Low-loss waveguide bend for compact and broadband photonic integrated circuits

We propose and demonstrate a low-loss, wavelength-insensitive waveguide bend via a silica-on-silicon delay line with a footprint of 10 mm × 7.5 mm. The bending loss of the 90^∘ Bloss and arc hybrid bend was simulated and compared to that of a circular arc. The results show that in addition to having ultra-low loss (0.0014 dB/90^∘ in 1310 nm), the proposed bend with a 1 mm radius has a flat spectrum across O- and C+L-bands. Two 2-meter-long delay lines, composed of 90^∘ bends and straight waveguides, were fabricated. The delay line using the proposed bend exhibits a propagation loss of 4.20 dB/m, a significant improvement over the design with circular arc bends, which has a 25.18 dB/m loss.