VDV Fiber Optics 2 — Questions and Answers
Question 1: Which splicing method typically produces the lowest insertion loss in single-mode fiber?
- Mechanical splice
- Fusion splice (Correct answer)
- Crimp splice
- Adhesive splice
Correct answer: Fusion splice
Fusion splicing melts fiber ends together creating a near-seamless joint, typically yielding losses below 0.1 dB.
Question 2: What is the primary purpose of an optical time-domain reflectometer (OTDR)?
- Measure fiber core diameter
- Locate faults and measure loss along a fiber link (Correct answer)
- Test connector return loss only
- Measure chromatic dispersion
Correct answer: Locate faults and measure loss along a fiber link
An OTDR sends pulses into the fiber and analyzes backscattered light to locate faults, splices, and measure distance-based loss.
Question 3: What does 'bend radius' refer to in fiber optic installations?
- The angle at which light enters the fiber
- The minimum curve radius a fiber can be bent without excessive signal loss (Correct answer)
- The diameter of the fiber cladding
- The radius of the fiber spool
Correct answer: The minimum curve radius a fiber can be bent without excessive signal loss
Exceeding the minimum bend radius causes microbending loss as light escapes the core through the cladding.
Question 4: Which fiber optic connector type uses a push-pull latching mechanism and is common in data center applications?
- ST connector
- FC connector
- LC connector (Correct answer)
- SC connector
Correct answer: LC connector
LC (Lucent Connector) uses a push-pull latch similar to an RJ-45 and has a small form factor suited for high-density data center use.
Question 5: What does 'numerical aperture' (NA) describe in a fiber optic cable?
- The number of fibers in a cable bundle
- The light-gathering ability and acceptance cone of the fiber (Correct answer)
- The fiber's resistance to physical stress
- The operating wavelength range
Correct answer: The light-gathering ability and acceptance cone of the fiber
Numerical aperture defines the half-angle of the cone of light a fiber can accept, determined by the refractive index difference between core and cladding.
Question 6: In fiber optics, what does 'modal dispersion' cause?
- Increased connector reflectance
- Pulse spreading that limits bandwidth over distance (Correct answer)
- Higher insertion loss at splices
- Increased chromatic aberration
Correct answer: Pulse spreading that limits bandwidth over distance
Modal dispersion occurs in multimode fiber when different modes travel at different speeds, causing pulses to spread and limiting data rates.
Question 7: What type of fiber is most commonly used for long-haul telecommunications exceeding 10 km?
- 50/125 µm multimode
- 62.5/125 µm multimode
- Single-mode 9/125 µm (Correct answer)
- Hard-clad silica fiber
Correct answer: Single-mode 9/125 µm
Single-mode fiber with a 9 µm core eliminates modal dispersion and supports very long transmission distances at high bandwidths.
VDV Fiber Optics 2
Which splicing method typically produces the lowest insertion loss in single-mode fiber?