Refractive index of optical fibre

In summary, the purpose of having a cladding with a lower refractive index than the core in an optical fiber is to achieve total internal reflection and keep light within the fiber for efficient data transmission. The cladding also serves to protect the core from mechanical stress and chemical deterioration, and prevent light from escaping through the side due to dirt or other substances.
  • #36
Misr said:
How could this happen?does the refractive index of the dirt higher than that of the core?
No. Read (e.g. wiki: http://en.wikipedia.org/wiki/Evanescent_wave) about TIR mechanism or very good explanation in Feynman Lectures on Physics.
The light is not reflected "sharp" on the boundary between media. The light enters to the lower index medium on some depth (order of magnitude its wavelength). If the lower index medium is not transparent, the light gets absorbed or scattered, rather than reflected.

It is a perfect demonstration: you send a laser beam through a glass prism such, that it is reflected by TIR. Then you blow some cigarette smokeinto the area behind the "reflecting" surface. You may see the smoke glowing, and if you have precise photometer, you may also notice that reflected beam gets a bit dimmer.
Similar demonstration is with total reflection between glass and water - then you add some milk or ink to the water: in both cases the reflected beam gets dimmer to such extend you may see it by naked eye.
Misr said:
you mean high??hmm that's confusing
Almost parallel to fibre axis. Even in multimode fibre the angle is much lower than 1°.
 
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  • #37
And one more school demonstration: take a glass prism (45°/45°/90°) and look through shorter side - then you see reflection by TIR of the object behind other short side.
Then touch the long side (reflecting) with a finger - you now may see very clearly the fingerprint mixed with the reflection of what you were watching. That visible darkening of the reflected light in some places is caused by light loss on so small amount of dirt behind reflecting surface, as a grease left by fingerprint.
 
  • #38
There is energy 'in' the low index medium. But it's in the form of an evanescent wave, which doesn't propagate. A lossy medium will absorb this energy, right in close to the interface.
 
  • #39
Almost parallel to fibre axis. Even in multimode fibre the angle is much lower than 1°.
I think you mean that the angle of incidence is very big
 
  • #40
A read another explanation for the function of the cladding:
The cladding is of higher refractive index than air and lower than that of the core
so if some light rays fell at an angle less than the critical angle,it will refract to the cladding and the cladding will reflect them back to the core
Is that true?
 
  • #41
ok one more question,
can light penetrate the cladding?what happens in this case?
 
  • #42
@Misr,
it would be really great, if you read answers you already got to your questions before asking the same question again.
Be so nice and read answers #36 and #38, then follow a link to wiki you got.
 
<h2>1. What is the refractive index of optical fibre?</h2><p>The refractive index of optical fibre is a measure of how much light slows down as it travels through the fibre. It is typically denoted by the symbol "n" and is a ratio of the speed of light in a vacuum to the speed of light in the fibre.</p><h2>2. How is the refractive index of optical fibre measured?</h2><p>The refractive index of optical fibre can be measured using a variety of techniques, such as the prism method, the critical angle method, and the interferometric method. These methods involve measuring the angle of light as it enters and exits the fibre and using mathematical calculations to determine the refractive index.</p><h2>3. What factors affect the refractive index of optical fibre?</h2><p>The refractive index of optical fibre can be affected by several factors, including the composition and purity of the fibre material, the wavelength of light being used, and the temperature and pressure of the environment. Changes in these factors can cause the refractive index to vary, which can impact the performance of the fibre.</p><h2>4. How does the refractive index of optical fibre impact its performance?</h2><p>The refractive index of optical fibre plays a crucial role in determining the performance of the fibre. A higher refractive index means that light travels slower through the fibre, which can lead to increased signal loss and dispersion. On the other hand, a lower refractive index can result in better signal transmission and less distortion.</p><h2>5. Can the refractive index of optical fibre be changed?</h2><p>Yes, the refractive index of optical fibre can be changed by altering the composition of the fibre material or by using special coatings on the fibre. This can be done to optimize the performance of the fibre for specific applications, such as telecommunications or medical imaging.</p>

1. What is the refractive index of optical fibre?

The refractive index of optical fibre is a measure of how much light slows down as it travels through the fibre. It is typically denoted by the symbol "n" and is a ratio of the speed of light in a vacuum to the speed of light in the fibre.

2. How is the refractive index of optical fibre measured?

The refractive index of optical fibre can be measured using a variety of techniques, such as the prism method, the critical angle method, and the interferometric method. These methods involve measuring the angle of light as it enters and exits the fibre and using mathematical calculations to determine the refractive index.

3. What factors affect the refractive index of optical fibre?

The refractive index of optical fibre can be affected by several factors, including the composition and purity of the fibre material, the wavelength of light being used, and the temperature and pressure of the environment. Changes in these factors can cause the refractive index to vary, which can impact the performance of the fibre.

4. How does the refractive index of optical fibre impact its performance?

The refractive index of optical fibre plays a crucial role in determining the performance of the fibre. A higher refractive index means that light travels slower through the fibre, which can lead to increased signal loss and dispersion. On the other hand, a lower refractive index can result in better signal transmission and less distortion.

5. Can the refractive index of optical fibre be changed?

Yes, the refractive index of optical fibre can be changed by altering the composition of the fibre material or by using special coatings on the fibre. This can be done to optimize the performance of the fibre for specific applications, such as telecommunications or medical imaging.

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