BDS Fiber Optic Systems in HFC 2

Question 1

What does ONU stand for in fiber access networks?

Accepted Answer

Optical Network Unit

Answer

An Optical Network Unit (ONU) is a device at the subscriber end of a passive optical network (PON) that converts optical signals to electrical signals for delivery to the customer's devices.

Question 2

What is the typical wavelength used for downstream transmission in standard single-mode HFC fiber links?

Accepted Answer

1550 nm

Answer

1550 nm is the standard downstream wavelength for HFC analog/digital RF-over-fiber transmission because fiber has its lowest attenuation (~0.2 dB/km) at this wavelength, enabling long spans.

Question 3

What is chromatic dispersion in fiber optics?

Accepted Answer

The spreading of optical pulses over distance because different wavelengths travel at slightly different speeds in the fiber

Answer

Chromatic dispersion causes different wavelength components of an optical signal to travel at different velocities, causing pulse broadening that limits bandwidth-distance product in fiber links.

Question 4

What is the difference between single-mode and multimode fiber?

Accepted Answer

Single-mode has a smaller core that allows only one propagation mode, enabling longer distances; multimode has a larger core supporting many modes but is limited to shorter distances

Answer

Single-mode fiber (8–10 µm core) confines light to a single propagation mode, eliminating modal dispersion and enabling spans of tens of kilometers, while multimode fiber (50–62.5 µm core) supports shorter runs up to ~2 km.

Question 5

What is an EDFA and where is it used in HFC networks?

Accepted Answer

Erbium-Doped Fiber Amplifier — used to optically amplify 1550 nm signals in long fiber spans

Answer

An EDFA (Erbium-Doped Fiber Amplifier) amplifies optical signals at 1550 nm without converting to electrical form, enabling long-distance or wide-area fiber distribution without intermediate O/E/O conversion.

BDS - Broadband Distribution Specialist Practice Test

BDS - Broadband Distribution Specialist Practice Test

BDS Fiber Optic Systems in HFC 2