Diffraction grating DLLs don't work

  • 7 February 2020
  • 5 replies

I wanted to try out the new diffraction grating DLLs.  Following the example in the knowledge base article, when I get to the point of selecting one of the DLLs I get an error message "Unable to load 'UserParamNames' function from DLL".  The only DLL that seems to work is diff_samp_1.DLL

5 replies


I have the same question concerning the work with VBG dll (hologram_kogelnik.dll) files. We have Optic Studio 20.1 Premium but not Subscription-type license. Did you solve the problem of previos case? Are  there plans to allow  users of Optic Studio 20.1 Premium to work with this support or no? Are there any possibilities to obtain this support? Our laboratory is working with Volume Bragg Gratings so it will be interesting for us to get this oppotunity.


So you are telling me that with the annual support we just paid for, and the upgrade to Premium that we just paid for, the is functionality that we are ineligible for?  I was under the impression that Premium meant we got all functionality even though we still have the black USB keys.
Userlevel 6
Badge +2
Hi David,

When you say "new diffraction grating DLLs" are you referring to the ones released with 20.1? Specifically, the ones provided in either of the following articles?


If so, then you will need to make sure you are using a Premium Subscription-type license when you import those surfaces. A Premium Perpetual license will not work, and you will see the "Unable to load 'UserParamNames' function from DLL" error.

If you're not sure which license type you have, you can follow the instructions in the article "How to identify your OpticStudio license" to locate that information. In the updated License Manager (postdated June 2019) a subscription license will be shown in boldface font within the "View License Information" tab for softkeys or red USB keys. If you have a black USB key, then it is a Perpetual-type license. 
Userlevel 2
Badge +1
Hi David, 

To answer your question, yes, there are new functionalities released in OpticStudio 20.1 that are available to subscription license users only. This does mean that users of existing perpetual licenses who have renewed support for those perpetual licenses will not have access to new subscription features.

That said, we want to make sure that we appropriately educate our users so that we can mitigate any surprises when a new version of OpticStudio is released. Along those lines, you can find the release notes for OpticStudio 20.1 here. I'm also going to ask your Zemax Account Manager to follow-up with you and your License Administrator about this, so that they can discuss with you the processes and financial incentives we have in place to help migrate perpetual license holders to subscription licenses. 

Let me know if you have any questions here, and I'll be happy to help. 

Best Regards,


Userlevel 2
Badge +1

Hi Elena,

The .DLLs described here remain available only to subscription OpticStudio licenses. That said, in looking you up in our system, it appears that you're using an Educational Support Program license. We can certainly work with your university to transition this to a subscription license, under the new Zemax Global Academic Program. There are a number of options here, based on the type of work you're doing with your university, so I'll connect you with your account manager and our academic team via email to sort out the right option for you.