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Forum: Processes Involving Optical Photons
Date: 31 May, 2013
From: Ben Loer <Ben Loer>

Hi all,

I've seen a message below indicating that energy is not conserved during the WLS process as of 9.4 and 9.5, meaning that if your WLS absorption spectrum overlaps with the emission spectrum (which it almost always does), you can have a photon absorbed and then re-emitted at a shorter wavelength.

Is this still the case in 9.6? If not, can we make it an official bug??

Conservation of energy here isn't itself a problem, but there is a big problem with the results, especially if you are simulating long fibers:

1) In a real fiber, the light becomes more yellow the further down the fiber you look. Eventually you won't measure any photons with wavelength under the absorption region. With the current (up to 9.5 at least) approach, no matter how far along the fiber you look, you will see the total emission spectrum (except for point (2) below).

2) Every time a photon is absorbed and re-emitted, there's a high chance it will escape the fiber trapping. In a real fiber, once the light is all shifted out of the WLS absorption band, you don't have any more losses to this effect (you do still have bulk absorption and Raleigh scattering). But if energy is not conserved, you'll lose more light in a long fiber due to more WLS absorption.

Thanks, ~Ben

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1 Agree: Re: WLS emission to shorter wavelength?   (Gumplinger Peter - 31 May, 2013)
(_ Agree: Re: WLS emission to shorter wavelength?   (Ben Loer - 03 Jun, 2013)
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