field installable subminiature assembly (FSMA)
The FSMA connector is one of the first fiber optic connectors to be standardized internationally. It is standardized by the documentIEC- SC 86B( CO)20. The FSMA connector is a fiber optic connector with screw locking, in which the fiber is guided in a relatively long metallic ferrule with a pin diameter of 3.175 mm. The ferrule is ground flat on the contact surface.
The connector has no anti- rotation protection, which has a negative effect on insertion loss during multiple openings and closings. In addition, the connector can be affected by bending of the fiber guide at high tightening torques, which can drastically worsen its insertion loss. On the other hand, a loose connection can create an air gap between the ends of the conductors to be connected, thus providing additional attenuation.
The FSMA connector can be used for multimode fibers, gradient fibers and step fibers. Typical insertion loss is 0.5 dB for single- mode and multimode fibers. The optical fiber is permanently and reliably bonded to the connector by means of an adhesive.
The insertion loss achieved with this connector depends on a variety of criteria. For example, the attenuation of optical fibers with larger core diameters is significantly lower than that of fibers with smaller diameters. For the 50/125-µm fiber, attenuation values of 0.3 dB can be achieved under laboratory conditions when high-precision guides are used to accommodate the connectors. The use of the conventional metal adapter to MIL-C-83522/3B standard costs about 0.1 to 0.2 dB of additional attenuation. In field use, however, such values can hardly be achieved. In addition, there are mechanical problems, so that attenuation of typically 0.8 to 1.2 dB must be calculated in the field. The FSMA connector is available in two versions with a continuous cylindrical connector pin (version 905) and with a tapered connector pin for centering sleeves (version 906).