LED Characteristics

Optical Communications

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

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

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

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

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. 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

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

7. 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

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

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

10. 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

11. 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

12. 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

13. 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

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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