Magnifying Visors

How do you test the speed of fiber optics?

I have this science fair project that i have to turn in and I know someone could help me. My topic is "Testing the speed of fiber optics''. Can anyone help me? please?

Public Comments

1. You will need: A super accurate clock A length of fiber optic cable Method: Send a signal down the fiber optic cable and record the time in which you sent it. Record the time in which the signal was recieved at the other end of the fiber optic cable. The speed of the fiber optic cable is given by s=d/t where: s is the speed d is the length of the fiber optic cable t is the difference in time between the two time recordings.
2. Well, the Yeti is technically right, but it's really hard to do that for many reasons. The first one is that light travels REALLY fast. you'd have a hard measuring it like that. Also, the speed will change with the wavelength you use. So, here's my suggestion. You send light through the optic fiber and you get a cone of light at the other end. This opening of that cone is called the Numerical Aperture (look it up). So, you put a screen at a known distance, measure the radius of the cone and thus know the angle at which the light comes out (typically 15 degrees). if you're working in air, the angle will be equal to arcsin(sqrt(n^2-1)) So, you solve for n, since you know the angle already. n is then n= c/v where c is the speed of light and v the speed in your fibre. Remember. Keep your fiber straight. Your speed will change with color. Make sure you have a clean cleave at either end of your fiber. So, there are are more advanced and accurate ways to do what you're trying to do, but i think what i told you will do. If you have any more questions, feel free to write me. Edit: This is all for a step index fiber. If you have a more complex fiber, you have to use much more complex calculation. You'll have to calculate the individual speed of each mode (god knows i don't want to get into this tonight) and each wavelength. Now that I think about it, you'd have to calculate the speed of each mode and know what modes you have in your signal. But if you send light close to the cut-off wavelength (it's in your fibers specs), it'll be mono-mode and its speed will be roughly the same as if the light went right through slab of glass with that index.