Groups > sci.physics.relativity > #403741

Re: Why is the speed of light slower in glass and regains its normal speeds as it exits from glass?

From	moroney@world.std.spaamtrap.com (Michael Moroney)
Newsgroups	sci.physics.relativity
Subject	Re: Why is the speed of light slower in glass and regains its normal speeds as it exits from glass?
Date	2017-01-01 22:41 +0000
Organization	The World : www.TheWorld.com : Since 1989
Message-ID	<o4c0iv$7t0$1@pcls7.std.com> (permalink)
References	(16 earlier) <slrno6gkmi.vh2.nedlatham@woden.valhalla.oz> <o4abbc$ba$1@pcls7.std.com> <slrno6hqin.hjp.nedlatham@woden.valhalla.oz> <o4bich$5ib$1@pcls7.std.com> <slrno6itj5.ql.nedlatham@woden.valhalla.oz>

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Ned Latham <nedlatham@woden.valhalla.oz> writes:

>Michael Moroney wrote:
>> Ned Latham wrote:
>> > Michael Moroney wrote:
>> > > > > "The simplest type of optical fiber is called single-mode.
>> > > >
>> > > > Not the one you left intact. And if it was one of the others,
>> > > > why didn't you leave that one intact?
>> > >
>> > > Single mode fiber (which doesn't work by the light bouncing off the
>> > > surface of the inner fiber, the light goes straight down the core)
>> >
>> > There is no evidence for that whatever.
>>
>> Yes there is, in what you snipped. 

>Byllshit. "Theory"-based assertions are not ecidence.

No, this is not "theory" but well-established electromagnetic practice
including not only single mode fiber but microwave waveguide design.

>>                                     I quote myself:
>>
>>: Single mode fiber (which doesn't work by the light bouncing off the
>>: surface of the inner fiber, the light goes straight down the core) is the
>>: only type that works over a long distance.  Multimode fiber has lights
>>: travelling different path lengths since they travel at different angles in
>>: the fiber. Over a long distance, "slow" light sent first overlaps "fast"
>>: light sent later and the data gets "smeared" and is not usable.

>There is no evidebce for any of that. It's all speculation.

Again, not "theory" or "speculation" but well-established electrical
engineering practice.  Evidence is that your replies get sent out on the
very single mode fiber that you don't believe in and actually reach others.

>> You see, in multimode fiber, the "fast" light (which is going straighter
>> so travels a shorter distance in the fiber) catches up with earlier "slow"
>> light which is traveling at a larger angle so it travels a longer distance.
>> This "smears" the data so it is no longer distinct on-off pulses.

>You're babbling.

Nope.  See the multimode diagram at
http://cdn4.explainthatstuff.com/fiberoptics.gif (from the very website
you gave as evidence of "support").  The purple line takes a longer path
than the green line, which is longer than the light blue straight line
path.  The path lengrh is inversely proportional to the cosine of the
angle made with the straight line path.

> Try to explain this: if the graduated refractive index
>of a single-mode fibre really does prevebt TIRs from occurring, why do
>manufacturers build those fivres with cladding layers?

That's like asking why is there a need for the microwave "plumbing"  
itself in a microwave feed when the microwaves move through the air
inside.  It forms the waveguide.

>> Single mode fiber also works exactly the same way as single mode microwave
>> waveguides, which is technology that has been known and used since the
>> 1940s. It is also predicted by quantum theory.

>More same ole same ole.

Yet still the truth.

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