Optical Fibre communication(10EC72) - Question Bank

 Optical Fibre communication(10EC72) - Question Bank

Optical fibre communication(10EC72)

1. What is the numerical aperture of an optical fibre? Deduce an expression for the same.                                                                                                             (8marks)(Nov/Dec 2011)
2. Calculate NA of silica fibre with its core refractive index (n1) of 1.48 and cladding refractive index of 1.46. What should be the new value of ‘n’ in order to change the NA to 0.23?                                                                                               (8marks)(Nov/Dec 2011)
3. Distinguish step index from graded index fibres.                           (8marks) (Nov/Dec 2011)
4. Draw and explain the acceptance angle and numerical aperture of an optical fibre and derive expressions for both.                                                      (8marks) (May/June 12)
5. A fibre has a core radius of 25mm, core refractive index of 1.48 and relative refractive index difference is 0.01. If the operating wavelength is 0.84mm, find the value of normalized frequency and the number of guided modes. Determine the number of guided modes if D is reduced to 0.03.                                  (8marks) (May/June 12)
6. Draw and explain the refractive index profile and ray transmission in single mode and multimode step index fibres and graded index fibres. Write the expressions for the graded index fibre.                                                                     (6marks) (May/June 12)
7. A step index fibre has a core diameter or 7µm and core refractive index of 1.49. Estimate the shortest wavelength of light which allows single mode operation when the relative refractive index difference for the fibre is 1%.    (8marks) (May/June12)
8. A multimode step index fibre with a core diameter of 80µm and a relative index difference of 1.5% is operating at the wavelength of 0.85 µm. If the core refractive index is 1.48, estimate the normalized frequency for the fibre and the number of guided modes.                                                                                          (8marks) (Nov/Dec 2007)

9. Draw the structure of step index and graded index fibres with their typical dimensions.                                                                                                    (8marks) (Nov/Dec 2007)
10. Derive an expression for number of modes propagating in the graded index fibre from the first principles.                                                       (6marks) (April/May 2008)
11. The relative refractive index difference between the core and the cladding of a graded index fibre is 0.7% when the refractive index at the core axis is 1.45.Estimate values for the numerical aperture of the fibre along the axis when the index profile is assumed to be triangular.                                                          (8marks) (April/May 2008)
12. A 6km optical link consists of multimode step index fibre with a core refractive index of 1.5 and a relative refractive index of difference of 1%.Estimate the delay difference between the slowest and the fastest modes at the fibre output and the rms pulse broadening due to intermodal dispersion on the link. Also derive the expression involved in it.                                                                                       (8marks) (April/May 2008)
13. Explain with neat block diagram the fundamentals of optical fibre communication                                                                                                                    (6marks) (Nov/Dec 2008)
14. Mention the advantages of optical fibre communication systems.

                                                                                                                         (4marks) (Nov/Dec 2008)

15. Calculate the numerical aperture, cut-off parameter and number of modes supported by a fibre having µ1(core) = 1.54, µ2(cladding) = 1.5, core radius 25µm and operating wavelength 1300nm.                                                                            (6marks) (May/June 2009)
16. What are the various features of graded index fibre? Explain the refractive index profile and ray transmission in a multimode graded index fibre.                                                                                                                                                                               (8marks)(Dec/jan2016)
17. Derive necessary mathematical condition that the angle of incidence “θ” must satisfy for the optical skew ray to propagate in a step index fibre.      (6marks) (Dec/jan2016)
18. Calculate the number of modes of an optical fibre having diameter of 50 µm, n1=1.48, n2=1.46 and wavelength of 820nm.                                     (6marks) (Dec/jan2016)

Unit-2:Introduction, Attenuation, absorption, scattering losses, bending loss, dispersion, Intra model dispersion, Inter model

1. What do you mean by pulse broadening? Explain its effect on information carrying capacity of a fibre.                                                                                  (6marks) (Nov/Dec 2011)
2. 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 2nm spectral width is used? The material dispersion is 90ps/nm.km.                                                                                                                                  (8marks) (Nov/Dec 2011)
3. Explain the following with necessary diagram and expressions:

               (i)Non linear scattering loss and fibre bend loss.

              (ii) Material dispersion in optical fibre.                                          (8marks)(May/ June2012)

4.       What is the mean optical power launched into an 8km length fibre is 120MW; the mean      

optical power at the fibre output is 3µW? Determine

         (i)Overall signal attenuation in dB/km and

         (ii)The overall signal attenuation  for a 10km optical link using the same fibre With      splices at 1km intervals, each giving an attenuation                      (8marks)(Nov/Dec 2007)

5. Explain with suitable diagrams the different mechanisms that contribute to attenuation in optical fibres.                                                                                            (8marks)(Nov/Dec 2007)

6. Discuss in detail the intermodal dispersion with relevant expressions and diagrams.                                                                                                                                       (6marks)(Nov/Dec 2007)

7. Explain the scattering and bending losses that occur in an optical fibre with relevant diagrams and expressions.                                                               (6marks)(Nov/Dec 2008)

8. Discuss material and waveguide dispersion mechanisms with necessary mathematical expressions.                                                                                        (8marks)(Nov/Dec 2008)

9. Compute the total intermodal, intramodal and total dispersion for a fibre having fibre length 1km, line width 50nm, intermodal and intramodal dispersions5ns/km and 80 pcs/km respectively.                                                                                                            (6marks)(May/June 2009)

Unit-3:Introduction, LED’s, LASER diodes, Photo detectors, Photo detector noise, Response time, double hetero junction structure, Photo diodes, comparison of photo detectors.

10. Explain the different types of absorption losses in optical fibre (Dec/Jan 2016)

1. Compare LED with a LASER diode.                                                            (6marks)(Nov/Dec 2011)

2. With the help of a neat diagram explain the construction and working of a surface emitting LED.                                                                                              (6marks)(Nov/Dec 2011)

3. Explain the structure and working of silicon APD.                       (6marks)(Nov/Dec 2011)

4. Explain any two injection laser structures with neat diagrams.      (6marks)(May/Jun 2012)

5. A silicon p-i-n photodiode incorporated into an optical receiver has a quantum efficiency of 60% when operating at a wavelength of 0.9mm. The dark current is 3 nA and the load resistance is 4 KΩ. The incident optical power is200 nW and the post detection bandwidth of the receiver is 6. MHZ. Calculate the root mean square (rms) shot noise and thermal noise currents generated.                                                                                                                                     (8marks)(Nov/Dec 2011)

7. Discuss the principle of operation of LASER diodes. What are the effects of temperature on the performance of a LASER diode?                                             (8marks)(Nov/Dec 2007)

8. Explain the different lensing scheme available to improve the power coupling efficiency.                                                                                                                                             (6marks)(Nov/Dec 2007)

9. Explain the fibre splicing techniques with necessary diagrams. (6marks)(Nov/Dec 2007)

10. Explain briefly the three key processes involved in the laser action .Describe for a fabry perot resonator laser diode, modes and threshold conditions. Obtain its rate equations for steady state output.                                                                                                        (8marks)(April/May 2008)

10. What type of materials are used for optical sources. What are the advantages of double Hetro structure? Compare surface emitting and edge emitting LED structures .                                                                                                                                                                   (8marks)(April/May 2008)

11. Derive an expression for the internal optical power level generated in LEDs.

                                                                                                                                           (6marks)(April/May2008)

12. Draw and explain the different structures used to achieve carrier and optical confinement in laser diodes. (6marks)(Nov/Dec 2008)

13. Discuss the effects of temperature on the performance of a laser diode.  (Nov/Dec 2008)

14. Explain the step involved in splicing the fibre. Discuss the various splicing techniques employed between two fibres.                                           (8marks)(May/June 2009)

15. Explain the lensing schemes used to improve optical source - to- fibre coupling efficiency                                                                                                                                  (6marks)(May/June 2009)

16. Explain the basic LED configurations used as optical source. Derive the expression for quantum efficiency and optical power generated in LED’s.  (6marks)(May/June 2009)

17. Draw the cross section of GaALAs double hetro structure LED energy band diagram  RI variation. Explain their importance.(Dec/Jan 2016)

Unit-4:Introduction, fibre alignment and joint loss, single mode fibre joints, fibre splices, fibre connectors and fibre couplers.

18.With proper sketch briefly explain the structure of RPAD photodiode. (Dec/Jan 2016)

1. Explain the fibre optic receiver operation using a simple model and its equivalent circuit.                                                                                                                                    (6marks)(Nov/Dec 2011)

2. Explain the operation of pre-amplifier built using a FET.               (6marks)(Nov/Dec 2011)

3. Explain the measurement technique used in the case of                        (8marks)(Nov/Dec 2011)

         a. Numerical aperture

         b. Refractive index profile

        c. Fibre cut – off wavelength

        d. Fibre diameter.

4. Discuss the noise and disturbances affecting the optical detection (6marks) (Nov/Dec 2011)

5. Draw and explain the operation of high impedance FET and BJT pre- amplifiers                                                                                              (8marks)(May/Jun 2012)

6. A silicon p-i-n photodiode incorporated into an optical receiver has a quantum efficiency of 60% at a wavelength of 0.9µm.The dark current is 3 nA and load resistance is 4 KΩ. The incident optical power is 200nw and the receiver bandwidth is 5Mhz. Determine mean square quantum noise current, mean square dark current and mean square thermal noise current at a temperature of 20◦C.                                                                                    (8marks) (Nov/Dec 2007)

7. Draw and explain the operation of APD.                                                   (6marks) (Nov/Dec 2007)

8. Derive an expression for the bit error rate of an optical digital receiver.(8marks)(Nov/Dec 2007)

9. Discuss the different noise sources and disturbances in the optical pulse detection mechanism.                                                                                                                   (6marks) (Nov/Dec 2007)

10. Explain the operation of avalanche photodiode.                              (8marks)(April/May 2008)

11. The quantum efficiency of particular silicon RAPD is 80% for the detection of radiation at a wavelength of 0.9µm, when the incident optical power is 0.5µW.The output current from the device(after avalanche gain) is 11µA.Determine the multiplication factor of the photodiode under these conditions.                                                                            (8marks)(April/May 2008)

12. Draw the circuit diagram of high impedance pre-amplifier and explain its operation                                                                                                                (6marks)(April/May 2008)

13. Discuss the sources of errors in optical receivers.                       (6marks)(April/May 2008)

14. Discuss with necessary expressions those different types of noise that affect the performance of a photo detector.                                                        (6marks)(Nov/Dec 2008)

15. When 3 ×1011 photons each with a wavelength of 0.85µm is incident on the photodiode, on the average 1.2×1011 electrons are collected at the terminals of the device. Determine the quantum efficiency and responsively of the photodiode at 0.85µm . (8marks) (Nov/Dec 2008)

16. Draw and explain the high impedance preamplifier designs based on BJT and FET.                                                                                                                  (6marks)(Nov/Dec 2008)

17. With the neat sketch explain the operation of PIN photodiode and Avalanche photodiode.                                                                                        (6marks) (May/June 2009)

Unit-5 :Introduction, Optical Receiver Operation, receiver sensitivity, quantum limit, eye diagrams, coherent detection, burst mode receiver, operation, analog receivers.

18. Derive the expression for signal- to- noise ratio obtained at the output of an optical receiver.                                                                                                              (6marks) (May/June 2009)

1.With neat diagram explain the operation of trans impedance  preamplifier equivalent circuits.                                                                                                                              (6marks)(Dec/jan 2016)

2.Derive the expression for receiver sensitivity and also explain quantum limit. (6marks)(Dec/jan 2016)

3.  Discuss how the eye diagram is powerful measurement toll for assessing data handling  

  capability in digital transmission system.                   (8marks)(Dec/jan 2016)

4. With schematic diagram explain the working of optical receiver. (6marks) (June/july2016)

5.Discuss coherent detection with relevant block diagram.        (8marks)(June/july2016)

6.Explain the term receiver sensitivity. Derive the expression for receiver sensitivity in terms of photo detector noise.                                                                   (6marks)(June/july2016)

7.Write a note on analog receivers.                                                                                 (6marks)(Dec/jan 2014)

8.Discuss the possible sources of noise in optical receivers.                                      (8marks)(Dec/jan 2014)

9.Discuss how the eye diagram is the powerful measurement toll for assessing the data handling capability in digital transmission system.                                                                                                               (6marks)(Dec/jan 2014)

Unit-6:Analog links – Introduction, overview of analog links, CNR, multichannel transmission techniques, RF over fibre, key link parameters, Radio over fibre links, microwave photonics. Digital links – Introduction, point–to–point links, System considerations, link power budget, resistive budget, short wave length band, transmission distance for single mode fibres, Power penalties, nodal noise and chirping.

10.Differentiate between heterodyne and homodyne coherent detection schemes, with respect to probability of error function of a BER.                                                                                                        (8marks) (June/July 2011).

1.       Discuss the basic elements of an analog link and the major noise contributions of an analog link, with a neat diagram .                                          (8marks) (June/July 2011)

2.       Explain the polarization mode dispersion penalty in power penalties of a digital link.                                                                                                                                                       (6marks)(June/July 2011)            

3.       With a simplex point to point link, explain the key system requirements which are needed in analyzing a link and how to fulfil these requirements.           (8marks)(June/July 2011)

4.       Discuss the following:                                                                                                (8marks)(June/July 2011)

(i)                   Subcarrier multiplexing

(ii)                 Chirping

(iii)Extinction ratio penalty

5.       Briefly explain the rise time budget analysis with its basic elements contributing to system rise time.                                                                                             (8marks)(Dec/Jan 2017)

6.       Explain the various noise and disturbance associated with signal detection system.                                                                                                                                          (8marks)(june/July 2015)

7.      

Unit-7 &8:WDM concepts, overview of WDM operation principles, WDM standards, Mach-Zehender interferometer, multiplexer, Isolators and circulators, direct thin film filters, active optical components, MEMS technology, variable optical attenuators, tuneable optical fibres, dynamic gain equalizers, optical drop multiplexers, polarization controllers, chromatic dispersion compensators, tuneable light sources.

Explain with neat diagram radio over fiber links of a broadband wireless access network.                                                                                                                               (8marks)(june/July 2015)

1. Explain the principles of WDM.                                       (8marks)(April/May 2008)
2. Explain MEMS technology with neat diagram.         (4marks) (April/May 2008)
3. With a neat diagram explain the operation of a dielectric thin film filters.                                                                                                                              (4marks) April/May 2008).
4. With a diagram explain the operation of optical isolator.

                                                                                                             (4marks) (May/June 2010).

5. Write a note on optical add/drop multiplexer.                 (4marks) (Dec/Jan 2017)
6. Explain with help of relevant diagram various applications of fibre Bragg grating.                                                                                                                       (6marks) (Dec/Jan 2017).
7. Discuss the design and operation of polarization independent.                                                                                                                                               (6marks) (June/July 2016)
8. Derive an expression for difference in length for MZI multiplexer.                                                                                                                                        (8marks) (Dec/Jan 2017).