Robust and broadband tap couplers using misaligned waveguides based on thin-film lithium niobate

Robust and high-performance power splitters with an ability to partition the input light power into different proportions are vital for various on-chip optical systems. Here we propose and experimentally demonstrate several tap couplers with unbalanced power splitting ratios (PSRs) from 4%: 96% to 40%: 60% using misaligned waveguides on thin-film lithium niobate (TFLN). The device utilizes misaligned waveguide width differences to obtain a flat power splitting ratio over a broadband optical wavelength. The measured results indicate that all the proposed devices exhibit less than 2% PSR variation over a 120 nm optical bandwidth from 1500 nm to 1620 nm and over ±100 nm planar fabrication tolerance. The demonstrated tap couplers offer a promising application prospect in high-density photonic integrated circuits.