# I keep runing in circles around this optic fiber question...

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1. Jul 19, 2017

### Cartman

• Member advised to use the homework template for posts in the homework sections of PF.
Hi everyone

I can not seem to get the right formulas to finish this question.
I keep on beating my head against a wall for hours now.
It just feels like I can not get the right formula to help me out...Is this some sort of trick question?

Note if the image does not load here is the link -> http://imgur.com/a/8z7Et

This is what I have.

If I could just get the wavelength( λ ) I could easily get the diameter etc.
But λ = v/f neither if which I have. WHERE v = Normalized Frequency and λ = wavelength.
I cant find a way to get Normalized frequency to just frequency and I also do not know if I can use the function λ = c/f because I dont have c (Velocity of light in vacuum) or f.

This is what I have so far and I have no idea if its of any use.

I am trying to use this function to get the diameter of the core n1; V = ( 2π / λ )(a(NA)); Where a will be the diameter of the core.

c = 2.05^-8 m/s
m = 5000m
θa = 15.3
V = 33.5 normalized frequency
B(Maximum Bandwidth) = 1.5Mhz
Source = 900nm

NA = sin(θa) = 0.2638

n = C / Cs = 300x1-^-6 / 205x10^-6 = 60/41 = 1.463

I dont know where to go from here as there is thousands of little formulas but I cant seem to pinpoint even 1 to use.

Thanks

2. Jul 20, 2017

### scottdave

It has been awhile, since I have taken a fiber optics course, and I have not used it much. I don't remember most of the formulas, but I would like to offer a general suggestion. When I was taking a technical class, especially an advanced course, we would get into groups and study and do homework together. We could check our solutions with one another, and help each other, if one person was having trouble with some concepts.

It sounds like maybe you are having issues with some of the concepts. Even your professor can be helpful to explain something that you are not understanding. Most of them really want to help. This may not help you for this particular situation, but hopefully it will, moving forward.