Learn the key facts about coherent transmission in WDM systems covered on the Nokia 4A0-205 certification exam, including the need for carrier phase information at the receiver.
Table of Contents
Question
Which of the following statements about coherent transmission in WDM technology is TRUE?
A. Coherent systems need carrier phase information at the receiver.
B. Only multi-mode fibers can be used with coherent transmissions.
C. The channel allocation is flexible, according to the channel size of the signals.
D. At each receiver, a dispersion compensation unit is often necessary, depending on the fiber length.
Answer
A. Coherent systems need carrier phase information at the receiver.
Explanation
In coherent optical transmission systems, the phase of the optical carrier is used to encode information in addition to the amplitude. This allows for higher spectral efficiency and longer transmission distances compared to intensity modulation direct detection (IM-DD) systems. However, it requires the receiver to recover the phase of the incoming optical signal, which is done through a local oscillator laser that beats with the incoming signal.
The other statements are false:
B. Both single-mode and multi-mode fibers can be used with coherent transmission. Coherent detection works with the single spatial mode of SMF.
C. The channel allocation in WDM systems is fixed by the ITU-T grid, not flexibly allocated based on signal bandwidth.
D. Coherent receivers use digital signal processing to compensate for chromatic dispersion, so inline optical dispersion compensators are not needed.
In summary, a key aspect of coherent transmission is that the receiver must recover the phase of the optical carrier, but it is compatible with single-mode fiber, uses fixed WDM channel spacing, and can compensate for fiber dispersion effects without optical dispersion compensators. Understanding these fundamental concepts is important for the Nokia 4A0-205 exam.
Nokia 4A0-205 certification exam assessment practice question and answer (Q&A) dump including multiple choice questions (MCQ) and objective type questions, with detail explanation and reference available free, helpful to pass the Nokia 4A0-205 exam and earn Nokia 4A0-205 certification.