Optical grating coupling between low-index fibers and high-index film waveguides

Grating couplers between low-refractive-index (n ≈1.5) optical fibers and high-refractive-index (n ≈2.2) electro-optic planar guides have been analyzed and demonstrated. Coupling efficiencies of 6% between single modes of a film and a fiber have been observed. Efficiencies of approximately 86% between single-mode fibers and films using blazed backward-wave gratings are predicted. In addition, low-loss low-optical-aperture multimode fibers may be coupled to single-mode films with efficiencies greater than 50% and angular spreads less than 0.5°.