  The characteristics of mid-infrared laser diodes have been investigated
before and after the patterning of sub-wavelength metallic apertures on the
emitting facet. Before modification of the facet the emitted spectrum consisted
of a large number of peaks associated with different spatial modes, whereas
afterwards the spectrum was dominated by a single peak. Simulations showed that
the patterning of the facet caused the effective reflectivity to be different
for each lateral mode, suggesting that the peak in the measured spectra is
associated with the single lateral mode which is most strongly reflected from
the modified facet.
