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Fiber Coupling POP: Why does adding Φ9μm Fiber Core UDA on receiving end reduce coupling efficiency?

  • July 2, 2025
  • 2 replies
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A
Fully Spectral
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In reference to this KB article, “Single-Mode Fiber Coupling in OpticStudio”.

The receiving fiber is a Single-Mode. A SM fiber has fiber-core size = φ9.0 micron. Therefore, I added a φ9 micron aperture at the Image plane.

This resulted in a drastic drop in Coupling Efficiency: 0.99% to 0.72%. Why is that?

In a Laser fiber-coupling applications, doesn't the laser beam have to couple into the φ9.0μm dia. core? Or is it truly not the case, and the beams are much larger than the fiber core? Please help understand the reason behind this.

Thanks -Asuku

Best answer by David.Nguyen

​@Asuku 

 

I’m not an expert in fiber optics, but the Mode Field Diameter (MFD) is generally greater than the core diameter. See corresponding section of this article:
https://www.ofsoptics.com/how-to-speak-fiber-geek-article-4-single-mode-fiber-geometries/

I copied the relevant Figure and excerpt here for your convenience. Could it be the reason?

Though the drop you see is quite drastic as you say, I’m not sure its the only explanation.

Take care,

 

David

2 replies

David.Nguyen
Luminary
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  • David.Nguyen
  • Luminary
  • Answer
  • July 3, 2025

​@Asuku 

 

I’m not an expert in fiber optics, but the Mode Field Diameter (MFD) is generally greater than the core diameter. See corresponding section of this article:
https://www.ofsoptics.com/how-to-speak-fiber-geek-article-4-single-mode-fiber-geometries/

I copied the relevant Figure and excerpt here for your convenience. Could it be the reason?

Though the drop you see is quite drastic as you say, I’m not sure its the only explanation.

Take care,

 

David

A
Fully Spectral
Forum|alt.badge.img
  • Asuku
  • Author
  • Fully Spectral
  • July 3, 2025

Hello ​@David.Nguyen Yes, this is the reason. The MFD > CoreDia. However, how would one model the maximum allowable aperture on Image plane. Especially when deal with multiple beams and you want to isolate each beam to a certain location on the Image plane?

Asuku

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