Ultralow-loss waveguide crossing for photonic integrated circuits by using inverted tapers

An ultralow-loss silicon planar waveguide crossing operating in the O-band was experimentally demonstrated based on the Gaussian beam synthesis method. Elliptical parabolic inverted tapers were introduced in our design to reduce the crossing loss. According to the measurement results, the proposed device exhibits an insertion loss of 0.008 dB, which is the lowest reported loss for planar silicon waveguide crossings operating in the O-band. The device exhibits a low crosstalk below -40 dB over a 40 nm wavelength range with a compact footprint of 18 × 18 µm² and can be fabricated in a complementary metal-oxide-semiconductor-compatible process.