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© Fraunhofer IPMS
MEMS AO MICRO MIRROR DEVELOPMENT AT IPMS
- Status and Perspectives – Andreas Gehner
© Fraunhofer IPMS MEMS AO at IPMS I slide 2
Outline
MEMS AO Micro Mirror Development at IPMS - Status and Perspectives -
Introduction
MEMS AO Technology Platform at IPMS
Applications in Adaptive Optics
AO Demonstration System
Conclusion & Perspectives
© Fraunhofer IPMS MEMS AO at IPMS I slide 3
Key Component: Phase Controlling SLM
Benefits of MEMS SLMs High Spatial Resolution Significant Device Miniaturization
© Fraunhofer IPMS MEMS AO at IPMS I slide 4
Principle of Adaptive Optical Image Correction
Goal: Real-Time Compensation of Dynamic Wavefront Distortions
Distorted Wavefront
Turbulent Media
Wavefront Corrector
Wavefront Reconstruction Wavefront
Sensor
Corrected Image
Distorted Image
© Fraunhofer IPMS MEMS AO at IPMS I slide 5
General Application Fields of Optical Phase Control
Laser Beam Shaping / Focus Control Free space optical data communication Laser surgery, e.g. through rinse fluids
Temporal Laser Pulse Shaping Pulse compression (dispersion control) Control of molecular dynamics & excitation
Optical Imaging Correction Astronomy: atmospheric turbulences Ophtalmology: eye aberrations Microscopy: culture media & liquids Machine Vision: fluids & hot gases
Diffractive Optics Optical tweezers
© Fraunhofer IPMS MEMS AO at IPMS I slide 6
Outline
MEMS AO Micro Mirror Development at IPMS - Status and Perspectives -
Introduction
MEMS AO Technology Platform at IPMS
Applications in Adaptive Optics
AO Demonstration System
Conclusion & Perspectives
© Fraunhofer IPMS MEMS AO at IPMS I slide 7
240 x 200 Piston Micro Mirror Array (Phase-only)
Monolithic integration mirrors + CMOS circuitry
Analog addressing DRAM-like architecture (analog storage cells)
High-voltage CMOS process enables 27V addressing range
Entire design supports 0.5 µm stroke
Parallel programming of sub-arrays allows frame rates > 5 kHz
© Fraunhofer IPMS MEMS AO at IPMS I slide 8
Characteristics of previous 40µm 1-Level-Piston-Mirrors
RMS < 7 nm
Mirror Planarity
PtV = 20 nm
© Fraunhofer IPMS MEMS AO at IPMS I slide 9
Examples of Applied Deflection Patterns (Array Portions)
Benefits of fine segmented MEMS mirror arrays
Independent pixel deflection (no inter-actuator coupling)
High shape conformity for arbitray complex patterns
Step function capability
One-iteration step (open-loop capability)
© Fraunhofer IPMS MEMS AO at IPMS I slide 11
Outline
MEMS AO Micro Mirror Development at IPMS - Status and Perspectives -
Introduction
MEMS AO Technology Platform at IPMS
Applications in Adaptive Optics Ophthalmology
AO Demonstration System
Conclusion & Perspectives
© Fraunhofer IPMS MEMS AO at IPMS I slide 12
WaveScan®: Ophthalmic Diagnose System
Objective, spatially and timely resolved measurement using SHS wavefront sensing
Comprehensive determination of all refractive eye errors beyond sphere & cylinder
Obtained data form the basis for a personalized treatment
© Fraunhofer IPMS MEMS AO at IPMS I slide 13
WaveScan® Preview Option
Implemented acuity charts Rows of Snellen E's (62,5 - 200% VA) Siemens Star for subjective tests & accommodation control
Objectives Verification of aberration measurement Demonstration of the optical correction Individual assessment of the subjective gain in vision improvement
Laser
diode
continously adjustable
sphero-cylindrical precompensation
Shack-
Hartmann sensor
Visual acuity chart
Micro Mirror SLM
Measurement beam λ = 780 nm Target beam λ = 550 nm
© Fraunhofer IPMS MEMS AO at IPMS I slide 16
Correction of an Average Complex Eye Aberration
Corrected with 48K Micromirrors
RMS = 47 nm
Uncorrected
RMS = 293 nm
Pupil Size: 5.4 mm
© Fraunhofer IPMS MEMS AO at IPMS I slide 17
Outline
MEMS AO Micro Mirror Development at IPMS - Status and Perspectives -
Introduction
MEMS AO Technology Platform at IPMS
Applications in Adaptive Optics Temporal Laser Pulse Shaping
AO Demonstration System
Conclusion & Perspectives
© Fraunhofer IPMS MEMS AO at IPMS I slide 18
Lens
Input Laser Pulse
Shaped Laser Pulse
Grating (spectral decomposition)
Grating (superposition)
Lens
Principle of Laser Pulse Shaping
Phase-adjusting SLM in Fourier plane
Animation: http://www.physik.uni-wuerzburg.de/femto-welt/formerstart.html
input sinusoidal phase pattern output fs-pulse pulse train
THz pulse train generation
Pulse compression (dispersion control) input parabolic phase pattern output
compressed fs-pulse
dispersed pulse
© Fraunhofer IPMS MEMS AO at IPMS I slide 19
Experimental fs-Laser Pulse Shaping
M. Hacker et.al., Appl. Phys. B 76, pp. 711 (2003)
Cross-correlation with delayed reference pulse
MEMS SLM
Experimental set-up THz pulse train generation
Delay [ps]
Nor
mal
ized
cro
ss-c
orre
latio
n si
gnal
8.4 THz (119 fs)-1
4.2 THz (238 fs)-1
2.1 THz (476 fs)-1
8 pixel
4 pixel
Pulse compression (dispersion control)
FWH
M o
f cro
ss-c
orre
latio
n tr
ace
[fs]
Second order phase modulation [fs2]
Coherent control of molecular dynamics & excitation processes
λ = 404 nm no phase
modulation
sinusoidal phase grating
16 pixel
© Fraunhofer IPMS MEMS AO at IPMS I slide 20
Outline
MEMS AO Micro Mirror Development at IPMS - Status and Perspectives -
Introduction
MEMS AO Technology Platform at IPMS
Applications in Adaptive Optics Dynamic Diffractive Element (DOE)
AO Demonstration System
Conclusion & Perspectives
© Fraunhofer IPMS MEMS AO at IPMS I slide 21
Diffractive Image Formation (Far-Field)
Desired Pattern SLM Phase Representation Diffraction Image
CCD
BEM
S BS QWSLM
L
HeNeLaser M
BE S BS QW L
SLM phase pattern retrieval by iterative Fourier transform algorithm
Accomplishments: good structural resolution enabled by 256 phase levels + 48.000 pixels residual grannular substructure due to limited space-bandwidth product small diffraction or field angle < 1°
Applicability e.g. for Optical Tweezers has to be proved
© Fraunhofer IPMS MEMS AO at IPMS I slide 22
Phase Retrieval by Iterative Fourier Transform (IFTA)
Uk=DFT-1(Ock)
k++ (kth iteration) Ok=DFT(Uc
k)
Image Domain
Spectrum Domain
application of boundary conditions
Uk Uck
amplitude := const. keep phase (phase-only SLM)
amplitude phase
application of boundary conditions
Ok Ock
amplitude := desired pattern keep phase
amplitude phase
Start
Diffraction Pattern SLM (Phase) Pattern
© Fraunhofer IPMS MEMS AO at IPMS I slide 23
Outline
MEMS AO Micro Mirror Development at IPMS - Status and Perspectives -
Introduction
MEMS AO Technology Platform at IPMS
Applications in Adaptive Optics
AO Demonstration System
Conclusion & Perspectives
© Fraunhofer IPMS MEMS AO at IPMS I slide 24
CCD camera
Object (Test target)
Phase platesfor aberation generation
LED
CCD camera
Wavefront corrector(piston type SLM )
Object (Test target)
Phase platesfor aberation generation
Wavefront sensor(Shack-Hartmannsensor )
Dicroic BS
Phase Plates
SHS Wavefront Sensor
Dicroic BS
Laser 670 nm
CCD Camera
Polarizing BS
λ/4 plate
MEMS Wavefront Corrector
LED 505 nm
Object
AO System Design
© Fraunhofer IPMS MEMS AO at IPMS I slide 25
AO System Set-up
Demonstration of AO image correction for extended objects (USAF test chart) incoherent illumination
Quantitative performance analysis by MTF measurements
Near diffraction limit optical design
Phase errors introduced by phase plates
Modular Linos tube system stray light suppression dust protection
Compact, portable setup footprint: 60 x 40 cm2
MEMS SLM
© Fraunhofer IPMS MEMS AO at IPMS I slide 26
Correction of Low & Higher Order Aberrations
Spher. Aberration PV : 0.448 µm RMS : 0.134 µm
"Water Ripples" PV : 0.557 µm RMS : 0.108 µm
0.00 0.05 0.10 0.15 0.20 0.25 0.300.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 System MTF MTF of Disturbed System MTF of AO Corrected System
MTF
0.00 0.05 0.10 0.15 0.20 0.25 0.300.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 System MTF MTF of Disturbed System MTF of AO Corrected System
Normalized spatial frequency
MTF
MTF
Normalized spatial frequency
© Fraunhofer IPMS MEMS AO at IPMS I slide 27
Correction of Astigmatism & Coma
Astigmatism PV : 0.725 µm RMS : 0.117 µm
Coma PV : 0.676 µm RMS : 0.173 µm
0.00 0.05 0.10 0.15 0.20 0.25 0.300.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 System MTF MTF of Disturbed System MTF of AO Corrected System
Normalized spatial frequency
MTF 0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 System MTF MTF of Disturbed System MTF of AO Corrected System
MTF
Normalized spatial frequency
© Fraunhofer IPMS MEMS AO at IPMS I slide 28
Correction of Strong Aberrations by 2π Phase Wraps
PV: 9.1 µm
Proper MTF measurement affected: birefringency of plastic phase plate + polarizing beam splitter causes double images
modulo 2π mirror representation (18λ @ 505 nm) 0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 System MTF MTF of Disturbed System MTF of AO Corrected System
MTF
Normalized spatial frequency
© Fraunhofer IPMS MEMS AO at IPMS I slide 29
Outline
MEMS AO Micro Mirror Development at IPMS - Status and Perspectives -
Introduction
MEMS AO Technology Platform at IPMS
Applications in Adaptive Optics
AO Demonstration System
Conclusion & Perspectives
© Fraunhofer IPMS MEMS AO at IPMS I slide 30
Conclusion
IPMS provides MEMS micro mirror array for optical phase control High spatial resolution, precision & speed No inter-actuator coupling (cross talk) Polarisation insensitivity High spectral bandwidth (DUV to IR)
Successful application demonstrations Vision correction in ophthalmology Temporal laser pulse shaping Dynamic diffractive optical element Performance characterization within an AO test bed
Further technology improvements (under development) Key issues: larger stroke, higher fill-factor 2-level-mirror-architectures
© Fraunhofer IPMS MEMS AO at IPMS I slide 31
Future Development Prospects: Scalable Technology
2-Level Piston
1-Level Piston
2-Level Piston-Tip-Tilt
80 µm
2.5 µm
1.0 µm
0.5 µm
Stroke
Pixel Size 40 µm
© Fraunhofer IPMS MEMS AO at IPMS I slide 32
Realized 2-Level Hidden Hinge Designs
© Fraunhofer IPMS MEMS AO at IPMS I slide 33
Thank you for your attention !