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LED MCQs | LED Short Questions and Answers

Questions
41 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

Answer: 9.551*10-5
42 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

Answer: 3 dB
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43 The optical 3 dB point occurs when currents ratio is equal to
A ⅝
B ⅔
C ½
D ¾

Answer: ½
44 The optical bandwidth is _____________ the electrical bandwidth.
A Smaller
B Greater
C Same as
D Zero with respect to

Answer: Greater
45 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

Answer: 2.29*10-4
46 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

Answer: 3.48*10-4
47 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

Answer: 28.1
48 In surface emitter LEDs, more advantage can be obtained by using
A BH structures
B QC structures
C DH structures
D Gain-guided structure

Answer: DH structures
49 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 All the above

Answer: Higher, greater, reduced
50 The amount of radiance in planer type of LED structures is
A Low
B High
C Zero
D Cannot be determined

Answer: Low
51 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

Answer: 22.72
52 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 All above

Answer: 7.79*10-11
53 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

Answer: 59.39
54 In optical fiber communication, ______________ major types of LED structures are used
A 2
B 4
C 6
D 3

Answer: 6

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