The Difference Between Multimode and Single-Mode Fiber Optic Cables

Fiber optics is a communications medium that sends optical signals down hair-thin strands of pure glass cores. The light “pipe” is surrounded by cladding that traps the light in the core. The key difference between multimode and single mode fiber optic cable is the size of the core.

According to Camplex, a fiber optic solutions provider based in Saugerties, New York, fiber types are identified by the diameters of the core and cladding. These are expressed in microns. Multimode fiber is available in two sizes — 62.5 or 50 microns — and four classifications: OM1 (62.5/125 µm), OM2, OM3, OM4 (50/125 µm).

The diameter of a single mode core fiber cable, however, is nine microns. Both fiber types have a cladding diameter of 125 µm or microns.

In multimode fiber, light travels through through the large core in many rays. These are called modes. Due to refraction, the rays are reflected from the cladding surface back into the core as they move through the fiber.

Single mode fiber, on the other hand, has a much smaller core which forces the light to travel in one ray or mode (a single mode). There is little light reflection so the signal will travel further.

The user’s application requirements determine which mode is used. Single mode is typically used by outside broadcast vehicles, ENG crews, sports, live events and long haul networks. Multimode is often used by MADI digital audio, security systems, data centers, CCTV and Ethernet protocols.

The benefits of single mode fiber is lower signal loss, high signal quality and high bandwidth, while multimode fiber is less immune to contamination, less expensive and lower cost

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