A gradual gentle waveguide has sturdy light–issue interaction and therefore can improve the nonlinear process. The study in the LNPhC slow light waveguide began from the bulk LNPhC. Iliew et al. made use of a bulk LNPhC As an example that the majority bands can be used for period matching. https://lithium-niobate-crystal19618.angelinsblog.com/31874662/lithium-niobate-crystal-an-overview