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Author Topic: How Much data can a strand of this carry ?  (Read 25818 times)

Offline neilep

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How Much data can a strand of this carry ?
« on: 28/09/2007 15:11:04 »
Dearest All (hugs ewe..mwah mwah)

see this Fibre Optic ?


...

It's a thing of beauty isn't it ?..just sitting there being all busy whilst looking good !
But how much data can one strand of this stuff deliver ?...how many telephone calls ?..how does the data not get all scrambled with all the other data sent down the strand ?

I want to know and am asking you cos you know stuff !!


« Last Edit: 28/09/2007 15:24:26 by neilep »


 

Offline Karen W.

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Re: How Much data can a strand of this carry ?
« Reply #1 on: 28/09/2007 15:22:40 »
It is very complicated and depends a lot on the size and type of fiber  as to its functioning.
I have read this article and it seems to be pretty informative . The info must be carried through the light through out the plastic or glass lines.

Any way here you go. It doesn't answer all of your questions but some!

http://en.wikipedia.org/wiki/Optical_fiber
 

Offline neilep

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How Much data can a strand of this carry ?
« Reply #2 on: 28/09/2007 15:27:12 »
Thanks karen....nice frisbee on that link !!

hopfully some exact data will come this way too but I thank you for pointing me to that wiki article.
 

Offline Karen W.

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How Much data can a strand of this carry ?
« Reply #3 on: 28/09/2007 15:38:43 »
Your welcome. It was pretty was it not? I used to be an excellent frisbee participant and was very accurate in my throwing. My favorite time was in a big empty parking lot in town as a teenager on friday and saturday nights My girlfriend who died and I would cruise town trying to meet cute boys..LOL Then when we were done flirting we would park right in the middle of town in a big empty parking lot and we would throw frisbee. In the dark! eventually it was a routine and soon we found it quite fun because there was no need to cruise anymore, because all the guys we wanted to meet came and parked to play frisbee in the middle of town.. At first we got in trouble several times..LOL Then the police came and sent us home, but we came back and played some more and the building owner stood upo for us and let us use his lot as he said we were all good kids and what more could the police want then to have a group of nice kids playing frisbee in a parking lot untill 2:00 in the morning... We could have been doing alot worse! The police begrudgingly gave in after a petition was passed and we played for years in that lot. The kids do not do it anymore.. I remember a really cute fellow in an Bright orange Sting Ray who I really Liked .. LOL He was cute  and very nice! LOL I loved his car! LOL.. We did not need fiber optic lines to meet people back then just a frisbee and a smile!
 

another_someone

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How Much data can a strand of this carry ?
« Reply #4 on: 28/09/2007 18:12:12 »
It is very complicated and depends a lot on the size and type of fiber  as to its functioning.
I have read this article and it seems to be pretty informative . The info must be carried through the light through out the plastic or glass lines.

Any way here you go. It doesn't answer all of your questions but some!

http://en.wikipedia.org/wiki/Optical_fiber

It also depends on how long the fibre is (the distance between repeaters) - although this interacts with issues of how thick the fibre is.

There is ofcourse the ultimate theoretical limit of about 1/2 the frequency of the carrier (i.e. 1/2 the frequency of light, so probably in hundreds of Teraherz region).  Technological limits that causes light to smear out as it passes down the fibre (combined with the fact that the electronic devices at each end of the fibre cannot cope with such high frequencies) means that the realistic limits are many orders of magnitude less than that.

Very thin, graded (i.e. with a graduation of the refractive index from the outside to the inside of the fibre), you can reduce the amount the light wave smears out.

Ofcourse, the shorter the fibre, the less time for light to smear our as it travels along the fibre.
 

Offline Karen W.

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How Much data can a strand of this carry ?
« Reply #5 on: 28/09/2007 18:28:38 »
George what do you mean by smear out.. do you mean for the light to fade or deminish?? I don't understand the term?
« Last Edit: 29/09/2007 18:41:57 by Karen W. »
 

another_someone

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How Much data can a strand of this carry ?
« Reply #6 on: 28/09/2007 20:19:31 »
George what do you mean by smear out.. do you mean for the light to ade or deminish?? I don't understand the term?



Think of the above as a very crude notion of blobs of light (red dots) representing data travelling down a fibre (represented by the blue).

The first piece if fibre is very close to where the light enters the fibre, and you see the individual blobs of light distinctly separate.  As you go down the fibre, you see the light spreading out, until one blob of light becomes indistinct from the next, and you cease to be able to see where the light is on, or the light is off.
 

Offline daveshorts

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How Much data can a strand of this carry ?
« Reply #7 on: 29/09/2007 11:12:50 »
There are a couple of reasons that the light gets smeared out.

Light entering the fibre at different angles will move different distances in the same time because light going in a straight line moves more directly down the fibre.



So fibres are made very narrow so only light is going in a straight line.

Also different colours or wavelengths go at different speeds, which is a much more difficult problem as modulating the light into pulses spreads the wavelength of the light out, so it is impossible just to use one wavelength. This effect is called chirp.

It is possible to use a length of fibre which has the opposite dependence of speed on wavelength to unsmear the light again.
 

Offline neilep

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How Much data can a strand of this carry ?
« Reply #8 on: 30/09/2007 18:07:05 »
Just want to thank you for your continued responses Dave, George & Karen....they do not go unnoticed and I appreciate the time ewe take to respond.
 

Offline Karen W.

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How Much data can a strand of this carry ?
« Reply #9 on: 01/10/2007 09:34:22 »
I still don't understand how it keeps from getting scrambled as Neil asked earlier.....


Your welcome Neil Thanks for all the new topics they are great!
 

Offline McQueen

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How Much data can a strand of this carry ?
« Reply #10 on: 01/10/2007 14:43:32 »
Quote
I still don't understand how it keeps from getting scrambled as Neil asked earlier.....
Colours can be scrambled and unscrambled , can't they.
 

Offline ukmicky

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How Much data can a strand of this carry ?
« Reply #11 on: 01/10/2007 22:11:13 »
Quote
How Much data can a strand of this carry ?
i suppose that would depend on how small the lettering was in the books you hang from it. ;D
 

Offline neilep

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How Much data can a strand of this carry ?
« Reply #12 on: 01/10/2007 22:30:46 »
Quote
How Much data can a strand of this carry ?
i suppose that would depend on how small the lettering was in the books you hang from it. ;D

LOL !!..Michael knows the true meaning of my questions !!...I think I'll go back to doing potato prints now!!  *claps hands in elated glee*
 

Offline Bored chemist

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How Much data can a strand of this carry ?
« Reply #13 on: 02/10/2007 20:31:27 »
I think that a strand of optical fibre can be made to carry just about as much data as you want; eventually.
 

another_someone

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How Much data can a strand of this carry ?
« Reply #14 on: 02/10/2007 20:50:02 »
I think that a strand of optical fibre can be made to carry just about as much data as you want; eventually.

Well, no - you cannot get around the nyquist limit (although we are presently well short of that limit).
 

another_someone

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How Much data can a strand of this carry ?
« Reply #15 on: 02/10/2007 20:54:01 »
I still don't understand how it keeps from getting scrambled as Neil asked earlier.....


Your welcome Neil Thanks for all the new topics they are great!

I am not sure what you mean by scrambled?

The issues about blurring (the spreading out of the wave) have been addressed, but ignoring those issues (assuming that the fibres were optically perfect, and very thing, and had equal properties for all frequencies), then it is simply a matter of first in first out (the data will come out of the fibre in the same sequence it went in).
 

Offline Bored chemist

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How Much data can a strand of this carry ?
« Reply #16 on: 03/10/2007 20:28:31 »
"Well, no - you cannot get around the nyquist limit (although we are presently well short of that limit)."
I may have misunderstood, but I thought that Nyquist's work showed that the rate o data transfer was limited, not the quantity. If you want you can send all the data you have. It may take a long time if you have a lot of data or a poor bandwidth, but you can do it eventually.

(Slight giggle at the spell checker's ideas concerning "Nyquist")
 

Offline Karen W.

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How Much data can a strand of this carry ?
« Reply #17 on: 03/10/2007 20:50:29 »
I still don't understand how it keeps from getting scrambled as Neil asked earlier.....


Your welcome Neil Thanks for all the new topics they are great!

I am not sure what you mean by scrambled?

The issues about blurring (the spreading out of the wave) have been addressed, but ignoring those issues (assuming that the fibres were optically perfect, and very thing, and had equal properties for all frequencies), then it is simply a matter of first in first out (the data will come out of the fibre in the same sequence it went in).

That is what I meant, thanks for the explanation George I thought it could get all kinds of goofed up and wondered how it is kept straight!
 

another_someone

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How Much data can a strand of this carry ?
« Reply #18 on: 03/10/2007 21:51:21 »
"Well, no - you cannot get around the nyquist limit (although we are presently well short of that limit)."
I may have misunderstood, but I thought that Nyquist's work showed that the rate o data transfer was limited, not the quantity. If you want you can send all the data you have. It may take a long time if you have a lot of data or a poor bandwidth, but you can do it eventually.

OK, my misunderstanding - I did not apply the word "eventually" in the way that you had intended to mean it.
 

lyner

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How Much data can a strand of this carry ?
« Reply #19 on: 06/10/2007 23:38:52 »
The existence of multipath transmission  in optical fibres is   certainly one limiting factor , as is the dispersion due to changing wave speed.
However, the ultimate information carrying capacity depends upon  the way the information is coded and upon the signal to noise ratio. Every channel suffers from noise due to thermal agitation of the atoms / electrons. The actual information on a picture or piece of audio programme is not the same as the number of samples per second times the bits per sample.  That is a huge over estimate.
Shannon, in the 1940s, did a lot of theoretical work on information and transmission channels.  No communication channel has ever been constructed that remotely approaches the limit proposed by Shannon.  We all use data compression when we send files to each other. To get the maximum useful information rate across, you need to take a lot of delay in the system. This allows you  to code the information efficiently and to check and correct errors.  It's fiendishly complicated but 'they' are making advances all the time. It's why you can get such a lot of programme time on a DVD or MP3 player, these days.  Present systems still waste a lot of channel capacity because the coding is  not ideal. It gets better all the time, however.
 

another_someone

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How Much data can a strand of this carry ?
« Reply #20 on: 07/10/2007 01:24:04 »
We all use data compression when we send files to each other. To get the maximum useful information rate across, you need to take a lot of delay in the system. This allows you  to code the information efficiently and to check and correct errors.  It's fiendishly complicated but 'they' are making advances all the time. It's why you can get such a lot of programme time on a DVD or MP3 player, these days.  Present systems still waste a lot of channel capacity because the coding is  not ideal. It gets better all the time, however.


MP3 and DVD's (they use MPEG2, do they not) do not use lossless compression, so they are not merely making more efficient use of bandwidth (in the way that Huffman or LZW encoding do), but actually throw away data - hence the Shannon limits are not totally pertinent to them (this is compounded by massive amounts of error correction that reduce the efficiency of bandwidth usage).
« Last Edit: 07/10/2007 01:29:14 by another_someone »
 

lyner

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How Much data can a strand of this carry ?
« Reply #21 on: 07/10/2007 19:37:47 »
Fair enough - I quoted those well known forms of compression as the lossless compression methods are, perhaps,  not so well known.
I would disagree that error correction makes for inefficiency when you bring into the account the signal to noise consideration. You may get garbage out of a system that, with a good snr, is what you would call efficient but which is passed through a noisy channel. The way you demodulate and decode your received signal is the crucial thing in its information rate capacity.
You can cram more and more into a channel and get worse and worse inter symbol interference but, as long as the snr is high enough, you can get all the info out again. That's, basically, what Shannon says and I wouldn't lightly disagree with the Daddy.
To do the above, you need to filter over a longer and longer  time interval - which introduces a longer and longer delay into your channel and more complex processing..
Bandwidth Usage is not just a matter of raw data rate per Hz of channel space.
 

Offline neilep

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How Much data can a strand of this carry ?
« Reply #22 on: 08/10/2007 19:40:10 »
THANK EWE again for your continued wonedrful posts !!

May I ask please what a NYQUIST limit is?...and does it have anything to do with a flavoured milk drink?



 

Offline Karen W.

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How Much data can a strand of this carry ?
« Reply #23 on: 08/10/2007 19:43:44 »
Which I love!
 

Offline Alandriel

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How Much data can a strand of this carry ?
« Reply #24 on: 09/10/2007 17:09:38 »

NYQUIST limit?!?!?!

I have a friend who's last name is Nyquist (a quite commen Swedish name I believe).
Never knew she had a limit.

 ;D


Gosh - what an interesting thread


..... my braincells are devinitely doing backward and forward flips now.


So much to learn - so little time.......


 

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How Much data can a strand of this carry ?
« Reply #24 on: 09/10/2007 17:09:38 »

 

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