PRESSURE AND TEMPERATURE-INDUCED DETUNING OF GAIN AND REFLECTIVITY SPECTRA IN VERTICAL-CAVITY SURFACE-EMITTING LASERS

Low threshold current operation of vertical cavity surface emitting la sers (VCSELs) depends on a close match between the reflectivity resona nce and the gain peak. We have used differential pressure and temperat ure tuning of these two spectra to quantify the required matching. The temperature in the VCSEL was increased by increasing the injected pow er. Increased temperature red shifts the gain peak al a rate five time s that of the Fabry-Perot resonance resulting in a mismatch. At thresh old the mismatch is 23 nm, reaches a value of 29 nm at the peak light output and at similar to 50 nm lasing disappears. Increased mismatch i s accompanied by a decrease in the gain at the laser wavelength, which is responsible for the laser quenching at high injected powers. Hydro static pressure shifts the gain peak to shorter wavelengths with respe ct to the FP resonance, without modifying the gain spectra. The mismat ch was varied from 19 to -13 nm at 0.5 GPa. For positive mismatch the threshold current remained unchanged while for negative mismatch it in creased drastically by about a factor of 4 at -13 nm when lasing disap pears.