Abstract

The power transfer characteristics in a grating-assisted three-waveguide coupler are analyzed by using the nonorthogonal coupled-mode theory based on the isolated waveguide modes. The coupler consists of three asynchronous, parallel, planar waveguides in which the upper and lower surfaces of the intermediate waveguide are corrugated with different periods. When two phase-matching conditions and an additional constraint on the coupling constants are satisfied, the guided modes in the two outer waveguides couple selectively at a certain wavelength by means of the corrugated intermediate waveguide. It is shown that the wavelength selectivity in the power transfer between the two outer waveguides becomes noticeably sharper than that of the grating-assisted two-waveguide coupler and that the sidelobes in the wavelength response are almost completely suppressed.

© 1997 Optical Society of America

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