1. Determine the internal quantum efficiency generated within a device when it has a radiative recombination lifetime of 80 ns and total carrier recombination lifetime of 40 ns.
Correct : B. 80 %
2. Compute power internally generated within a double-heterojunction LED if it has internal quantum efficiency of 64.5 % and drive current of 40 mA with a peak emission wavelength of 0.82 μm.
Correct : B. 0.039
3. The Lambertian intensity distribution __________ the external power efficiency by some percent.
Correct : A. reduces
4. A planar LED fabricated from GaAs has a refractive index of 2.5. Compute the optical power emitted when transmission factor is 0.68.
Correct : C. 2.72 %
5. A planar LED is fabricated from GaAs is having a optical power emitted is 0.018% of optical power generated internally which is 0.018% of optical power generated internally which is 0.6 P. Determine external power efficiency.
Correct : D. 0.9%
6. For a GaAs LED, the coupling efficiency is 0.05. Compute the optical loss in decibels.
Correct : C. 13.01 db
7. In a GaAs LED, compute the loss relative to internally generated optical power in the fiber when there is small air gap between LED and fiber core. (Fiber coupled = 5.5 * 10-4Pint)
Correct : B. 32.59 db
8. Determine coupling efficiency into the fiber when GaAs LED is in close proximity to fiber core having numerical aperture of 0.3
Correct : A. 0.9
9. If a particular optical power is coupled from an incoherent LED into a low-NA fiber, the device must exhibit very high radiance . State whether the given statement is true or false.
Correct : A. true
10. The amount of radiance in planer type of LED structures is
Correct : A. low
11. In optical fiber communication, ______________ major types of LED structures are used
Correct : C. 6
12. As compared to planar LED structure, Dome LEDs have ______________ External power efficiency, ____________ effective emission area and _____________ radiance.
Correct : B. higher, greater, reduced
13. The techniques by Burros and Dawson in reference to ho*mo structure device is to use an etched well in GaAs structure. Determine the given statement is True or false.
Correct : A. true
14. In surface emitter LEDs, more advantage can be obtained by using
Correct : C. dh structures
15. Internal absorption in DH surface emitter Burros type LEDs is
Correct : D. very low
16. DH surface emitter generally give
Correct : A. more coupled optical power
17. A DH surface emitter LED has an emission area diameter of 60μm. Determine emission area of source
Correct : D. 2.826*10-9
18. 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.
Correct : D. 9.551*10-5
19. In a multimode fiber, much of light coupled in the fiber from an LED is
Correct : C. lost
20. 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.
Correct : C. 4.25*10-3
21. 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
Correct : A. 0.03
22. Mesa structured SLEDs are used
Correct : C. to reduce current spreading
23. The InGaAsP is emitting LEDs are realized in terms of restricted
Correct : A. length strip geometry
24. The active layer of E-LED is heavily doped with
Correct : A. zn
25. Intrinsically _________________ are a very linear device.
Correct : D. leds
26. Linearizing circuit techniques are used for LEDs. State whether the given statement is true or false.
Correct : A. true
27. The internal quantum efficiency of LEDs decreasing _______________ with ________________ temperature.
Correct : B. exponentially, increasing
28. To utilize _____________________ of SLDs at elevated temperatures, the use of thermoelectric coolers is important.
Correct : C. high-power potential
29. For particular materials with smaller bandgap energies operating in _____________ wavelength, the linewidth tends to ______________
Correct : B. 1.1 to 1.7 μm, increase
30. The active layer composition must be adjusted if a particular center wavelength is desired.State whether the given statement is true or false.
Correct : A. true
31. In optical fiber communication, the electrical signal dropping to half its constant value due to modulated portion of optical signal corresponds to _______
Correct : B. 3 db
32. The optical 3 dB point occurs when currents ratio is equal to
Correct : C. ½
33. The optical bandwidth is _____________ the electrical bandwidth.
Correct : B. greater
34. 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.
Correct : D. 2.29*10-4
35. 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.
Correct : A. 3.48*10-4
36. Determine the 3 dB electrical bandwidth at 3 dB optical bandwidth Bopt of 56.2 MHz.
Correct : B. 28.1
37. The 3 dB electrical bandwidth B is 42 MHz. Determine 3dB optical bandwidth Bopt:
Correct : B. 59.39
38. Determine degradation rate βrif constant junction temperature is 17 degree celsius.
Correct : A. 7.79*10-11
39. Determine CW operating lifetime for LED with βrt = -0.58 and degradation rate βr= 7.86*10-11 h-1.