A fabrication-aware inverse design method for thin-film lithium niobate photonic devices

Lithium niobate on insulator (LNOI) is a compelling platform for photonic integrated circuits, enabling compact devices with a unique combination of high-speed electro-optic modulation, high efficiency, and strong nonlinear optical effects. This makes it an ideal candidate for inverse-design-enabled devices. However, its anisotropic etching produces sloped sidewalls that degrade device performance, a critical challenge overlooked by conventional inverse design methodologies. We propose a fabrication-aware inverse design framework that directly integrates sidewall profile modeling into optimization. Using this method, we design a mode multiplexer/demultiplexer (MUX/DEMUX) achieving −26 dB extinction ratio and below 0.28 dB insertion loss over 100 nm bandwidth. The approach ensures robustness against fabrication variations, paving the way for practical high-performance inverse-designed LNOI devices.