Inverse design fiber-to-chip couplers for the O- and C-bands

High-efficiency fiber-to-chip couplers are essential for high-performance optical interconnects. In this Letter, we experimentally demonstrate two inverse-designed silicon-on-insulator (SOI) couplers tailored for single-mode fibers (SMFs) in the C and O telecommunication bands. The O-band coupler represents the first, to the best of our knowledge, experimental demonstration of a topology-optimized coupler for this band while maintaining a minimum feature size of 120 nm. Both couplers operate at an 8° angle and are optimized for TE polarization. The C-band coupler achieves a coupling efficiency of -3.3 dB with a 3-dB bandwidth of 64 nm, while the O-band coupler reaches -3.4-dB efficiency over a 3-dB bandwidth spanning from 1292 nm to 1355 nm. Measuring 12 μm by 12 μm, these devices are designed using a single optimized silicon layer, reducing fabrication complexity and achieving efficiencies comparable to those of much larger high-performance grating couplers. Their compact size can increase integration density and contribute to reducing fabrication costs. Additionally, these couplers could be suitable for spatial division multiplexing (SDM) interconnects using multicore fibers, where the mode field diameter is compatible with single-mode fibers. They could also be used with multimode fiber configurations, where multiple couplers could be combined to generate higher-order modes.