Adiabatically Bent Waveguides on Silicon Nitride Photonics for Compact and Dense Footprints

Low-loss bent waveguides drawn by an adiabatic profile with an offset at the interface between a bent and straight waveguides have been proposed, optimally designed, and experimentally evaluated for silicon nitride waveguide platforms, which compactness and high density are required. The profile is sinusoidal which can gradually increase the waveguide width up to 45° and then decrease the width up to 90° symmetrically. By employing the profile, modal confinement is increased and bending loss is decreased simultaneously. As a result of experimental evaluation, the characteristics of bending loss are improved. For instance, 0.215-dB/90° bending loss has been achieved at 5 μm radius. The loss of this bend is 0.4 dB/90° lower than that of a conventional bend. We also investigated bends when using a C-band light source theoretically. Less than 0.6 dB/90° bending loss has been shown using 3-D finite-difference time-domain simulations at 20 μm radius. Thus, it can be used in various applications using visible and infrared lights to reduce the device footprint.