Multimode Fiber Gains Traction for Shortdistance Highspeed Use

As data transmission demands continue to surge, the need for economical and efficient short-reach communication solutions has never been greater. Multimode fiber (MMF) has emerged as the preferred choice for enterprise networks, data centers, and campus environments, offering unique advantages that reduce equipment costs while expanding application boundaries through continuous technological innovation.

Multimode fiber serves as the cornerstone for short-distance data transmission, supporting applications within buildings or campus networks. Capable of delivering data rates up to 800 Gbit/s, MMF meets modern networking requirements for high bandwidth. Unlike single-mode fiber (SMF), MMF features a larger core diameter that permits multiple light modes to propagate simultaneously. However, this design introduces modal dispersion, which limits transmission distances.

Despite this limitation, MMF remains popular due to its cost-effectiveness. Equipment for MMF communication typically costs significantly less than SMF systems. In terms of performance, MMF can achieve:

• 100 Mbit/s over 2 km (using 100BASE-FX standard)
• 1 Gbit/s over 1,000 meters
• 10 Gbit/s over 550 meters

With its high capacity and reliability, MMF commonly serves as the backbone for building networks. Increasingly, users are extending fiber to desktops or work areas to fully leverage optical advantages. Standardized architectures like centralized cabling and fiber to the telecom enclosure allow electronic equipment to be concentrated in telecommunications rooms, reducing active electronics on each floor.

Beyond networking, MMF plays critical roles in:

• Optical signal transmission for miniature fiber-optic spectroscopic equipment
• Development of portable spectrometers
• High-power optical signal transmission for applications like laser welding

The fundamental difference between MMF and SMF lies in core diameter. MMF's larger core (typically 50–100 μm) enables multiple light modes to propagate, simplifying alignment and installation while reducing costs. This makes MMF ideal for short-to-medium reach data transmission in enterprise networks, data centers, and campus environments, supporting data rates up to 100 Gbps over distances typically ranging from 300 to 550 meters (depending on fiber type: OM3, OM4, OM5).

MMF systems can utilize lower-cost light sources like LEDs and vertical-cavity surface-emitting lasers (VCSELs), further reducing system costs while maintaining reliable performance. These operate at 850 nm and 1300 nm wavelengths, compared to SMF's 1310 nm or 1550 nm telecom wavelengths. However, MMF's bandwidth-distance product remains lower than SMF.

The larger core size makes MMF susceptible to modal dispersion, where different light modes travel at varying speeds. Additionally, LED sources produce multiple wavelengths that propagate at different velocities, causing chromatic dispersion—another factor limiting MMF cable length. In contrast, SMF lasers generate coherent single-wavelength light.

Industry standards differentiate MMF and SMF through jacket colors: yellow for SMF, orange or aqua for MMF (depending on type), with purple sometimes indicating higher-performance OM4 fiber.

MMF is characterized by core and cladding diameters (e.g., 62.5/125 μm) and may feature either step-index or graded-index refractive profiles, each with distinct dispersion properties affecting propagation distance. The ISO 11801 standard classifies MMF as OM1, OM2, OM3, OM4, or OM5 based on modal bandwidth.

Traditional 62.5/125 μm (OM1) and 50/125 μm (OM2) fibers have served building interiors for years, supporting applications from 10 Mbit/s Ethernet to 1 Gbit/s Gigabit Ethernet. Newer deployments typically use laser-optimized 50/125 μm MMF (OM3), which supports 10 Gigabit Ethernet up to 300 meters. Manufacturers have since improved processes to enable 400-meter 10 GbE support.

The transition to laser-optimized MMF (LOMMF)/OM3 has accelerated as users upgrade to higher-speed networks. While LEDs max out at 622 Mbit/s modulation rates, VCSELs support over 10 Gbit/s and power many high-speed networks.

Recent developments include wavelength-division multiplexing (WDM) on MMF for 200/400 Gigabit Ethernet, leading to the 2017 standardization of OM5 fiber supporting 850-953 nm wavelengths.

Jacket colors help identify MMF types: orange for OM1/OM2, aqua for OM3/OM4, lime green for OM5, with some vendors using purple for "OM4+" variants.

Modal dispersion—measured through differential mode delay (DMD)—remains a key challenge. LOMMF manufacturing techniques now minimize fiber variations that affect light pulse propagation, enhancing refractive index profiles to maintain signal integrity over longer distances.

The table below summarizes Ethernet variants' minimum transmission distances over various MMF types:

*Mode-conditioning patch cord required