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Old Nov 21st 2009, 01:40 AM   #1
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Red face optical fiber

A optical fiber consists of a cylindrical core n=1.46 surrounded by a concentric cylindrical jacket cladding n=1.43. The cladding in turn, is surrounded by air n=1.00. An incoming ray of light has a angle alpha to the central axis of the core. For what range of angles for alpha will the ray experience total internal reflection at the core-cladding interface?
Then what will the sketch look like until it reaches the right side of the optical fiber?

I do not know where to even begin.
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Old Nov 21st 2009, 03:12 AM   #2
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madam, i do not know what core/ clads are but my calculation shows that between 0 and 90 degrees, alpha has to be less than 17degrees .( on both sides, ie. a cone of 17 degree semi vertical angle)
if this matches answers, then i will tell u to just draw the figure neatly, apply snell law at two surfaces, one at air -core interface when ray enters core and the other at core - clad interface and apply total internal reflection conditions.if u need further explanation, please reply.
the relevant equations are 1 sin(alpha)=1.46 sin theta eq1 ......snell law at core air interface
so angle of incidence at core clad interface=90 - theta
critical angle = sin inverse(1.43/1.46)
so for TOTAL INT REFLECSION, 90 - theta>sin inverse(1.43/1.46)
so theta<90- sin inverse (1.43/1.46), take sine on both sides
sin theta<cos(sin inverse 1.43/1.46)
ie. sin theta<0.201677
now use eq 1 to replace sin theta, sin alpha/1.46<.201677
or, sin alpha<0.294448637
taking inverse
alpha< 17.1244 degrees.

Last edited by r.samanta; Nov 21st 2009 at 05:23 AM.
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Old Nov 22nd 2009, 10:35 PM   #3
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Optic Fiber Drawing

I've attached a drawing of the Optic Fiber in my Physics problem for your review. Can you help with the 'rays' from here?
Attached Files
File Type: doc Sample Drawing.doc (24.0 KB, 11 views)
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Old Apr 8th 2010, 12:17 AM   #4
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Great discussion! An optical fiber is a glass or plastic fiber that carries light along its length. Light is kept in the "core" of the optical fiber by total internal manifestation. Optical fiber are used in telecommunication and networking.

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