Ultracompact Polarization-Insensitive Waveguide Crossing Based on Dielectric Metasurface

A compact polarization-insensitive silicon waveguide crossing is proposed and experimentally demonstrated. The dielectric metasurface can extremely manipulate the effective refractive profile to keep high transmittance in the propagation direction and shrink the device footprint. Our designed crossing has an ultra-wideband operating bandwidth covering 1200 nm to 1700 nm for dual-polarization (insertion loss < 0.4 dB) and an ultra-compact footprint of only $4.8\times 4.8\,\,\mu \text{m}^{2}$ . The simulated results indicate the device has a good fabrication tolerance. Subsequently, an ultra-densely ( $30\times 30\,\,\mu \text{m}^{2}$ ) polarization-multiplexed integrated circuit consisting of a crossing and four polarization splitter-rotators is designed and fabricated. The measured circuit is characterized with low insertion loss and low crosstalk over 100 nm bandwidth. These compact components and circuits pave an alternative way for large-scale high-capacity optical communication system.