Ultra-broadband, high-efficiency and wafer-scale fiber-to-chip coupling using free-form micro-optical reflectors

Optical coupling between fibers and on-chip waveguides is a critical step in photonic testing and packaging. We demonstrated broadband surface-normal fiber-to-chip optical coupling based on free-form micro-optical reflector arrays integrated with foundry-processed SiN photonics. The couplers yield a low fiber-to-waveguide coupling loss of 0.5 dB at 1550 nm wavelength, and an exceptionally broad 1-dB bandwidth encompassing O to L bands (1260 nm to 1640 nm), only limited by the wavelength range of our testing setup. In-plane 1-dB alignment tolerances up to +/- 2.4 mu m and an out-of-plane 1-dB alignment tolerance up to 20 mu m were obtained at 1550 nm. We further show that the Optical Free-Form Couplers for High-density Integrated Photonics (OFFCHIP) platform is universally applicable for chip-to-chip, waveguide to free space, and waveguide to surface-normal device coupling, qualifying it as a universal high-performance optical coupling interface for diverse use scenarios.