Read the passage and answer the questions that follow on your understanding of the passage : Optical fibre communication is one among the new techniques have come up and are extensively used for communication purposes. The portion of the e.m. spectrum encompasses the optical region falls in the wavelength of 50 nm (Ultraviolet) to approximately 100 µm (Infrared) which includes visible light spectrum from 400 nm (Violet) to 700 nm (Red). The order of frequency corresponding to these wavelengths falls in the range 1014 to 1018 Hz. There are two types of transmission media used for optical communication i.e., atmospheric channel and guided wave channel. Out of the two, guided wave channel provide much more reliable and versatile medium of communication. The medium used for guided channels in optical range are non-metallic guides popularly known as optical fibre. The optical fibre link used for communication applications has several advantages over conventional copper cable links which makes possible to send much more data over long distances with negligible attenuation. Although some difficulties do exist in the making of optical fibre set and there are some challenges being faced yet this type of communication mechanism has made a great impact in the present scenario.
Which of the following are the cases of signal attenuation ? 1. Splicing
2. Intermodal Delay
3. Scattering
4. Chromatic Dispersion
1 & 3
The list contains two attenuation mechanisms and two dispersion mechanisms, and the question is really asking whether the difference is understood. The answer is 1 & 3, option 1.
| Item | Type | Effect |
|---|---|---|
| 1. Splicing | Attenuation | Power lost at the joint |
| 2. Intermodal delay | Dispersion | Pulse spread in time |
| 3. Scattering | Attenuation | Power redirected out of the core |
| 4. Chromatic dispersion | Dispersion | Pulse spread in time |
The distinction in one sentence : attenuation is measured in dB/km and describes power that never arrives; dispersion is measured in ns/km and describes power that arrives late. The first limits how far a link can reach before it needs a repeater; the second limits how fast it can be modulated before adjacent pulses overlap.
Scattering — the fundamental attenuation. Rayleigh scattering arises from microscopic fluctuations in density and composition frozen into the glass as it solidified. These are smaller than a wavelength, so they redirect light out of the guided mode, and the loss varies as
\(\alpha_{R}\propto\dfrac{1}{\lambda^{4}}\)
The steep wavelength dependence is why long-haul systems moved to 1.55 µm: Rayleigh scattering there is about sixteen times weaker than at 0.8 µm, and it sets the floor of roughly 0.2 dB/km that no purification can beat.
Splicing — the practical attenuation. Every joint costs power through lateral or angular misalignment, an end gap, or Fresnel reflection at a glass-air interface. A fusion splice loses about 0.05 dB and a mechanical connector 0.3 to 0.5 dB — small individually, but a link with many connectors can lose more at its joints than in its fibre.
Why the other two are excluded. Intermodal delay arises because different modes travel different path lengths; chromatic dispersion because different wavelengths travel at different speeds. In both cases all the energy arrives — simply smeared over time. No power is lost, and the remedy is different too: dispersion is fought with single-mode fibre, narrow-linewidth sources and dispersion compensation, whereas attenuation is fought with purer glass, better splices and optical amplifiers.
Hence, the attenuation mechanisms are splicing and scattering.
Similar Questions
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Losses in optical fibers are caused by
1. Impurities in the fibre material
2. Microbending
3. Splicing
4. Step index profileOf these statements :
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Reason (R) : Low power LASER beams are considered to be very powerful as compared to high power ordinary light beams.
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Choose the correct answer from the options given below :
Important Questions from Optical Fiber
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