Multi-mode fiber is thicker than single-mode fiber, with a core diameter typically 50–62.5 micrometers compared to 8–10 micrometers for single-mode fiber.

Core Diameter Differences

The primary structural difference between single-mode and multi-mode fiber lies in the core diameter. Single-mode fiber has a very narrow core, usually 8–10 micrometers, which allows only one light path to propagate, minimizing signal loss and modal dispersion over long distances . In contrast, multi-mode fiber has a larger core, typically 50 or 62.5 micrometers, enabling multiple light paths to travel simultaneously, which is suitable for short-distance, high-bandwidth applications .

Cladding and Overall Structure

Both fiber types have a cladding layer surrounding the core, usually 125 micrometers in diameter, which maintains total internal reflection. While the cladding thickness is similar, the larger core of multi-mode fiber makes it physically thicker in terms of light-carrying capacity .

Practical Implications

• Single-mode fiber: Ideal for long-distance communication, such as telecom backbones and high-speed data links, due to its narrow core and minimal modal dispersion .
• Multi-mode fiber: Best for short-range applications like data centers, LANs, and intra-building networks, where the larger core simplifies alignment and reduces installation costs . In summary, multi-mode fiber is thicker than single-mode fiber because its core is significantly larger, allowing multiple light modes to propagate, whereas single-mode fiber's narrow core supports only a single light path for long-distance, high-bandwidth transmission.