AMIETE – ET (OLD SCHEME)

 

Flowchart: Alternate Process: DECEMBER 2009Code: AE24                                                                       Subject: OPTO ELECTRONICS AND

                                                                                                    OPTICAL COMMUNICATION

Time: 3 Hours                                                                                                      Max. Marks: 100

 

NOTE: There are 9 Questions in all.

 

·      Question 1 is compulsory and carries 20 marks. Answer to Q.1 must be written in the space provided for it in the answer book supplied and nowhere else.

·      Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

·      Any required data not explicitly given, may be suitably assumed and stated.

 

 

Q.1       Choose the correct or the best alternative in the following:                                  (210)

                

a.       Wave propagation in optical fiber is due to    

 

                   (A)  Reflection                                     (B)  Diffraction

(C)    Total internal reflection                 (D)  Refraction

       

b.      SDH is a standard for ___________ networks.

            

                   (A)  Twisted pair cable                        (B)  Co-axial cable

(C)  Ethernet                                       (D)  Fiber optic cable

                 

             c.   LED is more suitable for which of the following fiber optic communication systems.  

                  

(A)    Bit rate more than 250 Mb/s, single mode  fiber in mW of power.

(B)    Bit rate less than 100-200 Mb/s, multimode fiber in tens of microwatt power

(C)    Bit rate more than 1 G bits/sec, single mode fiber coupled power in mW

(D)    Bit rate less than 1 G bits/sec, single mode fiber coupled power in the tens of microwatts.

 

             d.   Pulse broadening in GI fiber is due to   

 

(A)    Intermodal dispersion                  (B) Chromatic dispersion

(C)  Intramodal dispersion                   (D)  Both (A) and (C)

 

             e.   Optical fiber communication system uses, wavelength in the range of     

                  

(A)     UV                                              (B) Visible

(C)  X-ray                                           (D) IR rays

 

             f.    The unit for PMD is  

 

(A)     ns per nm per Km                        (B)  ns per Km

(C)  ns per                                (D)  none of the above

.

            


g.     Lasing action leads to

 

(A)   Light production                           (B)  Light amplification

(C) Refraction                                     (D)  Diffraction

 

             h.   One of the following is not a factor for selecting a line encoding format

 

(A)     Duty cycle                                    (B) Clock recovery

(C)  Transmission fault                         (D) Ease of detection and decoding

 

             i.    InGaAsP LED emitting at a peak wave length of 1310 nm has  radiative and nonradiative recombination times of 30 and 100 ns, respectively. Its internal quantum efficiency is

 

(A)   88%.                                            (B) 77%.

(C) 56%.                                             (D) 50%.

                  

             j.    The following semiconductor material has a direct band gap

 

(A)  Si                                                 (B)  Ge

(C)  GaAs                                           (D)  none of the above

 

 

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

 

  Q.2     a.   Describe major element of Optical fiber transmission link with block diagram.                     (8)

                  

             b.   A typical relative refractive index difference for an optical fiber designed for long distance transmission is 1%.  Estimate NA and solid acceptance angle in air for fiber when the core index is 1.46.  Further, calculate the critical angle as the core-cladding interface within fiber.                                      (8)

                                                                             

  Q.3     a.   A step index multimode fiber with a numerical aperture of 0.20 supports approximately 1000 modes at an 850 nm wavelength

.

                   (i) What is the diameter of its core?     

                   (ii)  How many modes does the fiber support at 1320 nm?                                  (8)

 

             b.   Describe the losses occurs in the Optical fiber communication systems.               (8)

                                                                                                                                                           

  Q.4     a.   Explain the structure of Fabry-perot resonator cavity LASER diode with neat sketch.                     (8)

 

             b.   An LED operating at 850 nm has a spectral width of 45 nm. What is the pulse spreading in ns/km due to material dispersion? What is the pulse spreading when a laser diode having a 2-nm spectral width is used? Find the material dispersion induced pulse spreading at 1550 nm for an LED with a 75-nm spectral width.                                                             (8)

       

  Q.5     a.   Describe the advantages and drawbacks of internal modulation and external modulation of laser diode.                                                                  (8)

                  

             b.   A GaAs optical source that has a refractive index of 3.6 is closely coupled to a step-index fiber which has a core refractive index of 1.465. If the source size is smaller than the fiber core and the small gap between the source and the fiber is filled with a gel that has a refractive index of 1.305, what is the  power loss in dB from the source into the fiber?                      (8)

                                                                             

  Q.6     a.   What is AGC and equalization? With the help of circuit diagram explain their importance in communication.                                                            (8)

 

             b.   Starting from basics, derive the SNR expression at the input of the amplifier used in photo detector receiver.                                                           (8)                                                             

 

  Q.7     a.   Define the Terms Avalanche effect and reach-through.  With a neat schematic explain the operation of RAPD.                                                (8)

 

             b.   (i)  Define quantum efficiency and responsivity of an optical detector.                  (2)                                                                                              (i)   The received optical power.

                   (ii) Briefly explain the concept of sub-carrier modulation.                                    (6)

                                                                                                                                                

  Q.8     a.   Describe fusion splicing technique.                                                                      (8)

 

             b.   Describe the Rise Time budget in detail.                                                              (8)

 

  Q.9           Write short notes on:-  (Any TWO)

 

                   (i)     Coherent systems.

                   (ii)    Optical Amplifiers

                   (iii)    Line coding.                                                                                            (16)