Bound modes in the continuum in integrated photonic LiNbO₃ waveguides: are they always beneficial?

We discuss several types of integrated photonic LiNbO₃ waveguides supporting propagation of modes which can be classified as bound states in the continuum (BICs). The key properties leading to the existence of BICs (or quasi-BICs) considered here are the material anisotropy, the waveguide birefringence, or the combination of both. Typical examples are titanium diffused and proton exchanged waveguides in bulk LiNbO₃ crystals and recently proposed dielectric-loaded waveguides on LiNbO₃ thin films. Proton exchanged waveguides in thin film LiNbO₃ are considered, too. These waveguide structures are discussed from the point of view of their benefit for applications, especially in electro-optic devices.