FO connectors provide a detachable FO plug connection between two optical fibers. Most fiber optic connectors do not distinguish between a male and a female fiber optic connector. Instead, the connector consists of two fiber optic connectors that are connected to each other via a guide coupling. Since FO connectors are components of the highest precision, the slightest mechanical manufacturing tolerances or changes due to frequent plugging and unplugging can affect the essential transmission parameters.
Transmission parameters of FO connectors
The quality of the entire optical transmission system depends on the FO connectors. For this reason, all transmission parameters must be strictly observed. Important transmission parameters are insertion loss and return loss. Other properties to be mentioned are The reproducibility of the transmission values under frequent stress, the number of mating cycles, a long service life, a stable mechanical design with easy handling, and compact dimensions.
When light is transmittedin an FOC connector, the two fibers are brought very close together to transfer as much light energy as possible from one fiber to the other. Light reflections and attenuation occur at the end faces of the two fibers. The attenuation that occurs depends on the size of the air gap between the two fibers, i.e. on the longitudinal offset of the two fibers. This offset is also called Radially Overfilled Launch (ROFL), and the light loss is called Gap Loss.
To achieve constant attenuation values during repeated mating cycles, it is crucial to keep the gap width as small as possible, but as precise as possible, to about 10 µm. This gap is achieved by precise ferrule lengths or by hollow polishing.
Mating properties of FO connectors
In addition, the attenuation is very much dependent on the lateral offset, the eccentricity between the two fibers. The lateral offset, i.e. the axial offset, increases the damping disproportionately. It is caused by inaccurate guidance of the ferrule in the coupling, eccentric or too large a bore in the ferrule, and when the core glass is offset from the center axis. The lateral offset is also referred to as offset launch( OL).
Furthermore, the tilt angle between the two fibers has a significant influence on the attenuation of the light signal. The tilt angle occurs with imprecise connection technology, especially with poor couplings with too large a bore or spring guide. Likewise with conical connectors that are too long and wobble in the cone.
Non-parallel end faces of optical fib ers and curved or rough fiber end faces also create additional attenuation. The latter can be dirt and or scratches or stains on the FO end faces
FOC connectors for single mode, gradient and polymer fibers
The aperture of the fibers also plays a role in connector attenuation: it is directly included in the attenuation values for the end face spacing. If two fibers have different numerical apertures, the two transmission directions have different attenuation values. If the radiation comes from an FOC fiber with a high aperture and is transmitted into one with a low aperture, it is not fully absorbed by this fiber. The situation is different in the opposite direction: the light energy from the fiber with the low aperture is completely absorbed by the fiber with the high aperture.
For the reasons mentioned above, the highest demands are placed on optical fibers and on the positioning accuracy and thus on the manufacturing tolerance of fiber optic connectors. Minimal tolerance deviations have a serious effect, especially when connecting monomode fibers, since with monomode fibers an axial offset of only 4 µm already causes an additional attenuation of approx. 0.4 dB.
0 For the connection technology of optical fibers, there are a large number of connectors which are incompatible with each other. The standard FO connectors include the ST connector, FC connector, SC connector, LC connector, MIC connector, mini- BNC connector, FSMA connector, E-2000 connector, F3000 connector and ESCON connector. In addition, among the multitude of others, the following are also worth mentioning: SMA connector, DIN connector, PKI connector, Biconic connector, Galaxy connector and Mini- MT connector, and among multi-fiber connectors, MTRJ connector and MPO connector.
The most commonly used connector systems for gradient fiber are the first six mentioned. They differ in design, closure, connection type and application. In universal cabling, the cabling standard prescribes the use of the duplex SC connector if it is not an existing installation with ST connectors. In such a case, ST connectors can still be used for new connections. In addition to the connector type, the cabling standard prescribes further requirements for the FO connector. For example, only fibers with 125 µm may be used (9/125 µm, 50/125 µm, 62.5/125 µm). The possible number of mating cycles must exceed 500 and the maximum insertion loss must be below 0.5 dB.
Some of the connectors mentioned can also be used for polymer fibers with 1,000 µm cladding diameter: Thus the SMA and ST connectors. In addition, there are some plastic connectors for these fibers, such as the HFBR connector and the OVK connector.
In addition, there are the SFF connectors, which have significantly smaller form factors compared to the conventional FOC connectors and thus enable a much higher packing density. Several different SFF versions exist, one of the better known of which is the LC connector.