The core: made of silica, molten quartz, or plastic, in which optical waves propagate. 5µm for multimode fiber and 9µm for single-mode. Understanding its internal structure is essential to appreciate how it functions efficiently in various applications, from telecommunications to medical devices. The core is the. Optical fibers are circular dielectric wave-guides used to contain and transmit light over short or long distances. They consist of three elements as shown in Figure 1: a central core, cladding and a protective coating. They support high-speed, interference-resistant communication and are particularly effective in applications that require high bandwidth, low latency, and strong signal integrity.