Lithium Niobate Optical Waveguides: Fabrication Methods and Performance
The most common methods for fabricating lithium niobate (LN) optical waveguides are proton exchange and metal diffusion. However, waveguides produced by these methods exhibit a small refractive index contrast between the waveguide layer and the substrate, resulting in weak optical confinement. Additionally, the foreign ions introduced during these processes may degrade the intrinsic properties of the LN crystal, negatively impacting waveguide performance.
In contrast, ridge-type waveguides based on lithium niobate-on-insulator (LNOI) thin-film technology significantly increase the core-cladding refractive index contrast, thereby enhancing optical confinement. This improvement boosts the nonlinear optical effects in LN waveguides. Furthermore, LNOI ridge waveguides exhibit a higher optical damage threshold, making them ideal for fabricating high-power frequency conversion devices.
