Single-mode adapters feature a smaller core size of 9µm, enabling them to support longer distances and higher bandwidth with reduced signal loss. 5µm, are optimized for shorter distances, typically between. 📦 For purchasing, use the RP Photonics Buyer's Guide for fiber-optic adapters. It provides an expert-curated supplier directory, buyer-focused technical background information, and structured selection criteria to support professional procurement decisions. What Are Fiber-optic Adapters? A. The most basic fiber optic measurement is optical power from the end of a fiber. Selecting the right type— APC (Angled Physical Contact), UPC (Ultra Physical Contact), or PC (Physical Contact) —depends on your application's precision, power, and compatibility requirements.