DCI Fiber Optic Installation 5 — Questions and Answers
Question 1: What is 'modal dispersion' and which fiber type is most affected by it?
- Wavelength-dependent loss affecting single-mode fiber
- Pulse spreading from multiple light paths, primarily affecting multimode fiber (Correct answer)
- Connector insertion loss in duplex links
- Polarization mode dispersion in SMF at high bit rates
Correct answer: Pulse spreading from multiple light paths, primarily affecting multimode fiber
Modal dispersion occurs in multimode fiber because different modes travel different path lengths, causing pulse spreading that limits bandwidth and distance.
Question 2: Which TIA standard specifies the color coding of optical fibers within a cable sheath?
- TIA-568-C.3
- ANSI/TIA-598-D (Correct answer)
- TIA-942
- TIA-526-14
Correct answer: ANSI/TIA-598-D
ANSI/TIA-598-D defines the color-coding scheme for optical fiber cables, ensuring consistent fiber identification across installations.
Question 3: A technician measures -18 dBm at the far end of a link with a launch power of -3 dBm. What is the total link loss?
- 15 dB (Correct answer)
- 18 dB
- 21 dB
- 3 dB
Correct answer: 15 dB
Link loss = launch power − received power = -3 dBm − (-18 dBm) = 15 dB.
Question 4: What is the function of a fiber optic patch panel (also called a fiber distribution unit)?
- To amplify optical signals between cable segments
- To provide a centralized termination and cross-connect point for fiber links (Correct answer)
- To convert optical signals to electrical signals
- To store excess fiber slack in the pathway
Correct answer: To provide a centralized termination and cross-connect point for fiber links
A fiber patch panel provides organized termination points allowing technicians to cross-connect or interconnect fiber links with patch cords.
Question 5: During a fiber optic installation, what is the purpose of 'slack loops' left inside enclosures or splice trays?
- To increase the fiber's attenuation for testing
- To provide extra fiber length for future re-splicing or re-termination (Correct answer)
- To prevent connector contamination
- To store unused patch cords
Correct answer: To provide extra fiber length for future re-splicing or re-termination
Slack loops ensure enough extra fiber length is available if a splice or connector must be redone, preventing the need to replace the entire run.
Question 6: Which cleaning method is considered best practice for fiber optic connector end-faces before mating?
- Blow compressed air only
- Wipe with a dry lint-free cloth once, then inspect with a fiber scope
- Wet clean with IPA followed by a dry wipe, then inspect with a fiber scope (Correct answer)
- Soak the connector in isopropyl alcohol for 30 seconds
Correct answer: Wet clean with IPA followed by a dry wipe, then inspect with a fiber scope
Best practice is a wet-then-dry clean using IPA-moistened then dry lint-free wipes or a reel cleaner, followed by inspection with a 200×–400× fiber scope.
Question 7: What does a high 'reflection event' spike on an OTDR trace most likely indicate?
- A fusion splice with high loss
- A mechanical connector, air gap, or fiber end causing Fresnel reflection (Correct answer)
- A section of fiber with high attenuation
- A tight bend in the cable
Correct answer: A mechanical connector, air gap, or fiber end causing Fresnel reflection
Fresnel reflections at air-glass interfaces (connectors, mechanical splices, or open fiber ends) produce sharp upward spikes on an OTDR trace.
DCI Fiber Optic Installation 5
What is 'modal dispersion' and which fiber type is most affected by it?