Key points are not available for this paper at this time.
A ray tracing method has been performed to calculate the focus spot size of two-dimensional focusing grating couplers that are produced by holographic interferometry of freely propagating wavefronts. The calculations have been used to optimize the constructing optical configuration. Diffraction limited spot diameters of about 2 μm can be achieved for couplers at wavelength 632.8 nm. These spot sizes have been experimentally verified for coupling and focusing TE modes which are guided in sputtered glass films on Si substrates.
Heitmann et al. (1981) studied this question.