UPC (Ultra Polished Connector)

The FC connector is a fiber-optic connector with a threaded body, which was designed for use in high-vibration environments. It is commonly used with both single-mode optical fiber and polarization-maintaining optical fiber. FC connectors are used in datacom, telecommunications, measurement equipment, and single-mode lasers. They are becoming less common, displaced by SC and LC connectors. The FC connector has been standardized in TIA fiber optic connector intermateability standard EIA/TIA-604-4.

The FC connector was originally called a “Field Assembly Connector” by its inventors. The name “FC” is an acronym for “ferrule connector” or “fiber channel”.

Some manufacturers have several grades of polish, for example an FC connector may be designated “FC/PC” (for Physical Contact), while “FC/SPC” and “FC/UPC” may denote “super” and “ultra” polish qualities, respectively. Higher grades of polish give less insertion loss and lower back-reflection.

For applications requiring very low back-reflection, the fiber end-face is polished at an angle (the typical industry standard being 8°) to prevent light that reflects from the interface from traveling back up the fiber. Because of the angle, the reflected light does not stay in the fiber core but instead leaks out into the cladding. Angle-polished connectors only mate properly to other angle-polished connectors.

Mating to a non-angle polished connector causes very high insertion loss. Generally angle-polished connectors have higher insertion loss than good quality straight physical contact ones. “Ultra” quality connectors may achieve comparable back reflection to an angled connector when connected, but an angled connection maintains low back reflection even when the output end of the fiber is unmated.

Angle-polished connections are distinguished visibly by the use of a green strain relief boot. The connectors are typically designated “FC/APC” (for Angled Physical Contact), or merely “FCA”.

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