Long Wavelength Vertical Cavity Lasers

Long-wavelength Vertical Cavity Lasers (VCLs) emitting at 1300 or 1550nm are considered as promising candidates as low-cost light sources in fiber optical communication systems Despite the success of their short-wavelength counterparts, and even the demonstration of well-above room temperature continuous operation of a double-fused VCSEL at 155nm /1/, their final demand on mirror reflectivity (>99.5%), uniform current injection and exact gain-cavity tuning, is even further pronounced in the long wavelength regime. This is mainly due to excessive losses (intervalence band absorption, Auger recombination and diffraction) and a relatively small refractive index difference in the InGaAsP/InP system. To overcome these problems, several generically different designs have been presented and investigated The so far most successful approaches use at least one wafer fusion step to combine an InGaAsP active layer with one or two AlGaAs/GaAs DBRs However, such solutions are rather complex from a processing point of view, not yet demonstrated as full two-inch compatible. A more attractive design in this respect is based on the combination of an InGaAsP/InP bottom DBR and a dielectric top mirror So far such lasers have been limited to low-temperature operation /2/, but significant improvements can still be expected from a better optimized current injection scheme or improved dielectric mirror quality Alternative approaches, e g., based on GaInNAs lattice matched to GaAs as active material may also become of importance.