Indoor optical fiber cables consist of a core, cladding, coating, strength members, and an outer jacket, each serving a specific role in signal transmission, protection, and installation safety.

Core

The core is the central part of the fiber that transmits light signals. It is typically made of ultra-pure silica glass (SiO₂) or, in some cases, plastic. The core size determines the fiber type: single-mode fibers have a small core (~9 µm) for long-distance, high-bandwidth applications, while multimode fibers have larger cores (50–62.5 µm) suitable for shorter distances like within buildings or data centers .

Cladding

Surrounding the core is the cladding, which has a lower refractive index than the core. This difference enables total internal reflection, keeping the light signals confined within the core and minimizing signal loss .

Coating

The coating or primary buffer is a protective layer applied directly over the cladding. It safeguards the fiber from physical damage, moisture, and minor abrasions during handling and installation. Common coatings include dual-layer acrylate polymers .

Strength Members

Indoor fiber cables include strength members, often made of aramid fibers (e.g., Kevlar), which prevent stretching and provide mechanical support. These fibers help maintain signal integrity by protecting the delicate core from tension and bending stresses during installation .

Outer Jacket

The jacket is the outermost layer, providing environmental protection and fire resistance. Indoor cables are designed to meet building safety standards, such as plenum (CMP), riser (CMR), or LSZH (Low Smoke Zero Halogen) ratings. The jacket material also contributes to flexibility and ease of installation in confined spaces .

Additional Considerations

• Buffering Design: Indoor cables often use tight-buffered construction, where each fiber is individually coated with a 900 µm buffer, simplifying termination and connectorization .
• Cable Type Selection: The choice between single-mode and multimode, tight-buffered or loose-tube, and jacket material depends on the installation environment, distance, and fire safety requirements .
• Connectors: While not part of the cable itself, indoor fiber cables are typically terminated with connectors like LC, SC, or ST to interface with network equipment . In summary, indoor optical fiber cables are carefully engineered assemblies where each component—the core, cladding, coating, strength members, and jacket—ensures reliable data transmission, mechanical protection, and compliance with building safety standards. Proper selection of these components is critical for optimal network performance and longevity.