I just returned from doing a bit of shopping and for reasons best known to Og I ended up buying a 6 foot tall fibre optic Christmas tree
Very nice it looks indeed, colours change every few secs.
Can anyone tell me how fibre optics work cos I’m baffled
Fiber optics work because light hitting a transition between two materials with differing refractive indexes will reflect if the incident angle is at or below a certain critical value. Fiber optics are made with a core of one optical material and sheath of another, each with its own refractive index. Light which hits the transition between these two materials is almost completely reflected, and it bounces its way down the fiber from one end to the other.
The fibers are very thin strands of glass which are made in such a way that the inside walls are highly reflective. Shine a light in one end, the photons bounce around the reflective walls until they reach the other end and come out, losing very little energy during the journey. High-quality fiber-optic cables can transmit light pretty far without using much power. The fibers in your Christmas tree are not of that quality, but they have the same effect.
All good answers. If you read the Wiki article on Total Internal Reflection as well it’ll explain more.
Given that fibre optics use TIR, you’ll often find they make a slight cut mid-fibre to let some light escape, so you have light patches along the length of the fibre. Or they may just cut the end to maximise the viewing angle. It’s really cool stuff!
tim
Very fine glass fibers are used for data transmission lines because the have the highest internal reflectivity.
Other applications such as christmas trees, childs’ necklases, etc. utilize plastic fibers for safety as well as lower cost and ease of handling.
Thank’s all
Darn you! Fibre Channel is something I actually know a little about. Here I was, all excited to finally have a question I am qualified to answer, like maybe the distance capabilities of long wave vs. short wave optics, will 4 gig accept 62.5 nm fiber or must it have 50 nm, or something exciting like that, but no. Not a GBIC or SFP in sight.
Now I’m sad. 
Cheer up my old cock, here’s a question for you.
How do the fibres change colour?
I have, red,blue, light green, dark green, purple,orange, white and a sort of silverish.
These colours don’t follow a regular pattern but are indiscriminately displayed.
Almost forgot, the colour travels along the thin optic and when it gets to the starburst at the end it changes colour
Look at the bright side. You could have gotten a Christmas tree that uses styrofoam pellets to make it look like it is snowing. A buddy bought one on impulse, but wherever he sets it up, breezes from doors opening spread styrofoam balls all over the place!
All the fibers come down to the light sorce. In between the light sorce and the fibers is a rotating wheel with colored plastic on it. As the light passes through the plastic it shines colored light onto the fiber and that color gets transmitted to the end of the fiber where you see it.
Right I think I have it.
When I assembled the tree I had to place the tree itself into a hard plastic base, I’m guessing the light source and rotating wheel are hidden in there
What with all our sophisticated technology, the color wheel may have been replaced by red, green, and blue LEDs.
I don’t think it really changes color. I suspect that only a portion of the light spectrum is escaping thru the sides, while most of the light continues along the fiber. The part escaping thru the side may be a specific wavelength (color), so it looks to be a different color light there. Rather like sunsets looking reddish, even though it’s the same light as at noon.
Or it may be simpler yet – the coating on the fibers is not clear, but colored. So that the light seen thru that coating looks a different color than when it comes out the end of the fiber.
When you take it down for the season, try plugging the base in with out the tree and see what happens.
And what if said light optical materials differ in opinion, causing several areas of one’s 9-foot artificial tree to not “light up”? Should one a) light tree on fire as revenge or b) pull out individual light bulbs, cursing as we go?
Seriously, what causes one part of a “guaranteed not to go out” tree to die?
Hi, Q.E.D. 
The words “guaranteed not to go out”… They do it every time…
Optical fibers for the transmission of digital information have lots of advantages when compared to copper wires. The former has extremely wide bandwidth and is almost entirely immune to EMI. And it usually has less mass (per unit length), which is one of the reasons the aerospace industry has shown a special interest in it. The drawback is that it’s more difficult to repair in the field.
To expand a little on Crafter_Man’s point (and giving me a chance to post), Fibre Channel is up to 8 gigabit per second (full duplex) for data with 10 gig ISL’s having been around for a couple years.
Fibre Channel is not really a communication protocol, it’s basically encapsulated SCSI with the benefits of routing and distance, and it uses fiber optics.
On close inspection:
The coating of each fibre is white(ish) but at the end of each there is a tiny blob, these blobs are of different colours.