Fromanordinarycondition,usingafullthree-dimensionalmodeltheoryandaninfiniteperturbationexpansionmethod,anexactsolutionofthere-flectioncoefficientforthecoatednarrowstripe-geometryopticalwaveguidedeviceshasbeenderived.Allsixcomponentsandthevectorpropertyoftheelectroma-gneticfieldhavebeenconsidered.Theresultsaresuitableforthesymmetricandasymmetricwaveguides.