In this paper, a novel two-chip-concept for an electrically pumped and micro-mechanically tunable vertical-cavity surface-emitting laser (VCSEL) operating in the 1.55 μm wavelength range is presented. One chip contains the active region with 5 quantum wells based on the material system AlGaInAs/InP and a buried tunnel junction (BTJ) to provide current confinement and waveguiding. A dielectric mirror forms the back reflector. The second chip consists of a curved mirror membrane that can be displaced by electro-thermal heating. The main advantage of this approach is that both parts can be optimized separately. Packaged laser devices show continuous-wave operation at room temperature with an output power of up to 200 μW and very good side mode suppression in the order of 45 dB. Single-mode operation was observed across a tuning range of more than 30 nm.
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.
A new approach for InP-based long-wavelength VCSELs based on buried tunnel junctions: the buried-tunnel-junction (BTJ) VCSEL is reviewed. Excellent cw laser performance has been demonstrated for BTJ-VCSELs in the 1.55μm wavelength range, such as sub-mA threshold currents, 0.9 V threshold voltage (at λ=1.55μm), operation voltages below 1.4V, 10-70 Ω series resistance, differential efficiencies >25%, up to more than 7mW optical output power, >100°C cw operation, stable polarization and single-mode operation with SSR of the order 50 dB. Also, recent achievements on high-speed long-wavelength VCSELs are reported.