How far can OM4 multimode fiber run at 100G?

OM4 supports roughly 400 m at 10G but only about 100–150 m at 40G/100G, because modal dispersion limits distance as speed increases. Single-mode OS2 can reach up to about 10 km at these speeds.

Should I use single-mode or multimode in a data center?

Multimode OM4 is common and cost-effective for short data center runs. Single-mode OS2 is chosen for longer distances, higher speeds over distance, and futureproofing. Many facilities use both, so a supplier that builds custom assemblies in either type simplifies procurement.

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Single-mode vs multimode fiber.

Q: What is the difference between single-mode and multimode fiber?

Single-mode fiber (OS2) has a small ~9 micron core that carries one light path over 1310/1550 nm lasers for long distances. Multimode fiber (OM3/OM4) has a larger 50 micron core that carries multiple light paths over 850 nm sources for shorter, cost-effective runs inside a data center.

OS2 single-mode and OM3/OM4 multimode fiber solve different problems. This guide compares core size, wavelength, real transmission distance at each speed, and cost — so you can spec the right fiber for your run.

The core difference

The names describe how light travels down the glass. Single-mode fiber (OS2) has a very small core — around 9 microns — so light follows a single path. That eliminates modal dispersion and allows extremely long distances at high speed, using 1310 nm and 1550 nm laser sources. Multimode fiber (OM3/OM4) has a larger 50-micron core that lets light travel multiple paths ("modes") using lower-cost 850 nm VCSEL optics. That makes multimode cheaper to deploy over short distances but limits how far a signal can travel before the modes spread out.

Specs at a glance

Property	OS2 (single-mode)	OM3 (multimode)	OM4 (multimode)
Core size	~9 µm	50 µm	50 µm
Source / wavelength	Laser · 1310 / 1550 nm	VCSEL · 850 nm	VCSEL · 850 nm
Bandwidth @ 850 nm	—	2000 MHz·km	4700 MHz·km
10G reach	up to ~10 km	up to ~300 m	up to ~400 m
40G / 100G reach	up to ~10 km	up to ~100 m	up to ~150 m
Relative cost	Higher optics, lower fiber	Lower optics	Lower optics
Jacket color (typical)	Yellow	Aqua	Aqua / violet

Distances are typical maximums for common transceivers and shorten as line rate increases; always confirm against your specific optics.

Why distance drops as speed rises (multimode)

Notice that the same OM4 fiber that handles 10G at 400 meters drops to roughly 100–150 meters at 40G/100G. That's modal dispersion: at higher line rates, the small timing differences between light paths in a large core start to smear the signal. Single-mode's tiny core avoids this, which is why OS2 holds up to ~10 km even at 100G.

How to choose

Short data center runs, cost-sensitive: OM4 multimode is the common, economical choice for switch-to-server and top-of-rack links.
Long runs, campus, or futureproofing: OS2 single-mode carries higher speeds far further and is increasingly used even inside large facilities for longevity.
Mixed environments: Many sites run both. Standardizing your BOM and sourcing both types from one builder keeps procurement simple.

Need custom OS2 or OM4 jumpers and trunks?

Tri-Valley Optics builds LC, SC, ST, and MPO/MTP assemblies in single-mode OS2 and multimode OM3/OM4 — any length, any quantity, most orders shipped in about 2 business days. Standard builds are TIA-568 compliant with a lifetime warranty.

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