Question

Modeling irregularity on an even asphere

  • 9 December 2020
  • 9 replies
  • 359 views
Matthias.Whitney

I have a design with the lenses out for fab with manufacturers. However, they've come back and told me that due to unforseen tooling issues, the lenses won't meet the irregularity spec. Is there a way to model irregularity on this even aspheric  surface short of increasing TEZI in my tolerancing analysis and rerunning the Monte Carlo?


Plot twist: the vendor said they could meet the irregurity spec in the inner zone of the aspheric surface (1 fringe) but the outter zone would be higher (4 fringes).

9 replies

Allie
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Userlevel 6
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Hi Matthias,


Since the irregularity spec is known, it would probably be useful to directly define a phase surface with the amount of irregularity specified by your manufacturer. We have a few methods for this, found here:



If you already have some Monte Carlo files generated, you could write a macro to apply the settings across all files and re-calculate the overall yield. I have previously created a macro to run through Monte Carlo files, perform some change, and extract the results. The examples can be found here. 


Would one of these methods work for you?


Best,


Allie

Allie | Team Lead Application Engineering | Zemax, Ansys
Mark.Nicholson
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Userlevel 7
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Hi Matthias,


Depending on where you are in the design cycle, you may also be able to re-optimize the other elements given the known asphere specification and tolerances. It is often a good strategy to get the most difficult pieces made and measured, and then re-optimize the easier pieces and get them made.


- Mark

Matthias.Whitney

I'm just now getting back to this. Allie, thanks for the resources! However when I add a Zernike Fringe Phase surface, I don't see the zernike terms in the lens data editor. Norm Radius is my last column. There are 8 unused parameters prior to the norm radius column. Are these the zernike terms?


 


Mark, that's a great suggestion, however the other lenses in the design have already been made for this prototype run. Moving forward we can compensate for this though.

Matthias.Whitney

Oh wait, I see you put in the number of max terms...my mistake.

Matthias.Whitney

This is modeling the irregularity well using the zernike phase surface. But I'm still unsure how to model zones of irregularity meaning the inner portion of the lens is held to 0.1 micron PV but the outer diameter is as high as 2 microns PV. Any suggestions on this?

Allie
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Userlevel 6
Badge +2

Hi Matthias,


In Sequential Mode, this may be tricky. I have discussed this with my colleagues and we have two ideas:


1. Utilize the Multi-Configuration Editor to change the aperture and Zernike coefficients. For example, Configuration 1 would have a Zernike surface with 0.1 um PV and an aperture which limits the radius to the inner portion. Configuration 2 would have a Zernike surface with 2 um PV and would have an obscuration which limits the aperture of the optic to the section between the inner portion and the edge of the lens. There are a few analysis windows which will take both configuration results into account at the same time - the Standard Spot Diagram is one example. This will work for you if your criterion is based on one of these analysis tools. If your analysis is based on the Wavefront Map, then this will not work. The Wavefront Map does not allow for the simulatneous evaluation of both configurations. 


2. Utilize a Grid Phase surface instead of Zernike phase surface. The Grid Phase surface allows you to define the phase of your surface point-by-point via the use of an external data file. This data file is able to be generated programmatically as I have discussed in this article. You can also use the ZOS-API to extract the phase profile of your two Zernike surface types (both levels of PV) and stitch them together. We have some guidance on extracting sag in this article. You can extract phase in a similar manner by using optimization operand SPHS instead of SSAG. The downside to this method is that the phsae of the surface will be static unless you import a new DAT file. 


Would something like this work for you? Let me know if you have any questions!


Best,


Allie

Allie | Team Lead Application Engineering | Zemax, Ansys
Mark.Nicholson
Rank
Userlevel 7
Badge +3

I'm sure some multi-configuration shenanigans would work as Allie says. Also, look at the Zernike Annular Phase surface as a way of adding annular phase data. Also check out the Binary 2, 3 and 4 surfaces. Lastly, the Zone Plate Lens surface might be useful too.

Matthias.Whitney

Would making a zernike phase surface with the aperture the size of the inner diameter and then putting that on top of a zernike annular phase surface work how I hope it would? Or would the zernike annular phase surface just block the smaller one?


The grid phase surface looks a little more complicated than I'm able to work out before I got on vacation at the end of the week, but that sounds promising. If the anular phase surface doesn't work how I hope it will then I'll have to revisit this in January when I have a little more time.


Thanks for looking into this with me!

Mark.Nicholson
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Userlevel 7
Badge +3

I think so. It would add no phase in the inner region, but could give you r^2, r^4 etc outside of this region. Worth a try :-)

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