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2019

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Subject with Code : Optical Fiber Communication [16EC430] Course & Branch: B.Tech - ECE Year & Sem: IV-B.Tech & I-Sem Regulation: R16

UNIT –I

Introduction to Optical Fibers

1. _________ among the following is provided by an optical receiver for the regeneration of data signal with

minimum error?

2. Light is confined within the core of a simple optical fiber by __________

3. __________ makes optical fibers immune to EMI?

4. _________ type of light source opt for single-mode fiber

5. Speeds of laboratory fiber optic Local Area Networks are now in the range of _________

6. Metals can ________ the light beams.

7. Metals are _______.

8. Metals can transmit these ______

9. Reflectivity of metals _________

10. Refractive index of materials is approximately equal to square root of ____________

11. Snell’s law relates ____________.

12. Bouguer’s law relates ____________.

13. Sky looks blue because the sun light is subjected to __________.

14. Luminescence is because of _________

15. Fluorescence occurs within _______.

16. Electro-luminescence occurs in _________.

17. Pyrometer works based on ________

18. Solar cell works based on ______

19. Optical fiber operates on the principle of _________

20. The first semiconductor used in optical fiber is __________

21. WDM stands for _______

22. The boundary between truly guided modes and leaky modes are defined as _______

23. The modes are cutoff when β = __________

24. Each LP0m mode is derived from an __________

25. The modes propagate with different phase velocities, and the difference between their effective refractive indices is called the fiber ___________

26. The number of degenerative modes for LP02 is ___________

27. The number of degenerative modes for LP11 is ___________

28. In the structure of fiber optic cable, the refractive index of core is always _______the refractive index of

cladding

29. In the structure of a fiber, ______ component provides additional strength and prevents the fiber from

any damage?

30. ______ method allows large number of independent, selectable channels to exist on a single fiber?

31. _______ type of optical fiber would best be used in the Multiple Channel Architecture (MCA)?

32. ________ type of light source opt for multi-mode fiber

33. Visible light’s wavelength range ______________.

34. Planck’s constant value is ____________

35. _________ Sum of these is unity

36. The operating wavelength of optical cable in the 2nd generation is ____________

37. The pulses that can preserve their shape by counteracting the negative effects of dispersion is _______

38. The maximum angle in which the light incidents on fiber to propagate down the fiber is __________

39. The _____ of a mode is equal to the number of field zeros across the guide.

40. In _________ generation optical amplifiers are used as replacement for repeaters

UNIT –II

Signal Degradation in Optical Fibers

1. Different indices of refraction, composition and attenuation coefficients is known as _________

2. The speed at _____ energy in a particular mode travels along the fiber

3. A measure of the information capacity of an optical waveguide is specified by the ________

4. Material Dispersion is also known as ___________ dispersion

5. The variation of the refractive index of the core material as a function of wavelength is _______

6. A single mode fiber confines only about 80% of the optical power to the core is ___________

7. Material Dispersion and Waveguide Dispersion are the main causes of ____________

8. Each mode having a different value of group velocity at a single frequency is known as ________

9. The resulting difference in propagation times Δτ between the two orthogonal polarization modes will

result in pulse spreading is called __________

10. For wavelengths below about 1 μm is _________

11. For wavelengths longer than 1 μm is ________

12. If the bend radius is made a bit smaller once this threshold point has been reached, the loss suddenly

becomes ________

13. For LEDs the rms spectral width is approximately ____ of a central wavelength

14. Empirical relationship is given as _________

15. αuv=CeE/E0 is known as ____________

16. Large curvature radiation losses are also known as _________

17. The radius that are large compared with the fiber diameter is called ________

18. The fiber axis that can arise _____ the fibers are incorporated into cables

19. The bends caused either by non uniformities in the manufacturing of the fiber or by non uniform lateral

pressures created during the cabling of the fiber is ________

20. By extruding a compressible jacket over the fiber can minimize _______

21. Signal attenuation is also known as __________

22. _______ determines the maximum transmission distance between a transmitter and a receiver or an in-

line amplifier

23. The basic mechanisms in a fiber are ________

24. As light travels along a fiber, its power ______ exponentially with distance

25. Optical powers are commonly expressed in units of __________

26, Attenuation coefficient is commonly expressed in units of _________

27. Absorption is caused by _________

28. ____ damage effects depend on the energy of the ionizing particles or rays, the radiation flux and the

fluence is

29. The higher the radiation level, the attenuation will be ________

30. Impurity absorption losses occurs because of _____________

31. ______ occurs when a photon interacts with an electron in the valence band and excites it to higher

energy level

32. ɗ Tmod = _______________

33. A fiber with a given index profile α will exhibit different pulse spreading according to the source

wavelength used is generally called ___________

34. Pulse distortion will increase less rapidly after a certain initial length of fiber because of ________

35. ______ method to reduce fiber dispersion by spreading the dispersion minimum out over a wide range

36. The cladding portion next to the core has s lower index than the outer cladding region is known as ____

37. The cutoff wavelength of the first higher order mode is _________

38. Scattering is associated with ____________

39. 1 rad(Si) = ______

40. When the material is in a perfect state with no density variations, impurities, material inhomogeneities

is called __________

UNIT –III

Fiber Optical Sources and Coupling

1. In a pure crystal at low temperature, the conduction band is completely _______ of electrons

2. In a pure crystal at low temperature, the valence band is completely _______ of electrons

3. The simplest recombination process of electrons and holes, having the same momentum value is called __

4. The conduction band minimum and the valence band maximum energy levels occurs at different values

of momentum is called __________

5. The spacing between the atoms or groups of atoms is called the _________

6. The _____ method creates regions of high resistivity, thus restricting the current to a narrow path between

these regions

7. The average time that the photon resides in the lasing cavity before being lost by absorption is called ___

8. The _____ is a function of the semiconductor band structure and the carrier concentration

9. When any losses that are speckle pattern dependent are present in a link is _________

10. Intensity fluctuations in the longitudinal modes of a laser diode is caused by _______

11. The coupled efficiency of a fiber is defined as ________

12. A device with a short length of optical fiber, attached in an optimum power coupling configuration is __

13. The reflection coefficient is the ratio of ________

14. R = (n1-n / n1+n)2 , Where R is the ___________

15. If the source emitting area is larger than the fiber core area then the optical power coupled into fiber is _

16. A permanent bond connection of fiber is generally referred to as a ________

17. A demountable joint connection of fiber is known as _________

18. Edge emitting diode have an emission pattern , in the plane perpendicular to active region, has a FWHM

of _______

19. Edge emitting diode have an emission pattern , in the plane parallel to the junction, has a FWHM of __

20. The fiber to fiber coupling loss LF is given in terms of Ηf _____

21. When the two axes form an angle so that the fiber end faces are no longer parallel is called _____

22. The principal light sources used for fiber optic communications applications are ____

23. Heterojunction structured semiconductors are ________

24. A ________ consists of two adjoining semiconductor materials with different band-gap energies

25. The optical output from an LED is _____

26. The optical output from an LASER is _________

27. LEDs have been employed in high speed local area applications in which one wants to transmits several

wavelengths on the same fiber, this technique is called ________

28. The isotropic pattern from a surface emitter is called a ________

29. The peak output power occurs at 810nm, The width of the spectral pattern at its half power point is

known as __________

30. FWHM stands for _______

31. The fraction of the electron –hole pair that recombine radiatively is known as _______

32. The ratio of the photons emitted from the LED to the number of internally generated photons _______

33. Stimulated emission will exceed absorption only if the population of the excited states is greater than

that of the ground state. This condition is called ________

34. The extrapolation of the lasing region of the power versus current curve is defined as _________

35. The central region has a higher refractive index than the outer regions _______ index

36. The central region of the active layer has a lower refractive index than the outer regions ____ index

37. In fiber transmission applications an LED must have a __________

38, Surface emitters and edge emitters are the two basic configurations of __________

39. The Plane of the active light emitting region is oriented perpendicular to the axis of the fiber __ emitters

40. The sources of the incoherent light, and two guiding layers is _________

UNIT –IV

Fiber Optical Receiver

1. The important characteristics of photo detector are its ________

2. Responsivity R =_______________________

3. In most photodiodes the power level falling on the detector at a given photon energy is independent of__

4. Avalanche photodiode ______ receiver sensitivity

5. The carrier multiplication mechanisms is called___________________

6. A commonly used structure for achieving carrier multiplication with very little excess noise is the___

7. To generate a large signal power, the photo detector must have a _____ Quantum efficiency

8. The photo detector and amplifier should be kept as ________ as possible.

9. The sensitivity of a photo detector in optical fiber communication system is describable in terms of___

10. The statistical nature of the production and the collection of photo electrons generates the_____

11. For PIN photodiode, M (multiplication) and F(M) noise figure are________

12. _____ photo detectors involve the conversion of photons to heat

13. A photocathode and the electron multiplier packaged in a vacuum tube are capable of very high gain and

very low noise is____

14. The current flow in an external circuit, with one electron flowing for every carrier pair generated is

called______________

15. The time taken by an electron or hole to recombine is known as_______________

16. The cutoff wavelength for Si in PIN photodector is about______________

17. The cutoff wavelength for Ge in PIN photodector is about__________________

18. The discrete nature of current flow in the device causes______________

19. The unwanted noise from atmosphere and equipment-generated is called_____________

20. ISI stands for___________________

21. BER =________________

22. The minimum received optical power required for a specified BER performance in a digital system is

called_________________

23. The Rise time of Ge for avalanche photodiodes is___________________

24. The bandwidth of InGaAs for PIN photodiodes________________

25. The mean square value ‹i2DS› = σ2DS = 2qILB is______________

26. The detector load resistor and the active elements of the amplifier circuitry dominates noises in___

27. The thermal noise is less important and the photo detector noises usually dominate in__________

28. To achieve a high quantum efficiency, the depletion layer width W must be much larger than____

29. The responsivity of silicon for PIN photodiodes is___________

30. The criterion for measuring the performance of a digital communication system is the ___Probability.

31. Electrons or holes which are thermally generated in the pn junction of the photo diode gives raise to___

32. The current which is dependent on surface defects, cleanliness, bias voltage, and surface area is______

33. In normal usage, the _______ is operated in fully depleted mode

34. The configuration, where boron and silicon are used as a dopants for silicon is______

35. The average number of electron-hole pairs created by a carrier per unit distance traveled is called the___

36. Electron ionization rate is denoted with _______________

37. Hole ionization rate is denoted with____________

38. The ratio k =______________

39. The noise caused by spontaneous fluctuations of current or voltage in electric circuits is__________

40. The random motion of electrons in a conductor generates______________

UNIT –V

Design of Analog &Digital Systems& WDM Concepts

1. Parity check codes is used to _____________________

2. Digital receiver performance is evaluated by__________________

3. A simple fidelity criteria for analog receiver is the evaluation of________

4. ______ is required in analyzing an optical fiber link

5. _________ coding , when 1 and 0 are to b transmitted, signal occupies logic high level and logic low

level respectively

6. Bit error rate of optical receiver normally varies between___________

7. _________ analysis determines the power margin between optical transmitter output and receiver

sensitivity

8. BER is defined as_____________

9. What are the error correction schemes______________

10. CRC is a type of________

11. _______analysis determines the dispersion limitations of the optical fiber link

12. For RZ format, maximum bit rate is given by_______

13. Reduction in SNR is known as_____________

14. ___________noise occurs when speckle pattern dependent losses are present in fiber link

15. Delivering information from source to destination with minimum error is called as__________

16. _______ occurs due to intensity fluctuations in longitudinal modes of multimode fibers

17. In _____coding, 1 is encoded by high to low pulse and 0 is encoded by low to high pulse

18. For NRZ format, maximum bit rate is given by______ 19. Error control is done by means of________

20. Parity check code is a common way to detect_________

21. WDM means __________

22. _____can be increased by means of multiplexing technique

23. _______technique operates in optical domain

24. ______components does not require any external control on their operation

25. _______means transmission of multiple signals at a given time

26. _______ components require external control on their operation

27. ______ is the passive component

28. ______ is used to separate the optical signal into appropriate detection channels for signal processing

29. In WDM ________is used to combine and separate individual wavelengths

30. Degree of interaction between the guides depends on__________

31. _______ allows very narrow wavelength band to be transmitted and all others are reflected

32. _________is a active component

33. Numbers of couplers required to from N X N star coupler ___________

34. Excess loss is defined as_____________

35. _________device that allows light to pass along a fiber in only one direction

36. _______ multiplexing technique is used to transmits analog signals

37. Dielectric Thin Film filters act as _____an optical fiber link

38. Diffraction grating is classified into________

39. _________ are removable joints which allows easy, fast manual coupling and uncoupling

of fibers

40. __________ is a device in which light entering at any particular port travels around the

circulator and exit at the next port

Prepared by: Dr.P.G.Kuppusamy & Y.Murali

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