VDV Fiber Optics 5 — Questions and Answers
Question 1: According to TIA-568 standards, what is the maximum channel insertion loss allowed for OM3 multimode fiber at 850 nm for a 100 m horizontal link?
- 0.5 dB
- 1.9 dB
- 3.5 dB
- 2.4 dB (Correct answer)
Correct answer: 2.4 dB
TIA-568 specifies a maximum channel loss of 2.4 dB for a 100 m OM3 horizontal link at 850 nm, accounting for connectors, splices, and fiber attenuation.
Question 2: What is 'chromatic dispersion' in single-mode fiber?
- Loss caused by core-cladding interface irregularities
- Pulse spreading caused by different wavelengths traveling at different speeds (Correct answer)
- Signal attenuation caused by OH ion absorption
- Mode coupling between the core and cladding
Correct answer: Pulse spreading caused by different wavelengths traveling at different speeds
Chromatic dispersion occurs because different wavelengths of light have slightly different velocities in the fiber, causing pulse broadening that limits bandwidth over distance.
Question 3: Which fiber optic cable construction uses individual tight-buffered fibers surrounded by a single outer jacket?
- Loose-tube cable
- Tight-buffered breakout (distribution) cable (Correct answer)
- Ribbon cable
- Armored cable
Correct answer: Tight-buffered breakout (distribution) cable
Tight-buffered breakout cables house individually buffered 900 µm fibers under one jacket, making each fiber directly connectorizable without a fan-out kit.
Question 4: A technician notices the OTDR shows a 'gainer' (apparent increase in backscatter level) at a splice point. What does this indicate?
- The splice is performing perfectly
- The fiber after the splice has higher backscatter than the preceding fiber section (Correct answer)
- The splice has zero insertion loss
- The OTDR is malfunctioning
Correct answer: The fiber after the splice has higher backscatter than the preceding fiber section
A gainer occurs when the fiber after the splice has a higher backscatter coefficient, making the splice appear to gain power; bidirectional OTDR testing averages out this artifact.
Question 5: What does the term 'OM5' designate for multimode fiber?
- Outdoor multimode fiber rated for direct burial
- Wideband multimode fiber supporting short-wavelength division multiplexing (SWDM) (Correct answer)
- 50 µm fiber with 100 GHz modal bandwidth
- Armored multimode fiber for industrial environments
Correct answer: Wideband multimode fiber supporting short-wavelength division multiplexing (SWDM)
OM5 (lime green jacket) is a wideband 50/125 µm multimode fiber optimized for SWDM transmission using wavelengths from 850 nm to 953 nm.
Question 6: In a fiber optic cable plant, what is the purpose of a 'splice closure' (or splice enclosure)?
- To terminate fiber to a wall outlet
- To protect and organize fiber splices in outdoor or underground environments (Correct answer)
- To amplify optical signals at intermediate points
- To convert optical signals to electrical signals
Correct answer: To protect and organize fiber splices in outdoor or underground environments
Splice closures provide environmental protection (moisture, rodents, UV) and mechanical organization for fiber splices in aerial, underground, or direct-burial applications.
Question 7: When performing an end-to-end insertion loss test per TIA-568, which reference method is used to establish the baseline optical power measurement?
- Method A (one reference cord) (Correct answer)
- Method B (two reference cords)
- Method C (three reference cords)
- Any method is acceptable without documentation
Correct answer: Method A (one reference cord)
TIA-568 Method A uses one reference cord to set the baseline, including the loss of one mated connector pair in the reference, and is the most common method for channel testing.
VDV Fiber Optics 5
According to TIA-568 standards, what is the maximum channel insertion loss allowed for OM3 multimode fiber at 850 nm for a 100 m horizontal link?