Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 7th Semester (Seventh Semester) 2018-2019 NEC 701 Optical Communication Question Paper
Paper 111: 130816 Roll No. I I I I I I 7 I I D
B.TECH
(SEM. VII) THEORY EXAMINATION 2018-19
OPTICAL COMMUNICATION
Time: 3 Hours T otal Marks: 100
Note: 1. Attempt all Sections.
2. Assume any missing data.
SECTION A
l. Attempt all questions in brief. 2 x10 = 20
State Goos-Hanchen effect?
What is the principle used in the working of ?bers as light guides?
What are step index and graded index ?bers?
What is pulse broadening?
Discuss the advantage and disadvantage of LED.
What is threshold current density of LASER? ?
What type of HOISC present in optical receiver2.
De?ne avalanche effect ? 1 '
What are the methods used for error detecuon and correction in an optical hnk
design? 1 1 ? 1? '
I. Write short note on Power pendines?7 ii;
,I
9-9.7?
F'Fqc r19
SECTION B
2. Attempt any three of the followmg ? 10 x 3= 30
a. What do you mean by Acceptance angle of an optical ?ber? Denve an expression for
numerical aperture of opticall ?ber A silica optical ?ben with a core diameter large
enough to be considered by ray theory analysis has a co?e refractive index of l. 5 and
cladding refractive index of I .47 determine Critical 511gle at core cladding interface,
NA tor the ?ber and Acceptance angle. 1
b. Describe the mechanism of intermodal disperston in a multimode step index ?ber.
Show that the total broadening of light pulse 6T5 due to intermodal dispersion in a
multimode step index ?ber may be gWen by STS ?:74? where L 15 the ?ber length,
NA 15 numerical aperture, 11; is the eore refractive index and c is the velocity of light.
e. Discuss Hetero- Junction in; Light Emitting Diode (LED). Explain the ef?ciency and
modulation capability of LED.
d. Explain the physical principle of AFB. What is the temperature effect on avalanche
gain? Describe Automatic gain control using OP-AMP.
e. Draw and explain avalanche photodiode receiver and derive expression for SNR.
MANISH KUMAR JHA I 24-DeC-2018 13:37:26 I 106.198.247.35
SECTION C
3. Attempt any one parts of the following: 10 x l = 10
:1. Sketch the block diagram of optical ?ber communication system. With the suitable
ray diagram, explain the propagation of skew rays in the optical waveguide and
compare it with meridional rays.
b. What is phase velocity & group velocity? Derive the relation between group velocity
& group index ofthe guide.
4. Attempt any one parts of the following: 10 x l = 10
a) Describe with the aid of simple ray diagrams:
(i) the multimode step index ?ber,
(ii) the single mode step index ?ber.
Compare the advantages and disadvantages of these two types of ?ber for use as an
optical channel.
b) What is Modal Birefringence? The beat length in a single- mode optical ?ber is 9 cm
when light from an injection laser with a spectral line width of 1 nm and a peak
wavelength of 0.9pm is launched into it. Determine the modal birefringence and
estimate the coherence length in this situation. In aggition calculate the difference
between the propagation constants for the two orthogonal modes and check the result
5. Attempt any one parts of the following: . 10 x 1= 10 1
a) Explain the working principle of LED How the quantum efficiency of a LEDI?g-t
de?ned? List out various parameters WhIc?h are needed to be optimized for getting
maximum output power from the LED '
b) Explain the principle of semiconductor lasers and, draw the emission characterlstlc A
ruby LASER contains a crystal length 4cm with refractive index of l 78. The peak
emission wavelength from the device is 0. 55pm. Determine ?the number of
longitudinal modes and then? frequency separation.
6. Attempt any one parts of the following: I?. 10 x l = 10
:1) Discuss the various factors which effect the launching .5on optical signal into ?ber
Determine the power coupled into step index ?ber whoSe nI=1.,48 n2 = l 4.6 if
surface emitting L ED radiates lSOpW of power ' '
b) Explain the working of PIN photodiode. A p-I?n photodiode has a quantum ef?ciency
of 55% at a wavelength of 0.9 micrometer Calculate
(i). Its responsivity at O 9 micrometer:
i
(ii). The received optical power Ifthe mean photocurrent is 10'8 A.
(iii). The corresponding numbergof received photons at this wavelength.
7. Attempt any one parts of the foliowmg 10 x l = 10
a) De?ne bit error rate (BER) of digital optical receiver. Obtain its expression for binary
receiver assuming noise distribution to be Gaussian.
b) Draw a block. diagram and explain the principle of coherent detection method in
optical ?ber. ,
MANISH KUMAR JHA | 24-Dec-2018 13:37:26 | 106.198.247.35
This post was last modified on 29 January 2020