Micromachined deformable mirrors (DMs) have enabled rapid advances in applications ranging from large telescope
astronomy and free space laser communication to biological microscopy and retinal imaging over the past decade. In
this talk I describe our efforts at Boston University and at Boston Micromachines Corporation to design, fabricate, and
control MOEMS DMs for adaptive optics (AO) applications. Integration of the DMs in AO systems is described, along
with results demonstrating unprecedented advances in resolution and contrast in microscopes and telescopes challenged
by unavoidable wavefront aberrations. MEMS-DM research offers the rare opportunity to introduce technology that is
both more economical and more capable than the state-of-the-art.
We report on the design, development and testing of a new low-power, light-weight and low-cost modulating
retroreflector system for free-space covert optical communication and remote sensor interrogation. The central
component of the system is a MEMS modulator mirror, which is physically similar to a very low modulation reflective
diffraction grating that has actively controlled groove depth and can operate at frequencies up to 1MHz. One facet of the
hollow corner cube retroreflector consists of the MEMS mirror, providing intensity modulation of a reflected
interrogating beam by switching from an unpowered flat mirror state to a powered diffractive state. The system is
optimized for performance at 1550nm and has a field of view of 60 degrees. For covert operation it uses "wake-up"
circuitry to control a low-power shutter that remains closed between data transfers. The system's compact driver
electronics employs power scavenging and resonant properties for minimal power consumption and extended
autonomous operational life. Interrogation field test results for the modulating retroreflector will be presented.
We have tested an aluminum-coated Iris AO Micro-Electrical Mechanical System (MEMS) segmented Deformable Mirror (DM) for its behavior in the presence of high energy 532 nm laser light. The DM was subject to several tests in which the laser power and the duration of its incidence was varied. The DM experienced an irradiance of 94.5 W cm-2 at the maximum laser power of 2 W. A slight permanent reduction in the amount of bow in each segment was observed. This is most likely due to annealing. The mirror remained fully functional during and after the tests. Measurements of the mirror's temporal stability and position repeatability were performed before the laser test. We found a 1.28 nm rms variation in the bow of segments that is highly correlated over the 16 minute test. The mirror's ability to return to its initial position was within the 1.34 nm rms instrument noise. These results are encouraging for applications such as the laser uplink correction of the Visible Light Laser Guidestar Experiment (Villages) and future multi-Laser Guidestar systems (LGS).
We present details of a MEMS-based holographic adaptive optics system. The modal wavefront sensing relies on
measuring the intensity of focal spots using a multiplexed hologram and multi-pixel photon counter. The basis set for the
sensing is a direct recording of the actuator responses in the deformable mirror. This allows us to directly control the
wavefront correction in closed loop without need for any calculations or computer. The entire system is compact and
lightweight and the limiting speed is set only by the dynamics of the deformable mirror and not the number of actuators.
We present an update on the Visible Light Laser Guidestar Experiments ViLLaGEs) taking place at the Lick
Observatory. The goal of phase one of these experiments is to demonstrate the practical feasibility of using MEMS
deformable mirrors in astronomical adaptive optics systems, including the use of open-loop wavefront sensing and
control. The goal of phase two is to incorporate a laser guide star and demonstrate laser up-link correction, again using a
MEMS deformable mirror running in open-loop. The overall set of experiments is designed to demonstrate these and
various other new concepts leading to feasible and low-cost laser guidestar adaptive optics that can be used for science
observing in the visible wavelength bands.
Our program for the upgrade of the Naval Prototype Optical Interferometer with large telescopes
and adaptive optics has produced a test-bed for the in system evaluation and testing of our MEMs
adaptive optics components and system performances. We have already reported in recent
publications the basic characteristics of the test-bed. In order to improve the capabilities of such
laboratory set-up we have started an upgrade that aims at developing a Multi Conjugate Adaptive
Optics (MCA) test-bed. This test bed is based on the use of multiple Liquid Crystal Spatial Light
Modulators (LCSLMs) for producing different phase screens at different spatial locations within the
set-up. Details of this new set-up are presented in another paper in these proceedings. This paper
specifically deals with the analytic portion of the MCAO test-bed.
Adaptive optics systems have advanced considerably over the past decade and have become common tools
for optical engineers. The most recent advances in adaptive optics technology have lead to significant
reductions in the cost of most of the key components. Most significantly, the cost of deformable elements
and wavefront sensor components have dropped to the point where multiple deformable mirrors and Shack-
Hartmann array based wavefront sensor cameras can be included in a single system. Matched with the
appropriate hardware and software, formidable systems can be operating in nearly any sized research
laboratory. The significant advancement of MEMS deformable mirrors has made them very popular for use
as the active corrective element in multi-conjugate adaptive optics systems so that, in particular for
astronomical applications, this allows correction in more than one plane. The NRL compact AO system and
atmospheric simulation systems has now been expanded to support Multi Conjugate Adaptive Optics
(MCAO), taking advantage of using the liquid crystal spatial light modulator (SLM) driven aberration
generators in two conjugate planes that are well separated spatially. Thus, by using two SLM based
aberration generators and two separate wavefront sensors, the system can measure and apply wavefront
correction with two MEMS deformable mirrors. This paper describes the multi-conjugate adaptive optics
system and the testing and calibration of the system and demonstrates preliminary results with this system.
Deformable mirror (DM) technology based on microelectromechanical systems (MEMS) technology produced by
Boston Micromachines Corporation has been demonstrated to be an enabling component in a variety of adaptive
optics applications such as high contrast imaging in astronomy, multi object adaptive optics, free-space laser
communication, and microscopy. Many of these applications require DMs with thousands of actuators operating at
frame rates up to 10 kHz for many years requiring sufficient device reliability to avoid device failures. In this paper
we present improvements in MEMS deformable mirrors for reliability along with test data and device lifetime
prediction that show trillions of actuator-cycles can be achieved without failures.
Compensating for atmospheric turbulence in meter-class telescopes and for free-space communications can require
deformable mirrors (DM) with hundreds of actuators. Advances in high-contrast imaging techniques and increased
telescope sizes require DMs mirrors with thousands of actuators -. In response to these needs, Iris AO has been
developing a nearly 500-actuator DM and is conducting pathfinding research into 3000-actuator class DMs. This paper
begins with an overview of the segmented DM design and describes improvements made to the DM over the prior year
in the areas of speed, high-quality dielectric coatings, and snap-in prevention structures. The paper then describes the
next-generation PTT489 DM design and fabrication process. Failure modes encountered during fabrication are presented
as well as test methods to detect the failure modes. Preliminary yield data are presented for the fabrication process as
well. The paper concludes with a view to the future showing pathfinding research into 3000-actuator DMs.
Improvements for open-loop control of MEMS deformable mirror for large-amplitude
wavefront control are presented. The improvements presented here relate to measurement
filtering, characterization methods, and controlling the true, non-differential shape of the
mirror. These improvements have led to increased accuracy over a wider variety of
deflection profiles including flattening the mirror and Zernike polynomials.
We present a model for MEMS deformable mirrors (DMs) that couples a 2-dimensional, linear 4th order partial
differential equation for the DM facesheet with linear spring models for the actuators. We estimate the
parameters in this model using the method of output least squares, and we demonstrate the effectiveness of this
approach with data from a 140-actuator MEMS test mirror produced at Boston University. A scheme for robust,
computationally efficient open-loop control, which is based on this model, is also presented.
The image resolution and contrast of microscopes are often detrimentally affected by aberrations that are introduced
when focusing deep into specimens. These aberrations arise from spatial differences in optical properties
of the specimen or refractive index mismatches. This is particularly problematic in multiphoton microscopy,
where short pulsed lasers are used to generate contrast through non-linear optical effects, such as two-photon
fluorescence or third harmonic generation. The non-linear nature of the signal generation process means that
the signal level is strongly affected by changes in the focal spot intensity. We have applied the techniques of
adaptive optics to measure and correct the aberrations, restoring image quality. In particular, this has been
demonstrated in harmonic generation microscopy of developing mouse embryos. Similar aberration problems
affect the resolution and efficiency of three-dimensional optical fabrication systems, such those used for the manufacture
of photonic crystals or optical waveguides. These systems are based around microscope optics and use
short pulsed laser illumination to induce localized multiphoton effects in a fabrication substrate. In this case,
significant aberrations are introduced when focusing deep into the substrate. We report on the development
of adaptive optics systems for these applications and discuss the specific challenges for wave front sensing and
correction that are presented by these systems.
We have developed an adaptive optics multiphoton microscope. The multiphoton imaging system combines an ultrafast
high-power laser, a scanning unit, a motorized Z-scan device and a photon-counting detector. The adaptive optics
module is composed of a Hartmann-Shack wavefront sensor and a MEMS deformable mirror. The impact of
compensating the aberrations of the laser beam is shown in a number of biological and non-biological samples. As
examples, nonlinear fluorescence and second harmonic generation images of non-stained ex-vivo ocular tissues are
compared with and without adaptive optics. The correction of the beam's aberrations increases both contrast and
resolution in the non-linear microscope images.
We report the programmable pulse shaping of ultrabroadband pulses by the use of a novel design of electrostatic deformable mirror based on push pull technology. We achieved the formation of double and triple pulses with programmable delay and a pulse length of email@example.comμm with spectrum tunability.
Adaptive optics (AO) improves the quality of astronomical imaging systems by using real time measurement of the
turbulent medium in the optical path using a guide star (natural or artificial) as a point source reference beacon . AO
has also been applied to vision science to improve the view of the human eye. This paper will address our current
research focused on the improvement of fluorescent microscopy for biological imaging utilizing current AO technology.
A Shack-Hartmann wavefront sensor (SHWS) is used to measure the aberration introduced by a Drosophila
Melanogaster embryo with an implanted 1 micron fluorescent bead that serves as a point source reference beacon.
Previous measurements of the wavefront aberrations have found an average peak-to-valley and root-mean-square (RMS)
wavefront error of 0.77 micrometers and 0.15 micrometers, respectively. Measurements of the Zernike coefficients
indicated that the correction of the first 14 Zernike coefficients is sufficient to correct the aberrations we measured. Here
we show that a MEMS deformable mirror with 3.5 microns of stroke and 140 actuators is sufficient to correct these
aberrations. The design, assembly and initial results for the use of a MEMS deformable mirror, SHWS and implanted
fluorescent reference beacon for wavefront correction are discussed.
This paper reports on new results of the development of a unimorph laser beam shaping mirror based on Low
Temperature Cofired Ceramics (LTCC). The deformable mirror is actuated by a side screen printed piezoceramic thick
film based on lead zirconate titanate (PZT). The reflective surface is electroplated copper that is diamond machined to
flatten the surface. We introduce the solder jet bumbing fixation technology to mount the deformable mirror into a
metallic mounting. This assembling technology introduces very little energy input and thus also very little deformation
into the mirror. The material of the mounting is CE7 that is especially thermal adapted to the deformable mirror. We will
present results on deflection and resonance frequency for two different mirror designs.
Iris AO has developed a full closed-loop control system for control of segmented MEMS deformable mirrors. It is based
on a combination of matched wavefront sensing, modal wavefront estimation, and well-calibrated open-loop
characteristics. This assures closed-loop operation free of problems related to co-phasing segments or undetectable
waffle patterns. This controller strategy results in relatively simple on-line computations which are suitable for
implementation on low cost digital signal processors. It has been successfully implemented on Iris AO's 111 actuator
(37 segment) deformable mirrors used in test-beds and research systems.
The development of an assembly and packaging process for MEMS deformable mirrors (DMs) with
through wafer via (TWV) interconnects is presented. The approach consists of attaching a DM die with
high-density TWV electrostatic actuator interconnects to an interposer substrate that fans out these
connections for interfacing to conventional packaging technology.
We report on the design, simulation, fabrication and testing of pseudo-analog micromirrors. Electrostatically
actuated piston micromirrors were fabricated using the SUMMiT V process with a goal of achieving nearly analog
displacement using digital voltage control. A mirror is controlled by multiple electrodes with varying areas that
correspond to a binary system. As an example, a mirror is actuated using four electrodes with unit areas of 1, 2, 4
and 8. The same voltage level is applied to one or more of the electrodes to control the vertical displacement. This
arrangement will allow up to 16 different displacements, with more levels possible with a larger number of
electrodes. The system is amenable to digital control and can be scaled to large arrays. Parametric numerical models
built in ANSYS simulations were used to predict performance and further refine the design parameter values derived
from the theoretical models. An interferometric microscope has been used to measure the vertical displacement of
the mirrors as voltage is applied. Experimental results show that mirror displacement is proportional to the total
electrode area used to actuate the mirror. Reasonable repeatability in displacement has been seen for a mirror
actuated by the same total electrode area and voltage.
Membrane deformable mirrors based on magnetic actuators have been known for years. State-of-the-art deformable
mirrors usually have large strokes but low bandwidth. Furthermore, this bandwidth decreases with the diameter. In this
paper, we present the results of a new actuator principle based on magnetic forces allowing high bandwidth (up to a few
kHz), very large stroke (>30μm) with a record pitch of 1.5mm.
The benefits of this technology will be presented for three applications: astronomy, vision science and microscopy. The
parameters of the mirrors have been tuned such that the inter-actuator stroke of the deformable (more than 2.0μm) in
order to fit the atmosphere turbulence characteristics. In vision science, efforts have been made to correct both
simultaneously the low and high order aberrations (more than 45μm of wavefront correction on astigmatism and focus).
Finally, we will demonstrate how we have developed a deformable mirror able to correct spherical aberrations
The last part of the article is devoted to give some perspectives about this technology.
We present a photo controlled deformable mirror based on a continuous membrane associated to a photoconductor. The membrane shape changes as a function of the intensity distribution of a light beam. The device has the advantage of generating non pixellated deformations with a simple electronic apparatus.