BDS Fiber Optic Systems and HFC Architecture 2 — Questions and Answers
Question 1: What is the purpose of a wavelength division multiplexer (WDM) in an HFC system?
- To combine multiple RF channels onto a single coaxial cable
- To combine or separate optical signals of different wavelengths on a single fiber (Correct answer)
- To convert between 1310 nm and 1550 nm optical signals
- To amplify multiple wavelengths simultaneously
Correct answer: To combine or separate optical signals of different wavelengths on a single fiber
A WDM allows multiple optical signals at different wavelengths to share a single fiber strand, increasing capacity without requiring additional fiber.
Question 2: What is clipping distortion in an HFC optical transmitter?
- Distortion caused by RF signal levels exceeding the linear range of the laser, causing the laser to momentarily turn off (Correct answer)
- Interference from adjacent wavelengths in a WDM system
- Noise generated by connectors with poor physical contact
- Distortion caused by fiber chromatic dispersion
Correct answer: Distortion caused by RF signal levels exceeding the linear range of the laser, causing the laser to momentarily turn off
Clipping occurs when the composite RF signal drives the laser below its lasing threshold, causing instantaneous cutoff and severe burst noise that degrades CNR and BER.
Question 3: What does the term 'node splitting' mean in HFC network evolution?
- Physically cutting a fiber to add a new splice point
- Dividing the coaxial service area of an existing node into smaller service groups with separate fiber feeds (Correct answer)
- Separating upstream and downstream signals onto different fibers
- Adding a second laser transmitter to a node for redundancy
Correct answer: Dividing the coaxial service area of an existing node into smaller service groups with separate fiber feeds
Node splitting reduces the number of homes passed per node by dividing a large service area into smaller groups, each with its own dedicated fiber, improving bandwidth per subscriber.
Question 4: What is the significance of the fiber's numerical aperture (NA) in HFC system design?
- NA determines the maximum data rate the fiber can carry
- NA describes the light-gathering ability of the fiber and affects splice and connector losses (Correct answer)
- NA specifies the fiber's operating temperature range
- NA determines the fiber's resistance to bending-induced loss
Correct answer: NA describes the light-gathering ability of the fiber and affects splice and connector losses
Numerical aperture describes the cone of light a fiber can accept; mismatches in NA between fiber segments or connectors increase coupling losses at splices and connections.
Question 5: A fiber span measures −3 dBm at the node receiver input. If the transmitter launches +7 dBm, what is the total optical path loss?
- 4 dB
- 7 dB
- 10 dB (Correct answer)
- 3 dB
Correct answer: 10 dB
Optical path loss equals the transmit power minus the received power: +7 dBm − (−3 dBm) = 10 dB total optical loss across the span.
Question 6: What is an OTDR used for in HFC fiber maintenance?
- Measuring the optical power level at a node receiver
- Locating faults, measuring splice losses, and characterizing fiber length using backscattered light (Correct answer)
- Testing the RF output of a node after optical-to-electrical conversion
- Measuring chromatic dispersion in a fiber span
Correct answer: Locating faults, measuring splice losses, and characterizing fiber length using backscattered light
An OTDR (Optical Time-Domain Reflectometer) sends light pulses into the fiber and analyzes backscattered reflections to locate breaks, measure splice losses, and determine fiber length.
BDS Fiber Optic Systems and HFC Architecture 2
What is the purpose of a wavelength division multiplexer (WDM) in an HFC system?