Optical Communications Questions and Answers – Semiconductor Photodiodes With Internal Gain

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This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Semiconductor Photodiodes With Internal Gain”.

1. ___________ has more sophisticated structure than p-i-n photodiode.
a) Avalanche photodiode
b) p-n junction diode
c) Zener diode
d) Varactor diode
View Answer

Answer: a
Explanation: Avalanche photodiode is second major type of detector in optical communications. This diode is more sophisticated so as to create a much higher electric field region.
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2. The phenomenon leading to avalanche breakdown in reverse-biased diodes is known as _______
a) Auger recombination
b) Mode hopping
c) Impact ionization
d) Extract ionization
View Answer

Answer: c
Explanation: In depletion region, almost all photons are absorbed and carrier pairs are generated. So there comes a high field region where carriers acquire energy to excite new carrier pairs. This is impact ionization.

3. _______ is fully depleted by employing electric fields.
a) Avalanche photodiode
b) P-I-N diode
c) Varactor diode
d) P-n diode
View Answer

Answer: a
Explanation: APD is fully depleted by electric fields more than 104V/m. This causes all the drifting of carriers at saturated limited velocities.

4. At low gain, the transit time and RC effects ________
a) Are negligible
b) Are very less
c) Dominate
d) Reduce gradually
View Answer

Answer: c
Explanation: Low gain causes the dominance of transit time and RC effects. This gives a definitive response time and thus device obtains constant bandwidth.

5. At high gain, avalanche buildup time ________
a) Is negligible
b) Very less
c) Increases gradually
d) Dominates
View Answer

Answer: d
Explanation: High gain causes avalanche buildup time to dominate. Thus the bandwidth of device decreases as increase in gain.
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6. Often __________ pulse shape is obtained from APD.
a) Negligible
b) Distorted
c) Asymmetric
d) Symmetric
View Answer

Answer: c
Explanation: Asymmetric pulse shape is acquired from APD. This is due to relatively fast rise time as electrons are collected and fall time dictated by transit time of holes.

7. Fall times of 1 ns or more are common. State whether the given statement is true or false.
a) False
b) True
View Answer

Answer: b
Explanation: The use of suitable materials and structures give rise times between 150 and 200 ps. Thus fall times of 1 ns or more are common which in turn limits the overall response of device.

8. Determine Responsivity of a silicon RAPD with 80% efficiency, 0.7μmwavelength.
a) 0.459
b) 0.7
c) 0.312
d) 0.42
View Answer

Answer: a
Explanation: The Responsivity of a RAPD is given by-
R = ηeλ/hc A/w whereη=efficiency, λ=wavelength, h =Planck’s constant.

9. Compute wavelength of RAPD with 70% efficiency and Responsivity of 0.689 A/w.
a) 6μm
b) 7.21μm
c) 0.112μm
d) 3μm
View Answer

Answer: c
Explanation: The wavelength can be found from the Responsivity formula given by-
R = ηeλ/hc. The unit of wavelength isμm.
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10. Compute photocurrent of RAPD having optical power of 0.7 μw and responsivity of 0.689 A/W.
a) 0.23 μA
b) 0.489 μA
c) 0.123 μA
d) 9 μA
View Answer

Answer: b
Explanation: The photocurrent is given byIP=P0R. Here IP=photocurrent, P0=Power, R= responsivity.

11. Determine optical power of RAPD with photocurrent of 0.396 μAand responsivity of 0.49 A/w.
a) 0.91 μW
b) 0.32 μW
c) 0.312 μW
d) 0.80 μW
View Answer

Answer: d
Explanation: The photocurrent is given byIP=P0R. Here IP=photocurrent, P0=Power, R= responsivity.
P0=IP/R gives the optical power.

12. Determine the Responsivity of optical power of 0.4μW and photocurrent of 0.294 μA.
a) 0.735
b) 0.54
c) 0.56
d) 0.21
View Answer

Answer: a
Explanation: The photocurrent is given by IP=P0R. Here IP=photocurrent, P0=Power, R= responsivity.
R=IP/P0gives the responsivity.

13. Compute multiplication factor of RAPD with output current of 10 μAand photocurrent of 0.369μA.
a) 25.32
b) 27.100
c) 43
d) 22.2
View Answer

Answer: b
Explanation: The multiplication factor of photodiode is given by-
M=I/IP where I= output current, IP=photocurrent.
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14. Determine the output current of RAPD having multiplication factor of 39 and photocurrent of 0.469μA.
a) 17.21
b) 10.32
c) 12.21
d) 18.29
View Answer

Answer: d
Explanation: The multiplication factor of photodiode is given by-
M=I/IP where I= output current, IP=photocurrent. I=M*IP gives the output current inμA.

15. Compute the photocurrent of RAPD having multiplication factor of 36.7 and output current of 7μA.
a) 0.01 μA
b) 0.07 μA
c) 0.54 μA
d) 0.9 μA
View Answer

Answer: a
Explanation: The multiplication factor of photodiode is given by-
M=I/IP where I= output current, IP=photocurrent. IP=I/M Gives the output current inμA.

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