QUESTION BANK - SIETK ECE Deptsietkece.com/wp-content/uploads/2016/08/IV-I-and-Optical... · Web viewQUESTION BANK (DESCRIPTIVE) Subject with Code : Optical Fiber Communication [13A04702]

QUESTION BANK 2017

SIDDHARTH GROUP OF INSTITUTIONS :: PUTTURSiddharth Nagar, Narayanavanam Road – 517583

QUESTION BANK (DESCRIPTIVE)

Subject with Code : Optical Fiber Communication [13A04702] Course & Branch: B.Tech - ECE

Year & Sem: IV-B.Tech & I-Sem Regulation: R13

UNIT –I

Introduction to Optical Fibers

1. Explain the Elements of an optical fiber Transmission link. [L2][CO. 1][10M]

2. Discuss the Mode theory of Circular Waveguides. [L2][CO. 1][10M]

3 a). Explain the function of each block with a help of neat block diagram of a digital optical fiber

communication system? [L2, L4][CO.1][6M]

b). A light wave is travelling in a semiconductor medium (GaAs) of refractive index 3.6.It is incident

on a different semiconductor medium (Al GaAs) of refractive index 3.4 & angle of incidence is

80○. Calculate numerical aperture & θa .Will it result in total internal reflection comment on the

result? [L4][CO. 1][4M]

4 a). List the applications of optical communication? [L3][CO. 1][6M]

b). Consider multimode fiber that has a core R.I of 1.480 and core cladding index difference 2.0%.

Calculate NA, Critical angle and acceptance angle? [L4][CO. 1][4M]

5 a). With the help of electromagnetic spectrum, explain about the historical development of optic fiber

communication? [L2, L4][CO. 1][5M]

b). List the advantages of optical communication? [L1][CO. 1][5M]

6 a). Write about total internal reflection with the help of suitable optical cable setup? [L3][CO. 1][5M]

b). What is MFD of single mode fiber? Explain with suitable structure [L1, L4][CO. 1][5M]

7 a). Determine the propagation modes in single mode fibers? [L3][CO. 1][6M]

b). Fiber has normalized frequency 26.6 & operating wavelength 1300nm, if the radius of the fiber

core is 25µm. Compute the numerical aperture. [L4][CO. 1][4M]

8 a). Compare step index & graded index fiber? [L4][CO. 1][5M]

b). Illustrate about the propagation modes in multi mode fibers? [L2][CO. 1][5M]

9 a). Illustrate about the propagation modes in single mode fibers? [L2][CO. 1][6M]

b). Calculate number of modes of an optical fiber having diameter of 50µm & n1 =1.48 &

n2=1.46 having operating wavelength 0.82µm. [L4][CO. 1][4M]

Page 1

QUESTION BANK 2017

10 a). Why do we prefer Step index single mode fiber for long distance communication?

[L2][CO. 1][2M]

b). Define Critical angle & Acceptance angle? [L2][CO. 1][2M]

c). what are Ray and Modes? [L1][CO. 1][2M]

d). A light ray is incident from glass to air. Calculate critical angle? [L4][CO. 1][2M]

e). Derive Snell’s Law in Optics? [L4][CO. 1][2M]

Prepared by: V. Viswanadha, P. Vijaya..

Page 2

QUESTION BANK 2017


QUESTION BANK (OBJECTIVE)



UNIT –IIntroduction to Optical Fibers

1. Which among the following is provided by an optical receiver for the regeneration of data signal with minimum error? [ ]

(a). Photo-diode (b). Signal Processing circuits (c). Linear Circuitry (d). None 2. Light is confined within the core of a simple optical fiber by [ ]

(a). Refraction (b). Total internal reflection at the outer edge of the cladding

(c). Total internal reflection at the core cladding boundary.

(d). Reflection from the fiber's plastic coating.

3. What makes optical fibers immune to EMI? [ ](a). They transmit

signals in as light rather than electric current.

(b). They are too small for magnetic fields to introduce current in them.

(c). Magnetic fields cannot penetrate the glass of the fiber.

(d). They are readily shielded by outer conductors in cable.

4. The type of light source opt for single-mode fiber [ ](a). LASERs (b). LEDs (c). Both LASERs and LEDs (d). None

5. Speeds of laboratory fiber optic Local Area Networks are now in the range of [ ](a). 1 M bits/sec. (b). 10 M bits/secs. (c). Gigabits per second. (d). Hundreds of megabits

per second.6. Metals can ________ the light beams. [ ]

(a). Reflect (b). Refract (c). Transmit (d). None

7. Metals are _______. [ ](a). Transparent (b). Opaque (c). Translucent (d). None

8. Metals can transmit these ____. [ ](a). Radio ways (b). Visible light (c). Microwaves (d). x-rays

9. Reflectivity of metals [ ](a). 0.05 (b). 0.50 (c). 0.95 (d). None

10. Refractive index of materials is approximately equal to square root of [ ](a). Electrical

permittivity(b). Magnetic

permeability(c). Electrical permittivity x

magnetic permeability(d). None

Page 3

QUESTION BANK 2017

11. Snell’s law relates ____________. [ ](a). Light reflection (b). Light refraction (c). Light transmission (d). Light Absorption

12. Bouguer’s law relates ____________. [ ](a). Light reflection (b). Light transmission (c). Light refraction (d). Light Absorption

13. Sky looks blue because the sun light is subjected to __________. [ ](a). Rayleigh scattering (b). Compton scattering (c). Both A and B (d). None

14. Luminescence is because of [ ](a). Photons emitted while

excited electrons drops down

(b). Knocking out of electrons by photons

(c). Photons stimulated by photons

(d). All

15. Fluorescence occurs within _______. [ ](a). 10-5 s (b). 10-5 ms (c). 10-5 μs (d). 10-5ns

16. Electro-luminescence occurs in _________. [ ](a). Electrical conductors (b). Electrical insulators (c). p-n junctions (d). All

17. Pyrometer works based on [ ](a). Laser technology (b). Photo-conduction (c). Thermal emission (d). Tyndall effect

18. Solar cell works based on [ ](a). Laser technology (b). Photo-conduction (c). Thermal emission (d). Tyndall effects

19. Optical fiber operates on the principle of [ ](a). TIR (b). Tyndall effect (c). Photo-electric effect (d). Laser technology

20. The first semiconductor used in optical fiber is [ ](a). GaAs (b). GaAsP (c). InGaAsp (d). GaAlAs

21. WDM stands for [ ](a). Wide division

multiplexing(b). Wavelength division

multiplexing(c). Wave division

multiplexing(d). Whole wave

division multiplexing

22. The boundary between truly guided modes and leaky modes are defined as [ ](a). Cutoff conditions (b). Active condition (c). Saturation condition (d). None

23. The modes are cutoff when β = [ ](a). n2k (b). n1k (c). n2k*n1k (d). n1k2

24. Each LP0m mode is derived from an [ ](a). HE0m (b). TE1m (c). HE1m (d). TM0m

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

(a). Beat length (b). Birefringence (c). V number (d). Degenerative mode

26. The number of degenerative modes for LP02 is [ ](a). 1 (b). 2 (c). 3 (d). 4

27. The number of degenerative modes for LP11 is [ ]

Page 4

QUESTION BANK 2017

(a). 1 (b). 2 (c). 3 (d). 4

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

(a). Less than (b). Equal to (c). Greater than (d). None

29. In the structure of a fiber, which component provides additional strength and prevents the fiber from any damage? [ ]

(a). Core (b). Cladding (c). Buffer Coating (d). Jacket

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

(a). Frequency Division Multiplexing.

(b). Time Division Multiplexing

(c). Analog Modulation

(d). Phase Modulation

31. What type of optical fiber would best be used in the Multiple Channel Architecture (MCA)? [ ](a). Refractive-Index. (b). Step-Index. (c). Graded-Index. (d). None

32. The type of light source opt for multi-mode fiber [ ](a). LASERs (b). LEDs. (c). Both A & B (d). None

33. Visible light’s wavelength range ______________. [ ](a). 0.39 – 0.77 mm (b). 0.39 – 0.77 μm (c). 0.39 – 0.77 nm (d). 0.39 – 0.77 cm

34. Planck’s constant [ ](a). 6.62x10-34 J.sec (b). 6.62x10-34 J.min (c). 6.62x10-34

Cal.sec(d). 6.62x10-34

Cal.min35. Sum of these is unity [ ]

(a). Reflectivity (b). Reflectivity + Refractivity

(c). Reflectivity + Refractivity + Transmitivity

(d). None

36. The operating wavelength of optical cable in the 2nd generation is [ ](a). 1.3μm (b). 0.8μm (c). 1.55μm (d). 2.6μm

37. The pulses that can preserve their shape by counteracting the negative effects of dispersion is [ ](a). Optical solitons (b). Optical solutions (c). Optical amplifier (d). Opto-coupler

38. The maximum angle in which the light incidents on fiber to propagate down the fiber is [ ](a). Numerical aperture (b). Critical angle (c). Acceptance angle (d). Skew rays

39. The _____ of a mode is equal to the number of field zeros across the guide. [ ](a). Leaky (b). Radiation (c). Order (d). Degenerative

40. In which generation optical amplifiers are used as replacement for repeaters [ ](a). 1st generation (b). 2nd generation (c). 3rd generation (d). 4th

generation


Page 5

QUESTION BANK 2017





UNIT –II

Signal Degradation in Optical Fibers

1. Describe any two types of Losses in Optical Fiber Communication System. [L2][CO. 2][10M]

2. Explain the Design Optimization of Single mode fibers. [L2][CO. 2][10M]

3. How attenuation is caused by scattering losses & bending losses? [L2][CO. 2][10M]

4 a). Define linear scattering? Explain about Rayleigh & Mie scattering? [L1,L2][CO. 2][5M]

b). Derive the expression for waveguide dispersion. [L4][CO. 2][5M]

5. Explain dispersion occurring in multimode fibers in detail with expressions? [L2,L4][CO.2][10M]

6 a). Distinguish between intrinsic & extrinsic Absorption ? [L4][CO. 2][4M]

b). Determine the theoretical cutoff wavelength for single mode fiber? [L4][CO. 2][4M]

7 a). What is attenuation? Explain in detail? [L2][CO. 2][4M]

b). Derive the expression for material dispersion. [L4][CO. 2][6M]

8 Analyze pulse broadening in graded index waveguides? [L4][CO. 2][10M]

9 a). Derive the total dispersion in single mode fiber? [L4][CO. 2][5M]

b). How refractive index profile optimizes the design in a single mode fiber? [L5][CO. 2][5M]

10 a). What are the two main causes of Intra Modal Dispersion? [L1][CO. 2][2M]

b). Explain the phenomenon of Rayleigh scattering in scattering loss? [L2][CO. 2][2M]

c). What are the Mechanisms which causes Absorption? [L1][CO. 2][2M]

d). How to minimize the micro bending losses in the fiber? [L1][CO. 2][2M]

e). Derive Signal distortion in single mode fibers? [L4][CO. 2][2M]

Prepared by: V. Viswanadha, P. Vijaya.

Page 6

QUESTION BANK 2017





UNIT –II

Signal Degradation in Optical Fibers

1. Different indices of refraction, composition and attenuation coefficients is known as [ ](a). Core & Cladding loss (b). Bending losses (c). Macro bending losses (d). Leaky loss

2. The speed at which energy in a particular mode travels along the fiber [ ](a). Bandwidth delay (b). Intramodal delay (c). Intermodal delay (d). Group velocity

3. A measure of the information capacity of an optical waveguide is specified by the [ ](a). Bw-distance product (b). BW product (c). Distance measure (d). None

4. Material Dispersion is also known as ___________ dispersion [ ](a). Waveguide (b). Chromatic (c). Intermodal (d). Intramodal

5. The variation of the refractive index of the core material as a function of wavelength is [ ](a). Waveguide

Dispersion(b). Intermodal

Dispersion(c). Material Dispersion (d). Intramodal

Dispersion6. A single mode fiber confines only about 80% of the optical power to the core is [ ]

(a). Waveguide Dispersion

(b). Intermodal Dispersion

(c). Material Dispersion (d). Intramodal Dispersion

7. Material Dispersion and Waveguide Dispersion are the main causes of [ ](a). Intermodal Dispersion (b). Intramodal Dispersion (c). Both A & B (d). None

8. Each mode having a different value of group velocity at a single frequency is known as [ ](a). Bandwidth delay (b). Intramodal delay (c). Intermodal delay (d). Group delay

9. The resulting difference in propagation times Δτ between the two orthogonal polarization modes will result in pulse spreading is called [ ]

(a). Intermodal dispersion

(b). Polarization mode dispersion

(c). Intramodal delay (d). Material Dispersion

10. For wavelengths below about 1 μm is [ ](a). Dominant loss (b). Infrared absorption (c).Isothermal loss (d). None

11. For wavelengths longer than 1 μm is [ ](a). Dominant loss (b). Infrared absorbtion (c).Isothermal loss (d). None

Page 7

QUESTION BANK 2017

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

(a). Small (b). Constant (c). Extremely Large (d). Medium

13. For LEDs the rms spectral width is approximately ____ of a central wavelength. [ ](a). 0.5% (b).10% (c). 15% (d). 5%

14. Empirical relationship is given as [ ](a). αuv=CeE/E0 (b). αuv=CeE0/E (c). αuv=CeE0/E2 (d). None

15. αuv=CeE/E0 is known as [ ](a). Allwave rule (b). Neper rule (c). Maxwell rule (d).Urbach’s rule

16. Large curvature radiation losses are also known as [ ](a). Macrobending losses (b). Bending losses (c). Both A & B (d). Leaky losses

17. The radius that are large compared with the fiber diameter is called [ ](a). Macroscopic bends (b). Random microscopic bends (c). Both A & B (d). None

18. The fiber axis that can arise when the fibers are incorporated into cables. [ ](a). Macroscopic bends (b). Random microscopic bends (c). Both A & B (d). None

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 [ ]

(a). Leaky loss (b). Packaging loss (c). Bending loss (d). Core loss

20. By extruding a compressible jacket over the fiber can minimize [ ](a). Macrobending

losses(b).Bending losses (c). Microbending

losses(d). Random

microscopic bends21. Signal attenuation is also known as [ ]

(a). Fiber loss (b). Bending loss (c). Absorption loss (d). Cladding loss

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

(a). Amplifier (b). Repeater (c). Attenuation (d). None23. The basic mechanisms in a fiber are [ ]

(a). Absorption (b). Scattering (c). Radiation loss (d). All24. As light travels along a fiber, its power ______ exponentially with distance. [ ]

(a). Increases (b). Decreases (c). Constant (d). None

25. Optical powers are commonly expressed in units of [ ](a). dB/Km (b).dB/m (c). dBm (d).dB

26. Attenuation coefficient is commonly expressed in units of [ ](a). dB/Km (b). dB/m (c). dBm (d).dB

27. Absorption is caused by [ ](a). Atomic defects (b). Impurity atoms (c). Basic constituent atoms (d). All

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

(a). Leaky (b). Radiation (c). Order (d). Mode

Page 8

QUESTION BANK 2017

29. The higher the radiation level, the attenuation will be [ ](a). Smaller (b). Equal (c). Very low (d). Larger

30. Impurity absorption losses occurs because of [ ](a). Electronic transition (b). Charge transitions (c). Both A & B (d). Only A

31. ______ Occurs when a photon interacts with an electron in the valence band and excites it to higher energy level [ ]

(a). Absorption (b). Scattering (c). Radiation (d). Order

32. ɗ Tmod = [ ](a). Tmax-Tmin (b). Tmax+Tmin (c). Tmin +Tmax (d). Tmin -Tmax

33. A fiber with a given index profile α will exhibit different pulse spreading according to the source wavelength used is generally called [ ]

(a). Polarization mode dispersion

(b). Material Dispersion (c). Profile Dispersion (d). Waveguide Dispersion

34. Pulse distortion will increase less rapidly after a certain initial length of fiber because of [ ](a). Mode coupling (b). Differential mode loss (c). Both A & B (d). None

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

(a). Dispersion Flattening (b). Dispersion shifted (c). Matched cladding (d). None

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

(a). Matched cladding (b). Depressed-cladding (c). Dispersion shifted (d). None

37. The cutoff wavelength of the first higher order mode is [ ](a). LP11 (b). LP01 (c). TM01 (d). TE01

38. Scattering is associated with [ ](a). Fiber Material (b). Structural Imperfections (c). Both A & B (d). Only A

39. 1 rad(Si) = [ ](a). 100 erg (b). 100 g (c). 100 g/erg (d). 100 erg/g

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

(a). External absorption (b). Internal absorption (c). Scattering loss (d). Fiber loss


Page 9

QUESTION BANK 2017





UNIT –III

Fiber Optical Sources and Coupling

1. a). Explain LED Structure with neat sketch. [L2][CO. 3][6M]

b). A planar LED is fabricated from GaAs which has a refractive index of 3.6. (i) Calculate the

optical power emitted into air as a percentage of the internal optical power for the device when

the transmission factor at the crystal-air interface is 0.68. (ii) When the optical power generated

internally is 50% of the electric power supplied, determine the external power efficiency. .

. [L4][CO. 3][4M]

2. a). Explain in detail the various Lensing schemes for coupling improvement [L2][CO. 3][5M]

b). Discuss about Fiber splicing. [L2][CO. 3][5M]

3. a). Determine the possible losses due to lateral and angular misalignment in an optical fiber?

[L2][CO. 3][6M]

b). Explain the various connectors used in fiber optics? [L2][CO. 3][4M]

4. a). Illustrate the factors involved in launching optical power from a light source to fiber.

. [L3][CO. 3][7M]

b). What is a pig-tailed device? [L1][CO. 3][3M]

5. a). What is fiber joint? Explain joint losses and alignment losses [L1,L2][CO.3][5M]

b). List out the advantages and disadvantages of pig tailing either as fiber optic source or as fiber

optic detector. [L1][CO. 3][5M]

6. a). Derive an expression for power coupling from a large surface emitting LED into smaller step

index fiber. [L4][CO. 3][5M]

b). A GaAs optical source with a refractive index of 3.6 is coupled to a silica fiber that has a

refractive index is 1.48. If the fiber and the source are in close physical contact then find the

Fresnel reflection at the interface and power loss in dB. [L4][CO. 3][5M]

7. a). Differentiate between dispersion limited and an attenuation limited fiber optic links.

[L4][CO. 3][5M]

Page 10

QUESTION BANK 2017

b). Discuss about the point to point fiber optical link. [L2][CO. 3][5M]

8. a). Explain about cylindrical ferrule connectors? [L2][CO. 3][5M]

b). An LED has a 500 µf space charge capacitance, 1.003 ρA saturation current and a 5 ns minority

carrier lifetime find out the half current and 10 to 90 percent risk time when the drive current is

a. (i) 50mA and (ii) 100mA respectively. [L4][CO. 3][5M]

9. a). Derive the expression for lasing and threshold condition of LASER. [L4][CO. 3][6M]

b). What power is radiated by an LED if its quantum efficiency is 3% and the peak wavelength is

. 670nm? [L4][CO. 3][4M]

10. a). Write a short note on Fiber Splicing. [L2][CO. 3][2M]

b). Draw the schematic diagram of a high radiance surface-emitting LED. [L1][CO. 3][2M]

c). Differentiate between spontaneous emission and stimulated emission? [L3][CO. 3][2M]

d). Derive rate equation for LASER diode? [L4][CO. 3][2M]

e). Define Population Inversion. [L2][CO. 3][2M]


Page 11

QUESTION BANK 2017





UNIT –III

Fiber Optical Sources and Coupling

1. In a pure crystal at low temperature, the conduction band is completely _______ of electrons [ ](a). Empty (b). Full (c). Medium (d). None

2. In a pure crystal at low temperature, the valence band is completely _______ of electrons [ ](a). Empty (b). Full (c). Medium (d). None

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

(a). Indirect band gap (b). Lattice constant (c). Epitaxial (d). Direct band gap

4. The conduction band minimum and the valence band maximum energy levels occurs at different values of momentum is called [ ]

(a). Indirect band gap (b). Lattice constant (c). Epitaxial (d). Direct band gap

5. The spacing between the atoms or groups of atoms is called the [ ](a). Lattice constant (b). Lattice Spacing (c). Both A & B (d). Lattice

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

(a). Neutron Implantation (b). Electron Implantation

(c). Proton Implantation (d). None

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

(a). Photon lifetime (b). DBR (c). Spontaneous lifetime (d). None8. The _____ is a function of the semiconductor band structure and the carrier concentration [ ]

(a). Photon lifetime (b). DBR (c). Spontaneous lifetime (d). None9. When any losses that are speckle pattern dependent are present in a link is [ ]

(a). Leaky noise (b). Modal noise (c). Thermal noise (d). Photon noise10. Intensity fluctuations in the longitudinal modes of a laser diode is caused by [ ]

(a). Leaky noise (b). Modal noise (c). Thermal noise (d). Mode partition noise11. The coupled efficiency of a fiber is defined as [ ]

(a). η=PE/PF (b). η=PF/PE (c). η=PF/PS (d). η=PS/PF

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

Page 12

QUESTION BANK 2017

(a).Fly lead/ Pigtail (b). Fly load (c). Radiance (d). None13. The reflection coefficient is the ratio of [ ]

(a). r = (n-n1)/(n1+n) (b). r = (n1+n)/(n1-n) (c). r = (n-n1)/(n+n1) (d). r = (n1-n)/(n1+n)14. R = (n1-n / n1+n)2 , Where R is the [ ]

(a). Reflection coefficient (b). Fresnel reflection (c). Radiance reflection (d). None

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

(a). Maximum (b). Minimum (c). Medium (d). Constant16. A permanent bond connection of fiber is generally referred to as a [ ]

(a). Connector (b). Splice (c). Lead (d). Node17. A demountable joint connection of fiber is known as [ ]

(a). Connector (b). Splice (c). Lead (d). Node

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

(a). 15-55 o (b). 5-10 o (c). 30-50o (d). 30-60 o

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

(a). 15-55 o (b). 5-10 o (c). 30-50o (d). 30-60 o

20. The fiber to fiber coupling loss LF is given in terms of Ηf [ ](a). -10 log ηF (b). 10 log ηF (c). 20 log ηF (d). None

21. When the two axes form an angle so that the fiber end faces are no longer parallel is called [ ](a). Axial

displacement(b). Longitudinal

displacement(c). Angular

misalignment (d). None

22. The principal light sources used for fiber optic communications applications are [ ](a). LASER (b). LED (c). ILDs (d). All

23. Heterojunction structured semiconductors are [ ](a). LASER (b). LED (c). Both A & B (d). None

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

(a). Heterojunction (b). Homojunction (c). ILDs (d). None25. The optical output from an LED is [ ]

(a). Coherent (b). Incoherent (c). Monochromatic (d). Spectral26. The optical output from an LASER is [ ]

(a). Coherent (b). Incoherent (c). Monochromatic (d). Spectral

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 [ ]

(a). Monochromatic (b). Homojunction (c). Spectral Slicing (d). Coherent28. The isotropic pattern from a surface emitter is called a [ ]

(a). Surface emitters (b). Edge emitters (c). Lambertian pattern (d). Lattice

Page 13

QUESTION BANK 2017

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

(a).FWHM (b). FMHW (c). FHMW (d). None

30. FWHM stands for [ ](a). Full width half

minimum(b). Full width half

maximum(c). Full wide half

maximum(d). Full wide half

minimum31. The fraction of the electron –hole pair that recombine radiatively is known as [ ]

(a). Internal quantum efficiency

(b). External quantum efficiency (c). Both A & B (d). None

32. The ratio of the photons emitted from the LED to the number of internally generated photons [ ](a). Internal quantum

efficiency(b). External quantum

efficiency (c). Both A & B (d). None

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 [ ]

(a). Internal quantum efficiency

(b). External quantum efficiency

(c). Population Inversion

(d). Full width half maximum

34. The extrapolation of the lasing region of the power versus current curve is defined as [ ](a). Threshold current (b). Threshold density (c). Density curve (d). None

35. The central region has a higher refractive index than the outer regions [ ](a). Positive index (b). Negative index (c). Neutral index (d). None

36. The central region of the active layer has a lower refractive index than the outer regions [ ](a). Positive index (b). Negative index (c). Neutral index (d). None

37. In fiber transmission applications an LED must have a [ ](a). High radiance

output(b). Fast emission

response time(c). High quantum

efficiency (d). All

38. Surface emitters and edge emitters are the two basic configurations of [ ](a). LASER (b). LED (c). ILDs (d). All

39. The Plane of the active light emitting region is oriented perpendicular to the axis of the fiber [ ](a). Surface emitters (b). Edge emitters (c). Lattice (d). None

40. The sources of the incoherent light, and two guiding layers is [ ](a). Surface emitters (b). Edge emitters (c). Lattice (d). None


Page 14

QUESTION BANK 2017



Subject with Code : Optical Fiber Communication [13A04702] Course & Branch: B.Tech – ECE


UNIT –IV

Fiber Optical Receiver1. a). Explain in detail the operation of Avalanche Photo Diode with its structure. [L2][CO. 4][6M]

b). A photo diode has a quantum efficiency of 65% when photons of energy of 1.5 x 10'19 J are

incident upon it. (i) Find the operating wavelength of the photodiode, (ii) Calculate the incident

optical power required to obtain a photo current of 2.5 nA when the photodiode is operating as

described above. [L4][CO. 4][4M]

2. a). Discuss any one type of Preamplifier in detail. [L2][CO. 4][6M]

b). Give the comparisons of photo detectors. [L4][CO. 4][4M]

3. a). Explain the principle behind the operation of an PIN photo diode. [L2][CO. 4][6M]

b). Draw and explain the simple energy band diagram for a PIN photodiode? [L2,L4][CO. 4][4M]

4. a). Illustrate how noises are entered into photo detector? [L3][CO. 4][5M]

b). With simple model and equivalent circuit, explain photo detector receiver? [L2,L4][CO. 4][5M]

5. a). Derive the equation for S/N ratio of an optical fiber? [L4][CO. 4][5M]

b). Explain surface dark current and bulk dark current? [L1,L2][CO. 4][5M]

6. a). Derive the expression for response time of a photodiode? [L4][CO. 4][4M]

b). Explain the working of depletion layer photocurrent with diagram? [L2,L4][CO. 4][6M]

7. a). List the operating parameters of Si, Ge, InGaAs for PIN diode and avalanche photodiode?

[L1][CO. 4][6M]

b). A given silicon avalanche photodiode has a quantum efficiency of 65% at a wavelength of 900

nm. Suppose 0.5 μW of optical power produces a multiplied photocurrent of 10 μA. Calculate

the multiplication M? [L4][CO. 4][4M]

8. a). Explain the digital signal transmission for an optical receiver? [L2][CO. 4][5M]

b). How the noise sources are generated in optical receiver? [L1][CO. 4][5M]

9. a). Explain the mechanism of noise sources and disturbance in the optical pulse detection with

diagram? [L2][CO. 4][6M] Page 15

QUESTION BANK 2017

b). Define intersymbol interference with diagram? [L1,L4][CO. 4][4M]

10. a) Define quantum efficiency? [L2][CO. 4][2M]

b) What are the conditions to be met to achieve a high S/N ratio [L1][CO. 4][2M]

c) List out the factors that the Response time depends on. [L1][CO. 4][2M]

d) Define bit error rate? [L2][CO. 4][2M]

e) What are the various noise sources and disturbances in optical pulse detection mechanism

. [L1][CO. 4][2M]

Prepared by: V.Viswanadha,P.Vijaya.





UNIT –IV Fiber Optical Receiver

1. The important characteristics of photo detector are its

(a). Quantum efficiency (b). Response speed (c). Both A & B (d). None [ ]

2. Responsivity R=(a). IP/ P0 (b). P0/ IP (c). nq/ nh (d). hv/ nq [ ]

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

(a). Responsivity (b). Quantum efficiency (c). Response speed (d). None [ ]

4. Avalanche photodiode ______ receiver sensitivity(a). Decreases (b). Medium (c). Increases (d). Constant [ ]

5. The carrier multiplication mechanisms is called

(a). RAPD (b). Reach through (c). Quantum (d). Impact

ionization [ ]

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

(a). RAPD(b). Reach through construction

(c). Quantum (d). Impact ionization [ ]

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

Page 16

QUESTION BANK 2017

(a). Medium (b). Low (c). High (d). Constant [ ]8. The photo detector and amplifier should be kept as ________ as possible.

(a). Medium (b). Low (c). High (d). Constant [ ]

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

(a). Minimum detectable optical power

(b). Maximum detectable optical power

(c). Threshold voltage (d). None [ ]

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

(a). Shot noise (b). Quantum noise (c). Both A & B (d). None [ ]

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

(a). Constant (b). Unity (c). Low (d). High [ ]

12. _____ photo detectors involve the conversion of photons to heat(a). Pyroelectric (b). Photomultiplier (c). Photoconductor (d). Photodiodes [ ]

13. A photocathode and the electron multiplier packaged in a vacuum tube are capable of very high gain and very low noise is(a). Pyroelectric (b). Photomultiplier (c). Photoconductor (d). Photodiodes [ ]

14. The current flow in an external circuit, with one electron flowing for every carrier pair generated is called(a). Photocurrent (b). Photomultiplier (c). Photoconductor (d). Photodiodes [ ]

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

(a). Diffusion length (b). Photocarrier (c). Carrier lifetime (d). Photocurrent [ ]

16. The cutoff wavelength for Si in PIN photodector is about(a). 1.25μm (b). 1.6 μm (c). 1.75 μm (d). 1.06 μm [ ]

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

(a). 1.25μm (b). 1.6 μm (c). 1.75 μm (d). 1.06 μm [ ]

18. The discrete nature of current flow in the device causes(a). Internal Noise (b). External Noise (c). Thermal Noise (d). Shot Noise [ ]

19. The unwanted noise from atmosphere and equipment-generated is called (a). Internal Noise (b). External Noise (c). Thermal Noise (d). Shot Noise [ ]

20. ISI stands for(a). Inter symbol

interference(b).Inter signal

interference(c). Intra signal interact

(d). Interaction symbol interference [ ]

21. BER = (a). Ne/ Bt (b). Ne/ Nt (c). Both A & B (d). None [ ]

22. The minimum received optical power required for a specified BER performance in a digital system is called(a). Minimum detectable signal (b). ISI (c). Quantum limit (d). None [ ]

Page 17

QUESTION BANK 2017

23. The Rise time of Ge for avalanche photodiodes is(a). 0.4-0.6 (b). 0.7-0.9 (c). 0.6-0.8 (d). 0.5-0.8 [ ]

24. The bandwidth of InGaAs for PIN photodiodes(a). 1-2 (b). 2-3 (c). 3-4 (d). 4-5 [ ]

25. The mean square value ‹i2DS› = σ2

DS = 2qILB is(a). Bulk dark current (b). Surface dark current (c). Quantum current ((d). Reverse current [ ]

26. The detector load resistor and the active elements of the amplifier circuitry dominates noises in(a). PIN photodiode (b). Avalanche photodiodes (c). Both A & B (d). None [ ]

27. The thermal noise is less important and the photo detector noises usually dominate in(a). PIN photodiode (b). Avalanche photodiodes (c). Both A & B (d). None [ ]

28. To achieve a high quantum efficiency, the depletion layer width W must be much larger than(a). 1/ αs (b). αs/ 1 (c). αs/ αp (d). None [ ]

29. The responsivity of silicon for PIN photodiodes is(a). 0.5-0.8 (b). 0.6-0.4 (c). 0.4-0.6 (d). 0.3-0.7 [ ]

30. The criterion for measuring the performance of a digital communication system is the ___Probability(a). Error source (b). Spontaneous error (c). Bit error (d). Average error [ ]

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

(a). Bulk dark current (b). Surface leakage current

((c). Quantum current (d). Reverse current [ ]

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

(a). Bulk dark current (b). Surface leakage current (c). Quantum current (d). Reverse

current [ ]

33. In normal usage, the _______ is operated in fully depleted mode(a). RAPD (b). Reach through (c). Quantum (d). Impact ionization [ ]

34. The configuration, where boron and silicon are used as a dopants for silicon is(a). p+πpn+ structure (b). p-πnp+ structure (c). npn structure (d). p-πpn- structure [ ]

35. The average number of electron-hole pairs created by a carrier per unit distance traveled is called the(a). Quantum rate (b). Impact rate (c). Ionization rate (d). None [ ]

36. Electron ionization rate is denoted with (a). α (b). β (c). Ω (d). η [ ]

37. Hole ionization rate is denoted with(a). α (b). β (c). Ω (d). η [ ]

38. The ratio k =

(a). α/ β (b). β/ α (c). η/ α (d). Ω/ β[ ]

Page 18

QUESTION BANK 2017

39. The noise caused by spontaneous fluctuations of current or voltage in electric circuits is(a). Internal Noise (b). External Noise (c). Thermal Noise (d). None [ ]

40. The random motion of electrons in a conductor generates(a). Internal Noise (b). External Noise (c). Thermal Noise (d). None [ ]



QUESTION BANK [DESCRIPTIVE]

Page 19

QUESTION BANK 2017



UNIT –V

System Design and Appliations1. Analyze the

Power Budget of

Optical Fibre

Communication in

terms of analog

system design.

[L4][CO.6][10M]

2. Describe in detail about Rise time Budget of Optical Fibre Communication in-terms of digital system design. [L4, L2][CO.6][10M]

3. a). Analyze the system performance using link power budget of analog systems. [L4][CO.6][6M]

b). How responsivity and sensitivity of optical receiver will effect on system performance

[L1][CO.5][4M]

4. a). Define CNR. Derive the mathematical form. [L1,L4][CO.5][6M]

b). LED spectral width of 40nm has rise time of 15ns, tmat is 21ns, trx is 14ns and tmod is 3.9ns. Find

total system rise time. [L4][CO.6][4M]

5. a). Explain optical power loss model for a point to point link. [L2][CO.6][6M]

b). What is significance of system consideration in point-to-point fiber links? Explain? .

. [L2][CO.5][4M]

6. a). What is meant by detector response type? [L1][CO.5][5M]

b). Calculate the responsivity of detector of with quantum efficiency of 10% at 800nm

[L4][CO.6][5M]

7. a). Considering the probability distributions for log 0 and 1 signal pulses, derive the expression

for BER and error function. [L4]

[CO.5][6M]

b). List the system specification for the design of digital system and explain it? [L1][CO.5][4M]

8. a). Derive the system performance using bandwidth budget for analog system. [L4][CO.5][5M]

b). An optical transmission system is constrained to have 500 GHZ channel spacing. How many

wavelength channels can be utilized in the 1536 to 1556 nm spectral band? [L4][CO.6][5M]

Page 20

QUESTION BANK 2017

9. a). Analyze the system performance using link power budget of digital systems. [L4][CO.5][6M]

b). Write short notes on multichannel frequency modulation? [L1][CO.5][4M]

10. a) What is Power Budget? [L1][CO.5][2M]

b). Define Receiver Sensitivity [L1][CO.6][2M]

c). Compare LED and LASER light sources? [L3][CO.5][2M]

d). Draw the block diagram of analog link. [L1][CO.5][2M]e). Derive carrier power for C/ N ratio? [L4][CO.6][2M]



QUESTION BANK [OBJECTIVE]



UNIT –V

System Design and Applications

1. HFC stands for [ ](a). Hybrid fiber/ coax (b). Hybrid fiber cable (c). Hyber fi cable (d). Hole fine cable

2. The simplest form used by optical fiber links is [ ](a). Amplitude

modulation(b). Frequency

modulation (c). Direct intensity

modulation (d).Phase modulation

3. Harmonic distortions, inter modulation products, RIN in the laser , and the laser clipping is called [ ]

(a). Signal pairments (b). Signal impairments (c). Hybrid fiber/ coax (d). None4. To send a signal free of linear distortion, the fiber should have a [ ]

(a). Flat amplitude (b). Group delay response (c).Both A and B (d). None5. ASE stands for [ ]

(a). Amplified spontaneous emission

(b). Analog signal emission

(c). Analog Sign Entry (d). None

6. Avalanche photodiode bias voltages ranges from [ ](a). >10 (b).> 40 (c). > 5 (d). >20

7. In choosing a particular photo detector, we must need to determine [ ](a). Minimum optical Power (b). Maximum optical Power (c). Very high power (d). None

8. The spectral output of LASER is [ ](a). Broad (b). Narrower (c). Shallow (d). None

Page 21

QUESTION BANK 2017

9. Laser diodes typically couple from [ ](a). 5 to 10 dB (b). 10 to 20 dB (c). 10 to 15dB (d). 20 to 25 dB

10. _____ tends to be used with multimode fibers [ ](a). LED (b). LASER (c). Both A and B (d). None

11. A single mode fiber can provide the ultimate bit rate distance product, with values of over [ ](a). 200 Gb/s (b). 300 Gb/s (c). 400 Gb/ s (d). 500 Gb/s

12. For higher values, a laser must be used at these wavelengths [ ]

(a). 3600 Mb/s (b). 2500 Mb/s (c). 4000 Mb/s (d). 2800 Mb/s13. If the core-cladding index difference Δ = 0.01, the numerical aperture NA = [ ]

(a). 0.12 (b). 0.36 (c). 0.02 (d). 0.2114. As Δ increases, correspondingly the fiber coupled power [ ]

(a). Increase (b). Decreases (c). Constant (d). None15. The better fiber-optic system is [ ]

(a). 3 repeaters (b). 8 repeaters (c). 11 repeaters (d). 20 repeaters16. In an optical network, increase in the number of lasers ________the bit rate. [ ]

(a). Increases (b). Stabilizes (c). Decreases (d). None17. The typical wavelength of light emitted from epitaxially grown LEDs is [ ]

(a). 840 nm (b). 490 nm (c). 480 nm (d). 940 nm18. One of the following is not a characteristic of light detectors [ ]

(a). Responsitivity (b). Spectral response (c). Transmit time (d). Dispersion19. The unit of responsitivity is given as [ ]

(a). Ampere/volt (b). Ampere/watt (c). Watt/ampere (d). Volts/ampere

20. The parameter of light detector that determines the range or system length that can be achieved for a given wavelength is [ ]

(a). Transit time (b). Spectral response (c). Dark current (d). Responsitivity21. What is used to block light from a laser and let other light through [ ]

(a). Neutral density (b). Color (c). Interference (d). Spatial22. An important requirement for successful transmission system using light [ ]

(a). Powerful, reliable light source (b). Strong glass (c). Reliable, high cost

transmission medium(d). Powerful

regenerators23. FEC stands for [ ]

(a). Fast error correction

(b). Forward error correction

(c). First error correction (d). None

24. The analyses to ensure that the desired system performance can be met by [ ](a). Link power budget (b). System time budget (c).Both A & B (d). None

25. _______ Determines the power margins between the optical transmitter output and the minimum receiver sensitivity [ ]

(a). Link power budget (b). System time budget (c).Both A & B (d). None26. In carrying out a link power budget, we first decide at which ______ to transmit. [ ]

Page 22

QUESTION BANK 2017

(a). Frequency (b). Bandwidth (c). Attenuation (d). Wavelength

27. The distance where the data are to be transmitted is not too far means ,the wavelength can be operated in [ ]

(a). 800-900 nm (b).1300-1550nm (c).900-1100 nm (d). 1100-1350nm

28. The distance where the data are to be transmitted is too long means , wavelength can be operated in [ ]

(a). 800-900 nm (b).1300-1550nm (c).900-1100 nm (d). 1100-1350nm29. PIN photo diode bias voltages are normally less than [ ]

(a). 10 (b). 40 (c). 5 (d). 2030. RIN stands for [ ]

(a). Real inter noise (b). Relative intensity noise (c). Real intra noise (d). None31. With increasing Δ, dispersion becomes [ ]

(a). Smaller (b). Medium (c). Greater (d). Unity32. The _____ is derived from the sequential loss contributions of each element in the link [ ]

(a). Link loss budget (b). Rise time Budget (c). System Budget (d). Power Budget33. Loss= 10 log Pout/ Pin [ ]

(a). Rise time Budget (b). Link loss budget (c). System Budget (d). Power Budget

34. The analysis to allow for component aging, temperature fluctuations and losses arising from components is [ ]

(a). Rise time Budget (b). Power Budget (c). Link power margin (d). System Budget35. The generally used link power margin for the systems is [ ]

(a). 6-8 dB (b). 7-9 dB (c). 5-7 dB (d). 8-10 dB

36. The total power loss PT is given as [ ](a). Ps+PR (b). PR –Ps (c). PR +Ps (d). Ps-PR

37. The convenient method of analysis for determining dispersion limitation of an optical fiber link is [ ]

(a). Rise time Budget (b). Link loss budget (c). System Budget (d). Power Budget38. The time interval between g(t) = 0.1 and g(t) = 0.9, is known as [ ]

(a). 10-20% rise time (b). 10-90% rise time (c). 20-100% rise time (d). 80% rise time39. To increase the end to end fidelity of an optical transmission line,we can use [ ]

(a). FER (b). BER (c). FEC (d). None40. The system requirements needed to analyze a link are [ ]

(a). Transmission distance (b). Channel Bandwidth (c). BER (d). All

Page 23

QUESTION BANK 2017


Page 24

Documents

QUESTION BANK - SIETK ECE Deptsietkece.com/wp-content/uploads/2016/08/IV-I-and-Optical... · Web viewQUESTION BANK (DESCRIPTIVE) Subject with Code : Optical Fiber Communication [13A04702]