A ferrule (from Latin viriola, meaning little bracelet) is a ring or cap attached to an object to protect against damage, splitting, or wear. In fiber optic, a ferrule is a component (usually a rigid tube) used to align and protect the stripped end of a fiber.
A ferrule is used together with the connector that connects the fiber cable either to another cable or to a transmitter or receiver. The ferrule keeps the fibers accurately aligned within the connector. Ferrules can be made of glass, plastic, metal, or ceramic material. Ceramic is currently considered the best material for a number of reasons. For example, ceramic bonds well to glass and its expansion coefficient is close to that of the glass fibers, making it environmentally stable.