Multimode optical fiber (MMF) features a larger core (50–62.5 µm) allowing multiple light modes, supports short- to medium-distance high-speed data transmission, and is classified into OM1, OM2, OM3, OM4, and OM5 types with varying bandwidth and distance capabilities.

Core Characteristics

Multimode fiber has a core diameter of 50 µm or 62.5 µm and a cladding diameter of 125 µm, enabling multiple light modes to propagate simultaneously. This larger core simplifies alignment and installation, making MMF cost-effective for short- to medium-range applications in buildings, campuses, and data centers . MMF can have either a graded-index profile, which reduces modal dispersion, or a step-index profile, which has a sharper core-cladding transition .

Optical Sources and Wavelengths

MMF typically uses LEDs or VCSELs as light sources, operating at 850 nm and 1300 nm wavelengths. These sources are lower-cost and suitable for short-distance links, unlike single-mode fibers that require more expensive lasers at 1310 nm or 1550 nm . Laser-optimized MMF (LOMMF) is recommended for modern LAN and data center environments, especially with VCSELs .

Classification and Performance

MMF is classified according to ISO/IEC 11801 standards into five types:

• OM1: 62.5 µm core, orange jacket, LED source, supports 1G Ethernet up to 275 m and 10G Ethernet up to 33 m. Legacy fiber, mostly obsolete for high-speed networks .
• OM2: 50 µm core, orange jacket, LED source, supports 1G Ethernet and 10G Ethernet up to 82 m. Suitable for older 50 µm systems .
• OM3: 50 µm core, aqua jacket, laser-optimized for VCSELs, supports 10G Ethernet up to 300 m, 40G/100G up to 100 m. Common in modern enterprise and data center networks .
• OM4: 50 µm core, aqua jacket, enhanced laser-optimized, supports 10G Ethernet up to 550 m, 40G/100G up to 150 m. Backwards compatible with OM3 .
• OM5: 50 µm core, lime green jacket, supports shortwave wavelength division multiplexing (SWDM), enabling multiple wavelengths over a single fiber for higher aggregate bandwidth. Designed for future high-speed applications .

Bandwidth and Distance

The modal bandwidth and maximum transmission distance vary by fiber type. OM1 and OM2 are limited to lower data rates and shorter distances, while OM3, OM4, and OM5 support 10G to 100G Ethernet over hundreds of meters, making them suitable for modern data centers . Typical MMF distances range from 33 m (OM1 at 10G) to 550 m (OM4 at 10G).

Applications

MMF is ideal for short- to medium-distance communication, including:

• Enterprise LANs and campus networks
• Data center interconnects
• Fiber-to-the-desk or fiber-to-the-zone deployments
• High optical power applications like laser welding or spectroscopy equipment MMF provides a cost-effective, high-capacity solution for environments where distances are limited and multiple light modes can be efficiently transmitted.