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Communications MCQ Set 1

1. A multimode fiber has many cutoff wavelengths. State whether the given statement is true or false.
a) False
b) True

Answer: b [Reason:] A multimode fiber has many cutoff wavelengths. It is because the number of bound propagating modes is usually large.

2. What does ‘a’ stands for in the given equation?
Mg=(πa/λ)2(n12-n22)
b) Constant
c) Coefficient of refraction
d) Density

Answer: a [Reason:] The above equation gives the number of guided modes for a parabolic refractive index graded fiber, where a is the core radius and n1, n2 are the core and cladding indices respectively.

3. The _________ wavelength is defined as the wavelength greater than which the ratio of the total power and the fundamental mode power has to be decreased to less than 0.1dB.
a) Magnetic
b) Quasi
c) Cut-off
d) EIA

Answer: c [Reason:] The cut off wavelength is usually measured by increasing the signal wavelength in a fixed length of fiber until the mode is undetectable. It is usually called as effective cut-off wavelength.

4. How many methods are used to determine the effective cutoff wavelength?
a) Two
b) One
c) Four
d) Three

Answer: d [Reason:] Three methods are usually used for determination of the effective cutoff wavelength. These are bending-reference technique, power step method and alternative test method.

5. What is the name of the test used to determine the efficient values of the effective cutoff wavelength?
a) Round robin test
b) Mandarin test
c) Hough Werner test
d) Fulton test

Answer: a [Reason:] Round robin test is the effective method to determine the efficient values for the cutoff wavelength. It shows that in some methods, the values through round robin test are the same.

6. The effective cutoff wavelength for a cabled single mode fiber will be generally smaller than that of the un-cabled fiber. State whether the given statement is true or false.
a) True
b) False

Answer: a [Reason:] The effective cutoff wavelength for a cabled single mode fiber is always smaller than that of the un-cabled fiber. This is usually because of the bend effects.

7. How many bend effects are produced in the fiber?
a) One
b) Three
c) Two
d) Four

Answer: c [Reason:] Usually, two bend effects are produced. They are macro-bending and micro-bending. These effects incarcerate certain changes in the fiber efficiency.

8. _______________method does not require a leaky mode correction factor or equal mode excitation.
a) Bending-reference
b) Power step method
c) Alternative test method
d) Refracted near-field method

Answer: d [Reason:] Refracted near-field method is complementary to the transmitted near-field method. It has the advantage that it does not require a leaky mode correction factor. Moreover, it provides the relative refractive index directly without recourse to external calibration.

9. The _______ method is the most commonly used method for the determination of the fiber refractive index profile.
a) Refracted near-field method
b) Bending-reference
c) Power step method
d) Alternative test method

Answer: a [Reason:] It is the most commonly used technique. Also, it is the EIA reference test method for both multimode and single mode fibers.

Communications MCQ Set 2

1. ___________ measurements give an indication of the distortion to the optical signals as they propagate down optical fibers.
a) Attenuation
b) Dispersion
c) Encapsulation
d) Frequency

Answer: b [Reason:] Dispersion measurements provide the exact parameters to truly determine the quality and degradation to the optical signals. It gives an indication of the distortion to the optical signals as they propagate down the optical fibers.

2. The measurement of dispersion allows the _________ of the fiber to be determined.
a) Capacity
b) Frequency
c) Bandwidth
d) Power

Answer: c [Reason:] Dispersion measurements give an indication of distortion, which in turn determines the information carrying capacity of the fiber. This information carrying capacity of the fiber is purely dependent on the bandwidth of the fiber.

3. How many types of mechanisms are present which produce dispersion in optical fibers?
a) Three
b) Two
c) One
d) Four

Answer: a [Reason:] There are three major mechanisms which produce dispersion in optical fibers. These are: Material dispersion, waveguide dispersion and intermodal dispersion.

4. Intermodal dispersion is nonexistent in ________ fibers.
a) Multimode
b) Single mode
c) Step index- multimode
d) Al-GU

Answer: b [Reason:] Intra-modal as the name suggests need multimode fibers to propagate. In single mode fibers, only one mode is there to propagate. Hence, Intermodal dispersion is nonexistent in single mode fibers.

5. In the single mode fibers, the dominant dispersion mechanism is ____________
a) Intermodal dispersion
b) Frequency distribution
c) Material dispersion
d) Intra-modal dispersion

Answer: d [Reason:] In single mode case, the dominant dispersion mechanism is chromatic. Chromatic dispersion is called as intra-modal dispersion.

6. Devices such as ___________ are used to simulate the steady-state mode distribution.
a) Gyrators
b) Circulators
c) Mode scramblers
d) Attenuators

Answer: c [Reason:] The dispersion measurements on the fiber are performed only when the equilibrium mode distribution is set up within the fiber. Hence, filters or scramblers are used to simulate the steady state mode distribution.

7. How many domains support the measurements of fiber dispersion?
a) One
b) Three
c) Four
d) Two

Answer: d [Reason:] Fiber dispersion measurements can be made in two domains. These are time domain and frequency domain.

8. The time domain dispersion measurement setup involves _____________ as the photo detector.
a) Avalanche photodiode
b) Oscilloscope
c) Circulator
d) Gyrator

Answer: a [Reason:] The time domain fiber dispersion measurement involves the pulses to be received by the photo detector in order to determine the distortion in the optical signals. These pulses are received by avalanche photodiode.

9. In pulse dispersion measurements, the 3dB pulse broadening for the fiber is 10.5ns/km and the length of the fiber is 1.2 km. Calculate the optical bandwidth for the fiber.
a) 32 MHz km
b) 45 MHz km
c) 41.9 MHz km
d) 10 MHz km

Answer: c [Reason:] The optical bandwidth for the fiber is given by – Bopt= 0.44/ 3dB pulse broadening Where, 0.44 = constant.

10. Frequency domain measurement is the preferred method for acquiring the bandwidth of multimode optical fibers. State whether the given statement is true or false.
a) True
b) False

Answer: a [Reason:] Bandwidth is usually the difference in the frequency. Frequency domain measurement is usually the best method in order to find the bandwidth of the multimode optical fibers.

11. Intra-modal dispersion tends to be dominant in multimode fibers. State whether the given statement is true or false.
a) True
b) False

Answer: b [Reason:] Intra-modal dispersion is dominant in case of single mode fibers. In case of multimode fibers, intermodal dispersion comes handy and is dominant.

Communications MCQ Set 3

1. The ____________ affects the light gathering capacity and the normalized frequency of the fiber.
a) Numerical aperture
b) Amplitude modulation
c) Responsivity
d) Quantum efficiency

Answer: a [Reason:] Numerical aperture is an important optical parameter as it dictates the important characteristics of the optical fiber. This in turn dictates the number of propagating modes within the fiber.

2. The numerical aperture for a step index fiber is sine angle of the ____________
a) Efficient angle
b) Aperture
c) Acceptance angle
d) Attenuation

Answer: c [Reason:] The numerical aperture of a step index fiber is given by – NA = sinθa, where θa is the acceptance angle and NA is the numerical aperture.

3. The calculations of the numerical aperture from a refractive index data are less accurate for the graded index fibers than for step index fibers. State whether the given statement is true or false.
a) False
b) True

Answer: b [Reason:] The refractive indices of the core and cladding are fluctuating, thus causing the data to be less efficient. For graded index fibers, it is usually less accurate than for the step index fibers.

4. Far field pattern measurements with regard to multimode fibers are dependent on the _____________ of the fiber.
a) Amplitude
b) Frequency
c) Diameter
d) Length

Answer: d [Reason:] The accuracy of the measurement technique is dependent upon the visual assessment of the far-field pattern from the fiber. In case of multimode fibers, far field pattern measurements are dependent on the length of the fiber.

5. The screen is positioned 10 cm from the fiber end face. When illuminated from a wide angled visible source the measured output pattern size is 6.2 cm. Calculate the approximate numerical aperture of the fiber.
a) 0.21
b) 0.30
c) 0.9
d) 1.21

Answer: b [Reason:] The numerical aperture can be obtained from a trigonometric relationship given by- NA = A/(A2+4D2 )1/2, where A is constant(38.44) and D is the distance of the fiber end face from the screen in mm.

6. During the fiber drawing process, the fiber outer diameter is maintained constant to within ________
a) 2%
b) 1%
c) 5%
d) 10%

Answer: b [Reason:] During the fiber manufacturing stage, all processes needs to be performed efficiently. Especially, in the drawing process, the outer diameter should be compiled to within 1 % to avoid miscommunication through fibers.

7. What is the minimum value of accuracy in diameter is needed to avoid radiation losses in the fiber?
a) 0.1%
b) 0.2%
c) 0.3%
d) 0.03%

Answer: c [Reason:] Any diameter variations can cause excessive radiation losses and make accurate fiber-fiber connection difficult. Hence, on-line diameter measurement systems are used which provides accuracy of 0.3%.

8. Which of the following is a non-contacting optical method of on-line diameter measurement?
a) Brussels’s method
b) Velocity differentiator method
c) Photo detector method
d) Image projection method

Answer: d [Reason:] On-line diameter measurement technique uses fiber image projection method. It is also known as non-contacting optical method and shadow method.

9. The shadow method is used for measurement of the outer diameter of an optical fiber. The apparatus employs a rotating mirror with an angular velocity of 4 rad/s which is located at 10 cm from the photo detector . Compute the shadow velocity.
a) 0.1 μm μs-1
b) 0.4 μm μs-1
c) 0.87 μm μs-1
d) 1 μm μs-1

Answer: b [Reason:] The shadow velocity is obtained by the below equation: ds/dt = l. dϕ/dt, where l is the distance of the apparatus from the photodetector and dϕ/dt is the angular velocity.

10. The shadow velocity is given by 0.4 μm μs-1 and shadow pulse of width 300 μs is registered at an instant by the photodetector. Determine the outer diameter of the optical fiber in μm.
a) 100 μm
b) 120 μm
c) 140 μm
d) 90 μm

Answer: b [Reason:] The fiber outer diameter is given by- d0=We.Ds/dt, where We=pulse width and ds/dt = shadow velocity.

11. The techniques used to determine the refractive index profile can also be used to determine the core diameter. State whether the given statement is true or false.
a) True
b) False

Answer: a [Reason:] Some of the techniques used to determine the refractive index profile are interferometry, near field scanning and refracted ray technique. The core diameter for step index fibers is defined by the step change in the refractive index profile. Hence, they can be used to measure the core diameter.

Communications MCQ Set 4

1. ____________ affects both the fiber attenuation and dispersion.
a) Refractive index
b) Micro-bending
c) Connectors
d) Splices

Answer: b [Reason:] Effects such as micro-bending with a resultant mode coupling affect both the fiber attenuation and dispersion. It does not provide the overall characteristics of the transmission link.

2. Which of the following is not included in the optical fiber link measurement test?
a) Attenuation measurement
b) Dispersion measurement
c) Splice loss measurement

Answer: d [Reason:] It is necessary to perform some tests on the optical fiber link to enhance the productivity. Apart from receiver sensitivity, other measurement methods are required to test the fiber link.

3. In case of field measurements, the equipment must have _____ power consumption keeping in mind the battery operation.
a) Low
b) High
c) Negligible
d) Maximum

Answer: a [Reason:] The design criteria allows you to distinguish in parameters required for adaptation of battery operation and equipment handling. The power consumption must be low for an equipment to handle.

4. Which of the following are not considered as environmental conditions required for field measurements?
a) Temperature
b) Humidity
d) Power

Answer: d [Reason:] The equipment must be reliable and provide accurate measurements under extreme environmental conditions such as humidity, temperature and mechanical load. Power is an internal factor.

5. Complicated and involved fiber connection arrangements should be _________ in case of field measurements.
a) Provided
b) Avoided
c) Maximized
d) Minimized

Answer: b [Reason:] The equipment must be connected to the fiber in a simple manner. It should be connected without the need for fine or critical adjustment.

6. Which of the following cannot be used in equipment for field measurements?
a) Fiber
b) Connector
c) External triggering
d) Environmental factor

Answer: c [Reason:] The equipment cannot usually make use of external triggering and regulating circuits between the transmitter and receiver. This is because of their wide spacing on the majority of the optical links.

7. Which sensors are used for alteration of spectral range in equipment?
a) Wide-area photodiodes
b) Circulators
c) Gyrators
d) Photogenic sensors

Answer: a [Reason:] Wide area photodiodes such as silicon, germanium diodes are used for alteration of spectral range. It is generally preferred to have a measurement range from -100 dBm.

8. The handheld optical power meter has a measurement accuracy of ________
a) 0.01 dB
b) 0.25 dB
c) 0.8 dB
d) 1 dB

Answer: b [Reason:] The optical power meter detects the fiber type and switches to optical power measurements. It provides an accuracy of about +(or -) 25 dB.

9. _____________ may be used for measurement of the absolute optical attenuation on a fiber link.
a) Silicon photodiodes
b) InGaAsP photodiodes
c) Optical power meters
d) Gyrators

Answer: c [Reason:] Optical power meter employs cut-back technique. It is used for the measurement of the optical attenuation.

10. A large-area photodiode is utilized in the receiver to eliminate any effects from differing fiber and faces. State whether the given statement is true or false.
a) True
b) False

Answer: a [Reason:] The modulating voltage maintains the equilibrium between the transmitter and the receiver side. A large area photodiode is required to eliminate differing fiber and faces to maintain the equilibrium.

11. Optical time domain reflectometry is also called as backscatter measurement method. State whether the given statement is true or false.
a) False
b) True

Answer: b [Reason:] OTDR technique is used in both on-field and laboratory applications. It is also called as backscatter measurement method as it provides measurement of attenuation on an optical link down its entire length.

Communications MCQ Set 5

1. A major attribute of coherent optical transmission was its ability to provide _______________ for future multicarrier systems and networks.
a) Attenuation
b) Dispersion
c) Frequency selectivity
d) Noisy carriers

Answer: c [Reason:] A coherent optical transmission involves the wavelength, frequency and the distance as its main factors. It provides frequency and wavelength selectivity with narrow channel spacing’s for future multicarrier systems and networks.

2. The channel width is narrow for the coherent systems than the WDM systems. State whether the given statement is true or false.
a) True
b) False

Answer: a [Reason:] The coherent optical systems involve wavelength selectivity with narrow channel spacing. The conventional WDM systems use a far more relaxed channel spacing than the coherent systems.

3. The technique within the coherent multicarrier systems used to broadcast the optical signals over the network is the use of passive _____________
a) Star coupler
b) Optical resonator
c) Optical regenerator
d) Local oscillator

Answer: a [Reason:] In multicarrier systems, the channels are separated via various techniques. The use of passive star coupler ensures that the optical signals are broadcasted over the network within the coherent system.

4. Estimate the minimum transmitter power if number of photons per bit are 150, wavelength 1.3 micrometer with an optical bandwidth of 20 THz.
a) 0.2 mW
b) 0.5mW
c) 1 mW
d) 2.3mW

Answer: b [Reason:] The minimum transmitter power is given by – Ptx= Np hf B Here, Ptx= transmitter power, f =frequency, h=Planck’s constant and B=bandwidth.

5. The performance degradation due to nonlinear phase noise is referred to as _____________
a) Munich effect
b) Linear bipolar effect
c) Gordon Mollenauer effect
d) Delta effect

Answer: c [Reason:] The phase noise is a variant due to the RZ signal. The nonlinear phase noise causes severe performance degradation in terms of bandwidth and frequency.

6. ______________ facilitates the doubling of the feasible spectral efficiency through the transmission of independent information in each of the two orthogonal polarizations.
a) WDM
b) Gordon Mollenauer effect
c) EDFA control
d) POLMUX

Answer: d [Reason:] POLMUX is abbreviated as Polarization multiplexing. It provides a different approach to the multilevel modulation. It requires polarization control at the receiver side.

7. ____________ is a transparent multiplexing technique.
a) POLMUX
b) PDM
c) WDM
d) Munich

Answer: a [Reason:] It is a transparent technique as it is not dominated by polarization mode dispersion or polarization-dependant loss. It provides many advantages to the multilevel modulation format in comparison to the non-POLMUX signals at the same data rate.

8. Which of the following in not a drawback of POLMUX?
a) Polarization-sensitive detection at the receiver
c) Cross-polarization nonlinearities
d) Multilevel modulation

Answer: d [Reason:] The drawbacks of the POLMUX include receiver complexity, polarization sensitivity at the receiver side and the cross polarization nonlinearities. It is advantageous to the multilevel modulation scheme.

9. A multicarrier modulation format in which there has been growing interest to compensate for impairments in optical fiber transmission systems is _______________
a) OFDM
b) EDM
c) WDM