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

The far-field emission characteristics of mid-infrared angled-grating distr ibuted-feedback (alpha -DFB) lasers with W active regions are calculated us ing a self-consistent beam-propagation formalism that is more general than previous analyses. The theoretical projections are compared with the result s of an experimental study of optically pumped alpha -DFB devices. Near-dif fraction-limited beam quality is obtained both theoretically and experiment ally for pump stripes less than or equal to 50 mum wide. While simulations employing the theoretical linewidth enhancement factor of 1.7 for the homog eneously-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 onl y by assuming that inhomogeneous broadening increases the structure's linew idth 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 deg rees when temperature tuning shifts the gain peak away from the grating res onance. (C) 2000 American Institute of Physics. [S0021-8979(00)04401-2].