講義案例教案day

1、Advanced Imaging System Design Using OpticStudioTolerancing Irregularity5 - 2 Tolerancing IrregularityIrregularity of a surface is more difficult to tolerance than other parameters because it is not deterministicOpticStudio offers two methodsTIRR for conic asphere surfacesTEZI for conic aspheres, ev

2、en aspheres, and toroidal surfacesAlthough OpticStudio supports it, we do not generally mend that you tolerance aspheres by putting tolerances on aspheric coefficients directlyInstead, tolerance based on the departure of the real surface from the intended shape, as follows5 - 3 Tolerancing Irregular

3、ityOpticStudio supports two main methods for tolerancing irregularityTIRR works with Standard Surfaces (conic aspheres) only, and is modeled on an inspection technician measuring irregularity with a test plate and eyeballing the resultsTEZI works with Standard, Even Asphere and Toroidal surfaces and

4、 is modeled on measuring irregularity with an interferometer using a null referenceTo investigate how these two differ, set up a simple afocal system which is just a flat window in He-Ne light5 - 4 Test SystemEPD = 10 mm, l = 0.6328 m, afocal mode, 6 mm circular apertures applied to give edge height

5、 5 - 5 Tolerance with TIRRSet up the tolerance editor like so:5 - 6 Run a Tolerance AnalysisSave the file, and then set up a tolerance analysis like so:5 - 7 ResultsHeres what we get:5 - 8 Open Save FileOpen the file TSAV_MAX_0001.zmx, which is the file saved after setting TIRR to its maximum valueO

6、pticStudio has converted the Standard Surface to an Irregular surfaceNote the Spherical and Astigmatism that has been added5 - 9 TIRRTIRR assumes that the irregularity is 50% spherical aberration and 50% astigmatismLess extreme than 100% astigmatism, as spherical can be compensated for by a focal sh

7、ift but astigmatism cannot beThe Max and Min values are the irregularity in fringes measured at the maximum radial aperture of the surface, defined by its semi-diameterIn our file, the surface is set to have a maximum radial aperture of 5 mm, but it extends to 6 mm because of the apertures defined o

8、n itYou must be clear whether you define working or mechanical apertureDefinitions matter! l/2 measured at the edge, l/2 RMS error, and l/2 PTV error are all fine things to specify, but they are not the same!5 - 10 Irregular SurfaceThe irregular surface also provides surface decenter and tilt contro

9、ls, and these are programmed by the TSD*, TST* and TIR* operands (* = X or Y)The maximum and minimum sags are shown belowAlso, check out the Monte Carlo file sags, and note how the orientation of the sag error varies5 - 11 But WaitIf we specified + 1 waves of irregularity error, why do we see only l

10、/4 PTV in the OPD plot?5 - 12 Newtons FringesThe number of fringes is specified in terms of a Newtons fringe test, which is a double pass interferometer working in reflectionThe optical path length error introduced by a sag error Dz is given by Dz(n2-n1)In reflection (n2-n1) = 2, in transmission (n2

11、-n1) 0.5, so a reflection test is four times as sensitive as a transmission testThis is why Newtons rings are so useful: one fringe in reflection (easily observed) is l/4 in transmission (about the diffraction limit)!5 - 13 WavelengthsIn addition, remember that the operating wavelength of the system

12、 is usually not the same as the test wavelength of the surfaceMost surfaces are tested using He:Ne lasers or mercury lights, but they can then operate at any wavelength supported by the materials and coatingsOne wave of error at 0.6 microns is two waves at 0.3 microns!5 - 14 TEZIReturn to the starti

13、ng design, and replace the TIRR operand with a TEZI operand set up like so5 - 15 TEZIInstead of converting the surface to an Irregular surface, TEZI will convert it to a Zernike Standard Sag surfaceWhen using TEZI, the maximum tolerance is the RMS sag error in lens units of the real surface compared

14、 to the nominal surfaceCan be used with Standard, Even Asphere and Toroidal SurfacesThe minimum value is automatically set to the negative of the maximum value, since the RMS error is the same on either sideYou can control the range of Zernike terms usedThe Zernike terms describe the deviation from

15、the nominal surface sag5 - 16 Run the TolerancerRun the tolerancer as before, and look at the saved maximum file5 - 17 What is Happening?OpticStudio converts the surface under test to a Zernike Standard Sag surfaceDuring Sensitivity analysis, the specified range of coefficients of the Zernike polyno

16、mial are set to a value so that the square root of the sum of the squares of the coefficients yields the specified RMS valueAll coefficients are set to the same valueThis gives the required RMS deviation from nominal distributed over the required Zernike termsWhat effect does the range of terms have

17、?5 - 18 Upper limitHere are the wavefronts produced by upper limits of Z21 and Z365 - 19 Upper Term LimitTEZI takes a specified RMS sag deviation and distributes it over the specified number of Zernike termsAs the number of terms increases, the spatial frequency of the deviation increasesRays are be

18、nt by the slope of the surface, so more aberration is imparted by a fast variation than by a slow variationObtain from your manufacturer the highest significant order of wavefront error seen when testing with a null optic, and set the highest order used by TEZI no higher than this Generally, the low

19、er the RMS deviation is, the higher the maximum order the irregularity is distributed overWe are being a little unusual in keeping the amplitude fixed while varying the frequency5 - 20 Lower Term LimitThe lower term limit is adjustable because it may interact with other tolerancesThe piston term Z1

20、is always ignored as it is redundant with thicknessZ2 and Z3 can be considered as surface tiltsZ4 is a power error, and can be redundant with TRADIts important to only tolerance each defect once!5 - 21 Experimental MethodsDepending on how the measurement on the shop floor is made, you couldUse TRAD

21、for radius, TE* for surface tilts, and TEZI from order 5Use TEZI from order 2, and fold the power and tilt errors into irregularity5 - 22 TEZI and Monte CarloWhen doing sensitivity, all Zernike terms in the specified range have the same coefficients, normalized to give the required RMS deviation fro

22、m the nominal shapeWhen doing Monte Carlo, each coefficient is set to a random number between -1 and +1, and the resulting set of data is then normalized to give the correct RMS deviationAdvanced Imaging System DesignUsing OpticStudioUser Defined Tolerances and Compound Groups5 - 24 Arbitrary Tilts

23、& DecentresIn some situations, using TE* to tolerance element tilts and decenters is not sufficient to account for the real degrees of freedom in manufacture and assemblyThe tolerance operands TU* may be used insteadThese require you to insert appropriate Co-ordinate Breaks and pickupsThis allows yo

24、u to model complex pivoting about virtually any surface5 - 25 Pick-Ups and Double-PassConsider tolerancing a double pass optical systemWe will do an example nextIn this system the tolerance events are not independentOn the second pass, the rays must see the SAMERadius, irregularityMaterialLocationOr

25、ientationThe way to do this is via pickups to ensure these conditions are met, and TUDx and TUTx for tolerancing5 - 26 Pivoting About Nodal PointBy default OpticStudio pivots an element about its first surfaceNot a bad choice, as often lens mounts are designed to pivot about the same placeIt is easy

26、 to change this behavior by specifying a dummy surface at the tipping point5 - 27 Defining Compound GroupsBy default OpticStudio assumes that any glass elements surrounded by air form a single elementOther, more complex groups may exist5 - 28 Tolerance Nesting RulesMonte Carlo analysis considers all

27、 tolerance errors simultaneouslyElement tilt and decenter operations must be carried out in a specific manner to prevent conflict or ambiguityThis is no different, of course, to any other tilt/decenters, whether we are tolerancing or not!When performing TE* operations, OpticStudio inserts coordinate

28、 breaks before and after the group of surfaces that make up the elementTilts and decenters introduced by one CB must be undone by another CBThe two operations must take place at the same location in 3D spaceOpticStudio uses pickup and position solves to enforce these conditionsIf the surface ranges

29、for two tolerances overlap, the effects will not be uniquely defined5 - 29 Tolerance Nesting RulesBy nesting tolerances, an unambiguous order can be given to the tilts and decenterse.g. arbitrary tilts and decenters of a series of lenses that are then placed in a housing that is tilted and decentere

30、dThe nesting rules are simple, and are what you would do if you built the CBs by handAll element tilts and decenters must be nestedThe outermost pair of surfaces must be listed firstIn many cases, setting the CBs up by hand gives you more control over exactly what OpticStudio doesAdvanced Imaging Sy

31、stem DesignUsing OpticStudioTolerancing in Double Pass5 - 31 Double Pass SystemsIn a double-pass system, tolerance events are not independentIf the surface is irregular, it must have the same irregularity in double passIf the element is decentered, it must be in the same position for the double pass

32、etc.So we need to use carefully placed coordinate breaks, pickups, and user-defined tolerances to model this5 - 32 Double-Pass Laser Focusing LensBack to tolerancing!We will design a two-lens lens relay, in double pass, as an exampleWe will add the coordinate breaks necessary for tilting and decente

33、ring, and use TU* to define the tolerancesThe key is manual testing before we run the tolerancer!5 - 33 Start PointLoad up a stock lens to save timeLinos Photonics 033484000 is a nice laser monochromatRemove marginal height solve, use quick focus, RMS Wavefront-centroidPut stop on a dummy surface, 3

34、0 mm before lensMake it the global coordinate reference surface5 - 34 PrescriptionYou should have this:5 - 35 SystemImagine the IMA plane is a mirrorLight is retro-reflected back through the lensA beamsplitter or similar feeds the retro-reflected light into a second optical systemWe will ignore the

35、“second system”, and concentrate on the double pass opticsHow does the performance of the system vary as we introduce manufacturing tolerances into the elements, and as we tilt/decenter them?In a double-pass system, tolerance events are not independentIf a surface is irregular, it must have the same

36、 irregularity in double passIf an element is decentered, it must be in the same position for the double pass5 - 36 First StepMake the lens a double-pass lensNeed to insert MIRROR, “re-write” lens data in reverse order with negative thicknessesOpticStudio has a tool built to do all of this: Select Ma

37、ke Double Pass:from the toolbar in the Lens Data Editor5 - 37 Double Pass FileWe now have a double pass lens!Switch to Afocal mode and Float-by-Stop apertureSave as Double Pass.zmx5 - 38 Why Float-by-StopWhen the lens was designed, it used Entrance Pupil aperture definition because that was what is

38、was desired to achieveNow we come to tolerance the lens, the aperture is actually defined by a piece of metal with a hole in itThe size of this hole has a tolerance!Important general point:Many things are useful during design, like F/# solves, paraxial definitions, real or paraxial image heightWhen

39、we tolerance, we need to define things by what they actually are, not what we want them to be!Always remove constraints from the design, because when we tolerance, we get what we get, not what we want!5 - 39 Tidy Up FileGive the mirror surface a 5 mm semi-diameter and apertureModify solves used on s

40、econd pass thickness values from pickup solves to position solves Position solves will lock to the absolute positions and so will track as we enter coordinate breaksFix the last thickness at -30 (i.e. remove the solve)Because output is afocal so the exact distance does not matterThe file double pass

41、.zmx in the short course folder has the design at the end of this stage5 - 40 Lens FileYou should have this:5 - 41 Mounting ArrangementsWe will assume that the lenses are mounted in a barrel, so that the same mount contains both lensesThe two singlet lenses are mounted on their front faces inside th

42、is barrel, and they have separate element tilts and decentersTheir rear faces can then be wedged with respect to their front facesWe will use the Tilt/Decenter Elements tool three times to build these element tilts and decenters by handThe golden rule:Start with the outer elements first, and then ne

43、st the inner ones5 - 42 Barrel PositioningWe will define how the barrel is misaligned by building a set of Coordinate Break surfaces across the whole first-pass assembly Note zero values for all data, as the nominal system is not misaligned5 - 43 Element 1 MisalignmentThe first element can be decent

44、ered or tilted with respect to the barrel5 - 44 Element 2 MisalignmentSame is true for element 25 - 45 ReviewUsing color and comments for each set of Coordinate Breaks makes it easier to understand what is happening in the systemThe compensating thickness used to keep best afocus is now surface 14,

45、so give it the comment field compensatorWe now need to place each second pass surface at the same location as its first pass surfaceThere is a very useful Coordinate Break Return solve that does exactly this for us5 - 46 LDE at this Stage5 - 47 The Second PassOn the second pass, the lens surfaces mu

46、st be located exactly at the location of their first pass equivalent surfaceBest take this one at a time to get it right!Set up two 3D layout plots, one showing the first pass and the second showing the second pass 5 - 48 Surface 17Surface 16 has a position solve on it that locks surface 17 at the s

47、ame position in z as surface 10, the rear face of the second lensOpen the properties for surface 16 , and make it a Coordinate BreakThen place a Coordinate Break Return solve on it in its Tilt/Decenter tab5 - 49 Trust but Verify!Use Coordinate Break Surface 2 (Barrel misalignment) or Coordinate brea

48、k Surface 8 (second element misalignment)Use 3D Layout Plot and Prescription Report Global Vertex Data to verify that surface 17 (note updated surface number) is at the same location and orientation as surface 105 - 50 Next SurfaceWe now want to lock surface 18 to be in the same position as surface

49、9 (the front face of the second lensClick on Surface 18, press insert to create a new surfaceMake the new surface a Coordinate BreakUse a Return Solve to lock to surface 95 - 51 Next SurfaceNow lock surface 20 (front lens rear) to surface 5Then lock surface 22 (front lens front face) to surface 4 Fi

50、nally lock surface 24 to surface 1Use Orientation XY only (as it is afocal output the z position does not matter, although it will not do any harm to lock on z as well)Now TEST that any perturbations added to Coordinate Break surfaces 2, 3 and 8 (which control the barrel, first element and second el

51、ement errors) flush through the system correctly, and that the second pass lens is always in the same position and orientation as its first-pass cousin5 - 52 Double-Pass TolerancingGlass Type is picked-up so that any offset is applied equally on both passesWe have assumed that the lens may be decent

52、ered and tilted about its front vertex, and will place CBs around itWhat about surface irregularity, wedge, etc.?To model surface tilts and irregularitiesMake second-pass surfaces irregular, with pickups to original surfaces, even though there is nothing there at the moment!When tolerancer makes ori

53、ginal surfaces irregular and populates the parameter data, pickups will transfer values to the second pass surfaces!5 - 53 Double-Pass TolerancingHow to set up the tolerancing?Build tolerances by hand this timeWhat can vary?Lens radii, thicknessIrregularity of lens surfaceWedge of lensTilt/decenter

54、of lensMaterial of lensMirror radius, tilt, decenter, irregularity5 - 54 Tilt & Decenter of LensWe have pre-built the coordinate breaks, so do not want to use TE*It inserts coordinate breaks for usUse TU* instead, pointing to first CB surfacePickups built-in will track5 - 55 Build Tolerances by Hand

55、Open the Tolerance Data Editor, press INSERT mutiple times to create rowsFirst line is the compensator, which is the thickness of surface 14 (last lens to mirror)COMP, surface 14, code 0, min -1, max +1Next line is the test wavelength for any tolerances measured in fringesTWAV, 0.6328Now for the len

56、s radii tolerances, use + 0.5 fringes on all lens surfacesSurfaces 4, 5, 9 and 10Use TFRN, -.5, +.5, nominal is zero5 - 56 Thickness TolerancesOnly the thicknesses of surfaces 4, 7, and 9 matter (everything else picks up)We decided earlier than the second lens position was independent of the first,

57、so the air gap (surface 7) compensates surface 4s thickness variationThe air gap after the second lens is already defined to be used as a compensator5 - 57 Thickness TolerancesEnter TTHI tolerances as follows:TTHI 4 7 -.1, +.1This means that position of surface 8 is not affected by thickness changes

58、 to surface 4Use + 0.1 mm tolerancesTTHI 9 9 -.1, +.1Thickness tolerance accumulates to total system length, but it is compensated by surface 14 anyway5 - 58 Element WedgeEach element has wedge, defined by a surface tilt of the rear face with respect to the frontBecause we are mounting each element

59、on the front faceLets say the wedge is defined by indicator run out The difference in edge thickness as the lens is rotatedCan be defined in x or y, we will choose YTIRY 5 -.1 .1TIRY 10 -.1 .15 - 59 Element WedgeEach element can have + 0.1 mm edge thickness variationHowever, the wedge can be oriente

60、d anywhere: well assume no control over the rotation of the wedged element in the mountThis corresponds to a z-rotation of each element, using the CB groups starting on surface 3 and 8TUTZ 3, nominal = 0, +180TUTZ 8, nominal = 0, +1805 - 60 Surface IrregularityEach lens surface can be irregularUse T