Optical Microelectromechanical Systems Research Articles

Diffraction based optical microelectromechanical systems microphone and its application to the measurement of sound intensity.

Diffraction based optical MEMS microphones and force feedback capabilities of these microphones are presented earlier [Bicen et al., J. Acoust. Soc. Am. 123, 3230 (2008)]. Further investigation is done in order to see the capabilities of these optical microphones in measuring the sound intensity. The biomimetic diaphragms of these microphones are designed for responding to pressure gradient which can be used for extracting the particle velocity required to measure the sound intensity. In order to show the velocity measuring capability of these microphones, an impedance tube method is used because the velocity and pressure at each point in the impedance tube can be found accurately. The comparison of the measured velocities and sound intensities with the optical microphone and commercially available sound intensity probes is presented. Model results are discussed in order to show the effect of the different mode shapes on the accuracy of the pressure gradient measurements. Optimization of these biomimetic diaphragms will result in the measurement of the sound intensity in a larger bandwidth without using any spacers and additional microphone adapters like in commercial sound intensity probes. [Work supported by National Institutes of Health (NIH) and the Catalyst Foundation.]

Micro‐Optical Blood Flow Sensor Based on System in Package (SiP) Technology that Fuses Optical MEMS and Intergrated Circuit to Detect Avian Influenza

As a fusion of micro‐electro‐mechanical systems (MEMS) and system in package (SiP) technologies, a very small wireless blood‐flow sensor to be attached to birds was fabricated. Pulse frequencies are output as Fourier‐transformed signals from a sensor that detects blood flow. Although blood flow fluctuates with the bird's movement, the minimum (resting) value detected is stable enough for comparison against a normal index value for healthy birds. The combination of blood flow (monitored remotely by this miniature blood‐flow sensor) and body temperature is expected to be effective for early detection of infection.

The effect of squeeze film constriction on bandwidth improvement in interferometric accelerometers

This paper studies the effects of a constricted squeeze film on the performance of an optical microelectromechanical system accelerometer. Squeeze films are shown to extend the sensor frequency range (bandwidth) in accelerometers without decreasing the mechanical sensitivity by retarding the resonate response. By restricting the venting of a squeeze film, this preferential behavior is observed at lower frequencies than is expected for ideally vented accelerometers. Due to this effect, constricted squeeze films may be used to improve the bandwidth performance of devices of lower natural frequencies and higher inertial sensitivities. A model, extended from the existing squeeze film theory, is developed for the squeeze film formed between circular plates with generalized mixed boundary pressure conditions to describe the boundary flow resistance. These effects are experimentally observed in a parallel plate Fabry–Pérot interferometric accelerometer through frequency response characterization at mechanical resonance under pressure variation. The analytical results for the constricted squeeze film are used to predict the performance gains due to the frequency-dependent squeeze film parameters. These results are experimentally confirmed by demonstrating improved bandwidth performance due to the constricted squeeze film.

Development and evolution of MOEMS technology in variable optical attenuators

Optical microelectromechanical systems (MEMS) technology or micro-optoelectromechanical systems (MOEMS) technology has proven to be an enabling technology for many components of optical networking applications. Due to their widespread applications, MEMS variable optical attenuators (VOA) have been one of the most attractive MEMS-based key devices in the optical communication market. Micromachined shutters and refractive mirrors assembled with 2D and 3D optics are the subjects of tremendous research activity. We conduct a comprehensive literature survey with respect to technologies such as fabrication processes, optical designs, actuators, and systems. Apparently, MEMS VOA technology is still evolving into a mature technology step by step. MEMS VOA technology is not only the cornerstone to support future optical communication technology, but also the best example for understanding the evolution of MOEMS technology and the commercialization of MOEMS devices.

Selected papers from Optical MEMS and Nanophotonics 2007

This special issue on optical MEMS and nanophotonics features papers presented at the International Optical MEMS and Nanophotonics Conference held in Hualien, Taiwan, 12?16 August 2007, chaired by J Andrew Yeh. Minoru Sasaki and Chennupati Jagadish served as Program Co-Chairs of optical MEMS and nanophotonics, respectively. The conference featured a broad range of technologies in both topical areas with participation from academia, government laboratories and industry. The conference covered the latest technical developments in the fields of optical micro-electro-mechanical systems (MEMS) and integrated micro-optics. Integration and miniaturization of photonic and optical MEMS components and systems towards micro- and nanoscale for various applications were discussed. The conference also featured nanophotonics which is expected to provide high-speed, high-bandwidth and compact photonic devices. The interaction of light with nanoscale structures including generation, manipulation and detection was discussed at the conference and covered photonic crystals, quantum dots, nanowires and plasmonics. Integrated systems combining nanostructures and optical MEMS were discussed. We would like to thank Hans Zappe for suggesting the special issue and providing timely advice on various related matters and also to Julia Dickinson and Claire Bedrock for their professionalism and help. Carol Chan of the National Tsing Hua University is gratefully acknowledged for her help with the conference. Administration by staff from the Instrument Technology Research Center is highly appreciated. The assistance of the students of the National Dong Hua University and the National Tsing Hua University made the conference most enjoyable. The next conference will be held in Freiburg, Germany, 11?14 August 2008 and will be chaired by Hans Zappe.

A Novel Integrated Multistage 2-D MEMS Optical Switch With Spanke–Benes Architecture

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Due to the emergence of high-capacity wavelength- division multiplexing transmission systems, new optical cross- connect (OXC) architectures that make a large number of fiber/wavelength counts to switch the signal in the optical domain are needed. Optical microelectromechanical system (MEMS) switches are regarded as the most promising optical switch technology to achieve such functionalities. In this paper, we propose a novel integrated multistage two-dimensional (2-D) MEMS optical switch design with Spanke-Benes architecture and compare it with the conventional crossbar architecture, the L-switching architecture, and Shuffle-Benes architecture. Our proposed architecture is very suitable for building large-port-count 2-D MEMS switches and achieves much better performance in terms of beam divergence loss, longest optical path, mirror radius, substrate size, port-to-port repeatability, and power consumption than the other three architectures. Furthermore, compared with the 2-D conventional crossbar switch commercially available now, the proposed architecture can save 50% mirrors, shorten 87.5% longest optical path, minify 65% mirror radius, and shrink 90% substrate size. </para>

Near-infrared spectroscopy of newly developed PEGylated lipids

Near-infrared (NIR) spectroscopy has been used to analyze a suite of synthesized PEGylated lipids (1–3) trademarked as QuSomes™. The three amphiphiles used in this study, differ in their hydrophobic chain length and contain various units of polyethylene glycol (PEG) head groups. Whilst the spectra of QuSomes™ show a common pattern, differences in the spectra are observed which enable the lipids to be distinguished. NIR absorption spectra of these new artificial lipids have been recorded in the spectral range of 4800–9000 cm −1 (∼2100–1100 nm) by using a new miniaturized spectrometer based on micro-optical-electro-mechanical systems (MOEMS) technology. Three NIR spectral regions are identified, (a) the high wavenumber region between 6500 and 9000 cm −1 attributed to the first overtone of the hydroxyl stretching and second overtone of the C–H stretching mode; (b) the 5350–5900 cm −1 region attributed to first overtone of the C–H stretching mode; and (c) the 4800–5300 cm −1 region attributed to the combination O–H stretching and second overtone of the C O stretching mode. For each of these regions, the lipids show distinctive spectra which allow their identification and characterization. NIR spectroscopy is a less used technique which does have great potential for the study of lipids, particularly to examine the behaviour of nanovesicles (liposomes) formed from lipids in aqueous suspensions. The study of such lipids is important since they are used as membrane models and prominent candidate for substance and drug delivery systems.

Principles of free-space optical microelectromechanical systems

Optical microelectromechanical systems (MEMS) combine miniature optical components with precision fixtures, elastic suspensions, and microactuators, and allow complex functionality at low cost. However, the effect of the bounded nature of the beams propagating through the system on design is profound. The current paper reviews the fundamental consequences. Using a Gaussian beam formulation, models of guided modes in gradient index media, bounded beams and imaging components are constructed. Propagation algorithms are described. The alignment tolerances for common component trains such as fibre-to-fibre and beam-to-fibre connections are derived, limits on the curvature of reflecting surfaces are established, the scaling laws of free-space optical MEMS are presented and the effect of beam size on filter performance is clarified. Examples such as variable optical attenuators, optical cross-connect switches, filters and tunable lasers are discussed.

Polyimide Spacers for Flip-Chip Optical MEMS

Multichip integration provides an attractive means to overcome space limitations for large-port-count optical microelectromechanical systems (MEMS) routing systems by allowing actuation and control wiring to be fabricated separately on one chip and then attached beneath a second chip that is populated with a densely packed mirror array. In such systems, vertical as well as horizontal chip alignment is critical when a large but very uniform separation must be maintained across the extent of the array. A technique for creating a structure that simultaneously provides accurate large-gap spacing and acts as a chip-bonding agent is presented here. Specialized processing of an 80- mum thick photoimaged polyimide structure for bonding mirror and electrode chips for a 1296-mirror array is described, along with measurements of height uniformity within 1% and structure characterization demonstrating suitability for production and long-term stability. The process parameters and simplicity of the technique make it suitable for a wide range of applications where MEMS must be integrated with electronic control circuitry. [2006-0042].

Optical microelectromechanical systems: designing for reliability

The interdisciplinary nature of optical microelectromechanical systems (MEMS) makes its design a highly involved process. To design a device that will meet the required specifications over its entire lifetime, reliability issues must be included in the design process. This work develops a method that can be used to create a step-by-step design process involving reliability issues at every stage. The process begins by listing out the constants and constraints of the design. Taking all such constraints into account, an optical design process is outlined. The effect of individual errors is studied on a key parameter like insertion loss. This gives the designer information about which parameters the design is more sensitive to, and will help in deciding the manufacturing tolerances required in the different stages. Using all of these data, an "ideal design" is developed. A Monte Carlo analysis is carried out on that design to show the effect of errors occurring simultaneously. The work concludes with a flow chart of a suggested design process to be used when designing optical MEMS devices.

Command-Shaping Techniques for Electrostatic MEMS Actuation: Analysis and Simulation

Precision positioning of microelectromechanical systems (MEMS) structures using electrostatic actuation has been widely used for optical and radio-frequency MEMS. How to achieve fast switching without exciting excessive residual vibration or structural impact is an important issue for these applications. This paper presents the analysis and simulation of applying command-shaping techniques for controlling MEMS electrostatic actuation. According to the nature of application fields, electrostatic actuators are classified into three categories: 1) lateral linear actuation; 2) vertical nonlinear actuation; and 3) pull-in actuation. Their corresponding linear or nonlinear command-shaping schemes are developed and presented. Both lumped element and continuous models of typical MEMS electrostatic actuated structures are simulated using Simulink and the finite-element method, and results indicate that the shaped command would yield a much superior response than that by the unshaped commands. Essential sensitivity studies are also conducted to examine the robustness of these shaping schemes, and results shows that within a certain level of parameter variation, these shapers are robust enough to retain the performance.

Optical True Time-Delay for Two-Dimensional $X$-Band Phased Array Antennas

An optical true time-delay (TTD) scheme for two-dimensional (2-D) X-band phased array antennas (PAAs) has been proposed. It is composed of a multiwavelength optical source and a delay line matrix consisting of 2times2 optical microelectromechanical system (MEMS) switches with fiber-optic delay lines connected between cross ports. A 2-bit times 4-bit optical TTD for 10-GHz 2-D PAAs has been implemented by cascading a wavelength-dependent TTD (WD-TTD) with a unit time delay of 12 ps in the x-direction and a wavelength-independent TTD (WI-TTD) with that of 6 ps in the y-direction. The time delay error for WD-TTD was measured to be less than 2.8 ps, mainly due to jitter incurred from gain-switching. On the other hand, the error for WI-TTD was less than 0.8 ps, which is within the equipment resolution. Insertion loss of both delay line matrices was less than 1 dB due to the column-wise control of the MEMS switches. This prevents the feed current applied to each antenna element from fluctuating at any radiation angles so that antenna gain and sidelobe level do not deteriorate in this scheme

Smart value-added fiber-optic modules using spatially multiplexed processing

Intelligent fiber-optic value-added modules (VAMs) are proposed using what we believe to be a novel spatially multiplexed processing technique implemented with both reconfigurable and nonreconfigurable predesigned pixels per impinging beam that enables desired optical power split states needed for realizing a two state reconfigurable VAM. The preferred design uses broadband micromirrors such as ones fabricated via optical microelectromechanical systems technology. The basic VAM design uses two broadband micromirror pixels, where each pixel has its specific location and area and only one of these pixels is electrically driven to adjust its small tilt angle. The areas of the pixels are chosen to obtain the desired tap power. A proof-of-concept VAM with 100% digital repeatability is demonstrated using a Texas Instruments Digital Micromirror Device (DMD) where several micromirrors per beam are used to produce the dual-pixel effect. Example tap ratios experimentally implemented at 1550 nm include 10:90, 20:80, 66.66:33.33, 50:50, 30:70, and 25:75. DMD multipixel diffraction limits output port optical losses to 3.2 and 3.6 dB. The proposed VAM can have an impact in both digital electronic and analog RF optically implemented systems.

Devices, structures, and processes for optical MEMS

AbstractNew processes and devices in the area of optical microelectromechanical systems (MEMS) as researched in the Berkeley Sensor &amp; Actuator Center (BASC) are described. A technique and fabrication procedure is presented to produce high‐quality microlenses at selected locations in a micro‐optical system. Polarization beam splitters are produced by another process, and their performance is measured and described. A new, much simplified process to fabricate vertically offset comb actuating structures is applied in the design of high‐performance scanners, which are in turn used to control a laser ablation system. Very favorable performance comparisons are demonstrated between the researched system and a conventional commercial laser ablation system. A second system demonstration is a prototype Shack–Hartmann (SH) sensor, in which microlenses are mounted in carriages that can be individually addressed using the selectivity of their mechanically resonant mountings. This design is shown to increase markedly the dynamic range in wave aberration to which the SH sensor can be applied. A final application of optical MEMS design is to a reduced‐size, enhanced‐performance, phase shifting interferometer. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

FIBを用いたカーボン型の作製及び&lt;br&gt;ガラス材料のマイクロ・ナノ成形

Micro/nano imprinting or hot embossing is of interest in the industrial production of microdevices. In fluidic MEMS (micro electro mechanical systems) applications, polymer materials have been employed, because of their low cost in the fabrication of economical products. However glass is much more suitable for higher temperature applications or strong chemical environments. In optical MEMS as well, glass is a good candidate materials because of their better optical properties. Si or Ni molds, usually employed for polymer forming, can not be used for glass forming because of their poor heat resistance and the difficulty of removal arising from cohesion between the mold and the glass. Glassy carbon (GC) is thus a suitable material for high-temperature embossing. In this study, FIB (focused ion beam) machining was employed for micro/nano 3D-structuring of GC materials, the machining characteristics are summarized as follows. 1) Machining depth is proportional to machining time, 2) nanomachining of 0.3μm resolution is possible, 3) smooth surface with maximum roughness of Ra=30nm after is formed 20μm deep machining, 4) implanted Ga ions precipitate up on 350°C annealing, but disappear after annealing in vacuum at elevated temperatures. Finally a Pyrex-glass embossed structure is successfully fabricated by hot embossing with a good fidelity of 10x10x7μm in size and with a 0.3 μm line and space pattern and 0.4 μm depth.

Fabrication of Microchannel with Thin Cover Layer for an Optical Waveguide MEMS Switch Based on Microfluidics

SUMMARY We propose and demonstrate a new fabrication process of a microchannel using the Damascene process. This process aims to integrate photonic circuits with microchannels fabricated in a glass film. The microchannel is fabricated by the removal of the sacrificial layer after a sacrificial layer is formed by the Damascene process and the cover is formed by sputter deposition. A thin cover layer can be formed by the sacrificial method, because the cover layer is supported by the sacrificial layer during film formation. The cover layer is hermetically sealed, since it is formed by radio frequency (RF) sputtering deposition. The thickness is 1 µ ma nd the width ranges from 3.5 to 8 µm. Using the proposed microchannel fabrication method, we prepared a microelectromechanical system (MEMS) optical switch using microfluidics, and we confirmed its functional operation. This optical switch actuates a minute droplet of liquid injected into the microchannel using Maxwell’s stresses. Light propagates straight through the waveguide so that the light passes through the microchannel when the droplet is in the microchannel, but the light rays are completely reflected into a crossed waveguide when the droplet is not in the microchannel. Since this fabrication method uses techniques common to those in the formation

Suppression of Stiction Force by All-Vapor Processes using HF, Ozone, and HMDS for MEMS Devices

We propose a surface treatment technique to effectively avoid both process stiction and in-use stiction of silicon MEMS (microelectromechanical system) devices by using all-vapor processes: vapor HF (hydrofluoric) acid for sacrificial release, UV ozone for oxidation, and vapor HMDS (hexamethyldisilazane) for SAM (self-assembled monolayer) coating of small surface free energy. Adhesion force at every stage of the surface treatment was studied by using the force-curve of the AFM (atomic force microscope) measurement. HMDS-SAM coated silicon surfaces were found to have small adhesive strength of one fifth of that between the oxidized silicon surfaces. The effectiveness of the surface treatment was also experimentally validated by applying to an electrostatic optical MEMS scanner, which was practically used as a fiber-optic component.

A Scalable $1\times N$ Optical MEMS Switch Architecture Utilizing a Microassembled Rotating Micromirror

We present a new architecture for a digitally operated 1timesN optical microelectromechanical systems (MEMS) switch supporting a large number of output ports. The switch is based on a novel microassembled rotating micromirror mounted on the top of an optimized micromotor using a rotor-pole-shaping technique. The rotating micromirror consists of a novel electrostatic rotary motor, onto which a 3-D micromirror structure is assembled using a robotic-based microassembly process. The rotating micromirror in the switch can digitally rotate with 480 steps per full revolution allowing for excellent and complete repeatability of the switch. A uniform coupling loss of 1.04 dB across all the output fibers is achieved with a maximum switching time of 24 ms at 70 V signal excitation

MEMS R&amp;D Trends

Micro-Electromechanical Systems (MEMS) has been regarded as one of the most promising technologies for the 21st Century. Recently, some highlight areas attract great attention including Inertial MEMS, Optic MEMS, RF MEMS, BioMEMS, Power MEMS, and NEMS. The state of arts on MEMS research in China is briefly introduced and research activities in Northwestern Polytechnical University such as MEMS CAD tool, inertial MEMS devices, flexible substrate for MEMS integration, micro mirror, micro battery and three dimension measurement are demonstrated.

Optical MEMS for Lightwave Communication

The intensive investment in optical microelectromechanical systems (MEMS) in the last decade has led to many successful components that satisfy the requirements of lightwave communication networks. In this paper, we review the current state of the art of MEMS devices and subsystems for lightwave communication applications. Depending on the design, these components can either be broadband (wavelength independent) or wavelength selective. Broadband devices include optical switches, crossconnects, optical attenuators, and data modulators, while wavelength-selective components encompass wavelength add/drop multiplexers, wavelength-selective switches and crossconnects, spectral equalizers, dispersion compensators, spectrometers, and tunable lasers. Integration of MEMS and planar lightwave circuits, microresonators, and photonic crystals could lead to further reduction in size and cost