Far-field characteristics of mid-infrared angled-grating distributed feedback lasers

The far-field emission characteristics of mid-infrared angled-grating distributed-feedback (alpha -DFB) lasers with W active regions are calculated using a self-consistent beam-propagation formalism that is more general than previous analyses. The theoretical projections are compared with the results of an experimental study of optically pumped alpha -DFB devices. Near-diffraction-limited beam quality is obtained both theoretically and experimentally for pump stripes less than or equal to 50 mum wide. While simulations employing the theoretical linewidth enhancement factor of 1.7 for the homogeneously-broadened W-laser gain spectrum predict that the good beam quality should be retained for stripes as wide as approximate to 200 mum, the data indicate a much more rapid degradation. That finding can be reproduced only by assuming that inhomogeneous broadening increases the structure's linewidth enhancement factor to approximate to5. The experiments and theory also yield a steering of the output beam to off-normal angles as large as 6 degrees when temperature tuning shifts the gain peak away from the grating resonance. (C) 2000 American Institute of Physics. [S0021-8979(00)04401-2].