Optical Fiber Communication

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 OFC Test 1-2009

PART –A

1. a) What is mode field diameter of single mode fiber                                           -4-

   b) What are the advantages and disadvantages of   multimode fibers and single mode fibers?                                                                                                                       -6-

2. What is numerical aperture? Derive an expression for numerical aperture and maximum acceptance angle in the case of a step index optical fiber in terms of refractive indices of core and cladding material.                                                                     -10-

PART-B

3. a) Explain what are the non linear scattering losses in optical fibers                  - 6-

    b) What are intermodal dispersion and intramodal dispersion                            - 4-

4. Find out the pulse broadening d_Ts and  rms pulse broadening  for a multimode step index fiber.                                                                                                              -10-

PART – C

5. Light traveling in air strikes a glass plate at an angle q ₁ =33⁰ , where q₁ is measured between the incoming  ray and the glass surface . Upon striking the glass part of the beam is reflected and part is refracted .If the refracted and reflected beams make an angle of 90^o with each other, what is the refractive index of the glass? What is the critical angle for the glass?                                                                                                                 -5-

6. A 6 km  optical link consists of multimode step index fiber with a core refractive index of 1.5 and a relative refractive index difference of 1%                                      Estimate: a) The delay difference between the slowest and fastest modes at the fiber output.

                b) The rms pulse broadening due to intermodal dispersion on the link.

                c) The maximum bit rate that may be obtained without substantial errors on the                   link assuming only intermodal dispersion.

                 d) The band width –length product corresponding to (c) .                 -5-

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                                                                     OFC TEST 3- 2009

PART –A

1. a) What is mode field diameter of single mode fiber                                           -4-

   b) What are the advantages and disadvantages of   multimode fibers and single mode fibers?                                                                                                                       -6-

2. What is numerical aperture? Derive an expression for numerical aperture and maximum acceptance angle in the case of a step index optical fiber in terms of refractive indices of core and cladding material.                                                                     -10-

PART-B

3. a) Explain what are the non linear scattering losses in optical fibers                  - 6-

    b) What are intermodal dispersion and intramodal dispersion                            - 4-

4. Find out the pulse broadening d_Ts and  rms pulse broadening  for a multimode step index fiber.                                                                                                              -10-

PART – C

5. Light traveling in air strikes a glass plate at an angle q ₁ =33⁰ , where q₁ is measured between the incoming  ray and the glass surface . Upon striking the glass part of the beam is reflected and part is refracted .If the refracted and reflected beams make an angle of 90^o with each other, what is the refractive index of the glass? What is the critical angle for the glass?                                                                                                                 -5-

6. A 6 km  optical link consists of multimode step index fiber with a core refractive index of 1.5 and a relative refractive index difference of 1%                                      Estimate: a) The delay difference between the slowest and fastest modes at the fiber output.

                b) The rms pulse broadening due to intermodal dispersion on the link.

                c) The maximum bit rate that may be obtained without substantial errors on the                   link assuming only intermodal dispersion.

                 d) The band width –length product corresponding to (c) .                 -5-

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Information Theory and Coding

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ITC TEST 2 -2009

PART A:

1. Given an eight symbol source with probabilities

P={0.25, 0.20, 0.15, 0.15, 0.10, 0.05, 0.05, 0.05}

 Construct two binary Huffman codes as directed.

(i)                  Place the composite symbol “as low as you can”

(ii)                Move the composite symbol  “as high as possible”.

In each case determine the variance of the word lengths and comment on the results.                                                                                             -10-

      2. (a)  A Binary Symmetric Channel has an error probability of 0.1. Find its capacities after deriving relevant relations.                                                                   -5-

      

           (b) Explain Binary Erasure Channel and find its channel capacity.       -5-

PART B:

3        (a) For a channel whose matrix is given below

                                                     Y

                                            0.6  0.2  0.2                                                         -8-

P[Y/X] = X   0.2  0.6  0.2

0.2    0.2  0.6

Find I(X,Y) and channel capacity given the input symbols occur with equal probability.

    

            (b) Define Mutual Information                                                                 -2-

4. Consider a source S = {s₁, s₂} with probabilities ¾ and ¼  respectively. Obtain Shanon-Fano code for source S. it’s 2^nd and 3^rd extensions. Calculate efficiencies for each case.                                                                                                                        -10-

  

PART C

5. Explain all the properties of Mutual Information                                               -5-

6. What is a Binary Erasure Channel. Find the Channel Capacity of a Binary Erasure Channel.                                                                                                                  -5-

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