Freiform (Mikro-)Optik zur Optimierung und Integration optischer Systeme

Transkript

1 Freiform (Mikro-)Optik zur Optimierung und Technische Universität Ilmenau, Institut für Mikro- und Nanotechnologien,, Postfach , Ilmenau

2 scientific staff: Dr.-Ing. Beate Mitschunas Dipl.-Ing. Martin Amberg technical staff: Dipl. Ing. Thomas Meinecke Dipl. Ing. Ralf Weber Dipl.-Ing. Meike Hofmann Dipl.-Ing. Roman Kleindienst Dipl.-Ing. Andreas Oeder secretary: Frau M. Klein Dipl.-Ing. Daniel Pätz Dipl.-Ing. Nail Sabitov Dipl.-Ing. Sebastian Stoebenau Dipl.-Ing. Marcel Teschke

3 Theory of imaging/ lens design scattered light in photolithographic lenses lens design for adaptive automotive head lights polarisation analysis in liquid crystal projectors modelling and design of imaging systems which incorporate optical microstructures (e.g.multifacet optics) Microoptics Ultraprecision machining for freeform optics (e.g. for computational imaging) holographic lithography and digital holography integrated microoptics (planar integrated optics) e.g. for complex (optofluidic) microsystems and micromanipulation (optical tweezers) synthesis and simulation of optical systems containing diffractive and holographic optical elements elimination of reflections by tilted optical elements active microoptics design, fabrication and dynamic generation of diffractive optical elements (DOEs) using LCOS modulators simulation of wave propagation through (micro-)optical elements (Hyper-)Spectral imaging diffraction Example of a system design using tilted optical elements pattern of a dynamic to avoid the negative impact of reflections DOE Microoptics for the optimization and integration of optical systems

4 Introduction Free-Form Optics Application and Implementation Fabrication of General Beam Shaping Optical Elements Holographic Lithography Ultraprecision Micromachining Applications Computational Imaging Planar Integrated Optical Microsystems Summary and Outlook

5 Geometry of optical elements: elements for imaging: general asphere hyperboloid paraboloid ellipse sphere ellipse generally used as rotationally symmetric elements

6 Geometry of optical elements: elements for general beam shaping: refractive: array components: diffractive:

7 Fabrication of microoptical elements

8 Introduction Free-Form Optics Application and Implementation Fabrication of General Beam Shaping Optical Elements Holographic Lithography Ultraprecision Micromachining Applications Spectral Sensing or Imaging Computational Imaging Planar Integrated Optical Microsystems Summary and Outlook

9 Variety of diffractive optical elements increasing diffraction efficiency Solution? problem: expensive manufacturing

10 Concept of holographic lithography

11 Challenges in holographic lithography - Limited flexibility because of the need for an object wavefront; use artificially (computer) generated object wavefronts; - Twin image non ideal illumination profile use artificially (computer) generated object wavefronts; - Replication is difficult for volume gratings; generate surface profiles through analog grey-scale lithography;

12 Concept of holographic lithography H. Bartelt, S. K. Case, Appl. Opt. 21 (1982) 2886.

13 Phase contrast imaging for holographic lithography Teschke, Sinzinger, Optics Letters; Vol. 32, No. 15

14 Phase contrast imaging for holographic lithography

15 Illumination profile after spatial filtering M. Teschke et.al., Appl. Opt. 47 (2008), M. Teschke, S. Sinzinger, Appl. Opt. 47 (2008), 26, pp

16 Analog lithography resist processing

17 Simulation of the development process of positive photoresists Realization of a customized tool for the simulation of resist profiles Setup for exposure intensity pattern + = Processing parameters specific resist response Processing parameters simulated resist surface absorption properties R(E)-curves Stoebenau et al, DGaO Proc. (2007)

19 Ultraprecision micromachining Microgantry nano4x Kugler GmbH, Salem (Germany) Technical specifications: - CNC-controlled 4-axes 4 machining centre (XYZC) - machine base and gantry setup in fine-grained granite - air-bearing X-X and Y-axes Y driven by ironless linear motors - integration of tool and workpiece measurement systems Integration of three machining modes: - micromilling - picosecond laser ablation - flycutting

20 Ultraprecision micromilling High-speed work spindle Technical specifications: rpm - tool diameter: < 50 μm 3 mm - integrated spindel growth detection and compensation system brass steel Processes: - milling, - drilling, - grinding of steel, nonferric metals and polymers for micromechanical, - optical and fluidic components and systems polymers

21 Examples Micromilling microlens array hexagonal array fabricated in PPSU...replicated in PDMS

22 Examples Micromilling microlens array integration with additional components hybrid optics e.g. monolithically integrated homogenizer

23 specifications: Zeiss Kolloquium, 7. Oktober 2008 Air-bearing machining spindle rpm - accuracy for rotation and translatory movement: : 0,05 μm Flycutting Air bearing (Al) processes: - Cutting of gratings - profiling of plane, spherical and rotationally symmetric surfaces.. - with monocrystalline diamond tools; diameter >50 μm - non-ferric metals, Polymers - Surface roughness: R a < 10 nm Plane mirror (brass)

24 Examples flycutting mechanical components for air bearings currently z z < 400 nm

25 Examples flycutting Large variety of shapes through inclination of the rotational axes Integration of plane mirrors and sperical lenses

26 Laserablation RAPID, Lumera Laser GmbH Specifications: - diode-pumped Nd:YVO 4 -Laser - pulse length: : < 10 ps - max. repetition rate: 600 khz - wavelengths: : 1064, 532, 355 nm - pulse energy: : < 30 μj - power: : < 3 MW GaN on sapphire processes: - laser- cutting, - drilling - surface modification - of metals, semiconductors, ceramics and glass, Chromium/Wolfram

28 Computational Imaging: optimization of the information transfer of optical imaging systems illumination object Objektebene optics Optik optics design image Bildebene Image processing e.g.: bright field dark field phase contrast fluorescence microscopy e.g.: aberration correction wave front coding (improved depth of focus)

29 Concept of wave front coding (WFC) Objective lens Tubus lens post processing with WFC fokussierte PSF FWHM = fokussierte PSF mit WFC x (μm) FWHM = object Phase plate limited depth of focus: parameters of influence -aperturestop - multiple imaging - wave front coding properties of wave front coding: - illumination intensity - constant spatial resolution - digital post processing necessary CCD defokussierte PSF mit WFC FWHM = PSF nach Verarbeitung FWHM = x (μm) defokussierte PSF without WFC FWHM = x (μm) Cathey, Dowski, Appl. Opt. 41 (2002)

30 Wave front coding (WFC) for improved depth of focus Defocus: 0 μm 50 μm 100 μm 200 μm without WFC with WFC after digital processing

31 Wave front coding with a cubic phase plate object objective lens phase function: wavelength: 630 nm objective lens: 5x / 0,14 quadratic aperture defocussing: cubic phase plate Tubus lens 200 μm 3 3 ( x y ) z = α + post processing CCD psf Spot-Ø diameter bei 5% at d. Maximalintensität 5% of peak intensity (μm) psf quality Spotqualität mit und ohne WFC Spot mit WFC vor Verarbeitung Spot ohne WFC Spot mit WFC nach Verarbeitung Defokussierung (μm) Defocussing [μm]

32 Design of the phase plate Similarity of focussed and defocussed psf Hilbert space angle - NA = 0,14 - λ = 630 nm - α = 0 0,05 - z = α (x³+y³) α > 0,003 Hilbert space angle (radians) ohne WFC fokussierter Spot mit WFC - defokussierter Spot mit WFC 0.8 α = 0 α =0.001 α =0.002 α = α =0.004 α =0.005 α =0.006 α = α =0.008 α =0.009 α = α = 0.02 α = 0.03 α = 0.04 α = Defokussierung (μm)

33 Design of the phase plate Modulation transfer function (MTF) at a defocus of 200 μm - NA = 0,14 - λ = 630 nm - α = 0 0,05 - z = α (x³+y³) - Def. = 200 µm MTF μm Defokussierung für verschiedene α Diffraction limited beugungsbegrenzt without ohne WFC WFC ideally focussed α = 0 α =0.001 α =0.002 α =0.003 α =0.004 α =0.005 α =0.006 α =0.007 α =0.008 α =0.009 α = 0.01 α = 0.02 α = 0.03 α = 0.04 α = 0.05 α < 0, with mit WFC 0,003 < α < 0,009 α = 0, Spatial Ortsfrequenz frequency (LP/mm) LP/mm

34 Fabrication of the phase plate micromilling - with 0,3 mm-mkd-kugelfräser in PMMA - Größe 8 x 8 mm² profiling depth 40 μm - R a < 27 nm; shape deviation < 250 nm (scanning range 2 5 mm) design 3 3 ( x ) z = 0,005 + y profilometer measurement Pätz et al., Proc. DGaO (2008)

35 Experiment - LED: 627 nm - pinhole: 5 μm - objective lens: 5x / 0,14 - Tubus lens: f = 200 mm - CCD: CMOS 1280 x 1024 Pixel 5,2 μm² / Pixel 8 Bit LED pinhole Lochblende objective phase plate tubus lens CCD LED Objektiv CPP Tubuslinse CCD lens

36 Experiment: PSF characterisation focussed psf defocus of 200 μm psf with WFC at a psf after digital processing fokussierte PSF defokussierte PSF defokussierte defocus of 200 PSF mit μmwfc Spot nach Verarbeitung FWHM = FWHM = FWHM = FWHM = Pixels Pixels Pixels Pixels

37 PSF over field - What causes contrast reduction? Shiftinvariance Resolution for high spatial frequencies Diffraction at milling structures? Accuracy of shape?

38 Diffraction caused by milling structures of CPP Parameters of influence: - meandering milling path (5 μm) - pressure-dependent (ca. 54 μm) 20 5 μm 10 z (μm) Diffraction order rest angle of diffraction 54 μm y (mm) x (mm) η 5μm (in %) η 54μm (in %) no significant influence of diffracted light

39 Accuracy of shape and roughness (nanopositioning machine and autofocus sensor) D measures data with fit Profile (μm) data points cubic fit Analysis of profile scan z (m) Scan distance (mm) x 105 Spatial frequency spectrum Specified surface : Measured surface : 4 2 z = z = x α 3 3 ( x + y ) Δα = x Δα = y x y α -5-5 y -4 3 Power (in mm) (in mm) app. 1.6µm max.deviation app. 0.3µm max.deviation µm Period (μm) good shape accuracy

41 Motivation Planar integrated microoptical systems + highly integrated + robust optical systems + degree of freedom for systems design overall systems efficiency ( refractive optical elements) aberration correction ( aspherical freeform surfaces diffractive or refractive)

42 Experiments Experimental setup: flexible optical setup for testing different types of aberration correction elements

43 Design and simulations object lens image Using standard off-the the-shelf refractive lenses Wavefront aberrations due to oblique optical axis Astigmatism flat mirror

44 Design and simulations Integration of two Aberration Correction Elements (ACEs( ACEs) - as refractive or diffractive elements -

45 Design and simulations Resulting surface profiles for x and y in mm: ( ) x, y = c x + c y + c x y c y z ACE 1: c 3 = c 5 = c 7 = c 9 = ACE 2 : c 3 = c 5 = c 7 = c 9 =

46 Ultraprecision micromilling Frame and alignment marks for a precise adjustment S. Stoebenau, M. Amberg, S. Sinzinger, Ultraprecision micromilling of freeform optical elements for planar microoptical systems integration, SPIE Photonics Europe (2008).

47 Ultraprecision micromilling Results of fabrication process: 2.4 x 2.4 mm² aberration correction elements average roughness height R a < 40 nm maximum surface tolerance < 400 nm a) b)

48 Experiments Uncorrected system: only flat mirror was applied wavefront aberrations astigmatism Point spread function in the image plane: Δz = -500 μm disc of least confusion Δz = +500 μm

49 Experiments Refractive aberration correction: 1/e 2 spot diameter = 15 μm

50 Experiments Refractive aberration correction: object field size 600 x 600 μm² image field size approx. 500 x 400 μm²

51 Experiments Diffractive aberration correction: - using binary DOEs - 1/e 2 spot diameter = 13 μm

52 Experiments Diffractive aberration correction: object field size 1000 x 1000 μm² image field size approx. 775 x 620 μm

53 Experiments Comparison Refractive correction Diffractive correction

54 Summary - analog holographic lithography can be a flexible fabrication technology for efficient diffractive optical elements; - ultraprecision micromachining (esp. micromilling) is an interesting alternative to diamond turning (e.g. alignment features, non rotationally symmetric freeform profiles); - demonstrations for Computational Imaging and Optical Microsystems; Outlook - ps-laser processing; - combine machining techniques e.g. for hybrid optical elements; - integration of subsequent polishing process;