Multimode optical fiber, physics beginner help :D

[Xenon02]

@sophiecentaur

Okey I've read some comments + this article Khanacademy link. Just like you said. I tried to understand it again, but I don't know if what I will say now is correct. I'll use some picture for it.
I'll try to explain some stuff of what did I understand. If you could if it's okey or Correct/Incorrect (sorry again for the problem).
I'm slowly getting it I guess.
So basically when I have two wavelengths that are connected to each other fully then it depends what happens. If the second wavelengths is in phase with the first then it is constructive interference, if the second one is shiftd 180 degree then it is Destructive.

I didn't understand the moment when it was written that it's leading to a new wave. Like creating ?
Maybe I'm wrong but I remember that when they meet each other at certain point then this point is constructive and when waves exit this place then it comes back to normal (maybe I am wrong).
Also about the phase shifts this one is also interesting : Phase shift

About the shifts I've watched some videos and read about how it actually works. I've seen the simulation that showed how it looks like for 2 slits which was also interesting.

Here it looks like it is now how to call it max constructive interference nor max destructive interference. Something between. And that's how it actually works I guess.
But what was disturbing me was how it was called this difference. In the article it was said that it is Path difference. On the video it was Wavelenght difference.
Usually when I hear wavelenght difference I imagine something like this :

Like one is slower and one is faster that is certainly a wavelenght difference. But there (for interference) it had a different meaning, or I just didn't understand it fully. It was the path that made the wave delay and it looked like it was shifted.

Something like that ?

 

[hutchphd]

For the multimode/singlemode fiber discussion the most important piece is the path length difference. The single mode fiber greatly diminishes the possibility of alternate paths for any given signal. So the result is much "cleaner" at the end.

 

[berkeman]

Thread closed for Moderation...

For the multimode/singlemode fiber discussion the most important piece is the path length difference. The single mode fiber greatly diminishes the possibility of alternate paths for any given signal. So the result is much "cleaner" at the end.

Exactly, which was the main question in the OP. But there was all kinds of other stuff about coherent interference and multi-wavelength interactions and so on, which has made this thread too muddled for me to be able to follow. I'll try to sort it out in the next couple of days, and maybe have the OP start a new thread on what they really want to ask. Lordy.

UPDATE -- I am discussing the issues with the OP in a PM.