Optical Communications Questions and Answers – Demodulation Schemes

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This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Demodulation Schemes”.

1. _________ heterodyne detection does not require phase matching between the incoming signal and the local oscillator.
a) Synchronous
b) Asynchronous
c) Noisy
d) Spatial
View Answer

Answer: b
Explanation: For heterodyne detection, a beat note signal produces the IF signal which is obtained using the square law optical detector. Hence, it does not require phase matching.
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2. In ___________ detection, the phase of the local oscillator signal is locked to the incoming signal.
a) Homodyne
b) Heterodyne
c) Spatial
d) Noisy
View Answer

Answer: a
Explanation: Phase diversity and multiport detection is considered to be a form of heterodyne detection. In case of homodyne detection, the incoming signal is bundled with the phase of the local oscillator signal.

3. The introduction of nonlinear element within the ______ is necessary to enable efficient carrier recovery.
a) PSK
b) ASK
c) FSK
d) PLL
View Answer

Answer: d
Explanation: Carrier recovery is done by slightly reducing the depth of the phase modulation. This is done by the introduction of the nonlinear within the phase locked loop(PLL).

4. What is the main attraction of the optical homodyne detection?
a) Receiver sensitivity
b) Transmission power
c) Modulation scheme
d) Line width
View Answer

Answer: a
Explanation: The main attraction of optical homodyne detection is the potential 3dB improvement in the receiver sensitivity. It also eases the receiver bandwidth requirement considerably.
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5. The phase difference between the local oscillator and the source must be ________ for high sensitivity reception.
a) Deep
b) High
c) Direct
d) Near zero
View Answer

Answer: d
Explanation: The phase difference must be held near zero for high sensitivity reception. As it moves towards 90 degrees, the output signal current becomes zero and the detection process will cease.

6. How many strategies of homodyne demodulation have proved to be successful for coherent optical fiber reception?
a) One
b) Three
c) Four
d) Two
View Answer

Answer: d
Explanation: Two homodyne demodulation strategies have been successful for optical fiber reception. They are the use of either a pilot carrier or a decision-driven optical phase locked loop.

7. In the __________ receiver, the incoming signal is not precisely shifted to the baseband.
a) Intra-dyne
b) Heterodyne
c) Homodyne
d) Optical
View Answer

Answer: a
Explanation: In homodyne detection, the incoming signal is precisely shifted to the baseband. In intra-dyne receiver, the incoming signal is shifted to a frequency lower than the transmission rate.
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8. The use of PLL can be avoided in the intra-dyne detection. State whether the given statement is true or false.
a) False
b) True
View Answer

Answer: b
Explanation: In intra-dyne receiver, the incoming signal is lower than the transmission rate. In place of PLL, a baseband filter in the form of electrical filtering can be used.

9. Phase diversity reception is also referred to as ______________
a) Homodyne detection
b) Noisy detection
c) Homodyne detection
d) Multiport detection
View Answer

Answer: d
Explanation: In phase diversity reception, phase is not locked. It also has bandwidth advantage over homodyne detection as it converts the incoming signal directly to baseband.

10. The received signal through polarization diversity reception is linearly polarized. State whether the given statement is true or false.
a) False
b) True
View Answer

Answer: a
Explanation: The received optical signal through polarization diversity reception is elliptically polarized. It is also uncontrollable unlike coherent receivers.

Sanfoundry Global Education & Learning Series – Optical Communications.
To practice all areas of Optical Communications, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn