Broadband and compact arbitrary ratio curved directional coupler enabled by inverse design

Silicon photonics has attracted considerable attention in datacom and telecom due to its Complementary- Metal-Oxide-Semiconductor (CMOS) compatibility, high integration, and low transmission loss. Optical splitter can be widely used as a building block in large-scale photonic integration chips, such as wave-division-multiplexing (WDM), optical modulating and optical switching. Suffering from waveguide dispersion, the power splitter exhibits high wavelength sensitivity. This imposes a huge impact on the overall performance of large-scale photonic integration. In order to achieve a significant optical response, we need to implement a beam splitter with large operating bandwidth and small footprint, as well as the ability to achieve arbitrary power-splitting-ratios. Enabled by inverse design, we propose broadband, compact arbitrary-ratio power splitters based on curved directional coupler (CDC). The enhanced particle swarm optimization (EPSO) algorithm is used to engineer the coupling region of the CDCs, greatly reducing the device footprint and improving the device optimization efficiency. The simulation results show that the proposed CDCs based on EPSO can achieve 80 nm operating bandwidth from 1260 nm to 1340 nm. The device coupling footprint can be reduced to 7.15 μm, with an excess loss of less than 0.01 dB. Inverse design allows for the reduction of the considerable time and labor required for manual adjustments. In addition, the optimization room of device footprint and operating bandwidth can be further exploited. With the comprehensive performance metrics, our proposed CDCs can be widely used in high-density photonic systems.