Mode-field half-width and divergence half-angle definitions for a planar waveguide

Mode-field half-width and divergence half-angle definitions for a planar waveguide with an arbitrary index profile are presented based on the near- and far-field distributions and their relations are given. Then, analytical formulae of these definitions are derived for the TE0 mode in a symmetrical step-index planar waveguide and numerical results prove that they are more suitable as the mode-field half-width and divergence half-angle of the Gaussian approximation for the near- and far-fields respectively. (letter)