In optical fibers, followingstatements are given :1. 1550 nm is zero dispersion Wavelength.2. 1330 nm is zero dispersion Wavelength.3. At 1330 nm, attenuation is Minimum.,4. At 1550 nm, attenuation is Minimum.

Which one of the following is correct ?(A) 1 and 4 are true.(B) 1 and 3 are true.(C) 2 and 4 are true.(D) 1, 2 and 3 are true.

List I List IIa. 1550 nm i. 100 GHzb. 0.8 nm ii. Visible lightc. 400-700 nm iii. Ultra violetd. 200 nm iv. 193 T HzCodes : A b c d(A) iv i ii iii(B) iv ii i iii(C) i ii iii iv(D) iv iii i ii

Assertion (A) : An EDFA is usually pumped at 980 nm wavelength, which means that Erbium ions at ground level absorb energy.Reason (R) : This absorbed energy is transferred to high frequency signals to boost up ans:A

.Assertion (A) : Optical fibers have broader bandwidth compared to conventional copper cables.Reason (R) : Low power LASER beams are considered to be very powerful as compared to high power ordinary light beams.

Ans: B

Consider the following statements :Losses in optical fibers are caused by1. Impurities in the fibre material2. Microbending3. Splicing4. Step index profileOf these statements :(A) 1, 3 & 4 are correct.(B) 2, 3 & 4 are correct.(C) 1, 2 & 3 are correct.(D) 1, 2 & 4 are correct. ( NET JUNE 14 III)

Assertion (A) : In optical fibre communication, light rays are guided by the total internalreflection at the interface between fibre core and cladding.Reason (R) : The Refractive Index of core is large than the Refractive Index of claddingans:AAssertion (A) : Optical fiber provides the attenuation of the order of 0.2 dB/km.Reason (R) : Rayleigh scattering increases with the increase in the operatingwavelength.ans:c

(A) : Stimulated emission is the key to the operation ofLASER.Reason (R) : An important property of LASER radiation is itscoherence, under which is meant the correlation between the phases of oscillation at different positions in space and at various moments of time

ans:B

(A) : A step graded junction is formed when there is an abrupt change from acceptor ion on one side to donor ions on the other side.Reason (R) : In step graded junctions,donor and acceptor concentrations are unequal and these junctions behaves as asymmetric junctions. Ans:A

Assertion (A): Optical fibers have broader band width to conventional copper cable. Reason (R) : The information carrying capacity of optical fibers is limited by Rayleigh scattering

Assertion (A): Optical fibers have broader band width to conventional copper cable. Reason (R) : The information carrying capacity of optical fibers is limited by dispersion

ans:B

ans : A or B

Assertion (A):LASER is a low noise optical source.Reason (R) : LASER operation is carried out in cryogenic temperature

A:modern optical communication systems use the 1.55m.R:pulse dispersion in optical fibers is minimum at 1.55m (JUNE 09)

C

Consider the quantum efficiency of the detector in optical communication.(i) Photo diode (ii) Photo transistor(iii) APD (iv) PIN diodeWrite the quantum efficiency of the above devices in decreasing order.(A) (iii) (iv) (ii) (i)(B) (iv) (iii) (ii) (i)(C) (ii) (i) (iii) (iv)(D) (i) (ii) (iii) (iv

List-I List-II(a) EDFA (i) Ability to collect the light(b) LASER (ii) Optical Amplifiers(c) Numerical Aperture (iii) Spontaneous Emission(d) LED (iv) Stimulated EmissionCodes : (a) (b) (c) (d)(A) (iii) (ii) (i) (iv)(B) (ii) (iv) (i) (iii)(C) (iv) (ii) (i) (iii)

Photo diode is reverse biased because(A) only one side is illuminated(B) majority carriers flow under these conditions.(C) reverse current is small as compared to photo current(D) reverse current is large as compared to photo current (NET SEP 13 III)

In optical fiber communication systems, FBG is used for(A) Dispersion compensation(B) Long haul communication(C) Non-linearity management(D) Source

Consider the following statements :(i) Rayleigh Scattering losses areproportional to1/()4(ii) The operating frequency of opticalfiber is 193 T Hz(iii) In III transmission windows, theattenuation is 5 dB/km.Which one is correct ?(A) (i) and (ii)(B) (ii) and (iii)(C) (i) and (iii)(D) (i), (ii) and (iii) (NET SEP 13 III)

.the following is true for multimode graded index fiber:1. the R.I varies as the function of radial distance from the centre2.the R.I undergoes sudden change at the the cladding boundary 3.it provides better band width and the data rate than the multimode step index 4.it provides the better bandwidth and data rate than single mode step indexa. 1,3b. 2,4c.1,4d.3,4 (NET DEC 14II)

the following are correct about a semiconductor LASER:1. it requires population inversion 2.it has shorter lifetime than LED3.it demonostrates spontaneous emission phenomenon 4.it genertates monochromatic incoherent light Find out the correct answersa.1,2b.1,3c.1,4d.2,4 .

The wavelength region 1.55m is important in optical communication because 1.it can be detected by Si PIN diode2.it corresponds to minimum attenuation3. it corresponds to minimum dispersion4.it can be amplified optically.1,2 are correctb.2,3 are correctc. 3,4 are correct d.2,4 are correct.

Inter modal dispersionphotodiodeIntramodal dispersionlaserResponsivetymultimode fiberQuantum efficiencysingle mode fiber(JUNE 09)