Vertical-cavity surface-emitting lasers (VCSELs) operating at long wavelength (1.3-1.55 µm) are of great interest as inexpensive, high-performance light sources for optical communication systems. The vertical geometry and the small dimensions of the laser cavity are advantageous for on-chip testing, packaging, effective fibre coupling and potential low-cost fabrication. Operation at long wavelength is favourable for applications in fibre-optical communication due to the superior transmission characteristics in standard silica fibres. However, in contrast to GaAs-based VCSELs operating at wavelengths below 1 µm, which have seen a tremendous development in recent years, the progress for the long-wavelength devices has been much slower. This is mainly due to intrinsic material problems in the GaInAsP alloy system. The limited refractive index contrast between InP and GaInAsP is of specific importance, impeding the fabrication of an all-epitaxial device structure with two monolithically integrated semiconductor distributed Bragg reflectors (DBRs) as it is common for GaAs-based VCSELs. Instead, the most successful designs have relied on the combination of a
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