A 19 element segmented MEMS deformable mirror(DM) based on electrostatic repulsive-force actuator is proposed and
fabricated using a commercial surface micromachining process PolyMUMPs. Impacts of different sizes of actuator on
DM’s characterizations such as stroke, work bandwidth, driving voltage and fill factor are analyzed and optimized. An
analytical analysis combined numerical simulation has been performed on the deformation of repulsive flexural beam
actuator regarding actuator size and boundary condition. These analytic insights could provide guidelines for future
MEMS DMs optimum design. A maximum stroke of the fabricated DM is 2.6μm, is larger than 2μm for the sacrificial
layer thickness of PolyMUMPs. The preliminary aberration correction of the whole DM array is also analyzed.
Compared to conventional MEMS DMs, this design demonstrates the advantage of large stroke over a standard surface
micromachining fabrication process with a thin deposited layer, and it would expand the application of MEMS DMs in
We propose, design and fabricate here an electrostatically actuated continuous single-crystal-silicon membrane deformable mirror (DM) for astronomical observation. To get a large stroke, a bimorph spring array is used to generate a large air gap between the mirror membrane and the electrode. A DM with a 1.8mm×1.8mm mirror membrane are fabricated by combining Au-Si eutectic wafer bonding and the subsequent all-dry release process. The stroke of the DM is 3.5μm at 115V. The influence function on the nearest neighbor is 51%. The fill factor of the DM is 99.9%.
Two new MEMS deformable mirrors have been designed and fabricated, one having a continuous facesheet with an
active aperture of 20mm and 2040 actuators and the other, a similarly sized segmented tip tilt piston DM containing
1021 elements and 3063 actuators. The surface figures, electro mechanical performances, and actuator yield of these
devices, with statistical information, are reported here. The statistical distributions of these measurements directly
illustrate the surface variance of Boston Micromachines deformable mirrors. Measurements of the surface figure
were also performed with the elements at different actuation states. Also presented here are deviations of the surface
figure under actuation versus at its rest state, the electromechanical distribution, and a dynamic analysis.
With the purpose of designing a variable-focal lens with large optical aperture, a liquid lens with liquid-membrane-liquid
structure and 30mm optical aperture is proposed. Function of the inserted membrane is stated that much stronger elastic
force takes place of interface tension, and enlarging aperture size of liquid lens becomes possible. Mechanics analysis of
membrane’s deformation and finite element simulation was employed to demonstrate the elastic force maintains the
deformation into a parabolic shape. Moreover, a prototype lens was designed and optical performance with a refractive
power range of 7.7Diopters, and 7.13line-pair/mm resolution was measured in experiments.
A MEMS deformable mirror is described that uses a novel actuation scheme to increase the optical focus range. In
this method electrostatic-pneumatic actuation is used to achieve a convex surface curvature of the mirror, while
direct electrostatic actuation creates a concave surface. The fabricated device consists of two membranes made of
the photoset epoxy SU-8. One membrane serves as the deformable mirror and the other one as the pneumatic
actuator. The pneumatic membrane also provides a built-in valve for pressure equalization. The principle of
operation, fabrication process and results are presented.
To meet the high contrast requirement of 1 × 10−10 to image an Earth-like planet around a Sun-like star, space telescopes equipped with coronagraphs require wavefront control systems. Deformable mirrors (DMs) are a key element of a wavefront control system, as they correct for imperfections, thermal distortions, and diffraction that would otherwise corrupt the wavefront and ruin the contrast. The goal of the CubeSat Deformable Mirror technology demonstration mission is to test the ability of a microelectromechanical system (MEMS) deformable mirror to perform wavefront control on-orbit on a nanosatellite platform. In this paper, we consider two approaches for a MEMS deformable mirror technology demonstration payload that will fit within the mass, power, and volume constraints of a CubeSat: 1) a Michelson interferometer and 2) a Shack-Hartmann wavefront sensor. We clarify the constraints on the payload based on the resources required for supporting CubeSat subsystems drawn from subsystems that we have developed for a different CubeSat flight project. We discuss results from payload lab prototypes and their utility in defining mission requirements.
We describe KAPAO, our project to develop and deploy a low-cost, remote-access, natural guide star adaptive optics (AO) system for the Pomona College Table Mountain Observatory (TMO) 1-meter telescope. We use a commercially available 140-actuator BMC MEMS deformable mirror and a version of the Robo-AO control software developed by Caltech and IUCAA. We have structured our development around the rapid building and testing of a prototype system, KAPAO-Alpha, while simultaneously designing our more capable final system, KAPAO-Prime. The main differences between these systems are the prototype's reliance on off-the-shelf optics and a single visible-light science camera versus the final design's improved throughput and capabilities due to the use of custom optics and dual-band, visible and near-infrared imaging. In this paper, we present the instrument design and on-sky closed-loop testing of KAPAO-Alpha as well as our plans for KAPAO-Prime. The primarily undergraduate-education nature of our partner institutions, both public (Sonoma State University) and private (Pomona and Harvey Mudd Colleges), has enabled us to engage physics, astronomy, and engineering undergraduates in all phases of this project. This material is based upon work supported by the National Science Foundation under Grant No. 0960343.
We evaluate the performance of a woofer-tweeter controller architecture for the new 3-meter Shane Telescope (Lick Observatory) laser guidestar adaptive optics (AO) system. Low order, high stroke phase correction is performed using the normal modal basis set of the Alpao woofer deformable mirror (DM). Since the woofer and tweeter DMs share the same wavefront sensor, the projected woofer phase correction is offloaded from the high-order, low stroke phase aberrations corrected by the tweeter DM. This ensures the deformable mirrors complementarily correct the input phase disturbance and minimizes likelihood of the tweeter actuators saturating. Preliminary analysis of on-sky closed-loop deformable mirror telemetry data from currently operating AO systems at Mt. Hamilton, as well as statistically accurate Kolmogorov phase screens, indicate that correction of up to 34 woofer modes results in all tweeter actuators remaining within their stroke limit.
We demonstrate enhanced focusing of polychromatic light through strongly scattering media. The experimental results
validate a theoretical relationship among source bandwidth, sample bandwidth, and initial contrast of a far-field
speckle. For various combinations of source bandwidth and sample bandwidth, we optimize far-field focal intensity
enhancement using a MEMS spatial light modulator to modulate the source beam prior to its propagation through the
medium. We achieve focus optimization using a sequential coordinate descent algorithm and Hadamard basis
functions to control the spatial phase of the modulator. Enhancement, the ratio of optimized focal intensity to initial
speckle mean intensity, is shown to vary monotonically with initial contrast.
Optical microscopy allows noninvasive imaging of biological tissues at a subcellular level. However, the optimal performance of the microscope is hard to achieve because of aberrations induced from tissues. The shallow penetration depth and degraded resolution provide a limited degree of information for biologists. In order to compensate for aberrations, adaptive optics with direct wavefront sensing, where guide-stars are used for wavefront measurement, has been applied in microscopy. The scattering effect limits the intensity of a guide-star and hence reduces the signal to noise ratio of the wavefront measurement. In this paper, we propose to use interferometric focusing of excitation light onto a guide-star embedded deeply in tissue to increase its fluorescence intensity, thus overcoming the signal loss caused by scattering. With interferometric focusing of light, we increase the signal to noise ratio of the laser guide-star through scattering tissue by more than two times as well as potentially extending the thickness of tissue that can be corrected using AO microscopy.
The optical imaging depth in biological materials is limited by the scattering of light in tissue. New methods which control light propagation through scattering media have been introduced with the potential to overcome the scattering of light in biological materials. These techniques shape the incident wavefront to pre-compensate for the scattering effects of light propagation in the material and beyond. However, living biological materials have speckle decorrelation times on the millisecond timescale. This fast rate of change makes liquid crystal spatial light modulation (LC-SLM) devices too slow for this task. To achieve the required wavefront control with high modulation speeds we present binary-amplitude off-axis computer-generated holography implemented on a digital micro-mirror device (DMD). Binary amplitude off-axis holography is a method for the generation of arbitrary wavefronts, and in particular uniform-amplitude phase-modulated images. As a result, we are able to simultaneously encode phase modulated wavefronts at the high frame rate of binary amplitude DMDs. This wavefront encoding technique allows for focusing through temporally dynamic turbid materials at a rate which approaches the decorrelation time of living biological tissue. We demonstrate this technique by high speed wavefront optimization for focusing through turbid media as well as through a dynamic, strongly scattering sample with short speckle decorrelation times. With this approach we attain an order of magnitude improvement in measurement speed over the previous fastest wavefront determination method and three orders of magnitude improvement over LC-SLM methods.
The performance of an adaptive optics (AO) system is typically measured using the wavefront sensor (WFS). However, another method is to use the point spread function (PSF), which is sensitive to scatter, does not act as a low pass filter and is not dependent on the WFS calibration. We decided to examine the performance of an AO system built for vision science that employed a micromechanical systems (MEMS) based deformable mirror (DM). Specifically, the MEMS DM consists of 489 actuators, resulting in 163 segments each with individual piston/tip/tilt control. Initial evaluation of the DM with a model eye included determining the ability of the DM to generate individual Zernike polynomials and evaluating the far field PSF to measure wavefront correction performance. For individual Zernike polynomial terms, the DM was found to be capable of correcting the aberration magnitudes expected from previously published human population studies.1, 2 Finally, the DM was used in an AO fundus camera to successfully acquire images of cone photoreceptors in a living human eye. This is part of ongoing work which will incorporate the MEMS DM into both an AO scanning laser ophthalmoscope (SLO) and an AO optical coherence tomography (OCT) system where the form of the PSF at the confocal pinhole/optical fiber is important for optimal imaging.