Ring Shaped Lithographic Aperture VCSEL

Tunnel junction (TJ) lithographic apertures provide a reliable approach for fabricating vertical-cavity surfaceemitting lasers (VCSELs), enabling precise dimensional control of the aperture and scalability for mass production. In such VCSELs the aperture is defined by etching the TJ in the areas where the current should be blocked. However, the refractive index step introduced by the TJ makes the VCSEL operate multimode even for small aperture size. Spectrum width, a critical parameter in optical fiber communication, has conventionally been controlled by reducing the aperture shape or diameter. However, reducing the aperture size significantly impacts thermal resistance, which in turn affects device rollover current and hence maximum achievable output power. Recent advancements have demonstrated thermal resistance below 2 K/mW at room temperature[1], but only for oxide apertures larger than 7μm. Alternatively, mode control has been achieved by selectively introducing optical losses for large oxide aperture, such as circular or ring-shaped mode filters [2].