# Optical Amplifier MCQ

## Optical Amplifier MCQ

Optical Amplifier MCQ, Multiple Choice Questions on Optical Amplifier, Optical Amplifier Objective Questions with Answer, GATE Question on Optical Amplifier, Semiconductor Optical Amplifiers (SOAs) Objective Questions, Raman fiber amplifiers (RFAs) MCQ, Erbium-doped fiber amplifiers (EDFAs) MCQ

### Multiple Choice Questions

Q.1 Optical amplifiers can be used as

• pre-amplifiers to precede the optical receiver.
• in-line amplifiers to compensate for fiber loss.
• power amplifiers to follow the optical transmitter.
• all of these.

Q.2. The difference between a regenerator and an optical amplifier can be best described by one of the following statements:

• A regenerator amplifies as well as restores the optical signal transmitted.
• A regenerator converts the optical signal into the electrical signal for amplification and then reconverts it into the optical domain, whereas an optical amplifier operates only in the optical domain.
• An optical amplifier compensates for transmission loss.
• Both are identical and as such there is no difference between the two.

Answer: A regenerator converts the optical signal into the electrical signal for amplification and then reconverts it into the optical domain, whereas an optical amplifier operates only in the optical domain.

Q.3. The difference in the structure of a semiconductor laser and a semiconductor optical amplifier can be best described by one of the following statements:

• The SOA is pumped electrically.
• The end facets of the active region have 50% reflectivity.
• The end facets of the active region have 100% reflectivity.
• The end facets of the active region in the SOA have 0% reflectivity.

Answer: The end facets of the active region in the SOA have 0% reflectivity.

Q.4. An optical amplifier when used as pre-amplifier has ____ optical gain and _____ maximum output power as compared to that of when used as in-line amplifier.

• low; low
• high; high
• low; high
• high; low

Q.5. The use of FP resonator which provides optical feedback, can _____ the gain of a semiconductor optical amplifier.

• significantly decrease
• significantly increase
• marginally increase
• marginally decrease

Q.6. The mirror reflectivity in typical SOAs is around

• 100%.
• 50%.
• 30%.
• 0%.

Q.7. Statement I: In a Fabry–Perot semiconductor optical amplifier, the input optical signal that enters the active region is reflected several times from cleaved facets and leaves the cavity with optical gain.

Statement II: In traveling-wave semiconductor laser amplifier, an input optical signal is amplified by a single passage through the active region with no optical feedback.

• Statement I is correct but Statement II is incorrect.
• Statement I is incorrect but Statement II is correct.
• Statement I as well as Statement II are correct.
• Statement I as well as Statement II are incorrect.

Answer: Statement I as well as Statement II are incorrect.

Q.8. Average total power of Amplified Spontaneous Emission (ASE) is given as

• $P_{ASE}=n_{sp}hfG(BW)$
• $P_{ASE}=2n_{sp}hfG(BW)$
• $P_{ASE}=(1/2)n_{sp}hfG(BW)$
• $P_{ASE}=\left [2n_{sp}hfG(BW) \right ]^{2}$

Answer: $P_{ASE}=2n_{sp}hfG(BW)$

Q.9. The optical gain and optical bandwidth in case of FPA as well as TWA are related to each other by the expression

• $BW_{TWA}\times \sqrt{G_{s}}\gg BW_{FPA}\times \sqrt{G_{FPA}(max)}$
• $BW_{TWA}\times \sqrt{G_{s}}\leq BW_{FPA}\times \sqrt{G_{FPA}(max)}$
• $BW_{TWA}\times \sqrt{G_{s}}\ll BW_{FPA}\times \sqrt{G_{FPA}(max)}$
• $BW_{TWA}\times \sqrt{G_{s}}\geq BW_{FPA}\times \sqrt{G_{FPA}(max)}$

Answer: $BW_{TWA}\times \sqrt{G_{s}}\gg BW_{FPA}\times \sqrt{G_{FPA}(max)}$

Q.10. The polarization dependence in SOAs can be reduced by

• making the active region as square as possible in cross-section.
• connecting two SOAs in series or in parallel to compensate for unequal gain in ortho–polarization.
• providing a double pass through the same active region.
• Any of these methods.

Q.11. Statement I: Raman gain (GR) becomes larger as fiber length L increases upto around 50 km where it reaches an almost constant value.

Statement II: Raman gain (GR) is increased as fiber core diameter is increased.

• Statement I is correct but Statement II is incorrect.
• Statement I is incorrect but Statement II is correct.
• Both Statements I as well as Statement II are correct.
• Both Statements I as well as Statement II are incorrect.

Answer: Statement I is correct but Statement II is incorrect.

Q.12. Raman fiber amplifiers are similar to Erbium-doped fiber amplifier in the sense that

• both of them operate in an all-optical domain.
• both of them can be used around the 1550-nm optical window.
• both of them can be employed for multichannel operation.
• both of them operate in the all-optical domain, can be used around the 1550-nm optical window as well as can be employed for multichannel operation.

Answer: both of them operate in all-optical domain, can be used around the 1550-nm optical window as well as can be employed for multichannel operation.

Q.13. EDFAs generally operate in the wavelength region near

• 1550 nm and can offer capacities exceeding 1000 Gbps.
• 850 nm and can offer capacities around 100 Gbps.
• 1150 nm and can offer capacities around 1000 Gbps.
• 1550 nm and can offer capacities around 100 Gbps.

Answer: 1550 nm and can offer capacities exceeding 1000 Gbps.

Q.14. Statement I: EDFAs are self-regulating amplifiers.

Statement II: The active medium in an EDFA is a small section of silica fiber which is heavily doped with rare-earth element erbium.

Statement III: EDFAs have been deployed in terrestrial and submarine links

• Only statements I and III are correct.
• Only statement II is correct.
• Only statements II and III are correct.
• Statements I , II as well as III all are correct.

Answer: Statements I , II as well as III all are correct.

Q.15. EDFA differs from a Raman fiber amplifier (RFA) in the way that

• An EDFA requires population inversion while the RFA does not.
• An EDFA operates on the principle of stimulated emission.
• A RFA operates on the principle of stimulated Raman scattering.
• Both operate on the same principle.

Answer: An EDFA requires population inversion while the RFA does not.

Q.16. Statement I: A co-propagating pump EDFA features higher output optical power with low noise.

Statement II: a counter-propagating pump EDFA provides lower output optical power but produces greater noise too.

• Statement I is correct but Statement II is incorrect.
• Statement I is incorrect but Statement II is correct.
• Both Statements I as well as Statement II are correct.
• Both Statements I as well as Statement II are incorrect.

Answer: Both Statements I as well as Statement II are incorrect.

Q.17. Which wavelength is the most appropriate one for pumping an EDFA?

• 850 nm
• 980 nm
• 1300 nm
• 1550 nm

Q.18. The optical gain in an EDFA depends on the following factors.

• Doping concentration
• Pump power
• Length of the doped fiber
• All of these

Q.19. The main difference between an SOA and an EDFA is that

• An SOA operates in the electrical domain, whereas the EDFA operates in the optical domain.
• An SOA is pumped electrically, whereas the EDFA is pumped optically.
• An SOA is pumped optically, whereas the EDFA is pumped electrically.
• An SOA amplifies 1300 nm wavelength, whereas the EDFA amplifies 1550 nm.

Answer: An SOA is pumped electrically, whereas the EDFA is pumped optically.

Q.20. Noise figure of EDFAs will be typically

• < 3 dB.
• 2.5–4.5 dB.
• 3.5–9 dB.
•  > 9 dB.