For this purpose, the monomode fibers are beveled at the ends; this bevel changes the light reflection at the FO end faces and improves the optical return loss. This improved return loss is referred to as high return loss( HRL). The inclination of the bevel is typically about 8 degrees and reflects light reflections from both conductors outward.
With helical-bevel coupling, unlike lens coupling, there is no direct contact between the two optical fibers. Angle Polished Convex( APC) offers a further improvement in reflection properties. This angled ground technology also has a slightly round polish, and the polished end faces have physical contact( PC). These connectors are very low attenuation and reflection-free, but difficult to polish.