Davies W. de Lima Monteiro Gleb Vdovin (project leader) Ourang Akhzar-Mehr Aleksey Simonov Mikhail Loktev Oleg Soloviev Lina Sarro

Transkript

1 wavefront Davies W. de Lima Monteiro Gleb Vdovin (project leader) Ourang Akhzar-Mehr Aleksey Simonov Mikhail Loktev Oleg Soloviev Lina Sarro Micro-optics group Electronic Inst. Lab. EEMCS TU-Delft The Netherlands sensor Aberration plane Deformable mirror

2 CD drive

3 Outline Adaptive Optics Deformable mirrors: membrane and thermal Liquid-Crystal wavefront correctors CMOS wavefront sensor Subnanometric interferometry Spherical and aspherical micro-optics Conclusions

4 Adaptive Optics What is adaptive optics? Dynamic sensing and correction of wavefronts (e.g.: atmospheric turbulance). What is a wavefront? Hypothetical surface with equal phase x test component ΞW z y pupil plane

5 Microtechnologies and Adaptive Optics mponents compatible with industrial and medical plications ompatibility with standard rocesses affordable costs design flexibilty calability reproducibility portability

6 Applications of Adaptive Optics Free-space optical communications Astronomical observations sta r sta r Ophthalmology (e.g.: retinal imaging) retina

7 Deformable mirrors (micromachined membrane) Fabrication of MMDM Parameters (15mm DM): response time ~ 1ms; stroke ~ 8µm Biasing condition top view membrane lateral view electrodes 12mm 15mm applied voltages V V V V V V V

8 Deformable mirrors (thermal) Principle Fabrication Parameters: response time ~ 15s; 40s, stroke ~ 6µm

9 Applications of deformable mirrors human eye (retinal imaging) telescopes scanning optical microscopes compression femtosecond pulses correction of terawatt lasers adjustable spectacles, etc.

10 Liquid Crystal wavefront corrector low cost no movable parts low control voltages low power (0.1mW/cm 2 ) large amplitude (tens λ) ive layer V 1... V N Cooperation of TU-Delft w/ University of Durham/ Lebedev Physics Institute (Russian Academy of Science)

11 Hartmann-Shack wavefront sensor (principle) artmann method plane wavefront aberrated wavefront plane wavefront Hartmann mask Y divergent wavefront Y mask X y x z detector imager Hartmann-Shack method convergent wavefront Y X arbitrary wavefront Y microlens array

12 5 cm CMOS-based wavefront sensor (fabricated) 600 µm 1.6-µm n-well CMOS process (DiMOS) 64 QCs + analog demultiplexer passive-pixel architecture = photodiode + switch set

13 Applications of wavefront sensors avefront sensing: estimation of distortions in optical wavefronts. diagnostic tool quality of optical components (e.g.: lenses, mirrors, human eye, laser beams, industrial parts). eyes of deformable mirrors adaptive optical systems: compensation of wavefront distortions (e.g.: astronomical imaging and retinal imaging, free-space optical communications)

14 Adaptive optical system deformable mirror laser spatial filter collimating lens photodiode d3 L4 f4 f3 aberration plane d1 L3 beam splitter L1 f1 wavefront sensor Aberration plane Deformable mirror distant screen with aperture micro objective d2 Hartmann mask f2 L2 sensor 6cm

15 Subnanometric interferometry (I) hat is an interferometer? imager (e.g. CCD) hy subnanometric interferometry? lithography smaller pattern sizes shorter avelength Extreme UV (EUV 11nm, 13nm) no lens precise mirror (accuracy 0.1nm; amplitude 3mm) roposed solution: measure emporal phase instead of spatial hase test surface beam splitter collimating lens spatial filter reference mirror lase

16 ustom CMOS chip: 24x24 pixels (11µm x 30µm) roposed signal processing: multiplication of the signal y continuous functions to achieve a phase accuracy of 0-4 rad. econd-order effects in circuits become relevant! CSEM 3D lock-in camera

17 Micro-optical components

18 Fabrication method (single mirror) < 100 > s Bulk anisotropic etching of silicon (single oxide mask) silicon 0 < 100 > < 111 > d 0 silicon d 0 1 Shop list : < 411 > Silicon wafer 2 SiO 2 Si 3 N 4 KOH (Potassium hydroxide) 3 H 2 O Relevant formulas : 4 sagitta: s = α d 0 5 diameter: D = h d D 6 s

19 Etching process - 3D view Relevant formulas : Radius of curvature: R = D 2 /8s focal length: d0 f = ( 1) α n h d 0

20 Micromirror and Microlens arrays regular grid of pits lateral overlap of mirrors sharp interfaces Advantages of this technology: parallelism of the optical axes high precision of the element positions 100% fill factor adjustable cavity diameter

21 initial Si surface Arbitrary aspherical surfaces final Si surface h

22 target structure evolving structure arbitrary surface (lateral size: 1mm) interferometric representation h=20 m h=40 m h=75 m h=150 m h=460 m

23 Conclusions adaptive optics has potential for industrial and medical applications microtechnologies can be used for the fabrication of adaptive optical components successful implementation of deformable mirrors, wavefront sensors, microlenses and phase plates silicon technologies for liquid-crystal wavefront correctors and subnanometric interferometry have been investigated affordable manufacturing costs, functionality and system integration are combined