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Sweep focal length of paraxial lens

  • 24 July 2023
  • 4 replies
  • 88 views
J
Userlevel 2

A source diode emits light that goes through a PBS and is then collimated by a paraxial lens. A detector is placed after the lens.

For a fixed position of the paraxial lens, I would like to sweep the focal length and pick the one that minimises the RMS angular radius at the detector. However, after defining a Merit Function, the drop down menu in the Universal 1D plot does not give me access to the focal length of the lens. How can I access this attribute within the Universal 1D plot?

 

Kind regards,

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Best answer by David.Nguyen 24 July 2023, 15:51

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David.Nguyen
Rank
Userlevel 7
Badge +2

Hi @Jonasz,

 

The X Focal Length, and Y Focal Length of a Paraxial Lens object are the parameters 3, and 4 respectively. If you don’t know how to check what parameter is a given column in the LDE or NCE, create a dummy surface or object, and look at the column header in the corresponding cell.

When clicking a cell from the Paraxial Lens, you see the actual header for the column of that object.
When clicking on the corresponding cell of a Null Object, you get to see the corresponding parameter (Par) number.

You should then be able to setup your Universal Plot like so:

I hope this helps.

Take care,

 

David

J
Userlevel 2

Hi David,

Great explanation. Thank you a lot!

David
Rank
Userlevel 6
Badge +4

David is quite right. I would also like to offer two additional comments. 

If you wish to control both focal lengths with one value, then you could set the other focal length as a pickup which gets its value from the first. For example, you could set the y focal length to pickup the x focal length value and then control the x focal length to control both. 

Also, to determine the best focal length you could use optimization. You can use the Optimization Wizard to create a merit function that targets zero RMS angular radius on the detector. Then make the focal length variable and optimize. In the attached file, the front and back radii of a standard lens are independent and optimized to collimate a source two angle. The file is attached as a zar in a zip.

 

 

1 Attachment
Kind regards, David
David.Nguyen
Rank
Userlevel 7
Badge +2

Thanks for the comment @David. Regarding your first point, that’s actually also what I did (it shows in my screenshot), but forgot to mention it!

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