📘 05-02: Fiber-Optic Cabling¶
📌 How Fiber Works¶
Fiber carries data as pulses of light through a glass/plastic core. Because it carries no electrical signal, it is immune to EMI/RFI and supports long distances and high bandwidth.
📌 Single-Mode vs. Multimode¶
| Single-mode (SMF) | Multimode (MMF) | |
|---|---|---|
| Core | ~9 µm (tiny) | 50 / 62.5 µm (larger) |
| Light source | Laser | LED / VCSEL |
| Distance | Very long (km) | Shorter (up to ~550 m) |
| Cost | Higher | Lower |
| Use | Long-haul, backbone, inter-building | Within a building / data center |
Mnemonic: Single-mode = Smaller core, Stretches further.
📌 Fiber Connectors¶
| Connector | Notes |
|---|---|
| LC | Small form factor, often duplex — most common today |
| SC | "Square" push-pull |
| ST | "Stick/twist" bayonet (older) |
| MTP/MPO | Multi-fiber, high density |
📌 Ethernet over Fiber¶
| Standard | Media | Distance |
|---|---|---|
| 10GBASE-SR | MMF (short reach) | ~300 m |
| 10GBASE-LR | SMF (long reach) | ~10 km |
📌 Handling Care¶
- Respect the minimum bend radius — over-bending causes macrobend light loss.
- Keep end-faces clean; contamination raises insertion loss and causes errors.
- Validate with a light source/power meter (dB loss) and characterize with an OTDR.
Tip
Key idea — Fiber = light, no EMI, long distance. Single-mode (small core, laser) for long haul; multimode (large core, LED) for shorter runs. LC is the dominant connector.
See also: Copper Cabling, Ethernet Standards & Transceivers
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