Comments on index nomenclature equivalencies for uniaxial materials (i.e. birefringent or two independent indexes of refraction):
The following expressions are equivalent:         ordinary ray, (n_o,n_w, or w),             E-field perpendicular to c axis (n^ )
The following expressions are equivalent:         extraordinary ray (n_e, n_e, or e)          E-field parallel to c axis (n )