DCI Fiber Optic Installation 4 — Questions and Answers
Question 1: What is 'return loss' (RL) in a fiber optic connector, and why does it matter?
- The total insertion loss measured in return direction
- The amount of light reflected back toward the source, measured in dB (Correct answer)
- The loss caused by cable bending
- The power difference between two fiber ends
Correct answer: The amount of light reflected back toward the source, measured in dB
Return loss quantifies the optical power reflected back toward the source; high return loss (e.g., >55 dB for UPC) means less reflection, which is critical for laser stability.
Question 2: What color is the jacket of an APC (angled physical contact) fiber optic connector by standard convention?
- Blue
- Beige
- Green (Correct answer)
- Yellow
Correct answer: Green
APC connectors are identified by a green color-coded body or boot, distinguishing them from UPC connectors which are typically blue or beige.
Question 3: An OTDR is set with a pulse width of 100 ns. Approximately how long is the resulting dead zone?
- 1 meter
- 10 meters (Correct answer)
- 100 meters
- 1 kilometer
Correct answer: 10 meters
A 100 ns pulse corresponds to approximately 10 meters of dead zone, since light travels about 0.2 m/ns in fiber (speed ÷ 2 for round trip).
Question 4: Which method is used to join fiber optic cables in an outside plant environment where a permanent, low-loss connection is required?
- Mechanical splice
- Fusion splice (Correct answer)
- Field-installable connector
- Pre-terminated pigtail
Correct answer: Fusion splice
Fusion splicing provides the lowest loss and most durable permanent joint for outside plant applications by welding the glass fibers together.
Question 5: What is the standard core diameter of a single-mode fiber (SMF) per ITU-T G.652?
- 50 µm
- 62.5 µm
- 9 µm (Correct answer)
- 125 µm
Correct answer: 9 µm
Standard single-mode fiber has a 9 µm core diameter, which supports only one propagation mode at 1310 nm and 1550 nm wavelengths.
Question 6: When installing fiber optic cable in an aerial application, what is the primary purpose of the messenger wire?
- To carry the electrical signal alongside fiber
- To provide mechanical support and carry the cable's weight (Correct answer)
- To act as a lightning ground
- To protect the fiber from UV radiation
Correct answer: To provide mechanical support and carry the cable's weight
The messenger wire (steel strand) carries the mechanical load of the cable span, relieving tension from the fiber itself.
Question 7: What is the recommended power level range for testing a fiber link with an optical power meter when using a 1310 nm source?
- -60 dBm to -40 dBm
- +10 dBm to +20 dBm
- Within the calculated link loss budget ±3 dB (Correct answer)
- Always exactly 0 dBm
Correct answer: Within the calculated link loss budget ±3 dB
The measured power should fall within the calculated link loss budget tolerance; exceeding the budget indicates a fault, while being far under may mean fiber type mismatch.
DCI Fiber Optic Installation 4
What is 'return loss' (RL) in a fiber optic connector, and why does it matter?