Design of compact optical bends with a trench by use of finite-element and beam-propagation methods

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Abstract
We address various approaches to the reduction of optical bending loss in photonic integrated circuits. Different methods, such as offsetting of waveguides and incorporation of the effect of an isolation trench on reduction of radiation loss, are demonstrated. A combination of the vectorial finite-element and the least-squares boundary residual methods is used to calculate transition losses and the required offset for their minimization. The semivectorial finite-element-based beam-propagation method is employed to calculate radiation loss. These vectorial approaches are also used to investigate several important properties, such as effects that are due to the sidewall slopes, rib heights, rib widths, and trench location, to optimize bend designs.