BDS Fiber Optic Systems and HFC Architecture 1 — Questions and Answers
Question 1: What does HFC stand for in cable broadband architecture?
- High-Frequency Coaxial
- Hybrid Fiber-Coaxial (Correct answer)
- High-Frequency Cable
- Hybrid Frequency Circuit
Correct answer: Hybrid Fiber-Coaxial
HFC (Hybrid Fiber-Coaxial) refers to the network architecture that uses optical fiber from the headend to neighborhood nodes, and coaxial cable from the nodes to subscriber homes.
Question 2: What is the primary function of a fiber node in an HFC network?
- To route IP packets between fiber segments
- To convert optical signals to RF signals for the coaxial distribution plant (Correct answer)
- To amplify the optical signal before it reaches the headend
- To encrypt subscriber data before transmission
Correct answer: To convert optical signals to RF signals for the coaxial distribution plant
The fiber node contains an optical receiver that converts the downstream optical signal to RF, and a laser transmitter that converts upstream RF signals back to optical for transport to the headend.
Question 3: What is the typical wavelength used for downstream optical transmission in an HFC network?
- 850 nm
- 1310 nm
- 1550 nm (Correct answer)
- 1625 nm
Correct answer: 1550 nm
The 1550 nm wavelength is widely used for downstream transmission in HFC networks because it offers lower fiber attenuation and is compatible with EDFA optical amplification.
Question 4: Which fiber optic connector type is most commonly used in the cable broadband industry for node and headend connections?
- FC/PC
- ST
- SC/APC (Correct answer)
- LC
Correct answer: SC/APC
The SC/APC (Subscriber Connector / Angled Physical Contact) connector is the dominant connector in HFC networks due to its low back-reflection, snap-lock design, and compatibility with industry standards.
Question 5: What is optical return loss (ORL) and why is it important in HFC systems?
- The signal lost in fiber splices; it reduces signal strength
- The ratio of reflected optical power to incident power; excessive reflections degrade laser performance (Correct answer)
- The attenuation per kilometer of fiber; it determines maximum span length
- The difference in power between two wavelengths; it causes wavelength-dependent loss
Correct answer: The ratio of reflected optical power to incident power; excessive reflections degrade laser performance
Optical return loss measures reflections back toward the laser transmitter; high reflections can destabilize the laser, increase relative intensity noise (RIN), and degrade CNR in the RF system.
Question 6: What is the typical downstream optical power budget for a single-fiber HFC node span?
- 1–3 dBm
- 5–10 dBm (Correct answer)
- 15–20 dBm
- −10 to −5 dBm
Correct answer: 5–10 dBm
HFC optical transmitters typically launch 5–10 dBm of downstream optical power to provide sufficient margin after fiber attenuation and splitting losses to the node receiver.
BDS Fiber Optic Systems and HFC Architecture 1
What does HFC stand for in cable broadband architecture?