A sharp 90 degree bend in a dual mode trench waveguide is analyzed by means of the MMP method. Through evolutionary strategy optimization, different configurations with low reflection, low radiation, low mode conversion, and therefore high transmission for the dominant mode are obtained. Three different types of bends are analyzed and compared: mirror-based structures, resonator-based structures, and structures with a small photonic crystal in the bend area. The local photonic crystal helps not only suppressing radiation but also provides solutions with fewer fabrication tolerance problems.
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