An inverted T-shaped grating coupler based on the Si3N4-LNOI platform

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Abstract
An inverted T-shaped grating coupler with a bottom mirror is proposed and designed on the Si3N4-LNOI platform. The impact of structural parameters on the coupler performance is systematically analyzed and discussed. Specifically, the short column parameters can adjust the effective refractive index, while the long column parameters influence the reflection and interaction of the coupled light. A particle swarm optimization (PSO) method is employed to optimize the grating structure, thereby enhancing the peak coupling efficiency and mode matching degree. Through apodization, the peak coupling efficiency is increased from 74% to 81%, and the −1 dB bandwidth is reduced from approximately 127 nm to approximately 117 nm. Additionally, the mode matching degree is improved by 5% via apodization. This work provides valuable support for optical interconnects in photonic integrated circuits on silicon nitride-lithium niobate composite platforms.
Funding Information
  • National Key R&D Project of China (2022YFB3605601)
  • National Natural Science Foundation of China (61675046, 61935005,62204022)

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