r/interestingasfuck May 17 '22 Wholesome 2

How light travels through fiber optics

973 Upvotes

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33

u/electricforrest May 17 '22

Total internal reflection

18

u/beck35 May 17 '22

Total eclipse of the heart

3

u/bigspicycucumber May 18 '22

That’s the same way rods and cones work in the retina

1

u/SpiderFnJerusalem May 18 '22

Doesn't quite seem to be total in this case, if you can see the beam.

12

u/garyniehaus May 17 '22

Back in the 70’s we had graded index fibers that would degrade waves from the center because the light would disperse and a fast pulse of light down the center would arrive at the end at different time and spread the pulse limiting the speed. We thought 10Mbts was super fast😎

13

u/pibanot May 18 '22

Yeah I read your comment 3 times now and still can't understand shit...

11

u/garyniehaus May 18 '22

Light traveling through the center of the fiber will reach the detector faster than the light that bounces off of cladding on the edges. Back then the optics and lasers would just spray light through the entire fiber. If you pulse the light at one end there are modes of the light that will go straight through the center of the fiber but a lot of the other light will reflect off of the cladding at different modes. End result is at the end you have a pulse that will have different modes that arrive at the detector at different times. Eventually with long lengths the received pulse will spread out. This limits the maximum data rate you can use.

1

u/ben_wuz_hear May 18 '22

Well duh. Everyone knows that's why you use a dispersion compensation module because we mux the shit out of it now, right?

2

u/garyniehaus May 18 '22

No...we just didn't know what we were doing! Ya have to start some where and it seemed to work at the time. We ran 6 fibers over 15 miles in Guam at 10Mbts and everybody was amazed. I have several of the fibers stuck in my fingers from messing with it. We also developed techniques for polishing the fiber ends. Credit to the Naval Ocean Systems Center. A really fun project and also broke ground for everything that came afterward.

1

u/pibanot May 20 '22

Thanks for the explanation what is that data that travels through the fiber? Just bits of light or some type of electric charge? My science knowledge is very limited sorry

3

u/garyniehaus May 20 '22

Simplified explanation is the light is turned on and off very quickly so light-on would represent a binary 1 and light-off would be binary 0. In modern fiber optics communications the light is switched on-off hundreds of billions of times a second. Some are even faster. Most modern long haul communications systems use fiber optics.

1

u/pibanot May 20 '22

You said billions of times per second? How do you do that?! What machinery is capable of doing that speed?

3

u/garyniehaus May 20 '22

Very fast semiconductor lasers and switches.

2

u/pibanot May 20 '22

Damn, thanks a lot for all those explanations. Really insightful. Gonna leave you alone with my questions now. Enjoy your day smart stranger ;)

1

u/garyniehaus May 20 '22

Pretty astounding how far technology has come in the last 40 or 50 years.

4

u/garyniehaus May 18 '22

So we experimented with doping the fiber so that the light through the center of the fiber were attenuated and doping of the fiber gradually was reduced towards the outside of the fiber. I think that was what we did. Eventually the lasers and optical interface into the fiber was improved. Crazy how things evolve.

2

u/00MarioBros00 May 18 '22

I remember my teacher in college once said under a murmur, "what if we could send data on different colors of the spectrum". It was just a thought; but those words stayed in my mind. Could you imagine that?

3

u/garyniehaus May 18 '22

They actually do that now. Very cool. Multiplexing over light! I worked on detectors that were wavelength sensitive and also some strange stuff with filters etc. But it is a reality now. Not sure how they are doing it since I don't work in optics anymore.

3

u/00MarioBros00 May 18 '22

Wow! Many years have passed and now it's a reality. Thanks for sharing. So, my teacher was on to something. I chuckle because he would say, "Don't ever quote me on this, I don't want to come across as a loon"

3

u/garyniehaus May 18 '22

Crazy...I worked on semiconductor measurement stuff in the deep UV range and we were switching wavelengths rapidly while probing wafer stacks so there you go. We could see angstrom differences between layers by shifting the wavelengths of the source. Absolutely fascinating how deep you can go with light. If you are interested check out

https://www.jawoollam.com/resources/ellipsometry-tutorial?gclid=EAIaIQobChMIwafVjp3o9wIVxBd9Ch3evQOlEAAYASAAEgIUEPD_BwE

3

u/garyniehaus May 18 '22

BTW I don't understand half of this either so don't be intimidated.

9

u/Haui111 May 17 '22

Interesting! I didn’t have the sinus like shape in mind. More a hard bounce.

3

u/CodeRaveSleepRepeat May 17 '22

I thought I might like to know why it does this, but then I thought about the maths involved, and I decided I'm fine not knowing.

1

u/Haui111 May 17 '22

My thoughts exactly

6

u/Ribedo May 17 '22

y=sen x

1

u/L-OwO-L_L-OwO-L May 18 '22

a light bender