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MICROMACHINING AND MICROFABRICATION TECHNOLOGY
FOR ADAPTIVE OPTICSOlav Solgaard
Acknowledgements:P.M. Hagelin, K. Cornett, K. Li, U. Krishnamoorthy, D.R. Pedersen, M. H. Guddal, E.J. Carr, V. Laible,
BSAC: R.S. Muller, K. Lau, R. Conant, M. Hart
Research Funding:
NSF, BSAC, SMART
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MIRRORS
Texas Instrument’s DMD
NASA's Next Generation Space Telescope (2008) with 4M micromirrors by Sandia NL
Lucent’s Optical X-Connect
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GRATINGS - DIFFRACTIVE OPTICS
Silicon Dioxide
Silicon Nitride
Silicon Substrate
25 to 100 µm
Top electrode 1-D and 2-D spatial light modulators (Projection displays - Silicon Light Machines)
Displacement sensors (AFM arrays - C. Quate)
Sensor integration, free-space communication
Diffractive lenses and holograms (Fresnel zone plates - M. Wu, UCLA)
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System on a chip
Laser-to-fiber coupling
Micropositioners of mirrors
and gratings
High-resolution raster scanner
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Why Micromachined Adaptive Optics?
Parallel processing, large arrays, system integration, diffractive optics• Standard IC materials and fabrication
• Integration of optics, mechanics, & electronics
Scaling of optics• Alignment, Resolution, Optical quality,
Mechanical actuation and stability
• Raster-scanning displays, Fiber-optic switches, Femto-second spectroscopy
Technology development• actuation, mirror quality, integration
Conclusion
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Micromirror Structure
Torsion Hinges
Support Frame
Mirror Surface
Electrostatic Combdrive
Substrate Hinge
Frame Hinge
Combdrive Linkage
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Fabrication
PolySi
Nitride
Oxide
Slider Hinge
MirrorV-groove for
alignment
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MicromirrorReliability
-0.50%
0.00%
0.50%
1.00%
1.50%
2.00%
1.E+04 1.E+06 1.E+08 1.E+10Ch
an
ge
in R
es.
Fre
qu
enc
y
measurement #0 10 20 30 40 50 60 70 80
-1
-0.5
0
0.5
1x 10-3
Ang
le (
degr
ees) “Off” position
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Video Display System Schematic
Computer modulates a 10 mW 655 nm laser diode
The emerging beam hits the fast scanning mirror
The beam is then imaged to the slow scanning mirror
1f
1f
2fThe light is coupled into a single-mode fiber
…and the image is projected onto a screen
• Demonstration system used two mirrors on separate chips
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Mirror Curvature Measurement
Static deformation 1.2 m
MUMPS Poly2
2-D Interferometry
Optical far-field measurements
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Mirror curvature due to actuation
-4 -3 -2 -1 0 1 2 3 4300
400
500
600
700
800
900
1000
1100
Mechanical deflection [deg]
Opt
ical
bea
m r
adiu
s (1
/e2)
[m
]
Mirror deformation due to actuation
-2 -1 0 1 2-.002
-.001
0
.001
.002
Degrees
Deg
rees
Wobble of actuated micromirror (motion on orthogonal axis)
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Video Display
100 200 300 400 500 600
50
100
150
200
250
300
350
400
450
Scanned Images
Resolution: 62 by 66 pixels, optical
scanning angles 5.3 and 5.7 degrees
a d
e
c
f
b
g h
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Fiber Optic Crossbar Switch
OpticalDMUX
Optical MUX
OXC
OXC123
Input Ports
123
Output Ports
Architecture of WDM Switch The optical input signals are demultiplexed, and each wavelength is routed to an independent NxN spatial cross-connect
MirrorFrame
Combdrive
Torsion bar
500 m
SEM of the micromirrors used in the two-chip switch
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Switch characteristics Horizontal axis is in volts squared
Optical Power Transmision [dB]
M1: 0V to 21.7VM3: 25.5V
M3: 0Vto 25.5VM1: 0V
M1
M3
M2
M4B
A
M1
M3
M2
M4B
A
-60
-40
-20
0
Output A
Output B
Demonstration of Crossbar Switch
Output Mirror Array
Input Mirror Array
2X2 OXC design
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Optical Coherence Tomography
Grating
760 m
5.3 cm
BeamSplitter
Delay line
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Polysilicon Grating Light Modulator
200 um
3um ribbons6um grating period
150um
electrodeanchor
ribbons
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GLM Operation
Side view
Beams up, reflection
Beams down, diffraction
Cross section
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Combdrive vs. parallel plate
2
2
2
20
2
20
20
2
44
2 :plate Parallel
:Combdrive
d
s
F
F
d
VAFNdhA
s
VAF
d
hVNF
pp
cd
cdcdcd
pppp
cd
=
=?=
=
=
ε
ε
ε
h
dd
Acd=4Ndh
End view
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Lessons for Adaptive Optics Standard processes and materials
• High-resolution optics
• Mechanical stability & reliability => electrostatic actuation
• Large-stroke actuation => Combdrives
Optical quality• SOI material
Integration • wafer bonding => optimization of optics,
mechanics and electronics
Novel functions - Diffractive optics• Spectral filtering??
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Conclusion Micromachining enables Adaptive Optics
• Miniaturization, arrays, integration, parallel processing, robustness, reliability
• Standard materials and processing Low cost Technology development
• Large-stroke electrostatic actuators• High-quality optics• Integration
Wafer bondingThrough-the-wafer interconnects
Novel functions• Diffractive optics??• Spectral filtering??