LED Characteristics MCQ’s

This set of Optical Communication Multiple Choice Questions & Answers (MCQs) focuses on “LED Characteristics”.

1. Linearizing circuit techniques are used for LEDs.
a) True
b) False

2. The internal quantum efficiency of LEDs decreasing _______________ with ________________ temperature.
a) Exponentially, decreasing
b) Exponentially, increasing
c) Linearly, increasing
d) Linearly, decreasing

3. Intrinsically _________________ are a very linear device.
a) Injection lasers
b) DH lasers
c) Gain-guided
d) LEDs

4. To utilize _____________________ of SLDs at elevated temperatures, the use of thermoelectric coolers is important.
a) Low-internal efficiency
b) High-internal efficiency
c) High-power potential
d) Low-power potential

5. The active layer composition must be adjusted if a particular center wavelength is desired.
a) True
b) False

6. The optical 3 dB point occurs when currents ratio is equal to _____________
a) 83
b) 22
c) 12
d) 34

7. For particular materials with smaller bandgap energies operating in _____________ wavelength, the linewidth tends to ______________
a) 2.1 to 2.75 μm, increase
b) 1.1 to 1.7 μm, increase
c) 2.1 to 3.6 μm, decrease
d) 3.5 to 6 μm, decrease

8. In optical fiber communication, the electrical signal dropping to half its constant value due to modulated portion of optical signal corresponds to _______
a) 6 dB
b) 3 dB
c) 4 dB
d) 5 dB

9. The optical bandwidth is _____________ the electrical bandwidth.
a) Smaller
b) Greater
c) Same as
d) Zero with respect to

10. The optical power at 20 MHz is 246.2 μW. Determine dc drive current applied to device with carrier recombination lifetime for LED of 6ns.
a) 3.48*10-4
b) 6.42*10-9
c) 1.48*10-3
d) 9.48*10-12

11. The 3 dB electrical bandwidth B is 42 MHz. Determine 3dB optical bandwidth Bopt.
a) 45.18
b) 59.39
c) 78.17
d) 94.14

12. When a constant d.c. drive current is applied to device, the optical o/p power is 320 μm. Determine optical o/p power when device is modulated at frequency 30 MHz with minority carrier recombination lifetime of LED i.e. 5ns.
a) 4.49*10-12
b) 6.84*10-9
c) 1.29*10-6
d) 2.29*10-4

13. Determine the 3 dB electrical bandwidth at 3 dB optical bandwidth Bopt of 56.2 MHz.
a) 50.14
b) 28.1
c) 47.6
d) 61.96

14. Determine degradation rate βrif constant junction temperature is 17 degree celsius.
a) 7.79*10-11
b) 7.91*10-11
c) 6.86*10-11
d) 5.86*10-11

15. Determine CW operating lifetime for LED with βrt = -0.58 and degradation rate βr = 7.86*10-11 h-1.
a) 32.12
b) 42
c) 22.72
d) 23.223

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