Smart guide: lithium niobate large index contrast waveguides fabricated by crystal ion slicing and wafer bonding

Abstract

Recently large index contrast optical waveguides are considered for the fabrication of integrated optical components. Electro-optical waveguides are particularly interesting since they have the potential to be used for switching devices. In this paper we introduce a new method for fabrication of large index contrast lithium niobate waveguides. The waveguides are fabricated using crystal ion slicing and wafer bonding. This allows the fabrication of high refractive index contrast waveguides with lithium niobate as the core and silicon dioxide as the low refractive index cladding. Electrodes can also be deposited between the layers for applying an electric field to the waveguide in the vertical direction. The structure can be fabricated on any substrate. Waveguides with a thickness of 700nm suitable for single mode operation at lambda=1.55micron have been successfully produced. The thin films are analyzed using different analytical techniques including atomic force microscopy and Rutherford backscattering (RBS). The RBS spectrum shows that the crystal structure of the fabricated thin films is very similar to bulk lithium niobate and the quality of the crystalline waveguide is excellent. Optical waveguiding and electro-optical modulation is demonstrated using the prism-coupling method. It is shown that the fabricated waveguide refractive indices and electro-optic coefficients are identical to bulk lithium niobate crystals. These large index contrast waveguides are ideal for fabrication of devices such as electro-optic micro-ring resonators, Mach-Zehnder interferometric modulators with reduced half wave voltage and nonlinear optical waveguide devices for second harmonic generation or parametric amplification. It is shown that this waveguide structure is an ideal structure for the fabrication of integrated optical components due to the good optical properties of lithium niobate and large index contrast achieved by the fabrication method.