The effects of beam size, number of lines, and rotational misalignment on coupled subwavelength gratings (CSWGs) were investigated in this paper using optical modeling. Period and thickness of the gratings were optimized for maximum evanescent wave coupling efficiency at a wavelength of 650 nm. The size of the input light beam and the number of grating lines were established for discernible transmission of higher diffraction orders, and the half-width at half-maximum for minimum noise was determined. A rotation of the far-field pattern, due to milling one grating on a fiber facet, was calculated and confirmed by simulations. These parameters will be included in a method using CSWGs for electronic chip security.