Reduction in Bend Losses of a Buried Waveguide on a Silicon Substrate by Adjusting the Core Location

A new technique for reducing pure bend and transition losses in a buried dielectric waveguide is discussed, using the imaginary-distance beam-propagation method. It is numerically shown that only the adjustment of a core location enables us to reduce the bend losses. The reason why a proper location of the core offers minimum bend losses regardless of a bending radius is explained in terms of the generation and suppression of a leaky wave. Significant loss reduction is achieved over a wide spectral range from 1.3 to 1.65 
$\mu {\rm m}$
. It is also revealed that a minimum pure bend loss is obtained regardless of the relative refractive index difference, when the air-cladding interface is placed at the position, where the field amplitude decays to approximately 12% of its peak.