Epitaxially-stacked multiple-active-region 1.55μm lasers for increased differential efficiency

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Abstract
Semiconductor lasers emitting at 1.55 μm with external differential efficiencies >1 have been created by monolithically connecting several active regions in series within a single optical waveguide. This is accomplished by epitaxially stacking a number of p–i–n multiquantum well active regions with intermediate n ++ –p ++ back diodes, which enable the entire terminal current to flow through each active region stages in series. Such lasers should also improve the impedance match as well as provide for low-noise, high-efficiency microwave links.