OSP Fiber Optic & Copper Cabling Systems 4 — Questions and Answers
Question 1: What is 'chromatic dispersion' in single-mode fiber and why does it matter in OSP design?
- Signal reflection caused by connector misalignment, limiting cable runs
- Pulse spreading caused by different wavelengths traveling at different speeds, limiting bandwidth-distance (Correct answer)
- Polarization mismatch between transmitter and fiber, causing signal loss
- Temperature-induced refractive index changes, causing attenuation spikes
Correct answer: Pulse spreading caused by different wavelengths traveling at different speeds, limiting bandwidth-distance
Chromatic dispersion causes optical pulses to spread as different wavelength components travel at slightly different velocities, becoming a bandwidth-limiting factor in high-speed, long-distance links.
Question 2: When designing a fiber distribution hub (FDH) for an FTTH network, what is the primary function of the splitter inside?
- To amplify the optical signal for longer reach to subscribers
- To passively divide a single feeder fiber signal among multiple drop fibers (Correct answer)
- To convert single-mode feeder fiber to multimode drop cables
- To monitor signal quality and report faults to the headend
Correct answer: To passively divide a single feeder fiber signal among multiple drop fibers
A passive optical splitter in an FDH divides the feeder fiber's optical power among multiple subscriber drop fibers without requiring electrical power.
Question 3: The '3 dB rule' in copper cable design refers to the frequency at which:
- Signal amplitude doubles compared to the source level
- Insertion loss equals 3 dB, defining the cable's usable bandwidth (Correct answer)
- Crosstalk between pairs reaches its maximum value
- Shield effectiveness drops below acceptable limits
Correct answer: Insertion loss equals 3 dB, defining the cable's usable bandwidth
The 3 dB bandwidth point is where insertion loss equals 3 dB (half power), commonly used to define the upper frequency limit for a given cable type and length.
Question 4: In outside plant design, a 'slack loop' of fiber cable is stored in a splice enclosure primarily to:
- Reduce back-reflection from the splice point
- Provide extra cable for future re-splicing, repairs, or rerouting (Correct answer)
- Prevent the splice from exceeding bend radius limits
- Serve as a dispersion compensation element
Correct answer: Provide extra cable for future re-splicing, repairs, or rerouting
Slack loops give technicians enough cable to open an enclosure, work comfortably, and re-splice if a fusion splice must be redone without running new cable.
Question 5: Which test is used to verify that all conductors in a multi-pair copper cable are correctly connected with no shorts, opens, or reversed pairs?
- Time domain reflectometry (TDR)
- Wiremap test (Correct answer)
- Return loss measurement
- Balance test
Correct answer: Wiremap test
A wiremap test verifies pin-to-pin continuity and detects opens, shorts, crossed pairs, reversed pairs, and split pairs in copper cable installations.
Question 6: Submarine fiber optic cables typically use which type of fiber sheath reinforcement to withstand hydrostatic pressure at depth?
- PVC jacketing with aluminum foil wrap
- Corrugated steel armor with double polyethylene sheath
- High-strength steel wire armoring with high-density polyethylene outer jacket (Correct answer)
- Fiberglass rodent protection with foam insulation
Correct answer: High-strength steel wire armoring with high-density polyethylene outer jacket
Deep-water submarine cables use high-tensile steel wire armor under a polyethylene jacket to withstand enormous crushing and tensile forces at oceanic depths.
Question 7: What is the function of a 'fiber optic attenuator' in an OSP link?
- To boost the signal level when spans are too long
- To reduce signal power when the receiver would otherwise be overloaded (Correct answer)
- To convert between single-mode and multimode fiber types
- To equalize chromatic dispersion across wavelength channels
Correct answer: To reduce signal power when the receiver would otherwise be overloaded
Attenuators intentionally reduce optical power to prevent receiver saturation in short links where transmitter power exceeds the receiver's maximum input level.
OSP Fiber Optic & Copper Cabling Systems 4
What is 'chromatic dispersion' in single-mode fiber and why does it matter in OSP design?