Walking into the fiber optic cable aisle (or browsing online) can feel overwhelming. OM1, OM2, OM3, OM4, OS2 — what do these designations mean, and how do you pick the right one?
This guide cuts through the jargon and helps you match the right fiber cable to your actual needs.
Multi-mode vs single-mode: the fundamental split
All fiber optic cables fall into one of two categories.
Multi-mode fiber (the OM cables) has a larger core — typically 50 or 62.5 microns — that allows multiple light paths (modes) to travel through the fiber simultaneously. It's designed for shorter distances and works with less expensive LED or VCSEL light sources. Multi-mode fiber is color-coded orange (OM1/OM2), aqua (OM3/OM4), or lime green (OM5).
Single-mode fiber (OS2) has a tiny 9-micron core that allows only one light path. This gives it far greater distance capability — up to 10 kilometers or more — but requires more expensive laser light sources. Single-mode fiber is color-coded yellow.
The choice between multi-mode and single-mode usually comes down to distance. Inside a building or campus (under 300-550 meters), multi-mode is standard. Between buildings, across campuses, or in telecom applications, single-mode is necessary.
The OM classifications
OM1 (62.5/125) — The original multi-mode fiber standard. Orange jacket. Supports 1 Gbps Ethernet (1000BASE-SX) up to 275 meters and 10 Gbps (10GBASE-SR) up to only 33 meters. OM1 is a legacy specification — adequate for maintaining existing installations, but not recommended for new builds.
OM2 (50/125) — The first 50-micron multi-mode standard. Orange jacket. Supports 1 Gbps up to 550 meters and 10 Gbps up to 82 meters. Like OM1, OM2 is considered a legacy standard today. If you're connecting to existing OM2 infrastructure, it's the right match. For new installations, OM3 or OM4 offer much better performance.
OM3 (50/125) — Laser-optimized multi-mode fiber. Aqua jacket. This is where modern multi-mode begins. OM3 supports 10 Gbps up to 300 meters and can handle 40/100 Gbps over shorter distances (100 meters). OM3 is the most popular choice for new multi-mode installations in enterprise networks, data centers, and campus backbones.
OM4 (50/125) — Extended-distance laser-optimized fiber. Aqua or sometimes violet/purple jacket. OM4 pushes 10 Gbps to 400 meters and extends 40/100 Gbps to 150 meters. It's the premium multi-mode option for data centers and high-performance computing environments where every meter of reach matters.
OM5 (50/125) — The newest multi-mode standard, designed for wavelength-division multiplexing (WDM) over short distances. Lime green jacket. OM5 is still emerging and primarily relevant for hyperscale data centers.
OS2 single-mode
OS2 (9/125) — The universal single-mode fiber standard. Yellow jacket. OS2 supports 1 Gbps, 10 Gbps, 40 Gbps, and 100 Gbps at distances of 10 kilometers or more, depending on the optics used. Single-mode fiber is the backbone of telecommunications networks, long-distance data links, and any application where multi-mode can't reach.
Within OS2, you'll encounter two connector polish types: UPC (Ultra Physical Contact) and APC (Angled Physical Contact). UPC connectors have a flat polish and are suitable for most data networking applications. APC connectors have an 8-degree angled polish that reduces back-reflection, making them ideal for analog video, CATV, and applications where signal quality is critical. APC connectors are identified by their green color.
Connector types
LC (Lucent Connector) — The most common connector in modern installations. Small form factor, push-pull latch, available in simplex and duplex.
SC (Subscriber Connector) — Larger than LC, push-pull design. Still widely used, especially in telecom and legacy networks.
ST (Straight Tip) — Bayonet-style twist-lock connector. Common in legacy installations and some industrial environments.
MTP/MPO — Multi-fiber connectors that carry 12 or 24 fibers in a single connector. Used for high-density data center backbone connections and trunk cables.
Which fiber should you choose?
For connections within a building (under 300m): OM3 or OM4 multi-mode with LC connectors. OM3 is the best value; OM4 adds distance headroom.
For campus or between-building links (300m to 10km): OS2 single-mode with LC connectors.
For maintaining existing infrastructure: Match the existing fiber type (OM1, OM2, etc.) to ensure compatibility.
For data center backbone/trunk: OM4 MTP trunk cables for multi-mode, or OS2 MTP for single-mode.
For high-sensitivity applications (CATV, analog video): OS2 APC (angled polish) connectors.
At Kentek, we carry a full range of fiber optic patch cables across all OM and OS classifications, with LC, SC, ST, FC, and MTP connectors, in both simplex and duplex configurations. All cables are UL listed.