Connector Fiber Polish Types

Fiber Optic Ferrules

The most common optical fibers have a cladding diameter of 125um which is too small and fragile to be polished directly. Ceramic, metal, composite(plastic) or glass ferrules are used to protect the fibers. The most commonly used fiber connectors employ ceramic or metal ferrules. Glass ferrules are preferred when optical coating is necessary after polishing for better adhesion.

Fiber Optic Connector Ferrule Shapes

Fiber optic connectors can have several different ferrule shapes or finishes, usually referred to as polishes. The polish on a fiber connector ferrule determines the amount of back reflection. Back reflection is a measure of the light reflected off the polished end of a fiber connector measured in negative dB.

Back Reflection Example

In the case of air gap connector, the first reflection occurs at the interface of the first fiber and the air (between two fibers). Without antireflection coating, the reflection is 5%, so the back reflection from the first interface is 10Log(0.05) = -13 dB.

• Air Gap
• 
• Typical Back Reflection: -20dB
• Flat
• 
• Same shape as the air gap connector, but the ferrules physically contact each other instead of a air gap in between
• Typical back reflection: -30dB
• PC (Physical Contact)
• 
• Typical Back Reflection: <-40dB
• UPC (Ultra Physical Contact)
• UPC has similar shape as the PC polish but has lower back reflection
• Typical Back Reflection: <-50dB
• APC (Angled Physical Contact)
• 
• Ferrule end has a 8° angle which minimizes back reflection
• Typical Back Reflection: <-60dB