Characterization of LiNbO3 Optical-Waveguide Film Grown on Sapphire by ArF Excimer Laser Ablation

Abstract

Heteroepitaxial growth of LiNbO3 film is expected to provide a novel hybrid integration of optical and electronic components and devices. In this paper, we present, for the first time, to our knowledge, characterization of LiNbO3 optical-waveguide film grown on c-cut sapphire by ArF excimer laser ablation. Almost droplet-free LiNbO3 film was deposited only by increasing the target-to-substrate distance d to 40 mm, where Li-rich LiNbO3 ceramics with the Li/Nb ratio of 2.1 was used as the target. The deposited LiNbO3 film also exhibited a strong (006) peak in the X-ray diffraction spectrum, showing good orientation along the c axis. Optical properties were characterized based on excitation of guided modes in the film with a prism coupler. The propagation loss of the TM0 mode was lowered to be 5 dB/cm at λ=0.633 µ m. The film indices were exactly determined, followed by evaluation of the chemical composition of the film from the measured index n e of the extraordinary wave. Lack of Li2O in the film became more significant as the distance d increased. A Bragg light deflector was then fabricated to evaluate the electrooptic coefficient r33 in the film deposited under the condition that d=40 mm. r33 was found to be as large as 4.9 pm/V, which was nearly one-sixth of the single-crystal value, irrespective of nonstoichiometry of the film.