Design and fabrication of efficient diffraction transmission gratings on step-index optical waveguides

Abstract

High-efficiency and low loss constant periodicity gratings have been fabricated and evaluated on single-mode planar optical wave guides. The most important parameters that will affect the lens performance are the coupling coefficient and the Q (or ρ) factor. The coupling coefficient has been found to be given by Kc = Δneff/(λ0/2). Investigation of the Δneff value has shown that for small groove heights larger Δneff can be obtained for CeO2 deposited grooves than for etched grooves. In grating structures where Q and ρ factors are high, the effect of the higher orders of diffraction is negligible, and there is a good agreement between the experimentally measured characteristics and the prediction from the coupled mode theory. However, minor variations in the fabrication processes (e.g., Δn ≃ 0.02) may cause the diffraction efficiency to vary as much as 15%, while the angular field of view does not seem to be affected by process variations.