High-power diode lasers under external optical feedback

Abstract

We carried out a comprehensive study on single emitters with different antireflection (AR) coatings in the wavelength range between 780nm and 976nm, which have been exposed to optical feedback to investigate the reversible and irreversible impacts caused by back-reflected light. By observing the near-field pattern while varying the probe current, we got information about the influence on filamentation and on peak-power densities with and without external optical feedback. For GaAs-based laser diodes, the energy gap of GaAs makes a distinction at a wavelength of about 870nm. For shorter wavelengths, e.g. at 808nm, a substantial part of the feedback light is absorbed by the substrate and GaAs cap layers very close to the front facet leading to a significant heating of the outcoupling facet. For longer wavelengths, e.g. 976nm, this energy intrusion is not a local one at the front facet, but rather spreads along the whole cavity length.