How about optical fiber without cladding and directly coated?

I have got some answers from here, but how about optical fiber without cladding and directly coated? and the coating material have a lower refraction index than the core which can make the total internal reflection (TIR) happen.

Or maybe it is because the coating material is opaque (like some kind of plastic) and will absorb the energy of light? And will the reflection happen on the interface between transparent material and opaque material? how it would be?


1 Answer 1


The answers you are linking are answering for the physical point of view.

Guiding coatings do exist for example in double clad fibers. In those fibers, the clad is guiding the signal and the coating is guiding the pump. Those fibers are used for fiber lasers or fiber amplifiers.

So I think your question is more about an engineering point of view. For monomode fibers (10µm core) if there is no cladding and you remove the coating to cleave/splice the fiber the mechanical resistance will be very low and the fiber will be very difficult to manipulate.

The other issue I see for fiber directly coated is about fiber fabrication. Normally fibers are made by pulling from a preform, and then coated. Without cladding, is it possible to protect the core from impurities during the process? Or is the resistance of the core enough to be transported to the coating machine?

  • $\begingroup$ I do not know whether I have got your point. From my point of view, after reading some papers, I knew that there are basically three layers from inside out: core, cladding and coating. Coating is for protection. Most papers would mention that the cladding provides a interface for TIR which seem to make the thickness of cladding meaningless, so the question is mainly about the functions of the cladding. From your answer, the cladding will provide mechanical resistance, prevent the core from impurities and form TIR. So is it possible that there are only two layers: core and cladding/coating? $\endgroup$
    – nevermind
    Commented Apr 20, 2022 at 6:27

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