Waveguide grating coupling of 2D focused beam under normal incidence: a phenomenological approach

The coupling of a 2D focused beam under normal incidence into a grating waveguide was solved by means of a coupled wave formalism where the phenomenological parameters are given by a simple plane wave diffraction analysis [1]. It is shown that the guided modes which must be considered in the situation of normal incidence are waves exhibiting a standing wave as well as a propagating character. The plane wave diffraction analysis of the poles corresponding to these modes reveals their interesting properties and helps establish the suitable phenomenological representation of the coupling event. The aim of this approach was to find out the conditions for maximum light confinement in a grating waveguide in the perspective of the high efficiency excitation of a high density pixellated array of biosensor sites.