Why can't we use opaque object in optical fibres?

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    Optical Optics
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Discussion Overview

The discussion centers on the use of opaque materials in optical fibers, specifically questioning why mirror-like surfaces cannot be employed instead of the traditional cladding with a lower refractive index. The scope includes theoretical considerations of light behavior, reflection, and absorption in optical systems.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that using a mirror-like surface could lead to partial absorption of light, as mirrors typically reflect only 85-99% of incident light compared to the near 100% reflection achieved through total internal reflection (TIR).
  • Others argue that opaque objects absorb all incoming light and do not exhibit any refraction, thus questioning their suitability for optical fibers.
  • One participant corrects a previous statement, clarifying that the phenomenon in optical fibers is total internal reflection, not refraction.
  • There is a suggestion that the efficiency of a mirror-like surface may vary with different wavelengths of light.
  • Concerns are raised regarding the cost implications of creating a mirror-like surface for optical fibers.
  • Some participants mention that metal waveguides operate differently, reflecting waves through induced currents rather than relying on TIR, which leads to losses over long distances.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the feasibility and implications of using opaque materials or mirror-like surfaces in optical fibers. The discussion remains unresolved with no consensus reached.

Contextual Notes

Participants note limitations regarding the efficiency of reflection in mirrors compared to TIR, the potential for light absorption by opaque materials, and the varying reflective properties of different materials at different wavelengths.

esha
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in an optical fibre the cladding used is ussually of a lesser refractive index so that total internal reflection occurs inside core. instead of using such a combination why can't we use a mirror like surface? will the use of opaque material partially absorb some amount of light?
 
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esha said:
will the use of opaque material partially absorb some amount of light?

I think so. Total internal reflection reflects nearly 100% (99.9+%) of the incident light, while most mirrors reflect perhaps 85-99%.
 
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Light is refracted in optic fibers due to the fact that the refractive index of the material (i think silica) is closer to that of vacuum and total internal refraction is observed. An opaque object will absorb all incoming light and will only give out luminosity. Thus opaque objects will not show total internal refraction (in fact no refraction at all).
P.S. I might be wrong.
 
PlancksApprentice said:
total internal refraction is observed

It's total internal reflection, not refraction. :smile:

PlancksApprentice said:
An opaque object will absorb all incoming light and will only give out luminosity. Thus opaque objects will not show total internal refraction (in fact no refraction at all).

The OP is asking about reflection off of the reflective surface of an opaque object.
 
Drakkith said:
It's total internal reflection, not refraction. :smile:
The OP is asking about reflection off of the reflective surface of an opaque object.
Ahhhh. Sorry.
 
I thought that a metal waveguide worked perfectly well in the way described, with mirror walls.
 
esha said:
why can't we use a mirror like surface?
It may also have to do with the fact that different materials become more or less reflective at various wavelengths.
 
In addition to the efficiency arguments presented, I would think creating a mirror-like surface would also be more expensive.
 
tech99 said:
I thought that a metal waveguide worked perfectly well in the way described, with mirror walls.

Waveguide walls do not work on TIR. They reflect the waves like a mirror, due to induced currents in a good conductor. A different mechanism, which is far from 100% reflective. You cannot use 100s of meters of waveguide without appreciable loss.
 

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