Fiber optic ferrules are mechanical fixtures, generally rigid tubes, which are used to confine the stripped end of a fiber or a fiber bundle. They align and polish optical fibers to prevent the scattering and dampening of the light signal. Most fiber optic ferrules are made of metals such as stainless steel, ceramics such as alumina or zirconia, or plastic materials. Fiber optic ferrules made of borosilicate glass and glass are also available. Most fiber optic ferrules are manufactured with direct-draw or redraw processes and cut to length with diamond saw blades. To prevent problems such as splice loss and end gaps, they are bored through the center at a diameter which is slightly larger than that of the fiber cladding. Lead-ins are then blown, acid-etched, or drilled countersunk.
Selecting fiber optic ferrules requires a careful analysis of product specifications and features. Fiber optic components for both single-mode and multi-mode fibers are commonly available. For both types of optical fibers, ferrule specifications such as inner diameter (ID), outer diameter (OD), length, concentricity, radius, and bore style are important to consider. Choices for bore style include single bore, double bore, and racetrack bore. Fiber optic ferrules with square and rectangular bores are also available. In terms of features, some fiber optic ferrules have a multi-step ID or a multi-step OD. Others have countersinks, anti-rotation notches, flats, slots, grooves, epoxy vent holes, and any-angle chamfers.
Fiber optic ferrules are used in fiber optic connectors, devices which are used to align and join two or more fibers together to provide a means for attaching to, or decoupling from, a transmitter, receiver, or other fiber optic equipment. There are many different types of fiber optic connectors. Examples include biconic, D4, ESCON, FC, FDDI, LC, loopback, MTP, MT-RJ, MU, SC, SMA and ST. Straight tip (ST) connectors, the most popular connector type for multi-mode networks, often use spring-loaded, ceramic fiber optic ferules. LC connectors are half the size of an ST connector, but are easily terminated an adhesive. MT-RJ connectors align multiple fibers in a single, polymer ferrule. FC, FDDI, and ESCON connectors use a standard, 2.5 mm fiber optic ferrule. This permits the use of hybrid mating adapters and allows technicians to use a set of multimode reference cables for a range of connectors.