How to find out the coefficient r^2, r^4 and r^6?

  • 21 August 2021
  • 9 replies
  • 364 views
S

Hello everyone,

I am doing sunlight collection using Fresnel lens. For that purpose i have purchased Fresnel lens from Edmund optics which has the following spec 

5" x 5", 4" Focal Length, Fresnel Lens

Aspherically Contoured Fresnel Lenses

Aspherically Contoured Fresnel Lenses

Stock #46-614

But for the above lens Edmund optics does not provide Zemax file. To design the above mentioned lens in opticstudio either i have to use “Fresnel” surface in sequential mode or “Fresnel 2” in non sequential mode. I supposed to work in non sequential mode. If I know how to design in sequential mode then I can convert the design into non sequential mode. But I am stuck at one point of designing Fresnel lens in sequential mode. The point where I am stuck is in determining the 2nd order, 4th order, and 6th order term in Fresnel lens.

I know rest of the things to design Fresnel surface in sequential mode. Can anyone help me with this issue?

 

 

 

9 replies

David
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Hi Sathya,

I looked at the Edmund part. They do not give these coefficients in the specs, but since it is intended as a concentrator I think it’s a good assumption that it’s parabolic. So I would use conic -1 with r chosen to produce the specified focal length and those higher order coefficients all zero. To do better you’d need to ask Edmund. 

You could also determine the coefficients by optimizing them for spot size with a focal length operant in the merit function. But again Edmund would be the final word. 

kind regards,

David

Kind regards, David
David
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I had another look this morning. I modeled the Edmund Fresnel in sequential and optimized only the radius and coni and got a conic of -0.937  and an RMS spot radius of 45um. We can’t know that is the design without them telling us, but it’s likely close. I’ve attached my model. (Since it uses Fresnel, its round rather than square.)

Best,

David

1 Attachment
Kind regards, David
S

Dear David,

Thank you so much for spending time to reply my query. I have asked my question in Edmund optics, but they have replied with document (attached here) to design Fresnel lens in any commercial software.

 

1 Attachment
David
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Hi Sathya,

Buried in their document I find this:

“The coefficients representing our Fresnel lenses are cataloged in the file named EdmundFresnel.zmf (75 Kbytes) to be used in Zemax as sequential components. Similarly, the file EFCAT.DAT (32 Kbytes) contains our catalog to be used in CODE V. Also included is the file search.seq, which replaces the old search.seq in the macro directory in CODE V. Lenses may be placed from the catalogs according to the procedures for the respective software package. The lenses are numbered as they are in our printed catalog.”

Presumably, if you can get the file “EdmundFresnel.zmf” it will have the coefficients needed. I do note that in the Zemax lens library for Edmund the part number 46614 does not appear, so this must be in a file not part of the Zemax distribution. Maybe they will provide it.

They also indicate how their lens would be designed. The state that the conic term is set to -1 and the radius higher order terms are optimized for minimum spot size. You could do this. Make the conic -1 and make R and the x^4, x^6, x^8 terms variable, with an EFFL operand to control focal length. I would leave the x^2 term zero since it is redundant to the conic.

Kind regards,

David

 

 

 

Kind regards, David
David
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Userlevel 6
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I should have mentioned that .zmf files are Zemax lens files. If you can get it, you should be able to put it in your Zemax/Stockcat drectory and the EdmundFresnel catalog will appear in the OpticStudio stock lens library.

Kind regards, David
S

Hi David, Thanks again for your feedback.

I made the higher order terms(2nd, 4th, 6th) variable in Fresnel lens to get smaller spot size. The resultant spot size is 28.35um. 

If I vary the radius it leads to larger spot size. I cannot able to reduce the spot size below 28.35um. To verify my design is correct I have designed the Fresnel lens which has zemax file already exists. The below one is already exists design for 254mm focal length.

Spot size - 8um.

 

But when I design the same lens of 254mm focal length i got the spot size to be 17um with three coefficients as varied.

Anywhere I committed mistake?

S

Regarding ZMF file, I have that file under lens catalog in optic studio. But the lens numbered 46614 is missing. So the best way is to design myself. 

 

Regards 

Sathya

David
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Userlevel 6
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Hi Sathya,

For comparison, I have attached a ZAR for a design with 101.6mm focal length. It fixes the conic at -1 and the 2nd order at 0, and varies R and the 4th and 6th order. Higher orders do not improve performance. It targets a focal length of 101.6mm by using an EFFL operand in the merit function. The rest of the merit function was generated using the wizard to minimize spot size. It has an RMS spot radius of 2.1um.

To optimize you really do need to allow R to be variable. If you are optimizing for spot size that should definitely not increase the spot radius.

Kind regards,

David

1 Attachment
Kind regards, David
S

Dear David,

Thank you so much for your help in designing Fresnel lens. Thanks again.

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