Optical Fibers Questions and Answers

Optical Communications Questions and Answers – Optical Fibers

This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Optical Fibers”.

1. The performance characteristics of multimode graded index fibers are ___________
a) Better than multimode step index fibers
b) Same as multimode step index fibers
c) Lesser than multimode step index fibers
d) Negligible

Explanation: A constant grading factor is used in multimode graded index fibres. Because of the index graded and lower attenuation, multimode graded index fibres have better performance characteristics than multimode step index fibres.

2. Multimode graded index fibers have overall buffer jackets same as multimode step index fibers but have core diameters ___________
a) Larger than multimode step index fibers
b) Smaller than multimode step index fibers
c) Same as that of multimode step index fibers
d) Smaller than single mode step index fibers

Explanation: The core diameter of multimode graded index fibres is less than that of multimode step index fibres. A tiny core diameter aids in the fiber’s stiffness, which helps it resist bending.

3. Multimode graded index fibers with wavelength of 0.85μm have numerical aperture of 0.29 have core/cladding diameter of ___________
a) 62.5 μm/125 μm
b) 100 μm/140 μm
c) 85 μm/125 μm
d) 50 μm/125μm

Explanation: Multimode graded index fibres with a core/cladding diameter of 100m/140m and a numerical aperture of 0.29. They are low-cost LEDs with a high coupling frequency and a wavelength of 0.85 m. They’re also useful for short-distance work.

4. Multimode graded index fibers use incoherent source only.
a) True
b) False

Explanation: Multimode graded index fibers are used for short haul and medium to high bandwidth applications. Small haul applications require LEDs and low accuracy lasers. Thus either incoherent or incoherent sources like LED’s or injection laser diode are used.

5. In single mode fibers, which is the most beneficial index profile?
a) Step index
b) Graded index
c) Step and graded index
d) Coaxial cable

Explanation: In single mode fibres, a graded index profile is preferable than a step index profile. Because of the graded index profile, dispersion-modified single mode fibres are produced.

6. The fibers mostly not used nowadays for optical fiber communication system are ___________
a) Single mode fibers
b) Multimode step fibers
c) Coaxial cables
d) Multimode graded index fibers

Explanation: Polarization-maintaining fibres are made from single-mode fibres, which is why they are so expensive. Multimode fibres, a more sophisticated but accurate alternative, are also available. As a result, single-mode fibres are never used in optical fibre transmission.

7. Single mode fibers allow single mode propagation; the cladding diameter must be at least ___________
a) Twice the core diameter
b) Thrice the core diameter
c) Five times the core diameter
d) Ten times the core diameter

Explanation: In single mode fibre, the cladding diameter must be ten times the core diameter. Larger ratios help to ensure correct light propagation. These dimension ratios must be present in order to avoid vanishing field losses.

8. A fiber which is referred as non-dispersive shifted fiber is?
a) Coaxial cables
b) Standard single mode fibers
c) Standard multimode fibers
d) Non zero dispersion shifted fibers

Explanation: Non-dispersion shifted fibre is a normal single mode fibre with a step index profile. These fibres are preferred for single-wavelength transmission in O-band because they have a zero dispersion wavelength of 1.31m.

9. Standard single mode fibers (SSMF) are utilized mainly for operation in ___________
a) C-band
b) L-band
c) O-band
d) C-band and L-band

Explanation: SSMFs are only used for O-band operation. It has high dispersion in the C-band and L-band, extending from 16 to 20 ps/nm/km. As a result, SSMFs are used in the O-band.

10. Fiber mostly suited in single-wavelength transmission in O-band is?
a) Low-water-peak non dispersion-shifted fibers
b) Standard single mode fibers
c) Low minimized fibers
d) Non-zero-dispersion-shifted fibers

Explanation: Non dispersion shifted fibres are standard single mode fibres with a step index profile that are used for single wavelength transmission in the O-band and have a zero-dispersion wavelength of 1.31m.

11. Multimode step index fiber has ___________
a) Large core diameter & large numerical aperture
b) Large core diameter and small numerical aperture
c) Small core diameter and large numerical aperture
d) Small core diameter & small numerical aperture

Explanation: The core diameter and numerical aperture of multimode step-index fibre are both large. These parameters allow for efficient coupling to light sources that are already present, such as LEDs.

12. A typically structured glass multimode step index fiber shows as variation of attenuation in range of ___________
a) 1.2 to 90 dB km-1 at wavelength 0.69μm
b) 3.2 to 30 dB km-1 at wavelength 0.59μm
c) 2.6 to 50 dB km-1 at wavelength 0.85μm
d) 1.6 to 60 dB km-1 at wavelength 0.90μm

Explanation: The resistance of multiplexing step index fibres varies from 2.6 to 50dBkm-1. The huge variations in attenuation both within and between the two general preparation procedures, melting and deposition, are the cause of the broad range in absorbance.

13. Multimode step index fiber has a large core diameter of range is ___________
a) 100 to 300 μm
b) 100 to 300 nm
c) 200 to 500 μm
d) 200 to 500 nm

Explanation: The core diameter of a multimode step index fibre can range from 100 to 300m. This is to make efficient connection to existing light sources easier.

14. Multimode step index fibers have a bandwidth of ___________
a) 2 to 30 MHz km
b) 6 to 50 MHz km
c) 10 to 40 MHz km
d) 8 to 40 MHz km

Explanation: The bandwidth of multimode step index fibres ranges from 6 to 50 MHz km. These fibres with this bandwidth are best suited for short-haul, low-cost applications with minimal bandwidth.

15. Multimode graded index fibers are manufactured from materials with ___________
a) Lower purity
b) Higher purity than multimode step index fibers.
c) No impurity
d) Impurity as same as multimode step index fibers.

Explanation: The purity of multimode graded index fibres is higher than that of multimode step index fibres. These fibres have greater impurities to reduce fibre losses.

A flexible, transparent optical fibre (or fibre in British English) is manufactured by pulling glass (silica) or plastic to a diameter slightly larger than that of a human hair. Optical fibres are most commonly used to convey light[a] between two ends of the fibre and are widely employed in fiber-optic communications, allowing transmission over longer distances and at higher bandwidths (data transfer speeds) than electrical connections. Signals pass through fibres with less loss than through metal wires, and fibres are immune to electromagnetic interference, an issue that metal wires suffer from.

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