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

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)

OPTICAL FIBRE COMMUNICATION (OFC), B.E. Electronics & Telecommunication, Semester 8, May 2009.

OPTICAL FIBRE COMMUNICATION (OFC),

B.E. Electronics & Telecommunication,

Semester 8, May 2009.

Con. 3142-09

(REVISED COURSE)

VR-4272

(3 Hours)

[Total Mark: 100]

N.B. (1) Question No 1 is compulsory.

(2) Answer any four questions out of remaining six questions.

1. Answer the following in brief:-

(a) Discuss the basic block diagram of optical communication system. ---- (5 Marks)

(b) What are direct and indirect semiconductors? Which types are suitable to be used as optical sources and detectors? ---- (5 Marks)

(c) How does the optical signal propagate through the GIF. ---- (5 Marks)

(d) What is the difference between coherent and non-coherent optical transmission? ---- (5 Marks)

2. (a) Explain the 'Different Modes' that can be supported by an optical fiber.---- (10 Marks)

(b) Using simple ray theory concept, discuss the transmission of light through single Mode fiber. What is the major advantage of this type of fiber? ---- (10 Marks)

3. (a) 'Optical signal distortion limits the information carrying capacity of the fiber' Justify the comment. ---- (10 Marks)

(b) List the important factors responsible for power loss in optical fiber. Explain each Factor briefly. ---- (10 Marks)

4. (a) What are the general requirements of a good optical source? Describe the technique used to give both electrical and optical confinement in injection lasers. ---- (10 Marks)

(b) Draw the structure of APD along with electrical field profile that exist in the various regions. Explain its working and also explain why it is also called RAPD. ---- (10 Marks)

5. (a) Describe two methods of splicing individual fibers together. What are some advantages and disadvantages of each method? ----- (10 Marks)

(b) Discuss a popular non-destructive technique for attenuation measurement. ---- (10Marks)

6. Describe three methods of preform fabrication. Include starting materials, heat sources, fabrication temperatures used and the technique used to make the preform for-each method. ---- (20 Marks)

7. Write short notes on any four:----- (20 Marks)

(a) Rise time budget

(b) Measurement of dispersion

(c) Radiative losses in optical fiber.

(d) PIN diode

(e) Double heterogenous LED.