Epitaxially-stacked multiple-active-region 1.55 /spl mu/m CW lasers for increased differential efficiency

Semiconductor CW lasers with external differential efficiencies >1 have been created by monolithically connecting several active regions in series within a single optical waveguide. This task has been accomplished at the technologically important 1.55/spl mu/m wavelength. This is achieved by epitaxially stacking a number of p-i-n multi-quantum well active regions with intermediate n/sup ++/-p/sup ++/ back-diodes, which enable the entire terminal current to flow through each active region stage in series. Such lasers should also improve impedance match as well as provide for low-noise, high-efficiency microwave links.