Limitations to beam quality of mid-infrared angled-gratingdistributed-feedback lasers

摘要

The far-field characteristics of mid-infrared angled-gratingndistributed-feedback (Α-DFB) lasers with W active regions arenstudied as a function of etch depth, stripe width, and optical pumpingnintensity. Whereas near-diffraction-limited output is obtained for 50nΜm stripes at ten times threshold, the beam quality degrades rapidlynwhen either the stripe width or the pump intensity is increased. A keynfinding is that most of the degradation may be attributed to the onsetnof Fabry-Perot-like lasing modes that propagate along the direct pathnnormal to the facets. We further show that these parasitic modes may beneffectively eliminated by using ion-bombardment to create angled virtualnmesas surrounded by loss regions. The bombarded structures shownsubstantial improvement of the beam quality for wide pump stripes andnhigh pump intensities, although in this first demonstration thenefficiency decrease was greater than expected