Two dielectric waveguides that are evanescently coupled to a square or rectangular region of increased refractive index can serve as a very compact integrated optical microresonator. We consider these devices in a spatial two-dimensional setting, where a rigorous mode expansion technique enables accurate and quite efficient numerical simulations of these configurations. The paper is concerned with single resonator units as well as with an add-drop filter constructed by cascading two square cavities. Besides calculating the power transmission spectra, we try to document as far as possible the characteristic electric field patterns that occur at major and minor resonance wavelengths. The influence of the various geometrical parameters on the resonator performance is investigated in detail.

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A thick, bimodal segment of specific length and height between two single mode sections of a planar waveguide can serve as an integrated optical interferometer. It is realized by etching a wide strip from a guiding film. A -vertically guided, laterally unguided -beam of light is then made to traverse the strip perpendicularly. For a wide range of materials the structure can be dimensioned such that it shows the proper behaviour of an interferometer: Depending on the phase gain of the two modes in the thick region, the guided light interferes either almost completely destructively at the transition to the output segment, i.e. the power is radiated away into the substrate and cover regions, or constructively, i.e. most of the power passes the device. We believe that for certain applications structures of this kind can be a simple substitute for instruments like Mach-Zehnder interferometers or directional couplers. This is illustrated by two numerically simulated examples: A polarizer constructed from silicon based waveguides, which offers ¿¼ dB polarization discrimination and ¼ ½ dB insertion loss with a total length of only ½¼ micrometers, and a proposal for an integrated magnetooptic isolator experiment, where the freedom in the lateral direction can be exploited for a proper tuning of the device.

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