Low-temperature performance of InP-based long-wavelength VCSELs

We have studied, for the first time, the parameters of long-wavelength InP-based buried tunnel junction (BTJ) VCSELs with substrate temperature varied in the range between 150 and 330 K. The BTJ-VCSELs with threshold currents < 1 mA were designed by VERTILAS (Germany) to operate near 1512 nm and 1577 nm at room temperature (models VL-1512 and VL-1577, respectively). Reducing the substrate temperature of the lasers from room temperature to 150 K resulted in more than a fourfold increase of the threshold injection current accompanied with threefold and twofold increases in output power and slope efficiency, respectively. We have observed continuous single-mode tuning over intervals up to similar to 20 nm (VL-1512) and similar to 22 nm (VL-1577) at constant injection currents and substrate temperatures varied in a 180 K range. The emission wavelength was found to shift linearly with temperature with rates of 0.11 nm/K and 0.12 nm/K for lasers VL-1512 and VL-1577, respectively. The single-mode laser output reached similar to 3 mW for both lasers cooled down to 173 K. Gas sensors based on BTJ-VCSELs can be temperature tuned over wide spectral intervals using either a cooler or a low ambient temperature to control laser substrate temperature. Ultra-sensitive gas concentration measurements under low ambient temperatures may include chemical analysis of the lower earth stratosphere and of the martian atmosphere.