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Tolerancing for several wavelengths simultaneously

I

Hello,

 

I want to perform tolerancing analyses for all wavelengths of my system simultaneously, not just the ‘test wavelength’. I understand that I could simply write the wavelength operand TWAV for each wavelength, followed by the list of other operands copied each time, however there are two problems with that: 1. It doesn’t take into account the weighing of different wavelengths. 2. I suppose it artificially increases the deviation of the criterion, namely, it sums the deviations (in the RSS meaning) of different wavelengths rather than averaging them.

 

Is there any way to tackle this?

 

Thank you.

 

Best answer by MichaelH

Hi Imanuel,

You don't need to add multiple TWAV operands and you should keep the current TWAV operand at the metrology wavelength (typically 0.6328 or 0.546).

When tolerancing, there are 2 wavelengths to consider:

  • Wavelength used to perturb the system with tolerance operands defined as fringes
  • Wavelength(s) used to evaluate the perturbed system

The TWAV operand (defaulted to the HeNe laser in a Fizeau interferometer @ 0.6328um) will modify the surface of any operand defined by TEXI, TFRN, or TIRR.  These surfaces are modify once as either a deviation in sag or a deviation in phase.  There is no weight associated with this individual wavelength because OpticStudio is converting a measurement (number of fringes) back into sag/phase.

When evaluating the new performance of the perturbed system, all defined system wavelengths with their respective weights, are used when evaluating the criterion (either the newly built Merit Function or the user defined Merit Function). 

So when tolerancing, the perturbed system is still evaluated at all defined wavelengths in the System Explorer but the actual modified surfaces are changed at the TWAV wavelength.  

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MichaelH
Ansys Staff
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  • MichaelH
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  • August 9, 2022

Hi Imanuel,

You don't need to add multiple TWAV operands and you should keep the current TWAV operand at the metrology wavelength (typically 0.6328 or 0.546).

When tolerancing, there are 2 wavelengths to consider:

  • Wavelength used to perturb the system with tolerance operands defined as fringes
  • Wavelength(s) used to evaluate the perturbed system

The TWAV operand (defaulted to the HeNe laser in a Fizeau interferometer @ 0.6328um) will modify the surface of any operand defined by TEXI, TFRN, or TIRR.  These surfaces are modify once as either a deviation in sag or a deviation in phase.  There is no weight associated with this individual wavelength because OpticStudio is converting a measurement (number of fringes) back into sag/phase.

When evaluating the new performance of the perturbed system, all defined system wavelengths with their respective weights, are used when evaluating the criterion (either the newly built Merit Function or the user defined Merit Function). 

So when tolerancing, the perturbed system is still evaluated at all defined wavelengths in the System Explorer but the actual modified surfaces are changed at the TWAV wavelength.  

~Michael
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    Imanuel.Peer
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  • Imanuel.Peer
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  • August 9, 2022

Thank you Michael for your response, that was very enlightening.

I please want to make sure I understood what you meant by the words “either the newly built Merit Function or the user defined Merit Function”. What do you mean by “newly built”? I know that you can choose the Merit Function as the criterion, or some other criterion from the list in the tolerancing menu, for example the RMS spot radius.

 

MichaelH
Ansys Staff
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  • MichaelH
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  • August 10, 2022

When you choose any of the Criterion options, except for Merit Function or User Script, a new Merit Function is built by the Tolerancer.  

This new Merit Function essentially runs the Merit Function Wizard in the background to rebuild a Merit Function based on the Criterion you selected:

 

If you want to see what this exact new Merit Function is, you can choose to save 1 Monte Carlo file, open it and then look at the MFE:

 

~Michael
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