Parameter tunable GaInNAs saturable absorbers for mode locking of solid-state lasers

Abstract

Passively mode-locked solid-state lasers require semiconductor saturable absorber mirrors (SESAMs) with a recovery time up to 10–30 times longer than the final pulse duration. GaInNAs SESAMs normally have a high defect concentration that supports a fast picosecond recovery time and have been used to passively mode-lock lasers at 1.3 μm. Post-growth annealing is a very useful technique to adapt the absorption edge of the GaInNAs absorber to the laser. However, larger absorption edge tuning reduces the defect concentration and increases the recovery time too much for picosecond pulse generation. We have developed a novel growth technique that allows wavelength tuning with post-growth annealing, but without any increase of the recovery time and without degrading the absorber performance. This was achieved by exposing the GaAs barrier to nitrogen from a plasma source for about 20 s before the GaInNAs quantum well was grown.