Improvement of diode cascade VCSEL performance

Summary form only. The performance of conventional VCSELs is generally limited by the extremely low roundtrip gain in the cavity. Thus, VCSEL devices require high mirror reflectivity but also are characterized by an increase in the threshold current density compared to edge emitting lasers. To overcome this distinct disadvantage, diode cascade VCSELs are proposed as excellent candidates to improve the performance of VCSEL structures. Such a VCSEL could also exhibit high differential quantum efficiency well exceeding unity that may be interesting for low noise applications. Previously, we could demonstrate the first continuous-wave, room temperature operating diode cascade VCSEL at 980 nm wavelength. In this letter, we present the improvement of the diode cascade VCSEL output characteristics by reducing the current spreading in the cavity region.