Fabrication of two-dimensional nonlinear photonic crystal by electron beam lithography

Abstract

In this paper, we present a study on quasi-phase matched (QPM) two-dimensional χ (2) lithium niobate (LN) nonlinear photonic crystal (NPC) for frequency doubling at λ = 1064nm. The NPCs were fabricated by electron beam lithography (EBL) through periodic polarization inversion of the ferroelectric domains and characterized with electrostatic force microscopy (EFM), atomic force microscopy and optical microscopy. Domain inversion occurred through the entire wafer thickness of 0.5mm as EFM images on the +c face of the z-cut wafer showed uniform domain structures throughout the corresponding electron beam irradiated regions of the c face. In addition, the intended periodicity was observed. Moreover, domain inversion was also seen to have taken place in bulk from the optical images of the chemically etched samples. The EBL technique offers great flexibility in superlattice design and relative ease of fabrication as compared to the conventional poling techniques as pattern transfer is direct without the need for a mask and/or a coating of resist. Besides, micro- or sub-micro scale superlattices corresponding to wavelengths in the visible and into the ultraviolet are highly feasible, restricted only by the transparency of the crystals.