What is a multimode fiber?

Multimode Fiber

Multimode fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multimode fibers are characterized by their ability to carry multiple light modes simultaneously, each at a slightly different reflection angle within the optical fiber core.

Core Diameter

Multimode fibers have a larger core diameter compared to single-mode fibers, typically ranging from 50 to 62.5 micrometers. This larger size allows for the transmission of multiple light modes.


Multimode fibers are commonly used in applications where high bandwidth and high speed are not required over long distances. This includes data and telecommunications in local area networks (LANs), CCTV installations, and fiber to the home (FTTH) services.


  • Higher capacity and flexibility in transmitting multiple signals simultaneously.
  • Cost-effective for short-distance communication due to the use of less expensive light sources like LEDs.
  • Easier to connect and install because of the larger core diameter.


  • Lower bandwidth compared to single-mode fibers over long distances.
  • More susceptible to modal dispersion, which can limit the transmission distance and data rate.

Types of Multimode Fiber

There are two main types of multimode fiber:

  1. Step-index multimode fiber: Features a core with a uniform refractive index, leading to different paths (or modes) that light can take through the fiber.
  2. Graded-index multimode fiber: Has a core with a varying refractive index that decreases towards the outer edge, reducing modal dispersion and allowing for higher data transmission rates.

In summary, multimode fiber offers a cost-effective solution for short-range communication systems, providing sufficient bandwidth for many applications while allowing for simpler, more affordable installations.

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