Fe ions in proton-exchanged LiNbO3 waveguides

Abstract
The valence state of Fe in proton‐exchanged LiNbO3 optical waveguides is studied by electron paramagnetic resonance (EPR) and loss measurements. Starting from a fully reduced substrate showing no Fe3+ EPR signal, the exchange process induces a strong Fe2+→Fe3+ conversion within the guiding region. A new EPR line is also observed to peak at 1650 G for B perpendicular to C‐axis which is attributed to a new Fe3+ center. Losses (at 442 nm) are about forty times lower in the guide than in the reduced substrate.