Rigorous evaluation of a Talbot waveguide coupler

The Talbot array Illuminator (TAIL) is well known as a diffractive element that efficiently transforms a monochromatic optical wave into an array of bright spots. To date, TAIL´s have been thoroughly studied both analytically and experimentally mainly within the frame of scalar diffraction theory and paraxial approximation. However, only little investigation has been done so far on what happens to the illumination characteristics when the TAIL´s feature size becomes of the order of the wavelength and whether illumination of less than one TAIL period can be in any way useful. In the following, we try to answer those questions by taking a look at the performance of a TAIL when acting as a coupling element to an optical waveguide. For simplicity we confine here our evaluation to optical structures that vary only in two dimensions, e.g., a slab waveguide, and TE illumination.