Single-mode fiber offers virtually unlimited bandwidth over long distances, while multimode fiber's bandwidth is limited by modal dispersion and core size, optimized for short-reach applications.

Bandwidth Characteristics

Single-mode fiber (SMF) has a very small core, typically 8–10 µm, allowing only a single light mode to propagate. This design eliminates modal dispersion, which is the main factor that limits bandwidth in optical fibers. As a result, SMF can support extremely high data rates over long distances, often exceeding 100 km, and is ideal for backbone networks, long-haul telecommunications, and high-speed carrier-grade applications. It typically operates at 1310 nm or 1550 nm wavelengths using laser sources, supporting technologies like DWDM and CWDM for ultra-long links . Multimode fiber (MMF) has a larger core, usually 50 µm or 62.5 µm, which allows multiple light modes to propagate simultaneously. This causes modal dispersion, where different light paths arrive at different times, broadening pulses and limiting bandwidth-distance performance. MMF is optimized for short-reach, high-speed applications, such as within data centers or enterprise LANs. Its bandwidth is often specified as Effective Modal Bandwidth (EMB) in MHz·km at 850 nm. Modern multimode fibers, from OM3 to OM5, have progressively higher EMB, with OM5 supporting shortwave wavelength division multiplexing (SWDM) to increase link capacity .

Practical Bandwidth Examples

• OM3: Supports 10G Ethernet up to 300 meters and 40G up to 100 meters.
• OM4: Extends 10G reach to 400 meters and serves as the baseline for 100G-SR4 up to 100 meters.
• OM5: Enables multiple wavelengths on a single fiber pair, effectively quadrupling capacity for short-reach high-speed links .

Summary

• Single-mode fiber: High bandwidth, long-distance, minimal dispersion, higher cost, laser-based light sources.
• Multimode fiber: Moderate bandwidth, short-distance, limited by modal dispersion, cost-effective, LED or VCSEL light sources, suitable for data centers and campus networks . Understanding these differences is crucial for network design, ensuring the right fiber type is chosen for distance, speed, and scalability requirements.