ABSTRACT
By correlating the far-field profiles such as those illustrated in Fig. 1 with theoretical near-field profiles, we can derive the etendue, which is roughly the product of the emission area and the solid divergence angle. We assume that the output beam is diffraction limited (DL) along the growth direction. For pulsed optical pumping at 10 x /th, the output beam is very close to the DL up to a stripe width of 150 pm (roughly 10 times the limit for an unpattemed Fabry-Perot device), and remains no worse than 8 x DL for stripes as wide as 600 pm. Beam etendue results for several PCDFB and a-DFB devices are shown in Fig. 1 (for references to the original works on these lasers, see Ref. [3]). The excellent beam quality obtained for the present PCDFB device (filled circles) comes with some penalty in the differential quantum efficiency. However, as long as the stripe is wider than 250 pm the efficiency is over 40% of that for an unpattemed EE device from the same wafer. Clearly, the present result constitutes a considerable improvement over all previous mid-IR semiconductor lasers with such broad stripes.
