We present a monolithic multispectral camera (MMC) for high contrast direct imaging of inner exoplanetary environments. The primary scientific goal of the camera is to enable eight color characterization of jovian exoplanets and interplanetary dust and debris distributions around nearby stars. Technological highlights of the design include: 1. Diffraction limited resolution at 350 nm through active optical aberration correction; 2. Greater than million-to-one contrast at narrow star separation using interferometry and post-processing techniques; 3. Demonstration of deep broadband interferometric nulling and interband image stability through the use of monolithic optical assemblies; 4. Optimization of multispectral throughput while minimizing components.
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.
MEMS deformable mirrors with thousands of actuators are under development for space-based operation, which require
fault tolerant actuators that will not fail due to electrical overstress. We report on advances made in the development of
MEMS deformable mirror actuators with enhanced reliability for space-based, high-contrast imaging instrumentation
that eliminate irreversible actuator damage resulting from snap-through.
We report on the development of high actuator count,
micro-electromechanical (MEMS) deformable mirrors designed
for high order wavefront correction in ground and space-based astronomical adaptive optics instruments. The design of
these polysilicon, surface-micromachined MEMS deformable mirrors builds on technology that has been used
extensively to correct for ocular aberrations in retinal imaging systems and for compensation of atmospheric turbulence
in free-space laser communication. These light-weight, low power deformable mirrors have an active aperture of up to
25.2mm consisting of a thin silicon membrane mirror supported by an array of 140 to 4092 electrostatic actuators which
exhibit no hysteresis and have sub-nanometer repeatability making them well suited for open-loop control applications
such as Multi-Object Adaptive Optics (MOAO). The continuous membrane deformable mirrors, coated with a highly
reflective metal film, are capable of up to 6μm of stroke, have a surface finish of <10nm RMS with a fill factor of 99.8%.
Presented in this paper are device characteristics and performance test results, as well as reliability test data and device
lifetime predictions that show that trillions of actuator cycles can be achieved without failures.
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.
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.
We present the progress in the development of a 4096-element microelectromechanical systems (MEMS) deformable mirror, fabricated using polysilicon surface micromachining manufacturing processes, with 4 µm of stroke, a surface finish of <10 nm rms, a fill factor of 99.5%, and a bandwidth of >5 kHz. The packaging and high-speed drive electronics for this device, capable of frame rates of 22 kHz, are also presented.
Small deformable mirrors (DMs) produced using microelectromechanical systems (MEMS) techniques have been used
in thermally stable, bench-top laboratory environments. With advances in MEMS DM technology, a variety of field
applications are becoming more common, such as the Gemini Planet Imager's (GPI) adaptive optics system.
Instruments at the Gemini Observatory operate in conditions where fluctuating ambient temperature, varying gravity
orientations and humidity and dust can have a significant affect on DM performance. As such, it is crucial that the
mechanical design of the MEMS DM be tailored to the environment. GPI's approach has been to mount the MEMS DM
using high performance optical mounting techniques rather than a typical laboratory set-up. This paper discusses the
design of the opto-mechanical mounting scheme for a 4096 actuator MEMS DM, developed by Boston Micromachines
Corporation for use in the GPI adaptive optics system. Flexures have been incorporated into the DM mount to reduce
deformations on the optical surface due to thermal fluctuations. These flexures have also been sized to maintain
alignment under varying gravity vector orientations. Finally, a system for environmentally sealing the mirror has been
designed to prevent degradation due to humidity effects. A plan for testing the mechanical mount to ensure that it meets
GPI's performance and environmental requirements is also presented.
The SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is a infrared space-borne telescope mission of
the next generation following AKARI. SPICA will carry a telescope with a 3.5 m diameter monolithic primary mirror
and the whole telescope will be cooled to 5 K. SPICA is planned to be launched in 2017, into the sun-earth L2 libration
halo orbit by an H II-A rocket and execute infrared observations at wavelengths mainly between 5 and 200 micron. The
large telescope aperture, the simple pupil shape, the capability of infrared observations from space, and the early launch
gives us with the SPICA mission a unique opportunity for coronagraphic observation. We have started development of a
coronagraphic instrument for SPICA. The primary target of the SPICA coronagraph is direct observation of extra-solar
Jovian planets. The main wavelengths of observation, the required contrast and the inner working angle (IWA) of the
SPICA coronagraph are set to be 5-27 micron (3.5-5 micron is optional), 10-6, and a few λ/D (and as small as possible),
respectively, in which λ is the observation wavelength and D is the diameter of the telescope aperture (3.5m). For our
laboratory demonstration, we focused first on a coronagraph with a binary shaped pupil mask as the primary candidate
for SPICA because of its feasibility. In an experiment with a binary shaped pupil coronagraph with a He-Ne laser
(λ=632.8nm), the achieved raw contrast was 6.7×10-8, derived from the average measured in the dark region without
active wavefront control. On the other hand, a study of Phase Induced Amplitude Apodization (PIAA) was initiated in an
attempt to achieve better performance, i.e., smaller IWA and higher throughput. A laboratory experiment was performed
using a He-Ne laser with active wavefront control, and a raw contrast of 6.5×10-7 was achieved. We also present recent
progress made in the cryogenic active optics for SPICA. Prototypes of cryogenic deformable by Micro Electro
Mechanical Systems (MEMS) techniques were developed and a first demonstration of the deformation of their surfaces
was performed with liquid nitrogen cooling. Experiments with piezo-actuators for a cryogenic tip-tilt mirror are also
This paper presents recent progress in the development of MEMS deformable mirrors for space and defense applications.
Two different MEMS DM designs are described, along with their corresponding uses in space and defense systems. The
designs build on a conventional surface micromachining technology and feature an electrostatic actuation architecture
pioneered at Boston University. Key performance characteristics are presented. The device characteristics make them
useful for a range of wavefront control applications that include
low-power optical modulation, adaptive optics imaging,
and laser communication, on both ground-based and space-based platforms.
This paper presents the progress in the development of a 4096 element MEMS deformable mirror, fabricated using
polysilicon surface micromachining manufacturing processes, with 4μm of stroke, a surface finish of less than 10nm
RMS, a fill factor of 99.5%, and bandwidth greater than 5kHz. The packaging and high speed drive electronics for this
device, capable of frame rates of 22 kHz, are also presented.
We report on the development of a new class of electrostatic MEMS deformable mirror (DM) fabricated through a
combination of bulk micromachining, wafer bonding, and surface micromachining. The combination of these
fabrication technologies introduces four major improvements over previous MEMS DMs, which are fabricated using
surface micromachining alone. First, the MEMS DM structural components (mirror surface and actuator array) are
made entirely of single crystalline silicon by use of the device layer of a whole 4-inch silicon-on-insulator (SOI)
wafer bonded together via anodic bonding. Unlike current MEMS DMs fabricated entirely using surface
micromachining, bulk micromachining steps in this fabrication process require no etch access holes, print through is
inexistent, and no polishing steps are required. This leads to reduced diffraction of light from the mirror surface,
improved mirror surface optical quality, and elimination of manufacturing processing steps. Second, through-wafer
interconnects are used to connect the densely-packed electrostatic actuator array to driver electronics. This
eliminates the need for wirebonding at the periphery of the DM, increasing the surface area available for actuators
and removes the need for bulky wire bundles to connect the device to its driver. Third, by using the full area of a
silicon wafer for each mirror, these MEMS DMs offer a larger optical aperture than any previously-reported MEMS
DM. The larger aperture will achieve higher angular resolution, providing larger wavefront correction. Finally, the
mirror and actuator thicknesses are not limited to several micrometers, unlike in surface micromachining. The
thickness limits using this fabrication process is prescribed by the device layer thickness in SOI wafers, which vary
between several micrometers to several hundred of microns.
In recent years, demanding adaptive optics applications have driven advancements in
microelectromechanical systems (MEMS) deformable mirrors. The latest developments in
adaptive optics for extremely large telescopes and other astronomical applications calling for
thousands of control points have pushed high actuator mirror arrays. The need to compensate for
large amplitude, high order wavefront aberrations in retinal imaging have pushed for high stroke,
high spatial resolution deformable mirrors. Aerospace and military defense applications with
long operational life times have created demands for rugged, highly reliable micromachined
devices. Finally, the impending commercialization of deformable mirrors for bioimaging
applications has created a requirement for a low-cost adaptive optics solution.
The variety of applications with their respective requirements has resulted in versatile MEMS
devices for advanced optical control and thus well-suited for many laser beam shaping
applications. This paper will describe the design, manufacturing, and testing results of the latest
generation of optical quality micromachined deformable mirrors. Recent testing of a 4096
actuator deformable mirror and a newly released a 140 actuator, six micron stroke mirror will be
demonstrated. A high-speed electronics driver for a 1024 actuator deformable mirror designed
for laser beam shaping in optical communication will also be demonstrated. This paper will show
how the applications of micromachined deformable mirrors can be extended to laser beam
shaping for industrial machining, laser communication, and femto-second pulse applications.
Recently, a number of research groups around the world have developed ophthalmic instruments capable of in vivo diffraction limited imaging of the human retina. Adaptive optics was used in these systems to compensate for the optical aberrations of the eye and provide high contrast, high resolution images. Such compensation uses a wavefront sensor and a wavefront corrector (usually a deformable mirror) coordinated in a closed- loop control system that continuously works
to counteract aberrations. While those experiments produced promising results, the deformable mirrors have had insufficient range of motion to permit full correction of the large amplitude aberrations of the eye expected in a normal population of human subjects. Other retinal imaging systems developed to date with MEMS (micro-electromechanical
systems) DMs suffer similar limitations.
This paper describes the design, manufacture and testing of a 6um stroke polysilicon surface micromachined deformable mirror that, coupled with an new optical method to double the effective stroke of the MEMS-DM, will permit diffraction-limited retinal imaging through dilated pupils in at least 90% of the human population. A novel optical design using spherical mirrors provides a double pass of the wavefront over the deformable mirror such that a 6um mirror
displacement results in 12um of wavefront compensation which could correct for 24um of wavefront error. Details of this design are discussed. Testing of the effective wavefront modification was performed using a commercial wavefront sensor. Results are presented demonstrating improvement in the amplitude of wavefront control using an existing high degree of freedom MEMS deformable mirror.
We report on the development of a new MEMS deformable mirror (DM) system for the hyper-contrast visible nulling coronagraph architecture designed by the Jet Propulsion Laboratory for NASA's Terrestrial Planet Finding (TPF) mission. The new DM is based largely upon existing lightweight, low power MEMS DM technology at Boston University (BU), tailored to the rigorous optical and mechanical requirements of the nulling coronagraph. It consists of 329-hexagonal segments on a 600μm pitch, each with tip/tilt and piston degrees of freedom. The mirror segments have 1μm of stroke, a tip/tilt range of 600 arc-seconds, and maintain their figure to within 2nm RMS under actuation. The polished polycrystalline silicon mirror segments have a surface roughness of 5nm RMS and an average curvature of 270mm. Designing a mirror segment that maintains its figure during actuation was a very significant challenge faced during DM development. Two design concepts were pursued in parallel to address this challenge. The first design uses a thick, epitaxial grown polysilicon mirror layer to add rigidity to the mirror segment. The second design reduces mirror surface bending by decoupling actuator diaphragm motion from the mirror surface motion. This is done using flexure cuts around the mirror post in the actuator diaphragm. Both DM architectures and their polysilicon microfabrication process are presented. Recent optical and electromechanical characterization results will also be discussed, in addition to plans for further improvement of DM figure to satisfy nulling coronagraph optical requirements.
We have demonstrated that a microelectrical mechanical systems (MEMS) deformable mirror can be flattened to < 1 nm RMS within controllable spatial frequencies over a 9.2-mm aperture making it a viable option for high-contrast adaptive optics systems (also known as Extreme Adaptive Optics). The Extreme Adaptive Optics Testbed at UC Santa Cruz is being used to investigate and develop technologies for high-contrast imaging, especially wavefront control. A phase shifting diffraction interferometer (PSDI) measures wavefront errors with sub-nm precision and accuracy for metrology and wavefront control. Consistent flattening, required testing and characterization of the individual actuator response, including the effects of dead and low-response actuators. Stability and repeatability of the MEMS devices was also tested. An error budget for MEMS closed loop performance will summarize MEMS characterization.
Optical-quality microelectromechanical deformable mirrors (DMs) and spatial light modulators (SLMs) are described. With such mirrors, the shape of the reflective surface can be modified dynamically to control an optical wavefront. A principal application is to compensate for aberrations and thereby improve image resolution in telescopes or microscopes: a process known as adaptive optics. μDMs are an enabling component for adaptive optics. Over several years, researchers at Boston University and Boston Micromachines Corporation have developed manufacturing processes that allow production of continuous and segmented deformable mirrors. We have produced mirror arrays with up to 22,500 actuators, 3.5μm of useful stroke, tens of picometer position repeatability, >98% reflectivity, and flatness better than 15nm RMS. Challenges to manufacturing optical quality micromachined mirrors in particular have been addressed: reducing surface roughness, increasing reflectivity, and eliminating post-release curvature in the mirror. These silicon based deformable mirrors can modulate spatial and temporal features of an optical wavefront, and have applications in imaging, beam-forming, and optical communication systems. New developments in DM design are discussed, and manufacturing approaches to microamachined DM and SLM production are presented, and designs that will permit scaling to millions of actuators are introduced.
This paper describes design and fabrication of a microelectromechanical metal spatial light modulator (SLM) integrated with complementary metal-oxide semiconductor (CMOS) electronics, for high-dynamic-range wavefront control. The metal SLM consists of a large array of piston-motion MEMS mirror segments (pixels) which can deflect up to 0.78 µm each. Both 32x32 and 150x150 arrays of the actuators (1024 and 22500 elements respectively) were fabricated onto the CMOS driver electronics and individual pixels were addressed. A new process has been developed to reduce the topography during the metal MEMS processing to fabricate mirror pixels with improved optical quality.
The design, manufacture, and testing of optical quality surface micromachined deformable mirrors (DMs) is described. With such mirrors, the shape of the reflective surface can be modified dynami-cally to compensate for optical aberrations and thereby improve image resolution in telescopes or microscopes. Over several years, we have developed microelectromechanical system (MEMS) processing technologies that allow production of optical quality of surface micromachined mirrors. These process steps have been integrated with a commercial foundry process to produce deformable mirrors of unprecedented quality. The devices employ 140 electrostatic actuators. Measurements of their performance detailed in this paper include 2µm of useful stroke, 3nm position repeatability, >90% reflectivity, and flatness better than 20nm RMS. A chemo-mechanical polishing process has been used to improve surface quality of the mirrors, and a gold coating process has been developed to improve the reflectivity without introducing a significant amount of stress in the mirror mem-brane. An ion bombardment technique has been developed to flatten mirrors. These silicon based deformable mirrors have the potential to modulate spatial and temporal features of an optical wave-front, and have applications in imaging, beam-forming, and optical communication systems. Design considerations and performance evaluation of recently fabricated DMs are presented.
The design, fabrication, and preliminary test results of a microelectromechanical, micromachined spatial light modulator (μSLM) with complementary metal-oxide semiconductor (CMOS) electronics, for control of optical phase is presented in this paper. An array of 32×32 piston-motion MEMS mirror segments make up the μSLM. Each mirror segment will be capable of altering the phase of reflected light by up to one wavelength for infrared illumination (? = 1.5 μm). The mirror segments are fabricated from metal in a low temperature process allowing for vertical integration of the μSLM with CMOS based, multi-bit, control electronics. The surface of the CMOS is planarized to facilitate μSLM-CMOS integration. The fabrication process and process development results, test results, including frequency response and electromechanical characterization of the (μSLM) actuators, will be presented.
The National Science Foundation Center for Adaptive Optics (CfAO) is coordinating a program for the development of spatial light modulators suitable for adaptive optics applications based on micro-optoelectromechanical systems (MOEMS) technology. This collaborative program is being conducted by researchers at several partner institutions including the Berkeley Sensor & Actuator Center, Boston Micromachines, Boston University, Lucent Technologies, the Jet Propulsion Laboratory, and Lawrence Livermore National Laboratory. The goal of this program is to produce MEMS spatial light modulators with several thousand actuators that can be used for high-resolution wavefront control applications that would benefit from low device cost, small system size, and low power requirements. The two primary applications targeted by the CfAO are astronomy and vision science. In this paper, we present an overview of the CfAO MEMS development plan along with details of the current program status.
A large-scale, high speed, high resolution, phase-only microelectromechanical system (MEMS) spatial light modulator (SLM) has been fabricated. Using polysilicon thin film technology, the micro mirror array offers significant improvement in SLM speed in comparison to alternative modulator technologies. Pixel opto-electromechanical characterization has been quantified experimentally on large scale arrays of micro mirrors and results are reported.
Recent progress on deformable mirror systems made at Boston University and Boston Micromachines Corporation is described. The mirror's optical, electrical, and mechanical performance characteristics are summarized, and the effects of air damping on performance are described. Two applications that have employed the μDM in laser communications and retinal imaging are introduced.
This paper presents a high-speed resolution phase-only microelectromechanical system (MEMS) spatial light modulator (SLM), integrated with driver electronics, using through- wafer vias and solder bump bonding. It employs a polysilicon thin film MEMS technology that is well suited to micromirror array fabrication and offers significant improvement in SLM speed in comparison to alternative modulator technologies. Vertical through-wafer interconnections offer scalability required to achieve 1M-pixel array size. The design, development, fabrication and characterization of a scalable driver integrated SLM is discussed. Pixel opto- electromechanical performance has been quantified experimentally on prototypes, and results are reported.
Design, microfabrication, and integration of a micromachined spatial light modulator ((mu) SLM) device are described. A large array of electrostatically actuated, piston-motion MEMS mirror segments make up the optical surface of the (mu) SLM. Each mirror segment is capable of altering the phase of reflected light by up to one wavelength for infrared illumination ((lambda) equals 1.5 micrometers ), with 4-bit resolution. The device is directly integrated with complementary metal- oxide semiconductor (CMOS) electronics, for control of spatial optical wavefront. Integration with electronics is achieved through direct fabrication of MEMS actuators and mirror structures on planarized foundry-type CMOS electronics. Technical approaches to two significant challenges associated with manufacturing the (mu) SLM is discussed: integration of the MEMS array with the electronic driver array and production of optical-quality mirror elements using a metal-polymer surface micromachining process.
Manufacturing of optical quality micromachined deformable mirrors for use in adaptive optic (AO) correction is described. Several non-standard manufacturing techniques have been developed to improve optical quality of surface micromachined mirrors. Two challenges to manufacturing optical quality micromachined mirrors are reducing surface roughness and increasing reflectivity. A chemo-mechanical polishing process has been used to improve surface quality of the mirrors, and a gold coating process has been developed to improve the reflectivity without introducing a significant amount of stress in the mirror membrane. Surface reflectivity and topography measurements of optically flat and smooth mirrors are presented. Based on these results, a new 1024 actuator mirror has been designed and is currently being fabricated. Design considerations and performance expectations for this mirror will be presented.
Deformable mirrors have been fabricated using microelectromechanical system (MEMS) technology. The mirrors have been integrated into an optical test bed capable of generating static and dynamic aberrations in the beam path. It was found that the DM could be used to improve optical system resolution in the presence of static aberrations. Strehl ratio was measured for the optical system under four test conditions. A Strehl ratio of 0.81 was obtained for the case in which an introduced aberration was compensated by the DM, compared to a Strehl ratio of 0.45 for case in which the aberration was uncompensated and the DM was removed from the optical path. A parallel stochastic gradient descent approach was used for control.
This paper describes design and development of a microelectromechanical, micromachined spatial light modulator ((mu) SLM) integrated with complementary metal- oxide semiconductor (CMOS) electronics, for control of optical phase in phase-only optical correlators. The (mu) SLM will consist of a large array of piston-motion MEMS mirror segments (pixels) each of which capable of altering the phase of reflected light by up to one wavelength for infrared (1.5 micrometers ) illumination. Results of a proof-of- concept study are presented along with an electromechanical model and details of the fabrication process for the (mu) SLM.
The design and development of a microelectromechanical, micromachined spatial light modulator ((mu) SLM) with complementary metal-oxide semimconductor (CMOS) electronics, for control of optical phase in phase-only optical correlators is presented in this paper. A large array of piston-motion MEMS mirror segments make up the (mu) SLM. Each mirror segment will be capable of altering the phase of reflected light by up to one wavelength for infrared illumination ((lambda) =1.5micrometers ). The mirror segments, or pixels, are fabricated from metal in a low temperature process allowing for vertical integration of the (mu) SLM with CMOS based, 8-bit, control electronics. Proof-of- concept results, a proposed fabrication process and, preliminary process development results are also presented.
The NSF Center for Adaptive Optics (CfAO) is coordinating a five to ten year program for the development of MEMS-based spatial light modulators suitable for adaptive optics applications. Participants in this multi-disciplinary program include several partner institutions and research collaborators. The goal of this program is to produce MEMS spatial light modulators with several thousand actuators that can be used for high-resolution wavefront control applications and would benefit from low device cost, small system size, and low power requirements. We present an overview of the CfAO MEMS development plan along with details of the current program status. Piston mirror array devices that satisfy minimum application requirements have been developed, and work is continuing to enhance the piston devices, add tip-tilt functionality, extend actuator stroke, create a large array addressing platform, and develop new coating processes.
A silicon micromachined deformable mirror ((mu) DM) has been developed by Boston University and Boston Micromachines Corporation (BMC). The (mu) DM employs a flexible silicon mirror supported by mechanical attachments to an array of electrostatic parallel plate actuators. The integrated system of mirror and actuators was fabricated by surface micromachining using polycrystalline silicon thin films. The mirror itself measures 3 mm X 3 mm X 3 micrometer, supported by a square array of 140 electrostatic parallel- electrode actuators through 140 attachment posts. Recently, this (mu) DM was characterized for its electro-mechanical and optical behavior and then integrated into two laboratory-scale adaptive optics systems as a wavefront correction device. Figures of merit for the system include stroke of 2 micrometer, resolution of 10 nm, and frequency bandwidth of 6.7 kHz. The device is compact, exhibits no hysteresis, and has good optical quality.