View
232
Download
3
Category
Preview:
Citation preview
Who’s afraid of freeform optics?*
Webinar – 17 January 2018
Outline• About the presenters • Spectrum Scientific, Inc. (SSI)• Challenges of using freeform optics• How to use freeform optics• Low cost replicas from complex components• Advantages of the replication process• Introduction to freeform optics• Benefits of utilizing freeform optics • Freeform surface design in OpticStudio• Manufacturability• Metrology • Transitioning into manufacturing• Assembly considerations
PresentersIntroductionSpectrum Scientific
Daphnie ChakranPresident & CEOSpectrum Scientific
PresenterDavid CookGeneral ManagerSpectrum Scientific
Q&ADave EricksonCTOSpectrum Scientific
PresenterZemax
Erin ElliottOptical Research & Prototyping EngineerZemax
Spectrum Scientific, Inc.
• Space qualified • Clean room facility• ISO 9001:2015 certified• In-house capabilities
o Manufacturingo Designo Coatingo System Assemblyo Engineeringo Precision Metrology
Spectrum Scientific, Inc. (SSI) was established in 2004
Spectrum Scientific, Inc.
Spherical mirrorsAspheric mirrorsFreeform mirrorsOff-axis parabolic mirrorsEllipsoidal mirrorsHolographic diffraction gratingsHollow retroreflectorsUV spectrometers
Capabilities
Challenges of using freeform optics
Understanding & Visualization
Designing & Specifying for Manufacturability
Cost
Assembling your Freeform
Measurement
How to use freeform optics
Add
Replace
Redo
Low cost replicas from complex components
Precision Machining Expensive Polishing Fixtures
Expensive Polishing & Metrology Processes
Expensive Original
Advantages of the replication processReplication is the most cost effective method for high volume applications
Spectrum Scientific’s replication process delivers:• High fidelity reflective aspheric mirrors• λ/10 reflective optics• High volume production of freeform mirrors at
a reasonable cost and with high repeatability
Advantages of the replication process• Exceptional quality surfaces are faithfully
replicated to very high fidelityo Component figure: macroscopic scaleo Scratches and digs; microscopic scaleo surface roughness: sub nanometer scale.
• Mounting features can be easily incorporated into the component
• Greater design flexibility• UV, VIS, IR coatings• Lower OEM cost than conventional polishing
and/or diamond machining
Master optic
Release agent
Thin film coating
Polymer layer
Replicated mirror
Introduction to freeform opticsDefinition of freeform: A curved optic without axial symmetry
1900s 2000s1970s 2010s1950s
Flat & Spherical optics1
Initial freeform designs2
Significant commercial freeform manufacturing:
Polaroid SX-703, 4, 5
Deterministic freeform manufacturing methods
(DT & MRF)1
Mainstream systems integrate freeforms into
production (Beam Shaping, HUDs, VR/AR)6
Introduction of commercially available
aspheric optics3
High precision, state of the art freeform manufacturing
Benefits of utilizing freeform optics• Single optical surface allowing for compound compensation• Improved system performance • Redistribution of tolerances in the system design • Reduces the number of optics• Additional aberration correction
The SCUBA-2 telescope 3, 5, 7
System design - freeform benefit example
Overall volume decreased from 530 cm3 to 100 cm3
Offner baselineall-spherical design
Offner compact freeform design8
Reimers, Jacob, et al. "Increased Compactness of an Imaging Spectrometer Enabled by Freeform Surfaces." International Optical Design Conference. Optical Society of America, 2017.
Freeform tools in OpticStudio• Surfaces in sequential mode
• Standard surfaces – allow a ROC and conic constant. • Biconic surfaces – allow separate ROCs and conics in X and Y.• Toroidal, superconic• Even Asphere, Extended Asphere, Odd Asphere, Extended Odd Asphere, Q-type Aspheres, Alternate Even/Odd Asphere• Zernike Standard Phase/Sag, Zernike Fringe Phase/Sag, Biconic Zernike• Polynomial, Extended Polynomial, Chebyshev Polynomial• Grid Phase/Sag
• Analysis tools• ISO Element drawings• Surface and curvature tables and cross-sections• Power as a function of pupil coordinate, field angle• Universal plots
• Optimization tools• FTLT/FTGT – full thickness less than and greater than• POWF – Power at a given field point• POWP – Power at a given point in the pupil• BFSD – Best fit sphere data• SCUR – Surface curvature at a given X and Y coordinate• SDRV – Derivative of the sag at a given X and Y coordinate
Optimizing with freeforms in OpticStudio• Three Mirror Anastigmat example• Traditionally done with decentered conics.• With freeforms, can mimic those shapes with on-axis parts.• But, freeforms open up the design space beyond the
traditional conics.• Design with freeforms requires caution!
• Optimization has many more parameters available. Typically need to reduce the # of parameters in an intelligent way.
• Never use terms that violate the symmetry of the system.• TMA has symmetry about the YZ plane, so terms that are odd
in X are disallowed.• Start with lowest-order term – power – by connecting X and Y
radii.• Then, release to allow astigmatism, then coma, etc.• Always include at least a very small field angle. Easy to create
systems that are perfect at one field point.• Never turn all the terms on to see what happens!• Never keep a term that doesn’t improve the performance!
Optical Testing of Freeforms• OpticStudio can be used to model the optical test setup for each
freeform.• The test method sets the maximum slope limitation for the
freeform part.• Typical optical testing methods:
• Interferometric testing (unassisted):• For freeforms without large departure from spherical surfaces.• Max. slope of the freeform part is limited by the resolution of the interferometer.
• Interferometric testing with a null lens:• Removes part of the wavefront departure so that the interferometer can resolve
the fringes.• Null lens must be designed for precision manufacture, so can’t be too complex.• Max. slope of the freeform part is limited by the precision required for the null
lens.• Interferometric testing with a CGH:
• Also removes part of the wavefront departure.• Max. slope of the freeform part is limited by the resolution of the CGH.
ManufacturabilityManufacturing Methods• Originals by direct manufacturing• Copies from masters (injection molding,
pressed glass, nano-imprint lithography)• Large volume, repeatable process using
the SSI replication process
Superior stray light performance from replicated mirror compared to diamond machined mirror
Metrology• Measurements down to a nm-scale• Wide range of contact & non-contact measurement methods
o Contact - common, slow µm-scaleo Non-contact - higher precision9
Transitioning Into manufacturing• Communication with the manufacturer is critical• Specifying the optical surface
o Surface equationo Sag table
• Additional parameters to considero Surface profile (figure error)o Micro-surface roughness (RMS)o Mid-spatial frequency (slope errors)11 Surface Equation10
Assemble – your instrument Alignment considerations for optic manufacturing and system integration
Summary
Nobody should be afraid of freeform optics*They can offer significant benefits and cost savings in modern optical systems
Thank YouThis is an exciting time in our industry
Freeforms have the potential revolutionize a lot of different markets
*with apologies to Edward Albee
References1. Thompson, Kevin P., and Jannick P. Rolland. "Freeform optical surfaces: a revolution in imaging optical design.” Optics and Photonics
News 23.6 (2012): 30-352. Kanolt, Clarence W. "Multifocal ophthalmic lenses.” U.S. Patent No. 2,878,721. 24 Mar. 1959.3. Fang, F. Z., et al. "Manufacturing and measurement of freeform optics.“ CIRP Annals-Manufacturing Technology 62.2 (2013): 823-846.4. Plummer, William T. "Free-form optical components in some early commercial products." Proc. SPIE. Vol. 5865. 2005.5. Henselmans, Rens. "Non-contact measurement machine for freeform optics." Macromolecules 35 (2009): 607-24.6. Cakmakci, Ozan, and Jannick Rolland. "Head-worn displays: a review." Journal of display technology 2.3 (2006): 199-216.7. Hoogstrate, André M., et al. "Manufacturing of high precision aspherical and freeform optics." Proc. SPIE. Vol. 8450. 2012Interferometric
Measurement of Mid-Spatial Frequency Wavefront Errors, Smythe, Aikens, IODC Denver June 2017.8. Reimers, Jacob, et al. "Increased Compactness of an Imaging Spectrometer Enabled by Freeform Surfaces." International Optical
Design Conference. Optical Society of America, 2017.9. Non-contact measurement of optical freeforms – current solutions and advantages, F. Reischer, S. Mühlig, E. Grüner, J. Siepmann, S.
Mika, A. Beutler, M. Lotz, A. Wiegmann, Mahr GmbH. Laser World of Photonics, June 2017.10. Zemax, LLC. “OpticStudio 16 SP2 Help Files." OpticStudio 16 SP2. (2016): 476. Print.11. ISO11010-8
Thank you!• Please submit your questions using the GoToWebinar controls
Recommended