Is NA in System and fiber coupling calculation same?

Question

Hi Zemaxers

I am reading this tutorial, and the NA in System and Fiber coupling confused me

https://optics.ansys.com/hc/en-us/articles/42661821960851-How-to-model-angle-cleaved-fibers

As far as I know, the fiber coupling efficiency does not use the system NA to calculate, but you need to input in the its own

And I am just wondering, why the two NA do not match? say, both NA 0.2 or NA 0.1

the tutorial shows a setup like

obj- lens- image

simulates source fiber - lens - receiver fiber

so shall the light source NA = source fiber?

it will be appreciated if you point out my misunderstanding

thank you

Yang

Jeff.Wilde · Accepted Answer

The system NA sets the maximum angle for source rays used in any ray tracing analysis. In the single-mode coupling efficiency analysis, the Source NA defines the 1/e^2 intensity angle for the fiber (or waveguide). In general, you want the system NA to be 1.5X to 2X larger than the fiber NA so that the tails of the Gaussian beam from the fiber are not clipped by the system aperture in any meaningful way. To better understand this effect, you can keep the fiber NA at 0.1 and vary the system aperture NA from say 0.05 to 0.2, and you will see the impact of fiber beam clipping by the system aperture.

Regards,

Jeff

Yang.Yongtao · Answer

Hi JeffThank you for your explanation!The system NA sets the maximum angle for source rays used in any ray tracing analysis. In the single-mode coupling efficiency analysis, the Source NA defines the 1/e^2 intensity angle for the fiber (or waveguide). In general, you want the system NA to be 1.5X to 2X larger than the fiber NA so that the tails of the Gaussian beam from the fiber are not clipped by the system aperture in any meaningful way. To better understand this effect, you can keep the fiber NA at 0.1 and vary the system aperture NA from say 0.05 to 0.2, and you will see the impact of fiber beam clipping by the system aperture.Regards,Jeff

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