Periodic Domain Inversion in Single Crystal Barium Titanate-on-Insulator Thin Film

Experimentally achieving the first-ever electric field periodic poling of single crystal barium titanate oxide (BTO, or BaTiO₃) thin film on-insulator is reported. Owing to the outstanding optical nonlinearities of BTO, this result is a key step toward achieving quasi-phase-matching (QPM). First, the BTO thin film is grown on a dysprosium scandate substrate using pulsed laser deposition with a thin layer of strontium ruthenate later serving as the bottom electrode for poling. The characterization of the BTO thin film using x-ray diffraction (XRD) and piezo-response force microscopy to demonstrate single crystal, single domain growth of the film that enables the desired periodic poling, are presented. To investigate the poling quality, both non-destructive piezo force response microscopy and destructive etching-assisted scanning electron microscopy (SEM) are applied, and it is shown that high quality, uniform, and intransient poling with 50% duty cycle and periods ranging from 2 µm to 10 µm is achieved. The successful realization of periodic poling in BTO thin film unlocks the potential for highly efficient nonlinear processes under QPM that seemed far-fetched with prior polycrystalline BTO thin films which predominantly relied on efficiency-limited random or non-phase matching conditions and is a key step toward integration of BTO photonic devices.