >1 by monolithically connecting several active regions in series within a single optical waveguide. In contrast to previous reports, we have accomplished this task at the technologically important 1.55 /spl mu/m wavelength.