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Fiber Optic Cable Types : Single Mode vs Multimode Fiber Cable

Although single mode fiber (SMF) and multimode fiber (MMF) cable types are widely used in diverse applications, the differences between single mode fiber and multimode fiber is still confusing. This article will focus on the basic construction, fiber distance, cost, fiber color, etc., to make an in-depth comparison between single mode and multimode fiber types.

Overview of Single Mode vs Multimode Fiber
Single mode means the fiber enables one type of light mode to be propagated at a time. While multimode means the fiber can propagate multiple modes. The differences between single mode and multimode fiber mainly lies in fiber core diameter, wavelength & light source, bandwidth, color sheath, distance and cost.

Core Diameter
Single mode fiber core diameter is much smaller than multimode fiber. Its typical core diameter is 9 µm even if there are others available. And multimode fiber core diameter is 50 µm and 62.5 µm typically, which enables it to have higher "light gathering" ability and simplify connections. The cladding diameter of single mode and multimode fiber is 125 µm.

Figure 1 Optical Fiber Core Diameters.png
The attenuation of multimode fiber is higher than SM fiber because of its larger core diameter. The fiber core of single mode cable is very narrow, so the light that passes through these fiber optical cables is not reflected too many times, which keeps the attenuation to a minimum.

9/125 Single Mode Fiber Simplex 50/125 OM3 Multimode Fiber
Attenuation at 1310nm 0.36 dB/km Attenuation at 850 nm 3.0 dB/km
Attenuation at 1550nm 0.22 dB/km Attenuation at 1300 nm 1.0 dB/km
Wavelength & Light Source
Due to the large core size of multimode fiber, some low-cost light sources like LEDs (light-emitting diodes) and VCSELs (vertical cavity surface-emitting lasers) that works at the 850nm and 1300nm wavelength are used in multimode fiber cables. While the single mode fiber often uses a laser or laser diodes to produce light injected into the cable. And the commonly used single mode fiber wavelength is 1310 nm and 1550 nm.

Bandwidth
Multimode fiber bandwidth is limited by its light mode and the maximum bandwidth at present is 28000MHz*km of OM5 fiber. While single mode fiber bandwidth is unlimited theoretically because it allows only one light mode to pass through at a time.

Color Sheath
According to the TIA-598C standard definition, for non-military applications, single mode cable is coated with yellow outer sheath, and multimode fiber is coated with orange or aqua jacket. Find more details about the Fiber Optic Cable Color Code here.

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