VDV Fiber Optics 4 — Questions and Answers
Question 1: What does an 'APC' fiber connector end-face polish provide compared to a 'UPC' polish?
- Lower insertion loss
- Higher return loss due to its angled 8-degree end-face (Correct answer)
- Faster mating and unmating
- Better performance at 850 nm only
Correct answer: Higher return loss due to its angled 8-degree end-face
APC (Angled Physical Contact) connectors have an 8-degree angled end-face that reflects light away from the core, achieving return loss >60 dB versus ~55 dB for UPC.
Question 2: Which parameter measured in dB represents the total allowed signal loss for a fiber optic link from source to receiver?
- Chromatic dispersion coefficient
- Optical power budget (loss budget) (Correct answer)
- Numerical aperture
- Modal bandwidth
Correct answer: Optical power budget (loss budget)
The optical power (loss) budget is the difference between transmitter output power and receiver sensitivity, defining the maximum allowable link loss.
Question 3: What causes 'Rayleigh scattering' loss in optical fiber?
- Physical bends in the fiber
- Microscopic density variations in the glass material (Correct answer)
- Connector end-face contamination
- Splice misalignment
Correct answer: Microscopic density variations in the glass material
Rayleigh scattering occurs when light interacts with tiny density fluctuations inherent in the glass structure, and is the dominant loss mechanism at shorter wavelengths.
Question 4: A VDV technician must install fiber in a plenum space. Which cable type must be used?
- OFNR (Riser rated) fiber
- OFNP (Plenum rated) fiber (Correct answer)
- OFNG (General purpose) fiber
- Any fiber with an outer jacket
Correct answer: OFNP (Plenum rated) fiber
OFNP (Optical Fiber Nonconductive Plenum) cables are required in plenum spaces because they have low-smoke, flame-retardant jackets that meet NEC Article 770 requirements.
Question 5: What is the typical core/cladding diameter of standard 62.5 µm multimode fiber?
- 50/125 µm
- 62.5/125 µm (Correct answer)
- 9/125 µm
- 100/140 µm
Correct answer: 62.5/125 µm
Standard 62.5 µm multimode fiber has a 62.5 µm core and 125 µm cladding diameter, making it compatible with LED-based transmitters.
Question 6: Which test instrument measures the optical power output of a fiber optic transmitter or the power at the end of a fiber link?
- OTDR
- Optical power meter (Correct answer)
- Visual fault locator
- Chromatic dispersion analyzer
Correct answer: Optical power meter
An optical power meter directly measures light power in dBm or watts and is used with a light source to perform insertion loss tests on fiber links.
Question 7: What is the main advantage of using a visual fault locator (VFL) during fiber installation?
- It measures exact dB loss of a link
- It visually identifies breaks, bends, and bad splices by showing red light leaking from the fiber (Correct answer)
- It tests fiber bandwidth at 10 Gbps
- It cleans fiber end-faces automatically
Correct answer: It visually identifies breaks, bends, and bad splices by showing red light leaking from the fiber
A VFL injects visible red laser light (typically 650 nm) into the fiber; breaks or severe bends glow red, making faults easy to locate visually.
VDV Fiber Optics 4
What does an 'APC' fiber connector end-face polish provide compared to a 'UPC' polish?