The D4 connector is an older-generation single-mode fiber optic connector developed by NEC. It was widely used in telecom networks from the 1980s through the early 1990s, and part of it may. This guide will walk you through the most common fiber connector types, explaining their characteristics, advantages, and typical use cases. By checking this box I confirm that I have read the Privacy Policy. The fiber connector types, sometimes referred to as terminations, link fiber optic cables together through terminals, switches, adapters, and patch panels, by bridging the gap between their. This unique DIN fiber optic connector gives high performance in a small, DIN 47256 compatible design suitable for a wide range of applications.