Multimode fiber core is small

Multimode fiber has a relatively large core, typically 50µm or 62.5µm, which is much bigger than single-mode fiber cores.Core Size ComparisonMultimode fiber (MMF) is designed to allow multiple light modes to propagate simultaneously, which requires a larger core diameter. The most common core sizes are 50 micrometers (µm) for OM2, OM3, OM4, and OM5 fibers, and 62.5 µm for OM1 fibers . In contrast, single-mode fiber (SMF) has a much smaller core, typically around 9 µm, allowing only one light mode to travel straight through the fiber . Despite the larger core, the overall fiber diameter including cladding is usually 125 µm for both multimode and single-mode fibers .Implications of Core SizeThe larger core of multimode fiber makes it easier to couple light from LEDs or VCSELs (vertical-cavity surface-emitting lasers), which are less spatially coherent than laser sources used in single-mode fibers . This also simplifies manufacturing and reduces costs for short-distance applications. However, the multiple light paths in multimode fiber lead to modal dispersion, which limits the maximum transmission distance and bandwidth compared to single-mode fiber . As a result, multimode fiber is typically used for short-range communication, such as within buildings, data centers, or local area networks.ApplicationsOM1 (62.5 µm core): Suitable for 100 Megabit and 1G Ethernet over short distances.OM2/OM3/OM4/OM5 (50 µm core): Optimized for higher-speed applications, including 10G, 40G, and 100G Ethernet, but still limited to shorter distances than single-mode fiber . In summary, multimode fiber cores are not small; they are intentionally larger than single-mode cores to support multiple light modes, making them ideal for short-distance, cost-effective optical communication.