VDV Fiber Optics 3 — Questions and Answers
Question 1: Which standard defines the performance requirements for 50/125 µm multimode fiber used in OM3 and OM4 applications?
- TIA-568-C.0
- TIA-492AAAC / ISO 11801 (Correct answer)
- ANSI/TIA-942
- IEEE 802.3
Correct answer: TIA-492AAAC / ISO 11801
TIA-492AAAC (aligned with ISO 11801) specifies the laser-optimized 50/125 µm fiber characteristics for OM3 and OM4 categories.
Question 2: What is the function of the cladding in an optical fiber?
- Protect the fiber from moisture
- Provide a lower refractive index to contain light within the core (Correct answer)
- Absorb excess light energy
- Conduct electrical signals alongside optical signals
Correct answer: Provide a lower refractive index to contain light within the core
The cladding has a slightly lower refractive index than the core, enabling total internal reflection to confine light transmission.
Question 3: A fiber optic link shows a sudden high-loss event at 500 m on an OTDR trace. What does this most likely indicate?
- Normal connector loss
- A fiber break or severe bend at that location (Correct answer)
- End of the fiber span
- Chromatic dispersion buildup
Correct answer: A fiber break or severe bend at that location
A sudden high-loss event (non-reflective or reflective spike) at a specific distance indicates a fiber break, sharp bend, or crush point.
Question 4: What is 'return loss' (RL) in fiber optic connectors?
- The total attenuation over the full link
- The measure of reflected light back toward the source at a connector (Correct answer)
- The difference between transmitted and received power
- The loss introduced by a splice
Correct answer: The measure of reflected light back toward the source at a connector
Return loss measures how much light is reflected back toward the source; higher RL values (e.g., >55 dB) indicate less reflection, which is better for system performance.
Question 5: Which wavelength window is most commonly used for single-mode fiber transmission in long-haul telecom?
- 850 nm
- 1300 nm
- 1550 nm (Correct answer)
- 1700 nm
Correct answer: 1550 nm
The 1550 nm window has the lowest attenuation (~0.2 dB/km) in silica fiber and aligns with EDFA amplifier gain bands, making it standard for long-haul transmission.
Question 6: What is the correct cleaning procedure before mating fiber optic connectors?
- Blow with compressed air only
- Wipe with a dry cloth, then inspect with a scope
- Clean with IPA using lint-free tools, then inspect with a fiber scope (Correct answer)
- Clean with water and dry with paper towel
Correct answer: Clean with IPA using lint-free tools, then inspect with a fiber scope
Proper cleaning uses isopropyl alcohol with lint-free tools followed by inspection under a fiber scope to confirm the end-face is clean before mating.
Question 7: In a wavelength-division multiplexing (WDM) system, what is being multiplexed?
- Multiple electrical signals on one copper wire
- Multiple optical signals at different wavelengths on one fiber (Correct answer)
- Multiple fibers within a single cable sheath
- Multiple OTDR test signals simultaneously
Correct answer: Multiple optical signals at different wavelengths on one fiber
WDM combines multiple optical channels at different wavelengths (colors) onto a single fiber, greatly increasing the fiber's transmission capacity.
VDV Fiber Optics 3
Which standard defines the performance requirements for 50/125 µm multimode fiber used in OM3 and OM4 applications?