Fiber Multimode Value

Multimode fiber (MMF) supports multiple light modes with core diameters typically 50–62.5 µm, and its performance is defined by parameters like modal bandwidth, numerical aperture, and V-number.

Core Diameter and Fiber Types

Multimode fibers have larger cores than single-mode fibers, usually 50 µm or 62.5 µm, allowing multiple light modes to propagate simultaneously, which simplifies alignment and reduces cost for short-distance links . The most common standardized types are:

• OM1: 62.5 µm core, LED source, orange jacket, suitable for 1 Gbps up to 275 m .
• OM2: 50 µm core, LED source, supports 1–10 Gbps up to 550 m .
• OM3: 50 µm core, laser-optimized, supports 10–40 Gbps up to 300–100 m .
• OM4: 50 µm core, higher modal bandwidth than OM3, supports 40–100 Gbps up to 150–100 m .
• OM5: 50 µm core, wideband multimode fiber (WB-MMF), supports short-wavelength division multiplexing (SWDM) for 40–400 Gbps, modal bandwidth 4700 MHz·km at 850 nm and 2470 MHz·km at 953 nm .

Modal Bandwidth and Effective Modal Bandwidth (EMB)

The modal bandwidth indicates the fiber's ability to transmit high-speed signals without significant pulse broadening due to modal dispersion. It is usually expressed in MHz·km at 850 nm. Higher EMB allows longer distances at higher data rates .

Numerical Aperture (NA)

The numerical aperture defines the light acceptance angle of the fiber. Typical multimode fibers have NA around 0.2–0.3, which affects the number of guided modes and coupling efficiency with light sources like LEDs or VCSELs .

V-Number (Normalized Frequency)

The V-number is a dimensionless parameter that determines the number of modes a fiber can support. For multimode fibers, the V-number is much larger than 2.405 (the single-mode cutoff), allowing hundreds of guided modes in standard 50/125 µm or 62.5/125 µm fibers . It is calculated using the core radius, numerical aperture, and operating wavelength.

Applications and Performance

Multimode fibers are ideal for short- to medium-distance links such as in-building networks, data centers, and campus backbones. They support high data rates (up to 100 Gbps for OM3/OM4 and higher for OM5 with SWDM) over distances typically ranging from 300 to 550 meters, depending on fiber type . MMF is cost-effective due to lower-cost transceivers and easier installation compared to single-mode fiber. In summary, the "value" of multimode fiber depends on core size, modal bandwidth, numerical aperture, V-number, and fiber type (OM1–OM5), which together determine the supported data rates, transmission distance, and suitability for specific network applications .