Optical Fiber and Cable Systems (fiber, copper cabling, jointing, testing)
This section covers Optical Fiber and Cable Systems: fiber types, copper cabling, jointing, and testing. The exam tests whether you can select cable, make a safe joint, and prove link performance.
Core rules and concepts
- Fiber: core, cladding, coating. Total internal reflection guides light when core index exceeds cladding index. Single-mode fiber has a small core (about 9 µm) and carries long-haul 1310/1550 nm signals; multimode (50 or 62.5 µm) uses 850/1300 nm for shorter links.
- Attenuation is measured in dB/km; splices and connectors add loss. Dispersion limits distance and bit rate. Bend radius and pulling tension must be respected.
- Connectors: SC, LC, ST. Joints: fusion splice (low loss, permanent) or mechanical splice. Joint closures must be sealed and strain-relieved.
- Copper: UTP categories, RJ45, punch-down blocks. Tests: continuity, wire map, length, attenuation, crosstalk. Fiber tests: visual fault locator, optical power meter with light source, and OTDR for loss and event location.
- Always clean and inspect connectors; dust causes high loss and damage.
Worked example
Link budget: transmitter +2 dBm; 10 km fiber at 0.25 dB/km = 2.5 dB; two connectors at 0.5 dB each = 1.0 dB; four splices at 0.1 dB each = 0.4 dB. Total loss = 3.9 dB. Received power = 2 - 3.9 = -1.9 dBm. If receiver sensitivity is -20 dBm, margin is 18.1 dB, which exceeds a 3 dB design margin, so the link passes.
Traps that cost marks
Using a single-mode source with multimode fiber; confusing µm core size with nm wavelength; reading one-way OTDR results without checking the far-end reflection; ignoring bend radius; and comparing dB loss with dBm power as if they were the same unit.