WKB analysis of asymmetric directional couplers and its application to optical switches

For an optical asymmetric directional coupler with graded-index profile, quasi-even and quasi-odd mode eigenvalue equations are derived using WKB approximation through connection formulas. Analysis of the guiding structures is based on a combination of the effective index approach and the derived quasi-even and odd mode eigenvalue solutions. Two-dimensional isotropic diffusion is assumed throughout. Excellent agreement is obtained when the results are compared with those of the finite difference method. Calculation of the normal mode approach is applied to a uniform directional coupler switch and the design parameters are illustrated for this case