  We propose a noble notion of the directional emission in microcavity lasers.
First, Shannon entropy of the far-field profiles in the polar coordinate can
quantify the degree of unidirectionality of the emission, while previous
notions about the unidirectionality can not efficiently measure in the robust
range against a variation of the deformation parameter. Second, a divergence
angle of the directional emission is defined phenomenologically in terms of
full width at half maximum, and it is barely applicable to a complicated peak
structure. However, Shannon entropy of semi-marginal probability of the
far-field profiles in the cartesian coordinate can present equivalent results,
and moreover it is applicable to even the cases with a complicated peak
structure of the emission.
