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Optical fibres are used to transmit light from one place to the other along curved path in a more effective manner. The optical fibres consist of thousands of strands of a very fine quality glass or quartz of refractive index about $ 1.7$ or so. The thickness of a strand is about $10^{-6}$ cm. The strands are coated with a layer of some material of lower refractive index (about $1.5$). The ends of the strands are polished and clamped firmly after aligning them carefully. When light is incident at a small angle at one end, it gets refracted into the strands (or fibres) and gets incident on the interface of the fibres and the coating. The angle of incidence being greater than the critical angle, the ray of light undergoes total internal reflections. It suffers internal reflection again and again.
enter image description here

If we consider fibre in circular shape and incident light at the angle greater than critical angle from one part of that fibre, light undergoes total internal reflections without being absorbed, so we can have the same light circulating all the time.

1.Suppose if we have the planning of home to be made in the same manner of the circle shaped fibre with same material as that of quartz. We can have same light circulating all over once incident. So, if this happens we can have light through out the house with out light being switched on for all the time. Is this possible?

2.I know there might be some difficulties which might arise, if so what are they? What can be done in order to over come those?

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  • $\begingroup$ Why not just cover your walls in mirrors? $\endgroup$
    – user21433
    Commented Jan 25, 2014 at 18:37
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    $\begingroup$ @SeanD: No, in that case there can also be loss due to absorption of energy. Coating the wall with walls is not the only matter. Light should also be incident at an angle greater than critical angle in the circle shaped home as fibre. Then, light will be totally reflected without absorption and you will have light through out the house, only if you switch on the light once and then switch off. $\endgroup$
    – Sensebe
    Commented Jan 25, 2014 at 18:55
  • $\begingroup$ If the fibre has edges it will come out from the edges ( velocity c). In any case there will be absorption because due to the heisenberg uncertainty principle no total reflection can be really total. For a house that shape the air should turn to quarz so it could not house people . $\endgroup$
    – anna v
    Commented Jan 25, 2014 at 19:39
  • $\begingroup$ @annav: Thank you for the comment. As we are assuming the home to be in the shell shape (3-D of circle). There will be no edges, so it rule outs your first difficulty. But your second line contradicts with total internal reflection theory, where we say the light to be totally reflected without any loss of energy. I would appreciate if you discuss w.r.t this, by giving an answer and solution to avoid it (if possible). $\endgroup$
    – Sensebe
    Commented Jan 25, 2014 at 19:44
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    $\begingroup$ total reflection is in classical electromagnetic theory. Once the quantum underlying level is considered total reflection is a large dimensional approximation that will fail due to the absoption of photons. And I do not see how you will get total reflection in a circular house with house walls and air. It is the index of refraction of glass that defines total reflection in optical fibers. $\endgroup$
    – anna v
    Commented Jan 25, 2014 at 19:51

2 Answers 2

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Since Community in its wisdom brought this up again, lets make things clear:

1.Suppose if we have the planning of home to be made in the same manner of the circle shaped fibre with same material as that of quartz. We can have same light circulating all over once incident. So, if this happens we can have light through out the house with out light being switched on for all the time. Is this possible?

Complete internal reflection depends on the index of refraction. To have a house where people can live one needs air and space to move through. Air has almost 1 index of refraction whereas glass about 1.5. Even if the walls are quartz no total reflection is possible in a space suitable for housing people, because people need air .

2.I know there might be some difficulties which might arise, if so what are they? What can be done in order to over come those?

described above and cannot be overcome

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    $\begingroup$ In my book label, it is given "Nothing is im-possible", the word itself says i'm possible:). You have answered majority of my questions, I missed you in some of the recent questions except the last one. Welcome back. Lets try to run our brains to see if there is a method to over come it. $\endgroup$
    – Sensebe
    Commented Mar 27, 2014 at 7:50
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Yes the light will be circulating but we will not see a thing!.Note that when light travel through the cable it just travels forward and there is "lateral leakage" of light.So it will still be dark.

For example,in the following image we don't see the optical fibre glowing.enter image description here

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    $\begingroup$ I think the OP was implying that the house would BE the optical fiber, so we would be inside the tube not outside of it. $\endgroup$
    – mcFreid
    Commented Jan 25, 2014 at 14:19
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    $\begingroup$ But then won't we come in the path of light? $\endgroup$
    – Sandesh Kalantre
    Commented Jan 25, 2014 at 14:20
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    $\begingroup$ Yes, we would, which would be one of the difficulties. But, we would be small compared to the size of the cavity. $\endgroup$
    – mcFreid
    Commented Jan 25, 2014 at 14:24
  • $\begingroup$ @SandeshKalantre: You didn't answer my question. Please read it once again. $\endgroup$
    – Sensebe
    Commented Jan 25, 2014 at 14:29
  • $\begingroup$ I just wrote that it is not possible to use the circular optical fibre as a light source.So 1. is not possible. $\endgroup$
    – Sandesh Kalantre
    Commented Jan 25, 2014 at 14:38

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