Divergence angle of light exiting a nano-etched single mode fiber

AI Thread Summary
The discussion focuses on the behavior of light exiting a single mode fiber with a 200 nm diameter hole at the tip, specifically regarding the divergence angle at 830 nm with a numerical aperture (NA) of 0.12. It highlights the challenge of calculating the cone of light due to the small aperture, which may introduce diffraction effects. The user seeks guidance on how to account for these effects when determining the acceptance angle and the resulting intensity profile. The conversation also references the potential for multiple modes when the light wavelength is shorter than 830 nm. Overall, the impact of the small hole on light propagation and divergence is the central concern.
melnop
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I am working with a single mode fiber at 830 nm with a NA of 0.12 (http://www.thorlabs.com/thorcat/19600/P3-830A-FC-2-AutoCADPDF.pdf). One end has a fiber tip coated in silver with a small hole of 200 nm diameter to essentially create a point source. My advisor told me that the fiber has a few modes when the light traveling through is shorter than 830 nm. I know that the acceptance angle may be calculated easily for a normal fiber, but I'm not sure how the small hole will affect things.

How could I calculate the cone of light that is coming out of the silvered end?

(I have included a diagram for clarity)
 

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