Modeling Freeforms in OpticStudio

Chris Normanshire, Engineering Services Manager, Europe, chris.normanshire@zemax.com

Erin Elliott, Optical Research Engineer, erin.elliott@zemax.com

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What do you need to design with freeforms?

• Specify

• Analyze

• Optimize/design

• Tolerance

• Export

• Produce

• Test

Freeforms

Specification

Production

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• OpticStudio can help every step of the way

What do you need to design with freeforms?

• Specify

• Analyze

• Optimize/design

• Tolerance

• Export

• Produce

• Test

Freeforms

Specification

Production

4

OpticStudio

• Surface/object types

• Surface and Power plots, universal plots

• Optimisation operands, Engineering support

• Modelling Irregularity

• ISO, Sag data, polynomial coefficients

• Build limits of testing into optimisation

What do you need to design with freeforms?

• Specify

• Analyze

• Optimize/design

• Tolerance

• Export

• Produce

• Test

Freeforms in OpticStudio

Specification

Production

5

• Many freeform descriptions available

• Polynomial

• Biconic, Toroidal

• Zernike Sag, Biconic Zernike

• Polynomial, Extended Polynomial, Chebyshev Polynomial

• Efficient and easily optimised, but coefficients affect whole of surface

• and arbitrary

• Grid Phase/Sag

• Offers full control of local surface profile

• (Currently) less easy to optimise

Specify

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• View surface sag

• Create custom plots of any value OpticStudio can compute

• Full field aberration

• ZOS-API provides direct access to analysis and plotting capabilities

• More coming soon…

Analyze

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Design• Freeforms can improve existing designs,

e.g. Three Mirror Anastigmat

• Traditionally done with decentered conic mirrors

• Freeforms can mimic those shapes with on-axis parts

• Optimization has many more parameters available

• …but the rules still apply

• Introduce variables one at a time, and know what each term is for

• Never keep a term that doesn’t improve the performance

• Never turn all the terms on to see what happens

• Use the symmetry of the system to simplify optimisation

• TMA has symmetry about the YZ plane, so all terms that are odd in X are disallowed

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Design

• But freeforms also open up the design space!

• Note that many of these design principles also apply to the freeform prism at the right. Used for enhanced reality goggles

• There is no magic button (although we are working on it. And you can make your own with ZOS-API)

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• Speak to your manufacturer. Do they need:

• Sag tables

• BFS data

• Polynomial coefficients

• OpticStudio can produce all of these

Export

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• Irregularity is a thorny problem

• Several approaches available. Choose the

one that best suits the available data

• Talk to your manufacturer

• Use Grid Phase for measured data

• OpticStudio includes a converter from .INT to .DAT

• Use Zernike Phase for simulated data

• Tolerance the Zernike coefficients

• Or use a macro/scripted tolerancing to set a specified RMS

• RMS wavefront in waves = sum of the Zernike coefficients

Tolerancing

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• For small parts, profilometry can be used

• Range of profilometer constrains max sag of the part

• For larger parts, usually use interferometric testing

• Max slope/departure of part is limited by the resolvable fringes on the interferometer’s detector

• These tests can be modeled in OpticStudio.

• Double-pass models

• Interferogram analysis

Optical testing of freeforms

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• If fringes are unresolved...

• Can add a null lens

• Creates an incident wavefront that better matches the part under test

• Must be extremely well characterized

• Setup can again be modelled in OpticStudio to determine if part is testable

• Understand the metrology and build in constraints during optimization

• Operands available to control curvature, sag and derivatives at and X/Y location on the part

Optical testing of freeforms

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• Much more coming soon!

• A new general full-field analysis

• Isolate field dependent and independent contributions

• Identify ‘worst offenders’

• Enhanced surface plots and sag tables for improved analysis and export

• Identify maximum slope and curvature. Remove BFS or base radius

• Locally optimizable grid sag surface

• Specific sections of the surface can be optimized independently

• Visual user interface for modifying the surface

• Knowledge base articles on testing, CGHs, etc.

• Please tell us what you need

Freeforms in OpticStudio