A fiber optic patch cord contains a glass or plastic fiber core, surrounded by cladding, reinforced with aramid yarn, and protected by an outer jacket.

Core and Cladding

The central component of a fiber optic patch cord is the fiber itself, which is typically made of high-purity glass (silica) or sometimes plastic. The core carries light signals, while the surrounding cladding has a lower refractive index to reflect light back into the core, minimizing signal loss and maintaining efficient transmission over distances . Single-mode fibers have a core diameter of about 9 µm, suitable for long-distance communication, while multimode fibers have larger cores, typically 50 µm or 62.5 µm, allowing multiple light modes for short-distance, high-bandwidth applications .

Strength and Protection

To protect the delicate fiber, patch cords include aramid yarn (Kevlar) as a strength member. This reinforcement helps the cable withstand pulling, bending, and handling without breaking the fiber . The fiber and aramid yarn are then enclosed in a protective outer jacket, which can be made from materials like PVC, LSZH (Low Smoke Zero Halogen), or plenum-rated OFNP, depending on fire safety and installation requirements .

Additional Features

Fiber optic patch cords may also use bend-insensitive fibers (G.657A1/A2) for tight spaces, such as in FTTH (Fiber to the Home) installations, reducing signal loss when the cable is bent . The outer jacket is often color-coded to indicate fiber type: yellow for single-mode, orange for OM1/OM2 multimode, aqua for OM3, violet for OM4, and lime green for OM5 . In summary, the "wire" inside a fiber optic patch cord is a glass or plastic optical fiber core, reinforced with aramid yarn and protected by a durable outer jacket, designed to transmit light signals efficiently while resisting physical stress.