Steven Cornelissen

MEMS Deformable Mirrors for Astronomical Adaptive Optics

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.

4096-element continuous face-sheet MEMS deformable mirror for high-contrast imaging

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 5 kHz. The packaging and high-speed drive electronics for this device, capable of frame rates of 22 kHz, are also presented.

A 4096 Element Continuous Facesheet MEMS Deformable Mirror for High-Contrast Imaging

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.

Megapixel wavefront correctors

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.

The use of a high-order MEMS deformable mirror in the Gemini Planet Imager

We briefly review the development history of the Gemini Planet Imagers 4K Boston Micromachines MEMS deformable mirror. We discuss essential calibration steps and algorithms to control the MEMS with nanometer precision, including voltage-phase calibration and influence function characterization. We discuss the integration of the MEMS into GPIs Adaptive Optics system at Lawrence Livermore and present experimental results of 1.5 kHz closed-loop control. We detail mitigation strategies in the coronagraph to reduce the impact of abnormal actuators on final image contrast.

MEMS spatial light modulators with integrated electronics

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.

Secure optical communication system utilizing deformable MEMS mirrors

An optical communication system suitable for voice, data retrieval from remote sensors and identification is described. The system design allows operation at ranges of several hundred meters. The heart of the system is a modulated MEMS mirror that is electrostatically actuated and changes between a flat reflective state and a corrugated diffractive state. A process for mass producing these mirrors at low cost was developed and is described. The mirror was incorporated as a facet in a hollow retro-reflector, allowing temporal modulation of an interrogating beam and the return of the modulated beam to the interrogator. This system thus consists of a low power, small and light communication node with large (about 60°) angular extent. The systems range and pointing are determined by the interrogator /detector/demodulator (Transceiver) unit. The transceiver is comprised of an optical channel to establish line of sight communication, an interrogating laser at 1550nm, an avalanche photo diode to detect the return signal and electronics to drive the laser and demodulate the detected signal and convert it to an audio signal. A functional prototype system was built using a modified compact optical sight as the transceiver. Voice communication in free space was demonstrated. The design and test of major components and the complete system are discussed.

Advances in MEMS deformable mirror technology for laser beam shaping

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.

Design and fabrication of reflective spatial light modulator for high-dynamic-range wavefront control

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.

MEMS Deformable Mirror Actuators with Enhanced Reliability

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.