I am trying to understand fiber optics basics. I read that the fiber optic cables have a tube in which there are many FIBERS. How many fibers are there actually inside a fiber optic cable?

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5 Answers

As many as the manufacturer puts in there. It can range from a single fiber to many hundreds.

Actually the question is not quite as silly, or as impossible to answer, as all that. In common practice for loose-tube cables (there are other cable types), each tube has 12 color-coded fibers (except for "less than 12-fibers total" cables) and higher fiber count cables have multiple color-coded tubes, with fiber count stepped up in units of 12. So a 288 fiber cable will have two large units or bundles, each of which has 12 tubes, each of which has 12 fibers. (it may also have 24 tubes, each "double-color-coded," rather than 2 bundles of 12)

individual fibers are coded

1.blue 2.orange 3.green 4.brown 5.slate(=gray) 6.white 7.red 8.black 9.yellow
10.violet 11.rose 12.aqua

The tubes (and, I believe, bundles, though I have not personally used that size) are coded the same way, so you might have blue bundle (1), green tube(3), brown fiber(4), which would be #28 of 288.

Ribbon fibers are color-coded the same way.

Note that this is individual fiber coding, not the exterior jacket (which is nearly always black on this size/type of cable.) Exterior color usually has some meaning (as far as fiber type) on 1-2 fiber patch cords, but it's the printing on the exterior jacket that rules in all cases for fiber type. There is no printing on the individual fibers.

It varies, a lot, from one to hundreds.

You only need one per circuit but as others say there can be many circuits/fibres in a cable.

This question is unanswerable, it depends on too many factors. Bandwidth, type of data, cable location i.e. fixed run or floating, minimum radius. Some will have redundancy built in to allow for limited mis-handling.