This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Fiber Attenuation Measurements”.
1. A technique used for determining the total fiber attenuation per unit length is ________ method.
Explanation: Fiber attenuation techniques have been developed in order to determine the total fiber attenuation. This fiber attenuation is from both scattering and absorption losses. Cut-back method is used as per unit length medium.
2. The system designer finds greatest interest in the ______________
a) Overall fiber attenuation
b) Fiber dispersion
c) Latitude of the fiber
Explanation: Fiber attenuation results from various aspects such as signal degradation and physical factors such as the environment. The system designer has to look upon the overall fiber attenuation while the relative magnitude is important for the development team.
3. How many parameters are usually worked upon by the measurement techniques in attenuation?
Explanation: The measurement techniques used to obtain fiber attenuation usually gives two parameters. One is spectral loss characteristic and the other is the spot measurement. The spot measurement is usually referred to as the loss at a single wavelength.
4. What type of light source is usually present in the cut-back method?
a) Tungsten or xenon
Explanation: A cut-back method usually calculates the spectral loss which eventually is used as a parameter to obtain total fiber attenuation. It consists of a white light source which is a tungsten halogen or xenon lamp.
5. The device used to remove any scattered optical power from the core is __________
a) Mode setup terminator
b) Nodal spectrum
c) Mode stripper
Explanation: A mode stripper is usually incorporated at the output end of the fiber. It removes the optical power that is scattered from the core to cladding down the fiber length.
6. What is the hierarchy of the process at the receiving end of the cut-back technique?
a) Photodiode – photo-detector – lock-in amplifier
b) Photodiode – lock-in amplifier
c) Photodiode – photo-detector – Attenuator
d) Photo-detector – lock-in amplifier – receiver
Explanation: The optical power at the receiving end is detected using the p-i-n or avalanche photodiode. The photo-detector is then index matched to the fiber output end. It is then fed to the lock-in amplifier.
7. What is the unit of measurement of the optical attenuation per unit length?
Explanation: The optical fiber attenuation per unit length is measured by unit dB/km. dB refers to the electrical parameter used to calculate the attenuation in the form of losses and spot measurements.
8. Determine the attenuation per kilometer for a fiber whose length is 2 km, output voltage is 2.1 V at a wavelength of 0.85μm. The output voltage increases to 10.7 V when the fiber is cut-back to leave 2 metres. Determine the attenuation per km for the fiber at wavelength 0.85μm.
Explanation: The attenuation per kilometer can be obtained by –
αdB = 10 log10(V2/V1)/(L1-L2) dB/km where L1-L2 = 1.998 and V2, V1 are output voltages.
9. ___________ are used to allow measurements at a selection of different wavelengths.
b) Spot attenuators
d) Interference filters
Explanation: The interference filters are located on a wheel at a length. These allow measurement at different wavelengths simultaneously and are accurate to a known level.
10. Cut-back technique is destructive.
Explanation: The cut-back method has some drawback. It is suitable for laboratory measurements but is far from ideal for attenuation measurements in the field. Hence it is termed as destructive.
11. Which technology is used by the backscatter measurement method?
b) Francis flat recovery
c) Optical time domain reflectometry
d) Optical frequency
Explanation: Backscatter method for attenuation measurement is the most popular non-destructive method. It uses optical time domain reflectometry and provides best results in laboratory as well as field measurements.
12. ________________ measurements checks the impurity level in the manufacturing process.
a) Material reflectometry
b) Material absorption loss
c) Material attenuation loss
d) Calorimetric loss
Explanation: The material absorption loss measurements check the absorption losses. It checks the impurity level in the fiber at the manufacturing stage. Thus, it is efficient than the attenuation measurement methods.
13. _____________ may be achieved by replacing the optical fibers with thin resistance wires.
c) Calorimetric calibration
d) Electrical calibration
Explanation: Electrical measurement measurements are also efficient. The calibration is done by many methods. Electrical calibration involves the use of resistance wires in place of optical fibers.
14. A scattering cell consists of ______ square solar cells called as Tynes cell.
Explanation: Fiber scattering measurements use scattering cell to detect the light which is scattered. This cell consists of six square solar cells which are called as Tynes cell. It contains index-matching fluid.
15. ___________ removes the light propagating in the cladding.
a) Cladding mode strippers
b) Core strippers
c) Mode enhancers
Explanation: The inaccuracies in the measurements resulting from the scattered light are removed by cladding mode strippers. These strippers are placed before and after the scattering cell.
Sanfoundry Global Education & Learning Series – Optical Communications.
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