Long-wavelength InP-based VCSELs with buried tunnel junction: properties and applications

Abstract

InP-based VCSELs (Vertical Cavity Surface Emitting Lasers) are interesting light sources for applications in spectroscopy and fiberoptical communication. Reviewed are devices with a buried tunnel junction (BTJ) and a dielectric backside reflector directly integrated on a electroplated gold-heatsink in the InGaAlAs/InP material system covering the wavelength range from 1.3 to 2.0 μm. The BTJ accomplishes both current confinement to the active region and wave-guiding by the refractive index distribution to achieve low threshold currents. Furthermore it allows for substitution of p-doped device parts by more suitable n-doped material. This approach already proved excellent device performance such as 7 mW output power (multi-mode) and good high temperature characteristics such as 0.5 mW at 80°C for 1.55 μm. Modulation at 10 Gbit/s was also demonstrated. Since the BTJ VCSEL concept covers a wide wavelength range, there is a high-potential field of applications in Tunable Diode Laser Absorption Spectroscopy (TDLAS). Demonstrated are representative measurements of NH3 and HCl. A specialty of TDLAS with VCSELs is the ability for rapid concentration determination with a time resolution up to the megahertz regime. Recent results and further developments of the device structure are also discussed.