Why the fiber endface is usually polished at 8-degree angle?PC, UPC, APC

SHENZHEN, China - June 7, 2023 - PRLog -- Signal loss always occur during fiber transmission. In telecommunications, return loss is the loss of signal power due to signal reflection or return by a discontinuity in a fiber optic link or transmission line. Generally speaking, return loss is the result of back reflections. It is usually expressed as a ratio in decibels (dB). The result is always a positive number, and a higher value is better. Typical optical return loss ranges between -15dB and -60 dB .

Causes of return loss in optical fiber systems usually has: caused by dirty connector end faces; the height of the fiber is controlled at +/-20nm, which can get a better return loss value; can be caused by core misalignments and air gaps; caused by poorly polished end faces. Micro and macro bends in the fiber that can occur as a result of installation stresses, such as exceeding bend radius or pulling tension requirements, can also affect return loss. In order the make sure precise alignment of two fibers to get high return loss, the ferrule end faces of fiber optic jumpers are usually polished by different angles. The angle of a connector end face can also have an impact on return loss.

When two flat end face of connectors mate, reflectance is directed straight back through the fiber core toward the source. Return loss can reach -50dB or lower. However, the angled end face of connector causes much of the reflected light to angle into and be absorbed by the cladding that surrounds the fiber core, which causes less reflected light back to the light source. Proven by rich experience and experimental verification, an angle of 8-degree is the best. An angled connector is typically -65dB or lower.

According to different end face angles, there are three types of optical fiber end face polishing methods: PC, UPC, and APC. The typically return loss of PC, UPC and APC connectors is 40dB, 55dB and 65dB respectively.

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