Multimode fiber optic cables (MMF) are designed for short- to medium-distance data transmission, supporting multiple light modes simultaneously with a larger core diameter for high-speed LAN and data center applications.

Overview

Multimode fiber (MMF) is an optical fiber that allows multiple light propagation paths, or modes, to travel simultaneously through a relatively large core, typically 50 or 62.5 microns, compared to the ~9-micron core of single-mode fiber . This design enables higher data throughput over short distances and allows the use of lower-cost light sources such as LEDs or VCSELs, making MMF cost-effective for in-building, campus, or data center networks .

Structure

Multimode fiber consists of three main layers:

• Core: The light-carrying region, larger in diameter to support multiple modes, which increases launch tolerance but introduces modal dispersion, limiting long-distance performance .
• Cladding: Surrounds the core with a lower refractive index to maintain total internal reflection, guiding light efficiently down the fiber .
• Coating/Jacket: Provides mechanical protection and environmental resistance, available in various colors and materials depending on fiber type and application .

Types of Multimode Fiber

Multimode fibers are classified according to the ISO/IEC 11801 standard into OM1, OM2, OM3, OM4, and OM5, each with different core sizes, bandwidths, and maximum transmission distances :

• OM1: 62.5 µm core, orange jacket, LED light source, supports 10 Gbps up to 33 meters, commonly used for 100 Mbps Ethernet .
• OM2: 50 µm core, orange jacket, LED source, supports 10 Gbps up to 82 meters, often used for 1 Gbps Ethernet .
• OM3: 50 µm core, aqua jacket, optimized for 10 Gbps up to 300 meters, uses VCSELs for higher-speed applications .
• OM4: 50 µm core, aqua jacket, supports 10 Gbps up to 550 meters and higher data rates like 40/100 Gbps over shorter distances .
• OM5: 50 µm core, lime green jacket, supports short-wavelength division multiplexing (SWDM), enabling multiple wavelengths (850–940 nm) for 40/100/400 Gbps applications, released in 2016 .

Performance and Applications

• Distance: MMF is optimized for short- to medium-range links, typically up to 550 meters at 10 Gbps, with longer distances possible at lower speeds .
• Bandwidth: Effective modal bandwidth (EMB) determines how much data can be transmitted over a given distance, with OM3–OM5 offering higher EMB for modern high-speed networks .
• Cost: MMF equipment is generally less expensive than single-mode fiber, making it ideal for enterprise LANs, data centers, and campus networks .
• Limitations: Modal dispersion limits long-distance performance, so MMF is less suitable for runs exceeding several hundred meters compared to single-mode fiber .

Summary

Multimode fiber optic cables are a cost-effective solution for high-speed, short- to medium-distance networking, offering multiple light modes, larger core diameters, and compatibility with lower-cost light sources. Choosing the right type (OM1–OM5) depends on required data rates, distance, and network architecture, with OM3–OM5 being the preferred choice for modern high-speed data center and enterprise applications .