This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Photonic Crystal Fibers & Attenuation”.
1. Photonic crystal fibers also called as
a) Conventional fibers
b) Dotted fibers
c) Stripped fibers
d) Holey fibers
Explanation: Photonic crystal fibers contain a fine array of air holes running longitudinally down the fiber cladding. The microstructure within the fiber is highly periodic.
2. Conventional optical fibers has more transmission losses than photonic crystal fibers. State whether the statement is true or false.
Explanation: Conventional optical fibers have several hundreds of losses in transmission. Photonic crystal fibers have resulted in reduction in overall transmission losses.
3. Losses in photonic crystal fibers are reduced to a level of
Explanation: Conventional fibers have losses of several hundred decibels per km. The invention of photonic crystal tubes has reduced the losses by hundreds of decibels.
4. The high index contrast enables the PCF core to be reduced from around 8 μmin conventional fiber to
a) Less than 1μm
b) More than 5μm
c) More than 3μm
d) More than 2μm
Explanation: PCF’s have a wider range of optical properties in comparison with standard fibers. The lesser the core, more is the intensity of light in the core and enhances the non-linear effects.
5. The periodic arrangement of cladding air holes in photonic band gap fibers provides for the formation of a photonic band gap in the
a) H-plane of fiber
b) E-plane of fiber
c) E-H-plane of fiber
d) Transverse plane of fiber
Explanation: Photonic band gap fibers are a class of micro structured fiber in which periodic arrangement of air holes is required. As a PBG fiber exhibits a 2-dimensional band gap, than the wavelengths within this band gap cannot propagate perpendicular to the fiber axis.
6. In index-guided photonic crystal fiber structure, the dark areas are air holes. What does white areas suggests?
Explanation: Index-guided photonic crystal fibers have greater index contrast because the cladding contains air-holes having refractive index 1. Both index guided and conventional fibers arises from the manner in which guided mode interacts with the cladding region.
7. The unit of measurement of attenuation in optical fibers is
Explanation: Attenuation is also referred to as transmission loss. Channel attenuation helped to determine the maximum transmission distance prior to signal restoration. Attenuation is usually expressed in logarithmic unit of decibel. It is given by
αdBL = 10 log10Pi / Po
Where αdB= signal attenuation per unit length
Pi & Po = Input and output power
8. The optical fiber incurs a loss in signal power as light travels down the fiber which is called as
Explanation: When the light is passed through the fiber, it travels a large amount of distance before it starts fading. It needs restoration in the path. This loss or fading is called as Attenuation.
9. If the input power 100μW is launched into 6 km of fiber, the mean optical power at the fiber output is 2μW. What is the overall signal attenuation through the fiber assuming there are no connectors or splices?
Explanation: Signal attenuation is usually expressed in decibels. It is given by
Signal attenuation=10 log10Pi / Po
Where, Pi & Po = Input and output power.
10. A device which reduces the intensity of light in optical fiber communications is
b) Optical attenuator
Explanation: A compressor compresses the signal before transmission. It does not affect the intensity of light. Optical attenuator is a device that affects the intensity of light and incurs a loss in transmission.
11. A decibel may be defined as the ratio of input and output optical power for a particular optical wavelength. State whether the following statement is true or false.
Explanation: Signal attenuation refers to the loss in transmission and it needs a logarithmic unit to express. Decibel is mainly used for comparing two power levels. It has the advantage that the operations of multiplication and division reduce to addition and subtraction.
12. When the input and output power in an optical fiber is 120μW & 3μW respectively and the length of the fiber is 8 km. What is the signal attenuation per km for the fiber?
Explanation: Signal attenuation per unit length is given by
αdBL = 10 log10Pi / Po
αdBL = 16 dB
αdB= 16 dB/L= 2dB/km.
Sanfoundry Global Education & Learning Series – Optical Communications.
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