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

Abstract
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°.