ETLs typically operate based on the principle of electrowetting or the manipulation of the refractive index of certain materials using an electric field. In electrowetting-based ETLs, the shape of a liquid lens changes in response to an electric field, thereby altering its focal length. In refractive index-based ETLs, materials such as liquid crystals or electro-optic polymers are used, where their refractive properties can be tuned electrically.
