Optical MEMS

Optical microelectromechanical systems (MEMS), microoptoelectromechanical systems (MOEMS), or optical microsystems are devices or systems that interact with light through actuation or sensing at a micro- or millimeter scale. Optical MEMS have had enormous commercial success in projectors, displays, and fiberoptic communications. The best-known example is Texas Instruments’ digital micromirror devices (DMDs). The development of optical MEMS was impeded seriously by the Telecom Bubble in 2000. Fortunately, DMDs grew their market size even in that economy downturn. Meanwhile, in the last one and half decade, the optical MEMS market has been slowly but steadily recovering. During this time, the major technological change was the shift of thin-film polysilicon microstructures to single-crystal–silicon microsructures. Especially in the last few years, cloud data centers are demanding large-port optical cross connects (OXCs) and autonomous driving looks for miniature LiDAR, and virtual reality/augmented reality (VR/AR) demands tiny optical scanners. This is a new wave of opportunities for optical MEMS. Furthermore, several research institutes around the world have been developing MOEMS devices for extreme applications (very fine tailoring of light beam in terms of phase, intensity, or wavelength) and/or extreme environments (vacuum, cryogenic temperatures) for many years. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on (1) novel design, fabrication, control, and modeling of optical MEMS devices based on all kinds of actuation/sensing mechanisms; and (2) new developments of applying optical MEMS devices of any kind in consumer electronics, optical communications, industry, biology, medicine, agriculture, physics, astronomy, space, or defense

MEMS Devices for Circumferential-scanned Optical Coherence Tomography Bio-imaging

Ph.DDOCTOR OF PHILOSOPH

MEMS Varifocal Mirror for High-Power Laser Focusing

Today, lasers are used in many surgical procedures due to their ability of performing precise incisions, and ablations. With the development of fiber-coupled lasers, even minimally invasive procedures started making use of laser tools. However, existing fiber tools do not provide the same performance as traditional laser systems, often causing significantly more tissue carbonization. This can be attributed to the lack of optics in fiber tools, which requires the tip of the fiber to be placed in direct contact with the tissue, increasing the collateral damage of the laser. To avoid this issue, a compact focusing system should be integrated in the fiber tool. However, traditional optical systems based on moving lenses are too large and bulky for that. To solve this problem, this thesis proposes a focusing system based on MEMS deformable mirrors. Using microfabrication methods, we develop a novel MEMS varifocal mirror, designed for focusing high-power laser in a fiber laser system. The design of this mirror is based on state-of-the-art MEMS deformable mirrors, which have been proposed for microscopy applications, with significant adaptations for high-power lasers, including different actuation mechanisms and control strategies. We explore the use of hydraulic actuation to achieve large focal length range, while providing compatibility with high-power laser. The deflection of the mirror is controlled using a feed-forward model, in which parameters are obtained through characterization of the fabrication process. This allows controlling the mirror without a beam splitter or external sensors, which contributes to the miniaturization of the focusing system

Design of an Adaptive Lightweight LiDAR to Decouple Robot-Camera Geometry

A fundamental challenge in robot perception is the coupling of the sensor pose and robot pose. This has led to research in active vision where robot pose is changed to reorient the sensor to areas of interest for perception. Further, egomotion such as jitter, and external effects such as wind and others affect perception requiring additional effort in software such as image stabilization. This effect is particularly pronounced in micro-air vehicles and micro-robots who typically are lighter and subject to larger jitter but do not have the computational capability to perform stabilization in real-time. We present a novel microelectromechanical (MEMS) mirror LiDAR system to change the field of view of the LiDAR independent of the robot motion. Our design has the potential for use on small, low-power systems where the expensive components of the LiDAR can be placed external to the small robot. We show the utility of our approach in simulation and on prototype hardware mounted on a UAV. We believe that this LiDAR and its compact movable scanning design provide mechanisms to decouple robot and sensor geometry allowing us to simplify robot perception. We also demonstrate examples of motion compensation using IMU and external odometry feedback in hardware.Comment: This paper is published in IEEE Transactions on Robotic

MEMS devices for the control of trapped atomic particles

This thesis presents the design and characterisation of novel MEMS scanners, for use in systems involving trapped atomic particles. The scanners are manufactured using multiuser silicon-on-insulator MEMS fabrication processes and use resonant piezoelectric actuation based on aluminium nitride thin films to produce one dimensional scanning at high frequencies, with resonance tuning capabilities of up to 5 kHz. Frequencies of ~100kHz and higher are required to enable for example resonant addressing of trapped atomic particles. This work demonstrates how the 200 μm and 400 μm diameter scanners can produce optical deflection angles upwards of 2° at frequencies from 80 kHz to 400 kHz. It proposes an addressing scheme based on Lissajous scanning to steer laser pulses onto 2D grids at a scale compatible with experiments involving single trapped atoms. It also examines frequency tuning capabilities of the scanners using localized on-chip Joule heating and active cooling ; frequency tuning and synchronization are shown to be critical to the implementation of 2-dimensional scanning with multiple scanners. These features are then demonstrated in a prototype implementation using fluorescing samples as a mock target to evaluate the optical performance of the scanning system. Finally, the thesis describes a proof-of-concept for integration of the scanners in a trapped atoms experiment, in which rubidium atoms trapped inside a magneto-optical trap are selectively pumped into a fluorescing state using a beam steered by the MEMS scanners.This thesis presents the design and characterisation of novel MEMS scanners, for use in systems involving trapped atomic particles. The scanners are manufactured using multiuser silicon-on-insulator MEMS fabrication processes and use resonant piezoelectric actuation based on aluminium nitride thin films to produce one dimensional scanning at high frequencies, with resonance tuning capabilities of up to 5 kHz. Frequencies of ~100kHz and higher are required to enable for example resonant addressing of trapped atomic particles. This work demonstrates how the 200 μm and 400 μm diameter scanners can produce optical deflection angles upwards of 2° at frequencies from 80 kHz to 400 kHz. It proposes an addressing scheme based on Lissajous scanning to steer laser pulses onto 2D grids at a scale compatible with experiments involving single trapped atoms. It also examines frequency tuning capabilities of the scanners using localized on-chip Joule heating and active cooling ; frequency tuning and synchronization are shown to be critical to the implementation of 2-dimensional scanning with multiple scanners. These features are then demonstrated in a prototype implementation using fluorescing samples as a mock target to evaluate the optical performance of the scanning system. Finally, the thesis describes a proof-of-concept for integration of the scanners in a trapped atoms experiment, in which rubidium atoms trapped inside a magneto-optical trap are selectively pumped into a fluorescing state using a beam steered by the MEMS scanners

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators

MEMS Technology for Biomedical Imaging Applications

Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community

Contribution au micro-actionnement multi-stable piloté par radiations optiques

In this work, a bistable mechanism based on antagonistic pre-shaped double beams was proposed. Employing the proposed bistable mechanism, a quadristable micro-actuator was designed. ln order to validate the quadristability of the device, a meso-scaled prototype was fabricated from MDF by laser cutting. After the quadristability was experimentally confirmed, a quadristable micro-actuator was realized on SOl wafer using DRIE technique. Strokes for inner row and outer row were reduced to 300 µm and 200 µm respectively. For the actuation of the quadristable micro-actuator,laser heated SMA elements with deposited Si02 layer were used to realize the optical wireless actuation. With the help of a laser beam steering micro-mirror, both inner row and outer row were successfully actuated. ln order to further reduce the stroke, a bistable actuator with stroke reducing structure was designed and a prototype eut from MDF was tested. Bistability was validated and a stroke of 1µm was experimentally achieved. Based on this bistable module, a multistable nano-actuator, which contains four parallel coupled bistable modules,was designed and simulated. The simulated result have indicated that it was capable of outputs 16 discrete stable positions available from 0 nm to 150 nm with a step of 10 nm between two stable positions.Cette thèse traite le sujet du micro-actionnement multistable employant des radiations optiques pour atteindre les différentes positions offertes par le micro-actionneur. Dans le cadre des travaux réalisés, un mécanisme bistable reposant sur un principe de doubles poutres préformées situées en position antagoniste est proposé, et, sur cette brique élémentaire, un micro-actionneur quadristable a été conçu. Afin de valider le principe de fonctionnement de micro-actionneur, des procédés de fabrication Laser (sur le matériau « médium - MDF») puis DRIE (sur un wafer SOI de silicium) ont été utilisés. Sur le prototype en silicium, permettant une réduction des courses du rang interne et du rang externe du micro-actionneur, celles-ci ont été fixées à 300 µm et 200 µm respectivement. L’actionnement à distance de ce micro-actionneur a été prouvé en utilisant le chauffage laser d’un élément actif en Nitinol structuré par un dépôt de SiO2, ceci générant un effet « deux sens » de l’élément actif permettant d’annuler la charge sur les poutres du micro-actionneur une fois celui-ci déclenché puis en position stable. L’utilisation d’un banc expérimental incluant une membrane MEMS de balayage laser a permis de démontrer la quadristabilité du micro-actionneur sur 90 000 cycles. Afin de réduire davantage la course de ce micro-actionneur, des concepts de dispositifs de réduction de course ont été développés pour démontrer, à partir de prototypes fabriqué en MDF par usinage laser, la capacité à atteindre une course de 1 µm. Enfin, à la suite de ces travaux de réduction de course, un concept de nano-actionneur multistable a été proposé. Ce nano-actionneur est composé de quatre modules bistables liés et disposés en parallèle pour offrir 16 positions discrètes sur une course rectiligne. Les simulations de cet actionneur montrent la possibilité d’atteindre les 15 positions espacées de 10 nm sur une course de 150 nm

Design of a high-speed, meso-scale nanopositioners driven by electromagnetic actuators

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 218-230).The purpose of this thesis is to generate the design and fabrication knowledge that is required to engineer high-speed, six-axis, meso-scale nanopositioners that are driven by electromagnetic actuators. When compared to macro-scale nanopositioners, meso-scale nanopositioners enable a combination of greater bandwidth, improved thermal stability, portability, and capacity for massively parallel operation. Meso-scale nanopositioners are envisioned to impact emerging applications in data storage and nanomanufacturing, which will benefit from low-cost, portable, multi-axis nanopositioners that may position samples with nanometer-level precision at bandwidth of 100s of Hz and over a working envelope greater than 10x10x10 micrometers3 This thesis forms the foundation of design and fabrication knowledge required to engineer mesoscale systems to meet these needs.The design combines a planar silicon flexure bearing and unique moving-coil microactuators that employ millimeter-scale permanent magnets and stacked, planar-spiral micro-coils. The new moving-coil actuator outperforms previous coil designs as it enables orthogonal and linear force capability in two axes while minimizing parasitic forces. The system performance was modeled in the structural, thermal, electrical, and magnetic domains with analytical and finite-element techniques. A new method was created to model the three-dimensional permanent magnet fields of finite magnet arrays. The models were used to optimize the actuator coil and flexure geometry in order to achieve the desired motions, stiffness, and operating temperature, and to reduce thermal error motions.A new microfabrication process and design-for-manufacturing rules were generated to integrate multilayer actuator coils and silicon flexure bearings. The process combines electroplating for the copper coils, a silicon dioxide interlayer dielectric, and deep reactive-ion etching for the silicon flexures and alignment features.(cont.) Microfabrication experiments were used to formulate coil geometry design rules that minimized the delamination and cracking of the materials that comprise the coil structure. Experiments were also used to measure the previously-unreported breakdown strength of the unannealed, PECVD silicon dioxide interlayer dielectric. The results of this research were used to design and fabricate a meso-scale nanopositioner system. The nanopositioner was measured to have a range of motion of 10 micrometers in the lateral directions, a range of 2 micrometers in the out-of-plane direction, an angular range of 0.5 degrees, and a first mode resonant frequency at 900 Hz. Open-loop calibration has been shown to minimize parasitic in-plane motion to less than 100 nm over the range of motion.by Dariusz S. Golda.Ph.D

Lateral bending liquid crystal elastomer beams for microactuators and microgrippers

With the rapid development of microsystems in the last few decades, there is a requirement for high precision tools for micromanipulation and transportation of micro-objects, such as microgrippers, for applications in microassembly, microrobotics, life sciences and biomedicine. Polymer based microgrippers and microrobots executing various tasks have been of significant interest as an alternative to the traditional silicon and metal based counterparts due to the advantages of low cost fabrication, low actuation temperature, biocompatibility, and sensitivity to various stimuli. The exceptional actuation properties of liquid crystal elastomers (LCE) have made these materials highly attractive for various emerging applications in the last two decades. Large programmable deformations and the benefits offered by the elastic, thermal and optical properties of LCEs are suitable for implementing stimuli-responsive microgrippers as well as various biomimetic motion in soft robots. In this thesis, a method and the associated processes for fabrication and molecular alignment in LCE were developed, which enabled new functionality and improved performance of the LCE based microactuators and microgrippers, providing controlled response by thermal and remote photothermal actuation, and allowing easy integration of the LCE end-effectors into robotic systems for automated operation. Lateral bending actuation has been demonstrated in LCE microbeams of 900 µm of length and 40 µm of thickness, owing to the new monolithic micromolding technique using vertical patterned walls for alignment. The effects of parameters such as the beam width, the size of the microgrooves, and the surface treatment method on the behavior of the microactuators were studied; the internal alignment pattern of liquid crystals in the structure was investigated by different microscopy methods. An efficient method for finite element modeling of the bending LCE actuators was developed and experimentally verified, based on the gradient of equivalent thermal expansion in the multi-layer structure, which was able to predict the bending behavior of the actuators in a large range of thicknesses as well as rolling behavior of the actuators of tapered thickness. The novel LCE microgripper with in-plane operation showed efficient thermal and photothermal actuation, achieving the gripping stroke of 64 µm under the light intensity of 239 mW/cm2 for the gripper length of 900 µm, which is more efficient than the typical SU-8 polymer based microgrippers of the same dimensions. The LCE gripper was successfully demonstrated for the application in manipulation of the objects of tens to hundreds of micrometers in size. Therefore, the novel LCE microgripper bridges the gap in the LCE-based gripper technologies for typical object size in applications for systems microassembly, biological and cell micromanipulation. The lateral bending functionality enabled by the proposed method expands design opportunities for thermal and photothermal LCE microactuators, providing an effective route toward realization of new modes of gripping, locomotion, and cargo transportation in soft microrobotics and micromanipulation