Single-mode fiber (SMF) supports one light mode for long-distance, high-bandwidth transmission, while multimode fiber (MMF) supports multiple light modes for shorter-range, cost-effective applications.

Core Diameter

• Single-mode fiber has a very narrow core, typically 8–10 µm, allowing only one mode of light to propagate, which minimizes modal dispersion and signal loss over long distances .
• Multimode fiber has a larger core, usually 50 µm or 62.5 µm, enabling multiple light modes to travel simultaneously, which simplifies connections but increases modal dispersion .

Light Propagation and Modal Dispersion

• SMF transmits light in a single, direct path, reducing scattering and attenuation, making it ideal for long-haul communication .
• MMF allows multiple light paths, which can cause modal dispersion, limiting the maximum transmission distance and signal integrity over longer runs .

Bandwidth and Distance

• Single-mode fiber offers theoretically unlimited bandwidth and can transmit data over tens of kilometers without significant signal degradation .
• Multimode fiber has limited bandwidth due to multiple light modes, with practical distances typically up to 550 meters for high-speed applications, depending on the fiber type (OM1–OM5), .

Light Sources and Wavelengths

• SMF commonly uses lasers or laser diodes at wavelengths of 1310 nm and 1550 nm, optimized for long-distance transmission .
• MMF often uses LEDs or VCSELs at 850 nm and 1300 nm, which are cost-effective for short-range, high-speed networks .

Cost and Handling

• Single-mode fiber is more expensive due to precise manufacturing and alignment requirements for coupling light into the narrow core .
• Multimode fiber is easier to handle and cheaper, making it suitable for data centers, LANs, and short-distance applications .

Applications

• Single-mode fiber: Long-distance telecommunications, backbone networks, and high-speed metro or intercity links .
• Multimode fiber: Local area networks (LANs), data centers, and short-distance high-speed connections where cost efficiency is important . Understanding these characteristics helps in selecting the appropriate fiber type for specific network requirements, balancing distance, bandwidth, cost, and installation complexity.