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1、Designing Manufacturable Aspheres and Freeforms Using Opticstudio e!AdministrationStart & end times8:30 start each day4:30 finish each dayLunch & breaksCoffee breaks at about 10:00 and 3:00Lunch about 12:00-1:30Please ask questions!2Course ObjectivesThe course is designed for Zemax OpticStudio users

2、 who want to: Familiarize yourself with what aspheric/freeform surfaces are available within Opticstudio.Understand how the aspheric/freeform surfaces may be used.Setup and optimize sequential optical systems and how aspheres may be used to improve them.Familiarize yourself with analysis tools and o

3、ptimization techniques to verify and control aspheric profiles.Familiarize yourself with tolerancing of aspheric lenses and what vendors look for on drawings. Give you hands-on practice so that you can use your time more effectively on your return to work3General CommentsFeel free to discuss questio

4、ns concerning any of the course material. If you have other questions, please reserve them for breaks.We will not derive a single equation! Equations and supporting theory will just be stated.4Obtaining Technical SupportAfter the course, you may still have questions! Please attach your file, this he

5、lps enormouslyUse the .zar archive format so we get everything we need in one file (FileCreate Archive)Note that taking the course, and having technical support, are two different things!5Course RequirementsWe assume that everyone taking this course is familiar with:Zemax OpticStudioOptical design t

6、heoryGeneral understanding of tolerancing6Good Optical Engineering BooksPractical Computer-Aided Lens Design, by Gregory Hallock Smith (Willmann-Bell)Excellent usage of computer-based methods, Zemax-basedOptical System Design, by Fischer & Tadic-Galeb, (McGraw-Hill)One book every optical engineer sh

7、ould haveOSA Handbook of Optics (McGraw-Hill)The other book every optical engineer should have!7Good Books for More TheoryIf you want a deeper theoretical treatment than we give here, then these books are excellent:Optics, by Jeff Hecht (Addison Wesley)Modern Optical Engineering, and Modern Lens Des

8、ign, both by Warren Smith (McGraw-Hill)Lens Design Fundamentals, Rudolph Kingslake (Academic Press)Aberrations of Optical Systems, Walter Welford (Adam Hilger Ltd)Other good books are listed in the Zemax Users Guide (Chp. 1) 8Table of Contents: 1: e12: Aspheres Uses and Considerations17: Example 1:

9、Simple Singlet36: Aspheric Testing/Metrology40: Aspheric Manufacturing Methods48: Aspheric Surfaces, Sequential Mode55: Example 2: Aspheric Surfaces94: Example 3: Comparison of the Even Asphere and Q-Type111: Aspheric Conversion Tool117: Tolerancing Aspheric Surfaces139: Example 4: Tolerance Paramet

10、ers (Q-Type)9Table of Contents: 149: Slope Error154: Tools for Specifying an Asphere for Production163: Example 5: Null Corrector Design175: Manufacturability: Inflection Points, Gull Wings, and Local Radius of Curvature195: Diffractive Optics217: Example 6: Thermal Objective245: Freeform Surfaces a

11、nd Objects251: Example 7: Freeform Imaging Prism276: Example 8: Chebyshev Polynomial Freeform Surface290: Example 9: NSC Freeform Illumination313: Example 10: Course Final Cell Phone Camera Lens10CopyrightThe copyright for these training course notes and slides is held by Zemax, LLCPlease dont copy

12、more than 2 pages without our written consent11Designing Manufacturable Aspheres and Freeforms Using OpticstudioAspheres Uses and ConsiderationsWhat is an Asphere? An aspheric surface is a surface profile that is not portions of a sphere or cylinder. Its the anti-sphere.Open DocumentsZemaxSamplesSho

13、rt CourseSC_asphere1.zmxNote:Configuration 1 is a spherical element.Configuration 2 is aspherical (conic asphere). What are a few of the differences? Shape AnalyzeSurfaceSag Cross Section (Surface 3)Performance AnalyzeRays & SpotsConfiguration Matrix Spot DiagramSurface Inputs Lens Data Editor and M

14、ulti-Configuration Editor13Dramatic improvementsA conic asphere can dramatically correct spherical aberration. We will do a full comparison design in a few minutes.14Common Uses of AspheresAberration correctionSpherical aberration correctionAstigmatism, comaField correction (field curvature), Distor

15、tion matchingAngular acceptance angle (either image telecentricity or cameras designed to accept a range of angles out to the edge of the array).Surface/Element ReductionRule of thumb: 1 asphere can remove 1 additional surface from a design. Reduce weight, and length from a system. Implementation an

16、d tolerancing are the keys to make this cost effective 15Consideration for Using AspheresManufacturabilityNumber of elements removed vs. aspheric manufacturing costs.Assembly timeFewer lenses may be cheaper to populate in an assembly.Alignment tolerancesBased on tolerances how will the lenses be ass

17、embled. An aspheric lens that requires an optical alignment may be significantly more expensive than two spherical elements that can be dropped in an assembly.16Designing Manufacturable Aspheres and Freeforms Using OpticstudioExample 1: A Simple SingletExample 1: Simple SingletThis is a example to d

18、emonstrate removal of spherical aberration.We will design a simple singlet, and review the aberration content.Then look at two singlets.And finally a singlet with a conic aspheric surfaceSelect FileNew18Example 1: Simple Singlet SpecificationOur design goalsWavelength: 0.6328umAperture: 20mm EPDFOV:

19、 0degSmallest RMS Spot RadiusF/310mm back focal distanceMonitor the lens mass to see how it changes19System ExplorerMerit FunctionExample 1: Simple Singlet - Initial SetupEnter the basic information.For a simple 0deg FOV singlet the stop will be out front. 20Example 1: Simple Singlet - Default Merit

20、 FunctionHigher order terms are mended for the Gaussian Quadrature fit when an asphere is implemented, so in preparation we will increase to 5 rings. If you recall this will fit higher order aberrations to the order of r(2n-1). In our case 5 rings = r9.21Example 1: Simple Singlet User OperandsWe nee

21、d to also control other important aspects of the design. Insert lines before the DMFS command.22Example 1: Simple Singlet Optimize!23Make the two radii, glass thickness, and back focal length variable.The resulting lens has an RMS spot radius of about 56um. Much larger than the airy disk radius.Exam

22、ple 1: Simple Singlet Spherical AberrationLower F/# lenses are often dominated by spherical aberration. Lets first try glass substitution and hammer for 1 minute to see if the N-BK7 can be replaced with something that will improve the spherical aberration.24Example 1: Simple Singlet - Further improv

23、ement! Glass substitution improved the design to an RMS spot radius of about 24um. We are not diffraction limited though. Lets try adding a lens!25Example 1: Simple “Doublet”Save the current file as sphericalsinglet.zmx. Why a Doublet? Two lenses will provide additional surfaces to correct for spher

24、ical aberration. Insert two surfaces at Surface 3. Make the new surface 4, a material pickup from Surface 2.Make surfaces 3 and 4, 3mm thick. Make the radii and thicknesses variable.26Example 1: Simple “Doublet” Optimize!Verify your MF is accounting for these additional surfaces.Save the current fil

25、e as sphericalsinglet2.zmx.Optimize!Hammer! Let it run for about 30 seconds.27Example 1: Simple “Doublet” - ImprovementsAfter only 30 seconds of hammering, we see significant improvement. We are diffraction limited!Review the spot diagram, ray aberration plot, OPD plot 28Example 1: Simple “Doublet”

26、- ConsiderationsWeve made a diffraction limited design. But at what cost?Two lenses increase complexity.Mechanically they are more complex for assembly. (Two lens seats or a spacer).Two lenses to tolerance and manufacture. Luckily we were able to use the same material.Weight look at TMAS. Can you li

27、ve with essentially doubling the weight of your lens assembly?Can we do it with one lens? Yes. But, we will have to weigh costs, complexity (tolerances), weight.29Example 1: Simple Singlet Conic AsphereSave your current file Reopen your saved sphericalsinglet.zmx filePlace a variable on the conic on

28、 surface 2Why surface 2 and not 3?Reoptimize and BOOM! A conic asphere will correct spherical aberration, but will be more sensitive to tolerances and may be more expensive to make than a spherical lens. (At high volumes using a moldable glass or moldable plastics will save significant money). Save

29、your file as asphericalsinglet.zmx 30Example 1: Simple Singlet Conic AsphereYour design may look like a meniscus with perfect or near perfect performance. 31Example 1: Simple Singlet Even AsphereOpen a second instance of OpticStudio and open your sphericalsinglet.zmx design.Make surface 2 an Even As

30、phere surface type.Make the 4th order term variable and optimize.Add the 6th order term as variable and reoptimize.Add the 8th order term as variable and reoptimize.We have reached the same point as the conic. 2nd order and radius, and 4th order and conic have similar effects and often conflict. The

31、 2nd order is not used by some aspheric generation machines, so use with caution. 32Example 1: Simple Singlet - Even AsphereSimilar performance to the Conic Asphere33Example 1: Simple Singlet Sag Tables34Lets look at the sage tables of the two designs.The sag table is located in either AnalyzeSurfac

32、eSag Table or ToleranceSag TableExample 1: Simple Singlet - ConclusionsCorrecting spherical aberration can be achieved by:Adding an additional surface/elementVarying the conic constantVarying a more complex asphere (unnecessary for just spherical aberration of an on-axis bundle).Engineering trades e

33、xist between size, weight, complexity, cost, material selection even in a simple system.35Designing Manufacturable Aspheres and Freeforms Using OpticstudioAspheric Testing/MetrologyAspheric Testing/MetrologyHow will you and your vendor confirm the asphere is correct?InterferometryStitching interfero

34、meters automatically combine multiple subaperture measurement to form a full-aperture measurement. This allows for aspheric measurements without the use of null lenses. They are ing more common, but cannot measure all aspheric curvatures.Traditional interferometry is referenced to a spherical or fla

35、t wavefront. Null Correctors Can be expensive (depends on complexity)Requires precision fabricationAspheric measurement is only as good as this can be made.37Aspheric Testing/MetrologyTraditional Interferometry (continued)Computer Generated Hologram (CGH)Moderately expensivePrecision alignment proce

36、duresRequires training, but is fairly easy to use once trained.Many include recorded alignment patterns/features to ease in use. Not appropriate for all aspheric shapes.38Aspheric Testing/MetrologyProfilometry Contact ProfilometersA small stylus contacts the surface and is dragged a distance across

37、the surface. Can leave fine scratches in the material if the material is soft.Non-contact ProfilometersThey do not contact the surface.Can be less accurate, especially in dirty environmentsBoth can be limited to a few linear scans (does not represent entire surface).Can be time consuming to setup.Me

38、asurement can be noisy.Both can provide measurements of complex profiles.39Designing Manufacturable Aspheres and Freeforms Using OpticstudioAspheric Manufacturing MethodsAspheric Manufacturing MethodsPrecision PolishingComputer controlled polishing adjusts the dwell parameters to polish away high sp

39、ots and create a very good surface.Interferometric and profilometer data may be fed back into the polisher to provide corrections. 41Aspheric Manufacturing MethodsMagnetorheological finishing (MRF)Surface is polished in a computer-controlled magnetorheological (MR) finishing slurry. The MR fluids sh

40、ape and stiffness are magnetically manipulated in real time. Interferometric and profilometer data may be fed back into the MRF to provide high precision corrections. Vendors have limitations with short concave radii.Primary use is for glass aspheres.42Aspheric Manufacturing MethodsSingle Point Diam

41、ond Turning (SPDT)Computer numerical control (CNC) machines used to precisely cut surface shapesFinal cuts are made with a diamond-tipped tool to achieve sub-nanometer level surface finishes and sub-micrometer form accuracies. Surfaces and seats can be cut in steps in a single mounting. For instance

42、 you can have near perfect wedge from the rear surface to the rear lens seat if you specify the seat to cut at the same time as the rear surface.Primarily used for metals (mirrors and mold forms), infrared materials (crystalline), and plastics. 43Aspheric Manufacturing MethodsMoldingGlass MoldingAsp

43、heres can be molded into glass pre-forms by heating the material and pressing the aspheric shape into the pre-form.Index shift associated with the process, so keep that in mind when designing. Some vendors provide glass catalogs with the molded index.Ability to mold in accurate mounting features.Lim

44、its for forms and tolerances. Plastic MoldingPlastic is injected into a mold with the aspheric form. Ability to mold in accurate mounting features and over-mold housings. 44Molding LimitationsGlass Molding limitations:Limited number of materials available. Low glass transition temperatures (Tg) are

45、needed.Preforms are required. Balls can be used for small volume, positive power elements. Ground and polished preforms can be used for larger volume shapes. See your vendor for their requirements.Limited diametrically approximately 0.5mm-70mm. Due to the cooling method an Index drop of approximatel

46、y 0.002-0.006 occurs. This must be accounted for in the optical design. Often time prototypes are designed with the unmolded material and recurved in OpticStudio with the index drop for production systems.Some tolerances are looser than other manufacturing methods. Discuss limitations with your vend

47、or!45Plastic Molding LimitationsPlastic Molding limitations:Limited number of plastic materialsPrecision tooling/pins/molds that have been adjusted for thermoplastic shrinking and tolerances are critical for precision parts. Once the molds have been adjusted to meet spec, the repeatability is very,

48、very good. Try to avoid large edge to center thickness variations. Strong bi-convex, bi-concave, and meniscus lenses are typically more difficult to mold.Stress birefringence can be an issue with molded plastics. If polarization must be controlled, consider the location, material type, and shape of

49、the lens. Communicate with the vendor to discuss minimizing the issue.Some tolerances are looser than other manufacturing methods. Discuss limitations with your vendor!46Aspheric Manufacturing MethodsReplicationAspheric glass replication is the process of applying a UV curable polymer onto a spheric

50、al glass surface. A mold of the aspheric profile is pressed into the polymer and then cured. At high volumes the cost is comparable to plastic molding. The UV material may be less durable under temperature extremes than a glass lens. Contact the replication vendor for additional information.Side not

51、e: You may consider modeling these as doublets; an aspheric surface made of the replication material on top of a spherical material base.47Designing Manufacturable Aspheres and Freeforms Using OpticstudioAspheric Surfaces, Sequential ModeAspheric SurfacesIn OpticStudio we define our surfaces with eq

52、uations that define the distance from the vertex at radial or X/Y points across the semi-diameter. This is referred to as the sag49The Standard SurfaceOne of the most important equations in optical design!c = curvature = 1/(radius of curvature)Radius of curvature is what we use experimentally, but e

53、quations work more smoothly with its reciprocal, the curvaturek = conic constantz is called the “sag” of a surface in the jargon of optical designThe “Standard” surface in Zemax is more generally called a “conic section” 50Conic SectionA conic section is a curve obtained by intersecting a cone with

54、a planeWikipedia has a nice discussion, including some useful historyIn the diagram below, from Wikipedia, (1) is a parabola, (2) shows a circle and ellipse, (3) shows a hyperbola51Properties of the Conic ConstantThe conic constant is: Less than -1 for hyperbolas-1 for parabolasBetween -1 and 0 for

55、ellipses0 for spheresGreater than 0 for oblate ellipsoidsFor a general ellipse of semi-major axis length “a” and semi-minor axis length “b”:52Sequential Aspheric SurfacesOpticStudio offers a variety of aspheric surfaces for sequential design. We will review a list of the Freeform surfaces later in t

56、he course. 53Comment on the ConicThe power of the conic constant on a standard surface was on display with an on-axis singlet in our previous example. It is a powerful tool for correcting spherical aberration. Lets increase complexity and look at some of our more advanced aspheres and how they chang

57、e the performance and curvature of a surface.54Designing Manufacturable Aspheres and Freeforms Using OpticstudioExample 2: Aspheric SurfacesExample 2: 20deg Singlet SpecificationLets create a slightly more complicated file from scratch. Our specification:Minimize RMS Wavefront ErrorAperture: 10mm EP

58、D, 1mm semi-diameter marginWavelength: 0.6328umFOV: 20deg FFOV (10deg FOV)F/5Maximum front vertex to image plane length = 60mmDesign experience says a singlet would need a floating stop to correct for off-axis asymmetry.Place the stop after the lens. Consider how your system will be built. Often tim

59、es its unrealistic to place a fixed stop before a lens.56Example 2: 20deg Singlet SetupLets create a new singlet. EPD = 10mm, semi-diameter margin = 1mmFOV = 10deg, 3 equal-area fieldsWavelength = 0.6328umGo to the LDE and insert 3 surfaces before the stop.57Example 2: 20deg Singlet - Merit Function

60、Create an RMS Wavefront, Centroid, 5 Rings, 6 Arms, No Boundary OperandsInsert several lines before the DMFSWFNO to control the lens to F/5TTHI/OPLT for surfaces 2-4, less than 60mmETGT set to 1mm (surface 2-2)MNCA set to 5mm (surfaces 3-4)Set Variables on the two Radii (surfaces 2-3), and two thick