LED Structures – Multiple Choice Questions and Answers (MCQs)

Set of MCQs (Multiple Choice Questions & Answers) with Answers on LED Structures of Optical Sources: The Laser and Light – Emitting Diode in ECE (Electronics & Communication Eng.).

1. The amount of radiance in planer type of LED structures is ____________
a) Low
b) High
c) Zero
d) Negligible

2. In optical fiber communication _____________ major types of LED structures are used.
a) 2
b) 4
c) 6
d) 3

3. As compared to planar LED structure, Dome LEDs have ______________ External power efficiency ___________ effective emission area and _____________ radiance.
a) Greater, lesser, reduced
b) Higher, greater, reduced
c) Higher, lesser, increased
d) Greater, greater, increased

4. The techniques by Burros and Dawson in reference to homo structure device is to use an etched well in GaAs structure.
a) True
b) False

5. In surface emitter LEDs, more advantage can be obtained by using ____________
a) BH structures
b) QC structures
c) DH structures
d) Gain-guided structure

6. Internal absorption in DH surface emitter Burros type LEDs is ____________
a) Cannot be determined
b) Negligible
c) High
d) Very low

7. DH surface emitter generally give ____________
a) More coupled optical power
b) Less coupled optical power
c) Low current densities
d) Low radiance emission into-fiber

8. A DH surface emitter LED has an emission area diameter of 60μm. Determine emission area of source.
a) 1.534*10-6
b) 5.423*10-3
c) 3.564*10-2
d) 2.826*10-9

9. Estimate optical power coupled into fiber of DH SLED having emission area of 1.96*10-5, radiance of 40 W/rcm2, numerical aperture of 0.2 and Fresnel reflection coefficient of 0.03 at index matched fiber surface.
a) 5.459*10-5
b) 1.784*10-3
c) 3.478*102
d) 9.551*10-5

10. In a multimode fiber, much of light coupled in the fiber from an LED is ____________
a) Increased
b) Reduced
c) Lost
d) Unaffected

11. Determine the overall power conversion efficiency of lens coupled SLED having forward current of 20 mA and forward voltage of 2 V with 170 μWof optical power launched into multimode step index fiber.
a) 1.256*10-5
b) 4.417*102
c) 4.25*10-3
d) 2.14*10-3

12. The overall power conversion efficiency of electrical lens coupled LED is 0.8% and power applied 0.0375 V. Determine optical power launched into fiber.
a) 0.03
b) 0.05
c) 0.3
d) 0.01

13. Mesa structured SLEDs are used ____________
a) To reduce radiance
b) To increase radiance
c) To reduce current spreading
d) To increase current spreading

14. The InGaAsP is emitting LEDs are realized in terms of restricted are ____________
a) Length strip geometry
b) Radiance
c) Current spreading
d) Coupled optical power

15. The active layer of E-LED is heavily doped with ____________
a) Zn
b) Eu
c) Cu
d) Sn

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