Lithium niobate waveguides with high-index contrast and preserved nonlinearity fabricated by a high vacuum vapor-phase proton exchange

Highly confining waveguides (Delta n(e) > 0.1) without a degraded nonlinear coefficient and low propagation losses have been fabricated in lithium niobate (LN) by a new process that we called high vacuum vapor-phase proton exchange (HiVac-VPE). Index contrast, index profile, nonlinearity, and crystallographic phases are carefully investigated. Original analysis of index profiles indicates that the waveguides contain sub-layers whose depths depend on the exchange durations. Propagation behavior, propagation losses, and second-harmonic generation response of HiVac-VPE channel waveguides are investigated at telecom wavelength. The results recommend HiVac-VPE as a very promising technique for fabricating efficient nonlinear photonic integrated circuits in LN crystals. (C) 2019 Chinese Laser Press