angled physical contact Archives

When selecting fiber optic cables or connectors, you may notice product descriptions labeled with terms like “PC Polish,” “UPC Polish,” or “APC Polish.” What do these designations mean? What are the key differences between these connector types? This article provides a detailed explanation of these classifications and their fundamental distinctions.

PC Polish

PC (Physical Contact) refers to a connector type manufactured through micro-spherical polishing: The ferrule surface is precision-ground into a slight spherical curvature, with the fiber core positioned precisely at the apex of the curvature. This design effectively minimizes air gaps between fiber components, ensuring direct physical contact between the two fiber end-faces.

Diagram of two flat fiber connector end faces in direct contact

UPC Polish
UPC (Ultra Physical Contact) is an enhanced polishing type based on PC. Unlike flat surfaces, UPC connectors feature a slightly curved end face to achieve more precise alignment. This design further optimizes the polishing process and surface finish, resulting in a visual dome-shaped appearance.

Diagram of two rounded fiber end faces making physical contact

APC Polish

APC (Angled Physical Contact) is characterized by its angled design: The fiber end face is typically polished at an 8° angle. This angled surface not only ensures tighter physical contact but also directs reflected light into the cladding (rather than back to the light source), significantly improving connection performance.

Diagram of two angled fiber end faces aligned for optical connection

Comparison of PC, UPC, and APC fiber connector polishing types with an 8-degree APC end face

Why Use Angled Polishing?
When light travels between media, a portion reflects back into the core due to physical reflection principles. This reflected light reduces signal energy and causes interference—unacceptable in optical communications where unidirectional light transmission is critical. The 8° angle redirects reflected light into the cladding, minimizing back reflections and enhancing return loss for stable signal transmission.

Optical reflection diagram for a rounded fiber connector end face

Optical reflection diagram for an angled fiber connector end face

How to Distinguish UPC and APC?

Color Coding: Green connectors indicate APC. Blue connectors denote UPC.

SC UPC and SC APC fiber connector comparison showing 0-degree and 8-degree end faces

Physical Inspection:
The APC’s angled end face (8°) is distinguishable from UPC’s near-flat surface under close observation (requires visual acuity).

Can UPC and APC Be Interconnected?
No. Their physical designs are incompatible: APC’s 8° angle and UPC’s flat curvature create an air gap at the junction. This results in a “fiber-air-fiber” path, causing high insertion loss (>3dB) and severe signal degradation.