VCSELs with Two-Sided Beam Emission for Sensing Applications

VCSELs with two-sided emission have been presented in the literature long times ago (see, e.g., [1]). In the common AlGaAs material system on GaAs substrates, this is most easily achieved with the use of compressively strained InGaAs quantum wells (QWs) which have a reduced bandgap energy and with current supply through a top ring contact and a bottom ring contact at the back side of the substrate. For photon energies exceeding approximately 920 nm, the GaAs substrate is essentially transparent. For VCSELs based on GaAs QWs with emission in the 850 nm wavelength range, substrate removal or substrate replacement with, e.g., a glass wafer are alternative options. As for most cases in optical sensing, the optical pressure sensor application described in [2] requires single-mode, single-polarization emission with a high side-mode suppression ratio. In the sections to follow we first describe the chosen device structure for emission close to 960 nm wavelength and its processing and mounting and then present the experimental results for static operation. It turns out that a high-quality anti-reflection (AR) coating at the substrate side is a necessity for proper laser output.