A Huygens’ Principle for Uniaxially Anisotropic Media*†

A Huygens’ principle for uniaxially anisotropic media is developed using a plane-wave representation of the electromagnetic field. The field emanating from an illuminated aperture in a uniaxial medium (with an optic axis which is arbitrarily oriented with respect to the axis of the aperture) may be represented as the superposition of a transverse electric (or TE) field and a transverse magnetic (or TM) field with respect to the optic axis of the medium. For the TE field, the field at an observation point and the aperture field distribution are related in the same manner as in isotropic media. An exact, closed-form expression is derived for the TM field, specifying the field at an observation point in terms of the field distribution over the aperture. A Huygens’ principle for anisotropic media emerges as a special case of this expression. The interpretation arrived at is that the field at an observation point is obtained by superposition of elliptical wavelets emanating from the aperture, with due regard to their phase differences when they reach the point in question.