How to avoid the TIR(total internal reflection) during the lens optimization

  • 25 March 2022
  • 8 replies
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Userlevel 5
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Sorry that this title is not accurate. The TIR occurs sometimes when we recreate something from a patent or we add extra operands other than the operands generated by the field wizard.

I have been asked several times. I got this error message during my current project. So I want to share some thoughts about how to do this:

  1. Reduce the field/ numerical aperture to remove the TIR first 
  2. Apply the RAID/ MXAI/MXRE/MXRI to constrain the incident angle
  3. You can optimize the lens shape to reduce the angle 

  4. Try HYLD in optimization wizard  Designing for as-built performance with High-Yield Optimization – Knowledgebase (zemax.com)


8 replies

Userlevel 5
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Hi Mark, Thank you so much for your comments! Using hammer is actually a practice I applied to my system when I was stuck with the local optimization for several days. I did not know how to improve the system, so I tried it. Then I saw the merit function went down quickly. I use this tool when I finished my day work so it can search by itself. You are right about the adding some kind of constraints for aspherical element optimization. Sometimes I just forgot to add them when everything seems fine. Thank you for reminding me about the FTGT/LT and the operands of the constrains on lens data, I used them during the optimization, I will add it to the post. Thank you again!

Userlevel 7
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I think the points you raise in that article are all very good. I wouldn’t blame the Hamme roptimizer though...its job is to lower the merit function, and that is all it does. Basically you always need to add some kind of constraint to stop the asphere from becoming too wild, or too rapidly changing for manufacture. SCUR and SDRV are all good operands to add to limit the degree of asphericity. The FTGT/LT operands are useful for constraining surfaces which do not have their minimum or maximum thickness at the center or edge, but at some intermediate zone.

Check out the user manual at The Optimize Tab (sequential ui mode) > Automatic Optimization Group > Merit Function Editor (automatic optimization group) > Optimization Operands by Category > Constraints on Lens Data for a listing of all the p[erands that can be useful to constrain aspheric surfaces.

  • Mark

 

Userlevel 5
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Thank you so much Mark! By the way, do you have some suggestions about the control of aspherical shape? I listed some here but I wonder if you have other methods.

How to control the aspherical surface during the optimization | Zemax Community

Userlevel 7
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The best advice is the one you already gave. Use ‘Improve Manufacturing Yield’ in the Optimization Wizard. Unless you are really needing the best possible result from as few surfaces as possible, you should always use this.

Userlevel 5
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Hi Mark,

I think I get your point! Thank you! I will confirm when the TIR warning message occurs. By the way, do you have any other suggestions to avoid the high incident angle?

Yuan

Userlevel 7
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Hi again, 

thanks for that. However, if TIR occurs during optimization the optimizer should back out of it automatically. If the optimizer makes some change that causes a ray in the MF to not trace, the optimizer should discard that change and try something else. If it doesn’t, it’s likely a bug.

 

-Mark

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Hi Mark, Thank you for your comment! I realize the title of this conversation is not accurate. The first line is for the TIR error message when we recreate files from certain patents. When the TIR error message happen during the optimization, this means the system is highly sensitive, this is the case we want to avoid as the TIR leads to both a low yield rate and stray light introduced by the TIR.

Userlevel 7
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Hi,

are you saying that during sequential optimization you are getting TIR and so the rays don’t trace? That’s a bug if so. If the optimizer does anything t

tyst stops a ray from tracing, it should automatically back out of that and only consider traceable systems.

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