butt joint
Face coupling is a coupling technique between two FO connectors. With face coupling, the two optical waveguides are ground flat and have a small distance between them. Due to the small air gap, this type of coupling results in low return loss, which is noticeable in reflections and reduces the light energy to be transmitted.
The end faces of the optical waveguides can also have a physical contact, Physical Contact( PC), which results in lower attenuation values. Besides the simple end face coupling with Physical Contact, there is also the one with ground and polished FO end face, namely Super Physical Contact( SPC) and Ultra Physical Contact( UPC). In addition, the oblique ground contact coupling and APC coupling, which are characterized by a particularly high optical return loss( RL), High Return Loss( HRL).
In addition to return loss, the various face couplings also differ in insertion loss( IL). Compared to lens coupling, face coupling has the advantage that no mechanical wear of the faces affects the transmission characteristics.
The end-face coupler can also be derived from end-face coupling. This is constructed in such a way that an optical waveguide or a polymer fiber covers the end faces of two FO fibers with its end face and scatters light into both.