Long-wavelength (λ ≥ 1.3 μm) InGaAlAs-InP vertical-cavity surface-emitting lasers for applications in optical communication and sensing

In this paper we present an overview of the properties and applications of long-wavelength vertical-cavity surface-emitting lasers (VCSELs) based on the InGaAlAs-InP material system. With respect to significant temperature sensitivity of active material gain as well as insufficient thermal conductivity of InP-based epitaxial compound layers, the effective thermal heat management appears as a major issue for application suitable device performance. In this context, the incorporation of a buried tunnel junction (BTJ) in connection with improved heat sinking resembles a breakthrough for long-wavelength VCSELs. With the utilization of n-type spreading layers and consequently ultralow series resistances, BTJ-VCSELs exhibit sharply reduced excess heat generation. Furthermore, the BTJ-approach enables self-aligned optical and current confinement. A hybrid dielectric stack with Au-coating yields an improved thermal heatsinking. The current status of BTJ-VCSELs encompasses a number of superior performance values. At 1.55 μm wavelength, this includes room temperature single- and multimode continuous wave (cw) output powers of more than 3 mW and 10 mW, respectively, laser operation for heat sink temperatures well exceeding 100°C, and optical data transmission rates up to 10 Gbit/s. The versatility of compound layer composition enables arbitrary emission wavelengths within a broad range of 1.3 and 2 μm. With respect to sensing applications, BTJ-VCSELs appear as ideal components for optical detection of infrared active gases.