Deeply Etched $\hbox{SiO}_{2}$ Ridge Waveguide for Sharp Bends

A deeply etched SiO
₂
ridge waveguide including the buffer, core, and cladding is presented for realizing sharp bends. The present SiO
₂
ridge waveguide has a strong confinement at the lateral direction, while it has a weak confinement at the vertical direction. Due to the strong confinement, a sharp bend (with a very small bending radius of about 10 mum) is obtained for an acceptable bending loss. A detailed analysis of the loss in a bent waveguide is given by using a finite-difference method. In order to reduce the transition loss, a narrow bending section with an optimal lateral offset is used. A low leakage loss is obtained by using wide straight waveguides, and linear tapers are used to connect the wide straight section and narrow bent sections