MICROMACHINING AND MICROFABRICATION TECHNOLOGY FOR ADAPTIVE OPTICS Olav 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

mMIRRORS Texas Instrument’s DMD NASA's Next Generation Space Telescope (2008) with 4M micromirrors by Sandia NL Lucent’s Optical X-Connect

mGRATINGS - DIFFRACTIVE OPTICS 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) Silicon Nitride 25 to 100 µm Silicon Substrate Silicon Dioxide

System on a chip Laser-to-fiber coupling Micropositioners of mirrors and gratings High-resolution raster scanner

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

Micromirror Structure Support Frame Mirror Surface Frame Hinge Electrostatic Combdrive Torsion Hinges Substrate Hinge Combdrive Linkage

Fabrication PolySi Nitride Oxide Slider Hinge V-groove for alignment Mirror

Micromirror Reliability -0.50% 0.00% 0.50% 1.00% 1.50% 2.00% 1.E+04 1.E+06 1.E+08 1.E+10 Change in Res. Frequency Micromirror Reliability x 10 “Off” position -3 1 0.5 Angle (degrees) -0.5 -1 10 20 30 40 50 60 70 80 measurement #

Video Display System Schematic Demonstration system used two mirrors on separate chips Computer modulates a 10 mW 655 nm laser diode The emerging beam hits the fast scanning mirror 1f The light is coupled into a single-mode fiber …and the image is projected onto a screen 2f 1f The beam is then imaged to the slow scanning mirror

Mirror Curvature Measurement Static deformation 1.2 mm MUMPS Poly2 2-D Interferometry Optical far-field measurements

Mirror curvature due to actuation Mirror deformation due to actuation Wobble of actuated micromirror (motion on orthogonal axis) 1100 1000 ) [mm] 900 .002 2 800 .001 700 Optical beam radius (1/e Degrees 600 500 -.001 400 -.002 -2 -1 1 2 300 Degrees -4 -3 -2 -1 1 2 3 4 Mechanical deflection [deg]

a d e c f b g h Scanned Images Resolution: 62 by 66 pixels, optical scanning angles 5.3 and 5.7 degrees Video Display

Fiber Optic Crossbar Switch Input Ports l1OXC Torsion bar Mirror l2OXC 1 Frame 2 l3 Output Ports Comb drive 3 Optical DMUX 1 2 3 500 mm Optical MUX Architecture of WDM Switch The optical input signals are demultiplexed, and each wavelength is routed to an independent NxN spatial cross-connect SEM of the micromirrors used in the two-chip switch

Demonstration of Crossbar Switch M1: 0V to 21.7V M3: 25.5V M3: 0Vto 25.5V M1: 0V M1 M3 M2 M4 B A -60 -40 -20 Output A Output B Input Mirror Array Optical Power Transmision [dB] Output Mirror Array 2X2 OXC design Switch characteristics Horizontal axis is in volts squared

Optical Coherence Tomography Delay line 760 m m Beam Splitter 5.3 cm Grating Scanning Mirror

Polysilicon Grating Light Modulator ribbons 3um ribbons 6um grating period 200 um 150um electrode anchor

GLM Operation Cross section Side view Beams up, reflection Beams down, diffraction Cross section Side view

Combdrive vs. parallel plate End view d h Acd=4Ndh

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??

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 bonding Through-the-wafer interconnects Novel functions Diffractive optics?? Spectral filtering??