The Periodically Poled Lithium Niobate (PPLN) Waveguide represents a significant advancement in the field of nonlinear optical devices. This waveguide is crafted using advanced techniques such as the proton exchange method and metal diffusion method, which are renowned for their efficacy in preparing lithium niobate waveguides. These methods, however, traditionally result in a small refractive index difference between the waveguide and the substrate layer, leading to a weaker light confinement capability. Additionally, the introduction of foreign ions during these processes can potentially alter the intrinsic properties of the lithium niobate crystal, impacting the waveguide's overall performance.

To address these challenges, the PPLN Waveguide utilizes a ridge waveguide structure based on lithium niobate single crystal film (LNOI). This innovative design significantly enhances the refractive index difference between the core and the shell of the waveguide. As a result, the optical limiting effect is improved, thereby enhancing the nonlinear optical effects of the lithium niobate waveguide. This improvement is crucial for applications requiring high efficiency and stability.

Moreover, the lithium niobate ridge waveguide boasts a higher optical damage threshold, making it particularly suitable for high-power frequency conversion devices. This characteristic ensures that the waveguide can handle intense optical powers without compromising its structural integrity or performance, making it an ideal choice for cutting-edge optical applications.