SRCE-Department of Electronics and Communication ...



SARDAR RAJA COLLEGE OF ENGINEERING-ALANGULAM

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

MICRO LESSON PLAN

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SUBJECT NAME : OPTICAL COMMUNICATION AND NETWORKS

SUBJECT CODE : EC72

YEAR /SEM : FINAL YEAR / VII

BRANCH : ECE

STAFF NAME: Ms. M.SYED FATHIMUTHU

Asst.Prof / ECE

SARDAR RAJA COLLEGE OF ENGINEERING-ALANGULAM

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

EC72 OPTICAL COMMUNICATION AND NETWORKS

AIM:

• To introduce the various optical fiber modes, configurations and various signal degradation factors associated with optical fiber.

• To study about various optical sources and optical detectors and their use in the optical communication system. Finally to discuss about digital transmission and its associated parameters on system performance.

OBJECTIVE:

• To learn the basic elements of optical fiber transmission link, fiber modes configurations and structures.

• To understand the different kind of losses, signal distortion in optical wave guides and other signal degradation factors. Design optimization of SM fibers, RI profile and cut-off wave length.

• To learn the various optical source materials, LED structures, quantum efficiency, Laser diodes and different fiber amplifiers.

• To learn the fiber optical receivers such as PIN APD diodes, noise performance in photo detector, receiver operation and configuration.

• To learn fiber slicing and connectors, noise effects on system performance, operational principles WDM and solutions.

Text Books:

• 1. Optical Fiber Communication – John M. Senior – Pearson Education – Second Edition. 2007

• 2. Optical Fiber Communication – Gerd Keiser – Mc Graw Hill – Third Edition 2000.

References:

• 1. J.Gower, “Optical Communication System”, Prentice Hall of India, 2001

• 2. Rajiv Ramaswami, “Optical Networks “ , Second Edition, Elsevier , 2004.

• 3. Govind P. Agrawal, “ Fiber-optic communication systems”, third edition, John Wiley & sons, 2004.

• 4. R.P. Khare, “Fiber Optics and Optoelectronics”, Oxford University Press, 2007.

EC72 OPTICAL COMMUNICATION AND NETWORKS L T P C 3 0 0 3

AIM:

• To introduce the various optical fiber modes, configurations and various signal degradation factors associated with optical fiber.

• To study about various optical sources and optical detectors and their use in the optical communication system. Finally to discuss about digital transmission and its associated parameters on system performance.

OBJECTIVE:

• To learn the basic elements of optical fiber transmission link, fiber modes configurations and structures.

• To understand the different kind of losses, signal distortion in optical wave guides and other signal degradation factors. Design optimization of SM fibers, RI profile and cut-off wave length.

• To learn the various optical source materials, LED structures, quantum efficiency, Laser diodes and different fiber amplifiers.

• To learn the fiber optical receivers such as PIN APD diodes, noise performance in photo detector, receiver operation and configuration.

• To learn fiber slicing and connectors, noise effects on system performance, operational principles WDM and solutions.

UNIT – I INTRODUCTION 9

Introduction, Ray theory transmission- Total internal reflection-Acceptance angle –Numerical aperture – Skew rays – Electromagnetic mode theory of optical propagation –EM waves – modes in Planar guide – phase and group velocity – cylindrical fibers –SM fibers.

UNIT – II TRANSMISSION CHARACTERISTICS OF OPTICAL FIBERS 9

Attenuation – Material absorption losses in silica glass fibers – Linear and Nonlinear Scattering losses - Fiber Bend losses – Midband and farband infrared transmission –Intra and inter Modal Dispersion – Over all Fiber Dispersion – Polarization- nonlinear Phenomena. Optical fiber connectors, Fiber alignment and Joint Losses – Fiber Splices– Fiber connectors – Expanded Beam Connectors – Fiber Couplers.

UNIT – III SOURCES AND DETECTORS 9

Optical sources: Light Emitting Diodes - LED structures - surface and edge emitters, mono and hetero structures - internal - quantum efficiency, injection laser diode structures - comparison of LED and ILD Optical Detectors: PIN Photo detectors, Avalanche photo diodes, construction, characteristics and properties, Comparison of performance, Photo detector noise -Noise sources , Signal to Noise ratio , Detector response time.

UNIT – IV FIBER OPTIC RECEIVER AND MEASUREMENTS 9

Fundamental receiver operation, Pre amplifiers, Error sources – Receiver Configuration – Probability of Error – Quantum limit. Fiber Attenuation measurements- Dispersion measurements – Fiber Refractive index profile measurements – Fiber cut- off Wave length Measurements – Fiber Numerical Aperture Measurements – Fiber diameter measurements.

UNIT – V OPTICAL NETWORKS 9

Basic Networks – SONET / SDH – Broadcast – and –select WDM Networks –Wavelength Routed Networks – Nonlinear effects on Network performance –Performance of WDM + EDFA system – Solitons – Optical CDMA – Ultra High Capacity Networks, OTDR.

Total = 45

Text Books:

• 1. Optical Fiber Communication – John M. Senior – Pearson Education – Second Edition. 2007

• 2. Optical Fiber Communication – Gerd Keiser – Mc Graw Hill – Third Edition 2000.

References:

• 1. J.Gower, “Optical Communication System”, Prentice Hall of India, 2001

• 2. Rajiv Ramaswami, “Optical Networks “ , Second Edition, Elsevier , 2004.

• 3. Govind P. Agrawal, “ Fiber-optic communication systems”, third edition, John Wiley & sons, 2004.

• 4. R.P. Khare, “Fiber Optics and Optoelectronics”, Oxford University Press, 2007.

|Hr.NO |WEEK NO |TOPIC |T/ R BOOK NO|PAGE.NO |A/ V CLASS |

|UNIT I –INTRODUCTION |

|1. |I |Introduction About the subject |T1 |1 to 10 |Yes |

|2. | |Ray theory Transmission-total internal Reflection | |14 to 16 |Yes |

|3. | |Acceptance angle , | |16 to 23 |Yes |

| | |Numerical aperture, Skew rays | | | |

|4. | |Electromagnetic mode theory of optical propagation -EM | |23 to 25 | |

| | |waves | | | |

|5. | |modes in Planar guide | |26 to 28 | |

|6. |II |phase and group velocity | |28 to 30 | |

|7. | |cylindrical fibers | |36 to 44 | |

|8. | |SM fibers. | |45 to 47 |Yes |

|9. | |Problems |T1& T2 |1 to 10 | |

|UNIT II -TRANSMISSION CHARECTERISTICS |

|10 |III |Attenuation |T1 |86 to 88 | |

|11 | |Material absorption losses in silica glass fibers | |88 to 91 | |

|12 | |Linear Scattering losses | |91 to 94 | |

|13 | |Nonlinear Scattering losses | |94 to 96 | |

|14 | |Fiber Bend losses | |97 to 99 |yes |

|15 |IV |Midband and farband infra-red transmission | |99 to 102 | |

|16 | |Intra Modal Dispersion | |107 to 110 | |

|17 | |Inter Modal Dispersion | |111 to 121 | |

|18 | |Over all Fiber Dispersion | |121 to 130 | |

|19 | |Polarization | |136 to 145 | |

|20 |V |Nonlinear Phenomena | |145 to 149 | |

|21 | |Fiber Alignment and Joint Losses | |212 to 226 |yes |

|22 | |Fiber Splices | |227 to 237 |yes |

|23 | |Fiber connectors | |237 to244 |yes |

|24 | |Expanded Beam Connectors | |244 to 249 |yes |

|25 |VI |Fiber Couplers | |249 to 270 |yes |

|UNIT III - SOURCES AND DETECTORS |

|26 |VI |LED structures - surface and edge emitters |T1 |386 to 393 |yes |

|27 | |Mono and Hetro Structure | |150 to 151 | |

| | | |T2 | | |

|28 | |Internal - Quantum Efficiency | |156 to 158 | |

|29 | |Injection laser diode structures |T1 |322 to 336 | |

| | | | | | |

|30 |VII |Comparison of LED and ILD Optical Detectors |T2 |336 to338 |Yes |

| | | | | | |

| | | | | | |

| | | | | | |

| | | | | | |

| | | |T2 | | |

|31 | |PIN Photo detectors construction, Characteristics and | |244 to 249 | |

| | |properties | | | |

|32 | |Avalanche photo diodes construction, Characteristics and | |249 to 252 |yes |

| | |properties, | | | |

|33 | |Comparison of Performance | |267 to 268 | |

|34 | |Photo detector noise –Noise sources | |252 to 257 | |

|35 |VIII |Signal to Noise ratio, Detector response time | |257 to 263 | |

|36 | |Problems |T1 & T2 | | |

|UNIT IV -FIBER OPTIC RECEIVER AND MEASUREMENTS |

|37 |VIII |Fundamental receiver operation |T2 |275 to 277 | |

|38 |VIII |Pre amplifiers | |305 to 312 | |

|39 | |Error sources – Receiver Configuration | |277 to 280 | |

|40 |IX |Probability of Error | |282 to 287 | |

|41 | |Quantum limit. | |288 to 289 | |

|42 | |Fiber Attenuation measurements- |T1 |779 TO789 | |

|43 | |Dispersion measurements | |789 to 796 | |

|44 | |Fiber Refractive index profile measurements | |796 to 802 | |

|45 |X |Fiber cut- off Wave length Measurements | |802 to 807 | |

|46 | |Fiber Numerical Aperture Measurements | |807 to 810 | |

|47 | |Fiber diameter measurements | |810 to 812 | |

|48 | |Problems |T1 & T2 | | |

|UNIT V – OPTICAL NETWORKS |

|49 |XI |Basic Networks |T2 |458 to 467 | |

|50 | |SONET / SDH. | |467 to 477 |yes |

|51 | |Broadcast and select WDM Networks | |477 to 482 | |

|52 | |Wavelength Routed Networks | |482 to 488 | |

|53 | |Nonlinear effects on Network performance | |488 to 501 | |

|54 |XII |Performance of WDM + EDFA system | |502 to 505 |yes |

|55 | |Solitons | |505 to 513 |yes |

|56 | |Optical CDMA | |514 to 516 | |

|57 | |Ultra High Capacity Networks | |516 to 519 | |

|58 | |OTDR | |550 to 554 | |

T1 -Optical Fiber Communication – John M. Senior – Pearson Education – Second Edition. 2007

T2- Optical Fiber Communication – Gerd Keiser – Mc Graw Hill – Third Edition 2000

QUESTION BANK

Unit I- INTRODUCTION

Part A

1. Define Numerical Aperture of a step index fiber?

2. Define Skey Rays.

3. Give the advantages of single mode fiber

4. Define Mode Field Diameter.

5. Define Cutoff wavelength.

6. Write the expression for the refractive index in Graded index fiber.

7. A silica optical has a core refractive index of 1.5 and a cladding refractive index 1.47. Determine the acceptance angle in air for the fiber.

8. What are the advantages and disadvantages of the ray optics theory?

9. A typical refractive index difference for an optical fiber designed for long distance transmission is 1%.Estimate the numerical aperture for the fiber when the core index is 1.47.

10. Define Angle of Incidence& Critical Angle.

11. Define Total internal Reflection (TIR) & Snell’s Law.

12. What is the difference between step index and graded index fiber?

13. What is the difference between bounded rays and unbounded rays?

14. Write the elements of an optical system?

15. What are the advantages of optical fiber?

16. A silica optical fiber has a core refractive index of 1.5 and a cladding refractive index of 1.47. Determine the acceptance angle in air for the fiber.

17. The relative refractive index difference between the core axis and the cladding of a graded index fiber is 0.7% when the refractive at the core axis is 1.45. Estimate the value for the numerical aperture of the fiber along the axis when the index profile is assume to be triangle.

18. A silica optical fiber with a core diameter large enough to be considered by ray theory analysis has a core refractive index of 1.5 and a cladding refractive index of 1.47.determine the numerical aperture and acceptance angle in air for the fiber.

19. A typical relative refractive index difference for an optical fiber designed for long distance transmission is 1%. Estimate the numerical aperture for the fiber when the core index is 1.47.

20. Calculate the numerical aperture, cut-off parameter and number of modes supported by fiber having µ1 (core) =1.54, µ2 (cladding= 1.5, core radius 25µm and operating wavelength 1300nm.

Part B

1. Discuss the structure of graded index& step index fiber.

2. a) Explain the optical communication system with neat diagram (8)

b) Discuss the modes in step index fibers. (8)

3. Explain in details about the advantages of optical communication

4. a) A multimode step index fiber with a core diameter of 80(m and a

Relative index difference of 1.5% is operating at a wavelength of 0.85(m.

If the core refractive index is 1.48, estimate the normalized frequency for

The fiber and the number of guided modes.(6)

b) Explain with a neat diagram the elements of an optical fiber transmission

link.(10)

5. a) Discuss about mode coupling.(6)

b)Sketch and explain the electric field distribution of the lower order guided

modes in symmetrical slab waveguide. (6)

c) Draw the structure of step index and graded index fibers with their typical

dimensions.(4)

6. Explain optical fiber modes and configurations.(16)

7. a) multimode GI fiber has an acceptance angle in air of 8º.Estimate the relative refractive index difference between the core axis and the cladding when the refractive index at the core axis is 1.52.(8)

b)A multimode step index fiber with a core diameter of 80µm and a relative index difference of 1.5% is operating at a wavelength of 0.85µm.If the core refractive index is 1.48. Determine. a) Normalized frequency of fiber. b ) the number of guided modes(8)

8. a )A typical refractive index difference for an optical fiber designated for long distance transmission is 1% .determine the NA and the solid acceptance angle in air for the fiber when the core index is 1.46. Calculate the critical angle at the core- cladding interface with in the fiber.(8)

b)Define and explain Goos- Haenchen shift.

9. i) Explain the concept of electromagnetic modes in a planar optical waveguide. (8)

ii) Define acceptance angle .How it is related to the NA and the refraction indices of the fiber

core and the cladding. (8)

10. i) Explain the concept of electromagnetic modes in a planar optical waveguide. (8)

ii) A graded index fiber with a parabolic refractive index profile core has a refractive index at

the core axis of 1.5 and a relative index difference of 1%. Estimate the maximum parsuble

core diameter which allows single mode operation at a wavelength of 1.3µm. (8)

Unit II- TRANSMISSION CHARACTERISTICS OF OPTICAL FIBERS

Part A

1. What is meant by attenuation loss?

2. What are the types of Attenuation?

3. What are the causes of absorption?

4. Define Urbach’s Rule?

5. Define Scattering Losses& Write the expression for Scattering Losses.

6. What is meant by bending loss and write its types?

7. Distinguish Dispersion shifted and dispersion flattened fibers.

8. Define Wave-guide Dispersion?

9. Briefly Explain About Group Delay?

10. Define Polarization Mode Dispersion?

11. Write the difference between intermodal and intra modal dispersion?

12. What is meant by pulse broadening?

13. Define Mie scattering.

14. Define optical birefringence.

15. What are the two major categories of fiber joints?

16. Define Fresnel reflection.

17. Define Fusion splices.

18. What are three major areas of fiber connectors?

19. Two polarization maintaining fibers operating at a wavelength of 1.3µm have beat lengths of 0.7mm and 80m.Determine the modal birefringence in each case and comment on the results.

20. The polarization mode dispersion in a uniformly birefringent single mode fiber is 300ps km-1. Calculate the maximum bit rate that may be obtained on a 20km repeater less link assuming only polarization mode dispersion to occur.

21. A 3.5 km length of two polarization mode PM fiber has a polarization crosstalk of -27dB at its output end. Determine the mode coupling parameter for the fiber.

22. What is a fiber coupler? What are their classifications?

Part B

1. a) Derive expression for material dispersion? (6)

b) Derive the expression for wave-guide dispersion? (6)

c) Discuss about mode coupling (4)

2. a) Discuss the signal distortion in single mode fibers? (8)

b) Discuss the pulse broadening in graded index fibers? (8)

3. a)When the mean optical power launched into an 8km length of fiber is 120(W ,the mean optical power at the fiber output is 3(W. Determine (6)

i) Overall signal attenuation in dB/Km and.

ii) The overall signal attenuation for a 10km optical link using the same fiber with splices at 1km intervals, each giving an attenuation of 1dB.

4. a)Discuss in detail intramodal dispersion with relevant expressions and

diagrams. (10)

b) Write a brief note on design optimization of single mode fibers.(6)

5. a) Discuss polarization mode dispersion and its limitations.(8)

b) Explain the scattering and bending losses that occur in an optical fiber with

relevant diagrams and expressions.(8)

6. a) Discuss about expanded beam connectors.(8)

b) Write a brief note on polarization.(8)

7. Explain briefly about fiber splicing techniques.

8. Explain briefly about different types of fiber couplers.

9. List the different types of mechanical misalignments that can occur between two joined fibers.

10. a ) When the mean optical power launched into an 8km length of fiber is 120µW, the

Mean optical power at the fiber output is 3µW.Determine:

1. The overall signal attenuation or loss in decibels through the fiber assuming there are no connectors or splices.

2. The signal attenuation per kilometer for the fiber.

3. The overall signal attenuation for a 10km optical link using the same fiber with splices at 1km intervals, each giving an attenuation of 1dB;

4. The numerical input / output power ratio in (c) coefficient for silica are 1.46 and 0.286 respectively. Determine the theoretical (8)

11. a) Silica has an estimated fictive temperature of 1400K with an isothermal compressibility of 7x10-11m2N-1. The refractive index and the photo elastic attenuation in decibels per kilometer due to the fundamental Rayleigh scattering in silica at optical wavelengths of 0.63, 1.00 and 1.30µm.Boltzmann’s constant 1.381x10-23JK-1.(8)

b) A long single –mode optical has an attenuation of 0.5dBkm-1 when operating at a wavelength of 1.3µm.The fiber core diameter is 6µm and the laser source bandwidth is pare the threshold optical powers for stimulated Brillouin and Raman scattering within the fiber at the wavelength specified. (8)

12. a) A multimode graded index fiber exhibits total pulse broadening of 0.1µs over a distance of 15km. estimate.

1. The maximum possible bandwidth on the link assuming on inter symbol interference

2. The pulse dispersion per unit length.

3. The bandwidth-length product for the fiber

b)The beat length in a single-mode optical fiber is 9cm when light from an injection laser with a spectral line width of 1nm and a peak wavelength of 0.9µm is launched into it. Determine the modal birefringence and estimate the coherence length in this situation.in addition calculate the difference between the propagation constants for the two orthogonal modes and check the result. (8)

13. a) An optical fiber has a core refractive index of 1.5. two lengths of the fiber with smooth and perpendicular end faces are butted together. Assuming the fiber axes are perfectly aligned. Calculate the optical loss in decibels at the joint (due to Fresnel reflection) when there is a small air gap between the fiber end faces.(8)

b) A single mode fiber has the following parameters,

Normalized frequency(V)=2.40

Core refractive index (n1)=1.46

Core diameter (2a)=8µm

Numerical aperture (NA)=0.1

Estimate the total insertion loss of a fiber joint with a lateral misalignment of 1µm and              an angular misalignment of 1º.

14. i. Describe the linear scattering losses in optical fibers. (8)

ii. Explain the mechanism of intermodal dispersion in a multimode step index fiber. (8)

15. i. What is Fresnel reflection in fiber joints? How it may be avoided.(8)

ii. Describe the common techniques used for the mechanical splicing of optical fibers.(8)

Unit III-SOURCES AND DETECTORS

Part A

1. What are the types of light sources in optical fibers?

2. What is meant By Hetro junction? Mention its advantages.

3. Distinguish direct and indirect band gap materials.

4. An LED has radiative and non radiative recombination times of 30 and 100ns respectively. Determine the internal quantum efficiency.

5. Define Responsivity?

6. Define LED light sources? & Write the types of LED?

7. Define Band Gap and its Types?

8. What are the sources of noises?

9. Define mode hopping.

10. What are the advantages of LED diodes?

11. Define modulation band width.

12. What are the requirements of optical detectors?

13. Define drift time & diffusion time.

14. Define quantum efficiency and responsivity.

15. Define dark current noise & thermal noise.

16. What are the advantages of injection laser diodes?

17. Draw the key transition processes involves in laser actions?

18. What is meant by modulation of laser diodes?

19. Define efficiency.

20. Calculate the ratio of the stimulated emission rate to the spontaneous emission rate for an incandescent lamp operating at a temperature of 1000K.It may be assumed that the average operating wavelength is 0.5µm.

21. A ruby laser contains a crystal length 4cm with a refractive index of 1.78.the peak emission wavelength from the device is 0.55µm.determine the number of longitudinal modes and their frequency separation.

22. The total efficiency of an injection laser with a GaAs active region is 18%.the voltage applied to the devices is 2.5V and the band gap energy for GaAs is 1.43eV. Calculate the external power efficiency of the device

23. The carrier velocity in a Si p-i-n photodiode with a 25µm depletion layer width Ia 3x104 ms-1.determine the maximum response time for the device.

24. GaAs has band gap energy of 1.43eV at 300K.Determine the wavelength above which an intrinsic photo detector fabricated from this material will cease to operate

25. Compare LED and ILD. (any two)

26. What are the characteristics of a good quality photo detector?

Part B

1. a)Draw and explain the LED structures based Double Hetero structure

configuration.(8)

b) Discuss the principle of operation of Laser diodes. What are the effects of

Temperature on the performance of a laser diode? (8)

2. a)Explain the different lensing schemes available to improve the power coupling

efficiency . (8)

b) Explain the fiber splicing techniques with necessary diagrams.(8)

3. a) Draw and explain the different structures used to achieve carrier and optical

confinement in laser diodes. (8)

b) Discuss the effect of temperature on the performance of a laser diode.(4)

c) Give a brief account of the modulation of an LED. (4)

4. a) What is meant by hetrojunction? Give example (8)

b) Derive the internal and external quantum efficiency of an LED. (8)

5. explain the operations of pin photodiode with neat diagram

6. Define noise and explain the types of noises.

7. Draw and explain the structure and operation of avalanche photodiode.

8. a) The output from a single mode semiconductor laser with a RIN value of 10-15dB Hz-1 is incident directly on an optical detector which has a bandwidth of 100MHz. the device is emitting at a wavelength of 1.55µm, at which the detector has a quantum efficiency of 60%. If the mean optical power incident on the detector is 2mW, determine a. The rms value of the power fluctuation and b. the rms noise current at the output of the detector.(8)

b)The radiative and non radiative recombination lifetimes of the minority carriers in the active region of a double hetrojunction LED are 60ns and 100ns respectively. Determine the total carrier recombination lifetime and the power internally generated within the device when the peak emission wavelength is 0.87µm at a drive current of 40mA. (8)

9. a) The quantum efficiency of a particular Si 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 is 11µA. determine the multiplication factor of the photodiode under these conditions. (8)

b) A germanium p-i-n photo diode with active dimensions of 100x50µm has a quantum efficiency of 55% when operating at a wavelength of 1.3µm.The measured dark current at this wavelength is 8nA.Calculate the noise equivalent power and specific detectivity for the device. It may be assumed that dark current is the dominant noise source. (8)

10. i) A photo diode has a quantum efficiency of 65% when photons of energy 1.5x10-19J are

incident upon it.

a. At what wavelength is the photodiode operating?

b. Calculate the incident optical power required to obtain a photocurrent of 2.5µA when the photodiode is operating as described above.

ii)When 3x1011 photons each with a wavelength of 0.85 µm are incident on a photodiode, on average 1.2x1011 electrons are collected at the terminals of the device. Determine the quantum efficiency and the responsivity of the photodiode at 0.85µm.

Unit IV-FIBER OPTIC RECEIVER AND MEASUREMENT

Part A

1. Define preamplifier

2. Define error sources in optical receiver.

3. What are the elements in optical receiver.

4. Define Quantum limit.

5. Write short notes about measurement of fiber attenuation.

6. Write short notes about measurement of fiber absorption loss.

7. Write short notes about measurement of fiber scattering loss.

8. Write short notes about measurement of fiber dispersion.

9. Write short notes about measurement of time domain.

10. Write short notes about frequency domain measurement.

11. Write short notes about interferometric methods.

12. Write short notes about Near field scanning method.

13. Write short notes about outer diameter measurement.

14. Write short notes about core diameter measurement.

15. Write short notes about Refracted near field method.

16. List the sources of noise in a fiber optic receiver.

17. Define fiber cutoff wavelength.

18. The shadow method is used for the on line measurement of the outer diameter of an optical fiber. the apparatus employs a rotating mirror with an angular velocity of 4 rad s-1 which is located 10 cm from the photo detector .At a particular instant in time a shadow pulse of width 300µs is registered by the photo detector. determine the outer diameter of the optical fiber in µm at this instant in time

Part B

1. Draw and explain operation of optical receiver with neat diagram.

2. Explain briefly about any two types of pre amplifiers.

3. Explain in details about measurement of spectral loss in optical fiber with neat diagram.

4. a. Explain in details about Calorimetric measurement of fiber absorption losses with neat diagram.(8)

b. Explain in details about measurement of scattering loss in optical fiber with neat diagram. (8)

5. Explain in details about measurement of fiber dispersion in optical fiber with neat diagram.

6. a)Explain in details about inter ferometric methods with neat diagram.(8)

b) Explain in details about near field scanning method with neat diagram.(8)

7. a)Explain in details about Refracted near field method.(8)

b) Explain in details about measurement of un cabled fiber cutoff wavelength.(8)

8. Explain in details about numerical aperture measurement.

9. Explain in details about different types of fiber diameter measurements.

10. a ) A 2km length of multimode fiber is attached to apparatus for spectral loss measurement. The measured output voltage from the photo receiver using the full 2km fiber length is 2.1V at a wavelength of 0.85µm. When the fiber is then cut back to leave a 2m length the output voltage increases to 10.7V. Determine the attenuation per kilometre for the fiber at a wavelength of 0.85µm and estimate the accuracy of the result. (8)

b )A He-ne laser operating at a wavelength of 0.63 µm was used with a solar cell cube to measure the scattering loss in a multimode fiber sample. With a constant optical output power the reading from the solar cell cube was 6.14nV.The optical power measurement at the cube without scattering was 153.38µV.the length of the fiber in the cube was 2.92cm.determine the loss due to scattering in dB km-1 for the fiber at a wavelength of 0.63µm. (8)

11. a )Pulse dispersion measurement are taken over a 1.2km length of partially graded multimode fiber. The 3dB widths of the optical input pulses are 300ps,and the corresponding 3dB widths for the output pulses are found to be 12.6ns.Assuming the pulse shapes and fiber impulse response are Gaussian calculate.(8)

12. A trigonometrical measurement is performance in order to determine the numerical aperture of a step index fiber. the screen is positioned 10.0cm from the fiber end face. When illuminated from a wide angled visible source the measured output pattern size is 6.2cm. Calculate the approximate numerical aperture of the fiber. (8)

13. Discuss about the various receiver configuration for better performance.(16)

Unit V-OPTICAL NETWORS

Part A

What are the elements in a network?

Define LAN, MAN and WAN.

Define nearest neighbor power budget.

What does u mean by throughput coupling loss and tap loss?

What are the parameters in power balance equation?

Define SONET / SDH

Draw the structure of WDM?

What do u mean by perfect shuffle.

What are the challenges in networks?

Mention the factors which are degrading network performance?

Write short notes about schemes which are used to reduce the power penalty effects of SBS?

Define frequency chirping.

What do u meant by four-wave – mixing?

Define dispersion compensation.

What is meant by link bandwidth?

Write short notes on Solitons?

Write short notes about solitons parameters.

Draw the structure of optical CDMA?

What is meant by Time slotted optical TDM?

Write short notes about Ultra high capacity networks?

Write a note on OTDR.

Part B

Explain in detail about different network topologies with neat diagram (8)

Explain in detail about performance of passive Linear Buses and star architectures. (16)

Explain in detail about basic structure of SONET frame and SONET / SDH rings? (16)

Explain in details about SONET / SDH networks? (8)

Explain in detail about broadcast and select single hop and multi hop networks. (16)

Explain in detail about wavelength routed networks? (16)

Explain in detail about nonlinear effects on network performance? (16)

Explain the following details

a) Link Bandwidth (8)

b) Crosstalk (8)

Explain in detail about solitons? (16)

Explain in detail about optical CDMA and OTDR? (16)

Explain in detail about Ultra high capacity networks? (16)

ASSIGNMENT TOPICS

ASSIGNMENT- I

1. A silica optical fiber has a core refractive index of 1.5 and a cladding refractive index of 1.47. Determine the acceptance angle in air for the fiber.

2. The relative refractive index difference between the core axis and the cladding of a graded index fiber is 0.7% when the refractive at the core axis is 1.45. Estimate the value for the numerical aperture of the fiber along the axis when the index profile is assume to be triangle.

3. A silica optical fiber with a core diameter large enough to be considered by ray theory analysis has a core refractive index of 1.5 and a cladding refractive index of 1.47.determine the numerical aperture and acceptance angle in air for the fiber.

4. A typical relative refractive index difference for an optical fiber designed for long distance transmission is 1%. Estimate the numerical aperture for the fiber when the core index is 1.47.

5. Calculate the numerical aperture, cut-off parameter and number of modes supported by fiber having µ1 (core) =1.54, µ2 (cladding= 1.5, core radius 25µm and operating wavelength 1300nm.

6. A multimode GI fiber has an acceptance angle in air of 8º.Estimate the relative refractive index difference between the core axis and the cladding when the refractive index at the core axis is 1.52.

7. A multimode step index fiber with a core diameter of 80µm and a relative index difference of 1.5% is operating at a wavelength of 0.85µm.If the core refractive index is 1.48. Determine. a) Normalized frequency of fiber. b ) the number of guided modes

8. A typical refractive index difference for an optical fiber designated for long distance transmission is 1% .determine the NA and the solid acceptance angle in air for the fiber when the core index is 1.46. Calculate the critical angle at the core- cladding interface with in the fiber.

9. Define and explain Goos- Haenchen shift.

10. Explain the advantages of optical fiber communication system.

11. Draw and explain the operations of fiber optical communication system.

ASSIGNMENT II

1. When the mean optical power launched into an 8km length of fiber is 120µW, the mean optical power at the fiber output is 3µW.Determine:

1. The overall signal attenuation or loss in decibels through the fiber assuming there are no connectors or splices.

2. The signal attenuation per kilometer for the fiber.

3. The overall signal attenuation for a 10km optical link using the same fiber with splices at 1km intervals, each giving an attenuation of 1dB;

4. The numerical input / output power ratio in (c) coefficient for silica are 1.46 and 0.286 respectively. Determine the theoretical

2. Silica has an estimated fictive temperature of 1400K with an isothermal compressibility of 7x10-11m2N-1. The refractive index and the photo elastic attenuation in decibels per kilometer due to the fundamental Rayleigh scattering in silica at optical wavelengths of 0.63, 1.00 and 1.30µm.Boltzmann’s constant 1.381x10-23JK-1.

3. A long single –mode optical has an attenuation of 0.5dBkm-1 when operating at a wavelength of 1.3µm.The fiber core diameter is 6µm and the laser source bandwidth is pare the threshold optical powers for stimulated Brillouin and Raman scattering within the fiber at the wavelength specified.

4. A multimode graded index fiber exhibits total pulse broadening of 0.1µs over a distance of 15km. estimate.

a. The maximum possible bandwidth on the link assuming on inter symbol interference

b. The pulse dispersion per unit length.

c. The bandwidth-length product for the fiber

5. The beat length in a single-mode optical fiber is 9cm when light from an injection laser with a spectral line width of 1nm and a peak wavelength of 0.9µm is launched into it. Determine the modal birefringence and estimate the coherence length in this situation.in addition calculate the difference between the propagation constants for the two orthogonal modes and check the result.

6. Two polarization maintaining fibers operating at a wavelength of 1.3µm have beat lengths of 0.7mm and 80m.Determine the modal birefringence in each case and comment on the results.

7. The polarization mode dispersion in a uniformly birefringent single mode fiber is 300ps km-1. Calculate the maximum bit rate that may be obtained on a 20km repeater less link assuming only polarization mode dispersion to occur.

8. A 3.5 km length of two polarization mode PM fiber has a polarization crosstalk of -27dB at its output end. Determine the mode coupling parameter for the fiber.

9. An optical fiber has a core refractive index of 1.5. two lengths of the fiber with smooth and perpendicular end faces are butted together. Assuming the fiber axes are perfectly aligned. Calculate the optical loss in decibels at the joint (due to Fresnel reflection) when there is a small air gap between the fiber end faces.

10. A single mode fiber has the following parameters,

Normalized frequency (V) = 2.40

Core refractive index (n1) = 1.46

Core diameter (2a) =8µm

Numerical aperture (NA)=0.1

Estimate the total insertion loss of a fiber joint with a lateral misalignment of 1µm and an angular misalignment of 1º.

ASSIGNMENT – III

1. Calculate the ratio of the stimulated emission rate to the spontaneous emission rate for an incandescent lamp operating at a temperature of 1000K.It may be assumed that the average operating wavelength is 0.5µm.

2. A ruby laser contains a crystal length 4cm with a refractive index of 1.78.the peak emission wavelength from the device is 0.55µm.determine the number of longitudinal modes and their frequency separation.

3. The total efficiency of an injection laser with a GaAs active region is 18%.the voltage applied to the devices is 2.5V and the band gap energy for GaAs is 1.43eV. Calculate the external power efficiency of the device.

4. The output from a single mode semiconductor laser with a RIN value of 10-15dB Hz-1 is incident directly on an optical detector which has a bandwidth of 100MHz. the device is emitting at a wavelength of 1.55µm, at which the detector has a quantum efficiency of 60%. If the mean optical power incident on the detector is 2mW, determine a. The rms value of the power fluctuation and b. the rms noise current at the output of the detector.

5. The radiative and non radiative recombination lifetimes of the minority carriers in the active region of a double hetrojunction LED are 60ns and 100ns respectively. Determine the total carrier recombination lifetime and the power internally generated within the device when the peak emission wavelength is 0.87µm at a drive current of 40mA.

6. The quantum efficiency of a particular Si 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 is 11µA. determine the multiplication factor of the photodiode under these conditions.

7. A germanium p-i-n photo diode with active dimensions of 100x50µm has a quantum efficiency of 55% when operating at a wavelength of 1.3µm.The measured dark current at this wavelength is 8nA.Calculate the noise equivalent power and specific detectivity for the device. It may be assumed that dark current is the dominant noise source.

8. The carrier velocity in a Si p-i-n photodiode with a 25µm depletion layer width Ia 3x104 ms-1.determine the maximum response time for the device.

9. GaAs has band gap energy of 1.43eV at 300K.Determine the wavelength above which an intrinsic photo detector fabricated from this material will cease to operate.

10. A photo diode has a quantum efficiency of 65% when photons of energy 1.5x10-19J are incident upon it.

a. At what wavelength is the photodiode operating?

b. Calculate the incident optical power required to obtain a photocurrent of 2.5µA when the photodiode is operating as described above.

11. When 3x1011 photons each with a wavelength of 0.85 µm are incident on a photodiode, on average 1.2x1011 electrons are collected at the terminals of the device. Determine the quantum efficiency and the responsivity of the photodiode at 0.85µm.

ASSIGNMENT IV

1. A 2km length of multimode fiber is attached to apparatus for spectral loss measurement. The measured output voltage from the photo receiver using the full 2km fiber length is 2.1V at a wavelength of 0.85µm. When the fiber is then cut back to leave a 2m length the output voltage increases to 10.7V. Determine the attenuation per kilometre for the fiber at a wavelength of 0.85µm and estimate the accuracy of the result.

2. A He-ne laser operating at a wavelength of 0.63 µm was used with a solar cell cube to measure the scattering loss in a multimode fiber sample. With a constant optical output power the reading from the solar cell cube was 6.14nV.The optical power measurement at the cube without scattering was 153.38µV.the length of the fiber in the cube was 2.92cm. Determine the loss due to scattering in dB km-1 for the fiber at a wavelength of 0.63µm.

3. Pulse dispersion measurement are taken over a 1.2km length of partially graded multimode fiber. The 3dB widths of the optical input pulses are 300ps, and the corresponding 3dB widths for the output pulses are found to be 12.6ns.Assuming the pulse shapes and fiber impulse response are Gaussian calculate.

4. A trigonometrical measurement is performance in order to determine the numerical aperture of a step index fiber. the screen is positioned 10.0cm from the fiber end face. When illuminated from a wide angled visible source the measured output pattern size is 6.2cm. Calculate the approximate numerical aperture of the fiber.

5. The shadow method is used for the on line measurement of the outer diameter of an optical fiber. The apparatus employs a rotating mirror with an angular velocity of 4 rad s-1 which is located 10 cm from the photo detector. At a particular instant in time a shadow pulse of width 300µs is registered by the photo detector. Determine the outer diameter of the optical fiber in µm at this instant in time.

ASSIGNMENT V

1. Explain SONET with neat diagram.

2. Write short notes for Solitons.

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