Fiber Optic Fundamentals
Multimode and singlemode fiber types, wavelengths, MPO connectors, polarity, color coding, and connector polish types.
- Differentiate multimode and singlemode fiber by core size, bandwidth, and distance
- Identify fiber jacket color codes for OM1 through OS2
- Explain MPO connector polarity methods A, B, and C
- Compare PC, UPC, and APC connector polish types and their return loss values
- Describe OFNR, OFNP, and other fiber cable fire ratings
Leçon 1
Multimode vs Singlemode Fiber
Two Families of Fiber
Fiber optic cables carry data as pulses of light through a glass or plastic core. Every data cabling installer must understand the two fundamental fiber families: multimode and singlemode. The difference comes down to the size of the glass core and how light propagates through it.
Multimode fiber has a larger core - typically 50 or 62.5 microns - that allows multiple light paths (modes) to travel simultaneously. Singlemode fiber has a much smaller core - 8.3 microns - that permits only one mode of light. This single path eliminates modal dispersion, giving singlemode fiber far greater distance and bandwidth capabilities.
Multimode Fiber
Core size: 50 or 62.5 microns
Light source: LED or VCSEL
Distance: Up to 550 m (10G)
Cost: Lower transceivers
Use: Campus and building backbone
Singlemode Fiber
Core size: 8.3 microns
Light source: Laser
Distance: Up to 10+ km
Cost: Higher transceivers
Use: Long-haul and inter-building
Multimode Fiber Types
TIA-568 recognizes several multimode fiber types designated by their OM rating (Optical Multimode):
| Designation | Core/Cladding | Bandwidth (850 nm) | Jacket Color |
|---|---|---|---|
| OM1 | 62.5/125 um | 200 MHz-km | Orange |
| OM2 | 50/125 um | 500 MHz-km | Orange |
| OM3 | 50/125 um | 2000 MHz-km | Aqua |
| OM4 | 50/125 um | 4700 MHz-km | Aqua |
| OM5 | 50/125 um | 28000 MHz-km | Lime Green |
Exam Tip
OM3 and OM4 are laser-optimized 50-micron fibers designed for VCSEL sources. OM1 and OM2 are legacy types. OM5 supports wideband multimode (SWDM) for wavelength-division multiplexing.
Singlemode Fiber Types
Singlemode fiber is classified under the OS designation (Optical Singlemode):
- OS1 - Indoor tight-buffered singlemode, attenuation 1.0 dB/km at 1310 nm
- OS2 - Outdoor or loose-tube singlemode, attenuation 0.4 dB/km at 1310 nm
Singlemode fiber uses 1310 nm and 1550 nm wavelengths, while multimode fiber operates primarily at 850 nm and 1300 nm.
Multimode fiber uses a 50 or 62.5 micron core with LED/VCSEL sources for shorter distances. Singlemode fiber uses an 8.3 micron core with lasers for long-haul links exceeding 10 km.