A multimode optical cable is a type of fiber optic cable designed to carry multiple light signals simultaneously over short distances, using a larger core to support multiple propagation paths.

Definition and Structure

Multimode optical fiber (MMF) has a larger core diameter, typically 50 or 62.5 microns, compared to single-mode fiber, which has a core around 9 microns. This larger core allows multiple light modes to propagate at the same time, enabling the transmission of multiple data streams simultaneously . The fiber consists of three main layers:

• Core: The central light-carrying region where multiple light paths travel.
• Cladding: Surrounds the core with a lower refractive index to reflect light back into the core.
• Coating: Provides mechanical protection and maintains signal integrity .

Performance and Limitations

Multimode fiber is optimized for short-distance communication, such as within buildings or on a campus, due to modal dispersion, where different light modes travel at slightly different speeds, potentially broadening signals over long distances . Typical maximum distances include:

• Around 550 meters at 10 Gbit/s
• Up to 2 km at lower data rates like 100 Mbit/s

Types of Multimode Fiber

Multimode fibers are classified into OM1, OM2, OM3, OM4, and OM5, each with different core sizes, bandwidths, and optimized light sources:

• OM1: 62.5 µm core, LED source, suitable for 100 Mbit/s Ethernet.
• OM2: 50 µm core, LED source, supports 1–10 Gbit/s Ethernet.
• OM3/OM4: 50 µm core, optimized for laser sources (VCSEL), supports 10–100 Gbit/s over short distances.
• OM5: Wideband multimode fiber, supports short-wavelength division multiplexing (SWDM) for higher-speed applications .

Applications

Multimode optical cables are widely used for:

• Enterprise and data center networks as backbone cabling.
• Short-range high-speed connections within buildings or campuses.
• Fiber to the desktop or telecom enclosures for centralized electronics.
• Specialized equipment like spectrometers or laser welding systems .

Advantages

• Lower cost than single-mode fiber and associated equipment.
• Easier installation due to larger core and alignment tolerances.
• Supports multiple data protocols including Ethernet and Infiniband.
• High reliability for short-range, high-capacity networks . In summary, a multimode optical cable is ideal for short-distance, high-bandwidth applications where multiple light signals can be transmitted simultaneously, offering a cost-effective and reliable solution for enterprise and data center networks.