Characteristics of grating-assisted couplers

Characteristics of grating-assisted coupling between two parallel waveguide s are analyzed. The influence of the grating parameters, such as groove dep th, duty cycle, and refractive indices is considered Chirped and parallel g ratings as well, as gratings with sinusoidal envelope periodicity are also addressed. The analysis is based on a unified coupled-mode formalism, with the transfer-matrix method as a general solution technique. It is shown how to modify the grating parameters to provide a specific spectral response ( reflectivity and transmission coefficients). As an example, two parallel gr atings are used to obtain a similar response to a single grating of double length. The location of the grating between the two waveguides as well as t he light-wave injection direction are very important. The presented methods and effects may be useful for design and analysis in the fields of optical communications, sensing, and processing. (C) 1999 Optical Society of Ameri ca OCIS codes: 050.1950, 050.2770, 130.2790, 230.7390.