LED Short Questions and Answers

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

View Answer

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

View Answer

Answer: 3 dB

43 The optical 3 dB point occurs when currents ratio is equal to

A ⅝

B ⅔

C ½

D ¾

View Answer

Answer: ½

44 The optical bandwidth is _____________ the electrical bandwidth.

A Smaller

B Greater

C Same as

D Zero with respect to

View Answer

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

View Answer

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

View Answer

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

View Answer

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

View Answer

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

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