Fiber optic patch cords connect switches, servers, ODFs, and transceivers — but the specification printed on the jacket determines whether your link runs at full performance or fails entirely. Here is a complete, practical guide to every designation you will encounter when ordering DAD LINK fiber optic cables.
The Fundamental Split: Multimode vs Single-Mode
Every fiber optic cable carries light through a glass core. The core diameter determines everything else:
- Multimode (OM series) — core diameter of 50 µm (or 62.5 µm for legacy OM1). Multiple light paths travel simultaneously. Works with inexpensive LED or VCSEL transceivers. Ideal for links inside buildings and data centers up to a few hundred meters.
- Single-mode (OS series) — core diameter of 9 µm. A single light path travels with minimal dispersion. Uses more expensive laser transceivers. Ideal for campus links, metro fiber, FTTH/GPON, and telecom — from a few kilometers to hundreds of kilometers.
Mixing multimode and single-mode is not possible — the 50 µm to 9 µm mismatch causes enormous insertion loss. Media converters with separate ports for each type are required to bridge them.
Multimode Fiber: OM1 Through OM4
The OM designation indicates the fiber's bandwidth-distance product, which determines how fast a signal can travel how far:
- OM1 (orange jacket, 62.5 µm core) — legacy standard, 1 Gbps up to 275 m, 10 Gbps only to 33 m. Still found in older buildings. OM1 LC-LC duplex patch cord
- OM2 (orange jacket, 50 µm core) — 1 Gbps up to 550 m, 10 Gbps to 82 m. Obsolete for new installations.
- OM3 (aqua jacket, 50 µm laser-optimized) — 10 Gbps up to 300 m, 100 Gbps up to 70 m. The workhorse of modern data center interconnects. OM3 LC-LC duplex patch cord
- OM4 (aqua jacket, 50 µm high-bandwidth laser-optimized) — 10 Gbps up to 550 m, 100 Gbps up to 150 m. The standard for high-density data centers and large campus backbones.
- OS2 (yellow jacket, 9 µm single-mode) — 10 Gbps+ up to 10 km; 100 Gbps over 40 km with appropriate transceivers. The choice for everything outside a building. OS2 LC-LC duplex patch cord
Bandwidth-Distance Quick Reference Table
| Type | Color | 1 Gbps | 10 Gbps | 100 Gbps |
|---|---|---|---|---|
| OM1 | Orange | 275 m | 33 m | — |
| OM2 | Orange | 550 m | 82 m | — |
| OM3 | Aqua | 1,000 m | 300 m | 70 m |
| OM4 | Aqua | 1,000 m | 550 m | 150 m |
| OS2 | Yellow | 10 km+ | 10 km+ | 40 km+ |
LC vs SC: Connector Form Factors
The connector determines what equipment the patch cord plugs into:
- LC (Lucent Connector) — 1.25 mm ferrule, small form factor. The dominant connector in modern SFP/SFP+ transceivers, switches, and servers. Half the size of SC, giving twice the port density in a patch panel. DAD LINK LC connectors use a push-pull latch mechanism with ceramic ferrule for low-insertion-loss connections.
- SC (Subscriber Connector) — 2.5 mm ferrule, square push-pull connector. Still standard in ODFs, FTTH terminal boxes, CATV equipment, and many older enterprise switches. Easier to terminate in the field.
- LC-SC hybrid patch cords — for environments with mixed equipment. OM3 LC-SC duplex bridges a modern switch SFP to a legacy ODF SC port.
UPC vs APC: The Polish That Changes Everything
The end-face polish of the fiber ferrule determines the return loss — how much light reflects back toward the source:
- UPC (Ultra Physical Contact) — flat end-face polished to a convex curve. Connector color: blue. Return loss: typically better than -50 dB. Standard for all Ethernet and data networking applications.
- APC (Angled Physical Contact) — end-face polished at an 8° angle. Connector color: green. Return loss: better than -60 dB. Required for FTTH/GPON (where reflected light interferes with the upstream signal), CATV, and long-haul telecom.
Critical: never mate UPC to APC. The 8° angle difference leaves an air gap that damages both signal quality and the connector end-faces. Green connectors only mate with green; blue with blue.
Duplex, Simplex, and Pigtails
- Duplex patch cord — two fibers in a zip-cord jacket, one for transmit (Tx) and one for receive (Rx). The standard choice for switches, servers, and most transceivers.
- Simplex patch cord — a single fiber, used with BiDi (bidirectional) SFP optics that transmit and receive on different wavelengths through one fiber. OS2 SC-SC simplex
- Pigtails — a connector on one end, 1–2 m of bare fiber on the other. Fusion-spliced inside ODFs and splice closures. See DAD LINK pigtails.
Insertion Loss and Return Loss: What the Numbers Mean
When comparing fiber patch cords, two performance numbers matter most:
- Insertion loss — the attenuation (signal reduction) the connector pair introduces. The lower, the better. A good LC connector pair adds less than 0.3 dB typical insertion loss. The entire installed channel (cable + connectors) must stay within the transceiver's loss budget.
- Return loss — how much light reflects back. Higher return loss values are better (−50 dB is better than −30 dB). Low return loss causes reflections that degrade signal integrity, especially in analog CATV and coherent optical systems.
Choosing the Right Fiber Patch Cord: Decision Guide
- Switch-to-switch in a rack (short run): OM3 or OM4 LC-LC duplex UPC.
- Building backbone (100–500 m, 10 Gbps): OM3 (to 300 m) or OM4 (to 550 m).
- Campus link or building-to-building: OS2 single-mode LC-LC duplex UPC.
- FTTH terminal box to ONT: OS2 SC-SC duplex APC (green connectors).
- ODF to legacy switch: LC-SC hybrid patch cord in the matching fiber type.
- Splicing into ODF: Pigtail in the correct fiber type and connector.
The Full DAD LINK Fiber Range
DAD LINK supplies a complete fiber optic ecosystem:
- OM1 LC-LC Duplex
- OM3 LC-LC Duplex
- OM3 LC-SC Duplex (hybrid)
- OS2 LC-LC Duplex
- OS2 SC-SC Simplex
- Pigtails (all types)
- Fiber Distribution Frames (ODF)
Frequently Asked Questions
Can I connect OM3 to OM4?
Yes — both are 50 µm laser-optimized fiber and are physically compatible. The link runs at OM3 distances and specifications (the weaker of the two).
Can I connect multimode to single-mode?
No. The core diameters (50 µm vs 9 µm) are incompatible. The connection will either fail completely or suffer massive insertion loss — typically 20+ dB. Media converters with separate multimode and single-mode ports are required to bridge the two technologies.
What color is which fiber optic cable?
Orange = OM1/OM2, aqua/teal = OM3/OM4, yellow = OS2 single-mode. Connector color: blue = UPC, green = APC.
What is the difference between UPC and APC fiber connectors?
UPC (blue, flat-polished end-face) is the standard for data networks with return loss better than -50 dB. APC (green, 8° angled end-face) provides better return loss (better than -60 dB) for FTTH/GPON and CATV. Never mate UPC to APC — the physical angle mismatch damages both connectors and destroys signal quality.
What fiber patch cord do I need for 10 Gbps?
OM3 supports 10 Gbps up to 300 m; OM4 supports 10 Gbps up to 550 m. For 10 Gbps over longer distances or any campus or inter-building link, OS2 single-mode supports 10+ Gbps over 10 km and beyond with appropriate transceivers.
What is the maximum distance for OM4 fiber?
OM4 supports 10 Gbps up to 550 m and 100 Gbps up to 150 m using short-wavelength division multiplexing (SWDM) or parallel optics. For longer distances, OS2 single-mode is required.
Explore all DAD LINK fiber patch cords or ask our team which specification fits your link budget and distance requirements.