Abstract

In model experiments with microwaves (λ = 6 mm) field distributions in the evanescent field near the waveguide surface are measured and compared with beam-propagation method calculations. Rectangular waveguides consist of foamed materials (Styrofoam n = 1.02 in air) and solid plastic materials (Polystyrol n = 1.6 in Styrofoam). Good agreement of calculated and measured field distributions was observed, even for waveguides with higher refractive indices. More complex structures may be formed as combinations of waveguide sections. Directional couplers with two parallel waveguides were investigated. The coupling length L can be evaluated directly from measured and calculated field distributions. At any waveguide discontinuity radiation modes are excited, changing the efficiency of waveguide components. We investigated fields behind step-like variations in cross-section and combinations of such steps with couplers and branches. The superposition of guided and radiation modes behind the step leads to interference beats with period λ_B. The transmission of complex devices shows periodic variations with the same period, independent of the following structure elements even in distances up to 10λ. Systematic investigations of low cost enlarged microwave model structures yield predictions for properties of the corresponding integrated optic components. The range and validity of numerical methods such as bpm are analyzed by comparison with measured field distributions.

© 1992 Optical Society of America