Low-Loss Waveguide Bends by Advanced Shape for Photonic Integrated Circuits

We report the design and experiment of advanced bends which are composed of widening width and varying radius. Advanced bends are based on silicon nitride waveguide for the wavelength of 850 nm and silicon waveguide for the wavelength of 1550 nm. The reduction of bending loss from 0.13 to 0.04 dB/90° by the advanced shape on a silicon nitride waveguide bend with 15 μm-radius at the wavelength of 850 nm was achieved. The bending loss from the silicon advanced bend was measured to be 0.012 dB/90° when R = 2 μm at the wavelength of 1550 nm. This is the best result of 2 μm-bends in a 220 nm-SOI platform at 1550 nm.