PC

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 (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.

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.

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.

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.

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

Physical Inspection:

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

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.