Electron-phonon coupling in lattice engineering of lithium niobate single crystal thin films

Abstract: Lithium niobate (LN) single crystal thin films are a high-performance photonic platform with applications in electro-optic modulators, nonlinear optical devices, optical frequency combs, and acousto-optic modulators. LN's significance in photonics parallels silicon's in electronics, addressing challenges like high power consumption and slow communication speeds, and offering potential for broad applications in optical communications, quantum computing, and artificial intelligence. Despite progress in developing LN-based photonic structures, achieving low-loss, reconfigurable, and large-scale devices requires improved processing techniques. This work introduces a quantum design methodology based on LN's crystal structure, utilizing electron-phonon coupling through external field perturbations. Multiscale structural analysis is performed with techniques such as time-of-flight secondary ion mass spectrometry, aberration-corrected transmission electron microscopy, and X-ray absorption spectra to identify and control defect structures. Angle-resolved Raman spectroscopy, femtosecond transient absorption spectroscopy, and Density Functional Theory further reveal the mechanisms of electron-phonon coupling. These findings establish a framework for designing LN-based quantum devices with enhanced performance and diverse functionalities.