A new algorithm is presented to analyze three optical slab waveguide directional couplers to obtain the power transferred and field distribution through slabs. Using the effective index method, The coupler is treated as three couplers, each consisting of two slabs and the effect of the remainder waveguide is taken into account. Coupling coefficient between two slabs is derived by approximate coupled mode theory. Power transferred is evaluated by using coupled wave differential equation system and Laplace transform. Transverse field distribution is calculated by using power contained through each waveguide. Two coupled waveguides can be isolated by putting an intermediate waveguide, which applies the isolation condition with higher value of propagation constant than that of the original waveguides. A simple calculation of the intermediate waveguide is derived. The effect of coupler parameters on power transferred is applied. The obtained results are compared with other published data and these results can be used as design guide curves.
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