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Black Box Explains...Multimode vs. Single-mode Fiber

Multimode vs. single-mode.

Multimode cable has a large-diameter core and multiple pathways of light. It can be used for most general data and voice applications, such as adding segments to an existing network.

Multimode comes in two core sizes and four varieties: 62.5-micron OM1, 50-micron OM2, 50-micron OM3, and 50-micron OM4. (OM stands for optical mode.) All have the same cladding diameter of 125 microns, but 50-micron fiber cable has a smaller core (the light-carrying portion of the fiber). Although all can be used in the same way, 50-micron cable, particularly laser-optimized OM3 and OM4 50-micron cable,  provides longer link lengths and/or higher speeds and is recommended for premise applications (backbone, horizontal, and intrabuilding links) and should be considered for new installations. OM3 and OM4 can also be used with LED and laser light sources.

Single-mode cable (OS1, OS2) has a small (8–10-micron) glass core and only one pathway of light. (OS stands for optical single-mode.) With only a single wavelength of light passing through its core, single-mode realigns the light toward the core center instead of simply bouncing it off the edge of the core as multimode does. OS1 is applied to inside-plant tight-buffered cable. OS2 is applied to loose-tube cables.

Single-mode provides far greater distances than multimode cable and can go as far as 40 km so it’s typically used in long-haul network links spread out over extended areas, including CATV and campus backbone applications. Single-mode cable also provides higher bandwidth than multimode fiber.

Specification comparison

OM1 62.5-/125-Miron Multimode Fiber

850-nm Wavelength:
Bandwidth: 160 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 220 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 500 m

OM2 50-/125-Micron Multimode Fiber
850-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 550 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 550 m

OM3 50-/125-Micron Multimode Fiber
850-nm Wavelength:
Bandwidth: 1500 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 550 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 550 m

OM4 50-/125-Micron Multimode Fiber
850-nm Wavelength:
Bandwidth: 3500 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 550 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 550 m

OS2 8–10-Micron Single-Mode Fiber

Premise Application:
Wavelength: 1310 nm and 1550 nm;
Attenuation: 1.0 dB/km;

Outside Plant Application:
Wavelength: 1310 nm and 1550 nm;
Attenuation: 0.1 dB/km