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Tuesday, August 5, 2014

OPTICAL FIBRE COMMUNICATION (OFC) DECEMBER 2012 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

(REVISED COURSE) KR-4695
(3 Hours) [Total Marks : 100]

N. B. : (1) Question No. 1 is Compulsory.
(2) Attempt any four questions out of remaining six questions.
(3) Figure to the right indicate full marks.

1. (a)	What are the advantages of optical fiber Communication ?	20
(b)	Explain Badwidth distance product.
(c)	What are Linearly Polarized modes ?
(d)	Compare direct band and indirect band semi conductors.
2. (a)	Derive the expression for Numerical Aperture of a step -index fiber. What will	10
	happen to N. A, If Cladding is removed ?
(b)	Compare step index and graded index fiber.	10
3. (a)	Starting from Maxwell's equation, derive the wave equation for step index fiber.	10
(b)	Explain the signifiance of V-number. Derive the expression for number of guided	10
	modes in graded index fiber.
4. (a)	What do you understand by intramodal dispersion ? Derive the expression for	10
	material dispersion.
(b)	What are the reasons for signal attenuation in a optical fiber ?	10
5. (a)	Give the structure of a surface emitting LED. Compare with an edge	10
	emitting LED.
(b)	Explain Avalanche Photodiode with proper structure and electric field. What is	10
	multiplication factor ?
6. (a)	What are splices ? Explain different types of splies.	10
(b)	Explain double Crucible method of fiber fabrication.	10
7.	Write short notes on any two :-	20
	(i) Linearly polarized modes
	(ii) OTDR
	(iii) Link Power Bugeting.

Monday, August 4, 2014

OPTICAL FIBRE COMMUNICATION (OFC) MAY 2012 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

Con.3705-12. (REVISED COURSE) GN-7643

(3 Hours) [Total Marks:-100]

N.B:- (1) Question No.1 is compulsory.
(2) Attempt any four from remaining six.
(3) All questions carry equal marks.

1. (a) Explain with a neat sketch the two categories of front end amplifiers used in optical
fiber communication systems. [5 Marks]
(b) State the spectral band designations used in optical fiber communications. [5 Marks]
(c) Discuss in brief single mode step index fiber and multimode step index fiber. [5 Marks]
(d) Name the key parameters for describing the signal transmission in single mode fiber and
multimode fibre. [5 Marks]

2. (a) Define the terms numerical apertures, critical angle, propagating modes and microbands
in the context of an optical fiber. [10 Marks]
(b) Calculate the required ∆ if a fiber with a 8 µm core and a 125 µm cladding is to be single
mode at 1300 mm. Assume that the core index is 1.46. [5 Marks]
(c) A 45˚ - 45˚ - 90˚ prism is immersed in alcohol (n=1.45). What is the minimum refractive
index the prism must have if a ray incident normally on one of the short faces is to be
totally reflected at the long face of an prism? [5 Marks]

3. (a) What do you understand by degenerating modes in step index fiber? [5 Marks]
(b) With a neat sketch explain fiber optical cable. [5 Marks]
(c) Name five connectors used in optical fiber communications. [5 Marks]
(d) What does the coupling efficiency equation? = (pf/ps) = (NA)² signify where pf is the
power coupled to the source ps source power. [5 Marks]

4. (a) What do you understand by double hetrostructure? State its limitations. [5 Marks]
(b) State the difference between LED and LASER. [5 Marks]
(c) A light source generating an optical power output equal to µw is coupled into an optical
fiber with a cross sectional area larger than the active area of the light source. Determine
the power coupled into the fiber. θ˚ equal to 15 ˚ [5 Marks]
(d) Draw the current optical power output curve for Fabry - perot Laser and explain to
relationships . [5 Marks]

5. (a) List all the parameters that contribute to photo current gain of APD. [5 Marks]
(b) Derive an expression for the responsibility "R" of the photo detector. [5 Marks]
(c) Briefly discuss the possible sources of noise in optical fiber receiver. Describe in
detail what is meant by quantum noise. Consider this phenomenon with regard to [10 Marks]
(I) Digital signalling
(ii) Analog transmission.

6. (a) In a point-to-point communication link it is given that launched power is - 10 dBm,
receiver sensitivity is - 40 dBm and the length of the link is 10 km. If the total losses in
the link add upto 27dB. Find the safety margin. If the fiber bandwidth is 1000 MHz.km
what is the maximum permissible data rate. If the risk time due to the source and the
detector is neglegible. [10 Marks]
(b) Draw and explain the test-set up for measuring the chromatic dispersion. [10 Marks]

7. Write short notes on any two:- [20 Marks]
(a) Linearly Polarized modes.
(b) Numerical aperture in GIF.
(c) Scattering losses in optical fiber.
(d) Distributed feed back laser.

OPTICAL FIBRE COMMUNICATION (OFC) MAY 2013 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

Con. 8209-13. (REVISED COURSE) GS-3268
(3 Hours) [Total Marks : 100]

N.B. : (1) Question No. 1 is Compulsory.
(2) Attempt any four questions out of remaining six questions.
(3) Assume suitable data wherever necessary.

1. (a)	Discuss the basic block diagram of optical communication system.	5
(b)	Draw the refractive index profile for the step index and graded index fiber. For	5
	each type give typical core and cladding diameters.
(c)	Differentiate between spontaneous and stimulated emissions.	5
(d)	Derive expression for the responsivity of an intrinsic photodetector in terms of	5
	quantum efficiency and wavelength.
2. (a)	Draw refractive index profile of a graded index fiber and show with neat diagram	10
	transmission of light through this fiber. Explain how GRIN fiber has transmission
	bit rate much higher than multimode step index fiber.
(b)	Find the core radius necassary for single mode operation at 820nm of stop index	10
	fiber with n1=1.482 and n2= 1.474. What is the numerical aperture and maximum
	acceptance angle of this fiber ? Calculate the corresponding solid angle.
3. (a)	List the importance factor responsible for power loss in optical fiber. Explain each	10
	factor briefly.
(b)	Explain interamodal and intermodal dispersion. How does despersion affect the	10
	transmission bandwidth of optical fibers.
4. (a)	What is the basic principle on which optical sources work ? With the help of a	10
	LED structure explain its working.
(b)	Draw the structure of Avalanche Photo Diode (ADP) along with the electric field	10
	profile that exist in the various regions of ADP structure. Explain the working.
5. (a)	Explain modified chemical vapour deposition (MVCD) method of fiber fabrication	10
	in detail.
(b)	Discuss a popular non-destructive technique for attenuation measurement.	10
6. (a)	Describe two methods of splicing individual fibers together. What are the	10
	advantage and disadvantage of each method.
(b)	What are the desirable requirement of a good fiber optic connector ? What are	10
	the lensing schemes for coupling improvement ?
7.	Write short notes on any two :-	20
	(a) OTDR
	(b) Link Power Budget
	(c) Coherent and Concoherent optical transmission.

OPTICAL FIBRE COMMUNICATION (OFC) MAY 2014 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

QP Code : MV-19218
(3 Hours) [Total Marks : 100]

N. B. : (1) Question No. 1 is Compulsory.
(2) Attempt any four questions out of remaining six questions.
(3) Assume suitable data wherever necessary and justify the same.

1. (a)	Compare dark current with optical current semiconductor.	5
(b)	Explain direct and Indirect band gap semiconductor.	5
(c)	What do you mean by optical waveguide? How it is different from Electrical	5
	waveguide?
(d)	Explain Bandwidth distance product.	5
2. (a)	Derive the expression for Numerical Aperture of a step -index fiber. What	5
	will happen to Numerical Aperture if cladding is removed?
(b)	Compare step index and graded index fiber.	5
(c)	What do you understand by intramodal dispersion? Derive the expression	10
	for material dispersion.
3. (a)	Explain the significance of V-number. Derive the expression for number of	10
	guided modes in graded index fiber.
(b)	Explain following terms:	5
	(i) Total internal angle
	(ii) Acceptance angle
	(iii) Critical angle
	(iv) Quantum efficiency
	(v) Responsivity
(c)	State the difference between LED and LASER.	5
4. (a)	Explain Modified Chemical Vapour Deposition (MCVD) method of fiber	10
	fabrication?
(b)	Explain with neat skeches fiber splicing techniques. Enlist the desirable	10
	requirements of a good connector.
5. (a)	A photodiode has a quantum efficiency of 65% when a photon of energy	10
	(i) At what wavelength is the photodiode operating.
	(ii) Calculate the incident optical power required to obtain photo current
	of 2.5 uA when the photodiode is operating as above.
(b)	Explain the various factors responsible for optical signal attenuation and	10
	dispersion.
6. (a)	With the help of reciver configuration circuit diagram, explain the working	10
	of optical reciver. Also derive the expression for output.
(b)	Explain all aspects of link power budget.	10
7.	Write short notes on (any four)	20
	(i) Linearly polarized modes
	(ii) OTDR
	(iii) WDM
	(iv) Compare PIN and APD diode
	(v) Optical amplitiers

OPTICAL FIBRE COMMUNICATION (OFC) MAY 2011 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

(3 Hours) [Total Marks:-100]

Q.1 (a) What do you mean by direct and indirect band gap semiconductors? [5 Marks]
(b) Explain following terms: - [10 Marks]
i) Total Internal Reflection ii) Acceptance angle
iii) Critical angle iv) Quantum Efficiency
v) Responsivity
(c) Which are the different connection problems occur while jointing fibers. [5 Marks]

Q.2 (a) Discuss inter modal and intra modal dispersion. [10 Marks]
(b) Find critical radius of curvature at which large bending losses occur for a multimode fiber
with a core refractive index of 1.5, a refractive index difference of 3% and an operating
wavelength of 0.82µm. [10 Marks]

Q.3 (a) Explain linear and non-linear scattering losses. [12 Marks]
(b) Explain working principle of Avalanche Photo diode. [8 Marks]

Q.4 (a) Define :- (i) Bit error rate (ii) Quantum limit [5 Marks]
(b) Write advantages of optical fiber communication over conventional electrical
communication. [5 Marks]

(c) Write advantages of LASER over LED. [5 Marks]
(d) Compare surface and edge emitting LEDs. [5 Marks]

Q.5 (a) (i) Explain measurement of spectral loss in optical fiber using cutback technique. [6 Marks]
(ii) A 2km length of multimode fiber is attached to apparatus for spectral loss measurement.
The measured output voltage from photo receiver using the full 2km fiber length is 2.1 V
at a wavelength of 0.85µm. When the fiber is then cut back to leave a 2 m length the
output voltage increase to 10.7 V. Determine the attenuation per kilometer for the
fiber at a wavelength of 0.85 µm. [4 Marks]

(b) Explain all aspects of link power budget. [10 Marks]

Q.6 (a) How preamplifiers used in optical fiber communication receivers are classified. Explain
different types. [10 Marks]
(b) Discuss how numerical aperture is measured using scanning photo detector and rotating
stage method. [10 Marks]

Q.7 Write note on(any two):- [20 Marks]
i) Splicing Techniques
ii) Fabrication techniques (List all Methods and explain one method only)
iii) Optical Fiber Communication System
iv) OTDR

Sunday, August 3, 2014

OPTICAL FIBRE COMMUNICATION (OFC) DECEMBER 2010 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

Con.5606-10. GT-8568

(3 Hours) [Total Marks:-100]

N.B: (1) Question No.1 is compulsory.
(2) Attempt any four questions out of remaining six questions.
(3) Assume any suitable data wherever required but justify the same.
(4) Figures to the right indicate full marks.

1. Answer the following in brief:-
(a) What is the meaning of 'Avalanche' in the term Avalanche photodiode? [5 Marks]
(b) Describe three types of optical fibers. For each type give typical core and cladding diameters.
Sketch their Refractive Index Profile. [5 Marks]
(c) What do you mean by optical wave guide? How it is different from Electrical
Waveguide? [5 Marks]
(d) Explain spontaneous emission and stimulated emission. [5 Marks]

2. (a) Derive an expression of Numerical Aperture of optical fiber in terms of Refractive
Indices. [10 Marks]
A silica optical fiber with a core diameter large enough to be consider by Ray Theory analysis
has a core Refractive Index of 1.50 and cladding Refractive Index of 1.47.
Determine:- (i) The critical angle at the core-cladding interface.
(ii) The numerical Aperture for fiber.
(iii) The Acceptance Angle in Air for the fiber.
(b) Explain the 'Different Modes' that can be supported by an optical fiber. [10 Marks]

3. (a) Compare and contrast, using suitable diagram, the Outside Vapour-Phase Oxidation(OVPO)
process and the Modified Chemical Vapour Deposition(MCVD) technique for preparation
of Low Loss Optical fibers. [10 Marks]
(b) Describe with the aid of suitable diagrams, three common techniques used for the Mechanical
splicing of optical fibers. [10 Marks]

4. (a) When a light pulse propagates through the optical fiber, attenuation of the signal (light pulse)
takes place. [10 Marks]
List the important factors responsible for Power Loss in optical fiber. Explain each factor
in brief.
(b) A Multimode step Index fiber has a Numerical Aperture of 0.3 and a core Refractive
Index of 1.45. The material dispersion parameter for the fiber is 250 ps nm⁻¹ km⁻¹ which
makes material dispersion the totally dominating intramodal dispersion mechanism. Estimate:
(i) The Total RMS pulse broadening per kilometer when the fiber is used with an LED source
of RMS spectral width 50 nm and (ii) The corresponding Bandwidth-length product for the
fiber. [10 Marks]

5. (a) Explain and compare pin diodes with Avalanche Photo Diode(APD) with the help of suitable
Electric field diagrams. [10 Marks]
(b) With the help of receiver configuration circuit diagram, explain the working of optical receiver.
Also derive the expression for output pulse. [10 Marks]

6. (a) List the important point-to-point link design used in optical communication. Explain each in
brief. [10 Marks]
(b) Explain with suitable diagram the Cutback Method for total fiber attenuation
measurement. [10 Marks]

7. Write short notes on any three of the following:- [20 Marks]
(a) Wavelength Division Multiplexing (WDM)
(b) Linearly Polarised Modes
(c) Optical Time Domain Reflectometer (OTDR)
(d) Laser Diode

OPTICAL FIBRE COMMUNICATION (OFC) MAY 2008 ELECTRONICS AND TELECOMMUNICATION SEMESTER 8

Con.3026-08. (REVISED COURSE) CO-4240

(3 Hours) [Total Marks:-100]

N.B: (1) Question No.1 is compulsory.
(2) Attempt any four questions out of remaining six questions.
(3) Any assumptions made should be clearly stated.

1. Answer the following question in brief:- [20 Marks]
(a) Explain optical communication with block diagram.
(b) What are the advantages of optical communication over electrical communication.
(c) Compare dark current with optical current.
(d) Explain the importance of numerical aperture in the analysis of optical fiber.
(e) What do you mean by linearly polarised optical wave. How they are different from
circularly polarised wave.

2. (a) Draw the structure of Avalanche Photo Diode(APD) alongwith electrical field profile that
exist in the various regions of APD structure. Explain the working and also explain why it is
also called reach through APD(RAPD). [10 Marks]
(b) Differentiate between the following terms in context with optical communication: [10 Marks]
(i) GIF and SIF
(ii) Optical Source and photo-detector
(iii) Coherent and non-coherent optical transmission.

3. (a) For GIF, prove that :- [10 Marks]

Where M = bounded mode
α = index profile
a = radius of core
k = propagation constant in free space
n₁ = core refractive index
∆ = relative refractive index variation
(b) Find the core radius necessary for single mode operation at 820 nm of SIF with n1 = 1.480
and n1 = 1.478. What is the numerical aperture and maximum acceptance angle of this fiber?
Also calculate corresponding solid angle. [10 Marks]

4. (a) Explain any one fiber fabrication process with a neat diagram. [10 Marks]
(b) Explain with neat sketches fiber splicing techniques. Enlist the desirable requirements
of a good fiber connector. [10 Marks]

5. (a) Discuss the operation of a si-RAPD. Compare it with PIN diode. Outline the advantages
and disadvantages of RAPD as a optical demodulator. [10 Marks]
(b) A photodiode ha as quantum efficiency of 65% when a photon of energy of 1.5 x 10⁻¹⁹

J are incident upon it: [10 Marks]
(i) At what wavelength is the photodiode operating.
(ii) Calculate the incident optical power required to obtain a photo current of 2.5 µA
when the photodiode is operating as above.

6. (a) Explain the various factors responsible for optical signal attenuation and dispersion while
propagating through optical fiber. [20 Marks]

7. Write notes on any four:- [20 Marks]
(a) Optical link power budget
(b) Multiplexing of optical signal
(c) Wave propagation in GIF
(d) OTDR- Meter
(e) Amplifiers used with photodetectors (receiver)