Optics Communications, published by Elsevier, has released a study from the Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, presenting a new method to design high-performance photonic devices for a promising material platform, thin-film lithium niobate on insulator (LNOI).

LNOI is a key material for next-generation optical circuits, enabling powerful applications in high-speed communications and quantum computing due to its superior electro-optic and nonlinear properties. To unlock its full potential, complex device shapes are needed, often designed through computational "inverse design" where an algorithm finds the optimal structure for a specific optical task. However, a significant problem has been that standard design methods assume perfectly vertical sidewalls after etching, while real-world fabrication of lithium niobate consistently produces slanted sidewalls, severely degrading device performance.

To address this critical "simulation-to-fabrication" gap, the research team developed a fabrication-aware inverse design framework. Their key innovation was to directly integrate a model of the sloped sidewalls into the optimization algorithm itself, rather than treating it as an afterthought. The team created a differentiable model that simulated how the etching process would create these slanted profiles. This model was embedded into the design loop, allowing the algorithm to anticipate and compensate for the performance loss caused by the slanted walls during the optimization process.

The researchers applied this novel framework to design a compact mode multiplexer/demultiplexer, a device crucial for increasing data capacity in optical networks. The resulting device demonstrated excellent performance. Over a 100-nanometer bandwidth, it achieved an extinction ratio below -26 dB and an insertion loss under 0.28 dB. Furthermore, the design proved highly robust against manufacturing variations, such as fluctuations in the material's refractive index, showing minimal performance degradation under simulated real-world imperfections.

This work provides a practical pathway for creating reliable, high-performance LNOI photonic devices. By ensuring that designs are optimized for the realities of the manufacturing process from the very beginning, this method helps bridge the gap between theoretical simulation and practical, manufacturable devices. It represents a significant step forward for the practical deployment of advanced integrated photonic circuits in areas like optical interconnects and quantum information processing.