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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??