We present a new micro optical devices, dynamic focusing lens (DFL) using a multi-layered piezoelectric bimorph micro actuator. DFL is structured to directly deform the lens shape as a crystalline lens of the human eye. The deformable lens is comprised of two thin glass diaphragms with a transparent working fluid sealed between them. The curvature of the lens shape is changed according to the applied voltage of the actuator. DFL shows quick response up to 150 Hz for focal plane shift because the mass movement can be minimized compared with the conventional focusing method of moving a lens position. We also propose digital all-in-focus microscope system as an application of DFL. This system realizes real-time observation for micro parts assembling with a deep depth of field, as well as three-dimensional shape measurement using only one image sensor. In this paper, a newly developed real-time algorithm called one pixel method for generating clear image having a deep depth of field is described. This method is able to process one original picture (640 x 480 pixels per frame) in approximately 1.0ms. Results of three-dimensional shape measurement in high accuracy using the contrast of brightness method are also discussed.
This paper describes some aspects of micro optical devices under the Japanese national micromachine project. The national R&D project, Industrial Science and Technology Frontier Program Micromachine Technology, was inaugurated in 1991 as a ten-year project, and aims to establish a technological paradigm of micromachine throughout the multidisciplinary R&D. The final goal of our R&D is to establish following three practical applications: 1) advanced maintenance system for power plant, 2) microfactory and 3) intraluminal diagnostic and therapeutic system. For these systems, many functions such as visual inspections, contact pressure detection, wireless energy supplying and so on are required. We have developed novel micro optical devices such as 1) visual inspection devices; micro optical scanning sensor, micro stereoscope and micro camera, 2) optical pressure detection devices, 3) micro photon energy transmission device and 4) micro laser catheter, micro laser welding device and so on. We describe some topics of the micro optical devices as an outline of developed devices.
We describe the fabrication and testing of deformable membrane mirrors over silicon backplanes using our in-house CMOS processing facilities. The fabrication of dense arrays of electrostatic actuators on the backplane potentially allows fine control of the membrane surface shape than can be produced when using a printed circuit board as the backplane. We presents a range of techniques for fabrication the membrane mirrors in various materials and mating the structure to a silicon backplane. We characterise membrane deflection with electric field for silicon nitride and polymer membranes over a passive silicon backplane consisting of 37 directly-addressed electrode pads configured in a hexagonal array.
In this paper, we present the feasibility of wavelength filtering by a hybrid liquid crystal Solc/Fabry-Perot filter device. The influence of the structure opto-geometric defects, such as the variation of the thickness, on the spectral response of the filter have been reported. Frequency and temporal characteristics are presented and discussed.
Imaging the transverse vibrations of a resonating fibre cantilever is shown to be an effective method for generating 1D and 2D laser line scans. The resonant bending modes were excited by mounting a short length of 0.633(mu) m single mode optical fibre on to a commercially available piezo-electric transducer. For an applied sinusoidal driving voltage of 20V pk-pk, the maximum displacement at the free end of an 11mm long fibre cantilever exceeded +/- 1.0mm at resonance. The motion at the free end of the fibre was imagined and magnified using a 2mm diameter graded index lens and the resulting flying spot line scan was found to subtend a maximum arc of +/- 10 degree(s). Two distinct signal detection schemes were implemented and evaluated using standard bar code targets printed on plain paper. 2D Lissajous scans were demonstrated by exciting the orthogonal transverse bending modes of optical fibres with non-circular cross sectional areas. Both D-shaped fibres and circular fibres modified by reactive ion etching were investigated. The principles underlying the design of this Fibre Optic Resonant Scanner (FORS) are directly applicable to the design of an integrated optoelectronic micro-electro-mechanical scanning device.
We describe a new configuration for an optoelectronic router integrated in a silicon-on-silicon waveguide structure. The device is based on the mode-mixing principle together with the injection-induced phase shift. The structure is composed by a single mode input optical channel waveguide, a two-mode active region and an output Y branch to separate the two output channels. The active region is designed to allow a (pi) shift between the two modes that it supports, by means of a Bipolar Mode Field Effect Transistor, which injects and controls the free carrier plasma inside the active region. By doing so it is possible to steer light from one output channel to the other, when switching from the OFF state to the ON state. The numerical device simulator MEDICI has been used for evaluation of the electrical performances of the device, while different numerical analyses have been exploited to understand its optical behavior. These simulations show optical losses of about 3dB/cm, an overall crosstalk of -10.5 dB and a maximum switching frequency of about 200 MHz.
Opto-MEMS refers to micro devices that either manipulate light or use it for sensing. Two examples of manipulating Opto-MEMS devices are the WDM and optical switch: The WDM splits information contained in wide band of frequencies into narrow bands for example by using tunable Fabry-Perot interferometer. The micromachined optical switch redirected such light to different optical fibers for example by using tilting micro=mirrors. Applications of optical sensor, on the other hand, can be found for wide range of applications from displacement sensors to chemical sensors. These sensitive sensors are based on the interaction between some physical phenomena (i.e., acceleration, chemical reaction, etc.) And the optical properties of the sensor and can be used to sense extremely minute effects. In some cases MEMS and particular Opto-MEMS do not follow the VLSI paradigm of high yield, repeatedly and mass production, even thought they relay on very similar technologies. This contradiction raises questions as to the commercial value of MEMS and Opto-MEMS. This talk will view the bottlenecks of MEMS with emphasis on Opto-MEMS and will discuss current research aiming to increase the compatibility of Opto- MEMS with conventional VLSI. In addition, examples of optical displacement sensors, and optical switches will be presented.
An optical pressure sensor for measuring hydraulic pressure in an aeronautical application is described. It is based on interferometry with low-coherence light coupled with single mode fibre. The design uses an anisotropically etched silicon diaphragm, electrostatically bonded to a borosilicate glass insert, mounted in a titanium body.
Spatially resolved, non-contact, displacement measurements are reported from the membrane surface of a piezoelectric-driven micropump. The measurement system uses a fibre optic interferometric technique which incorporates an air path to the pump in the signal arm, allowing measurements to be made remotely. The interferometer operates at 1523nm, has a bandwidth of 200Khz, a focussed spot size of 22(mu) m and a noise equivalent displacement of 0.36nm. Membrane displacement profiles while pumping air and water have been obtained using custom designed automated fringe counting and interpolation software to interpret the digitised fringe patterns from the interferometer. Measurements show significant differences in membrane velocity, displacement and settling time between the two different pumping media. Transient underdamped vibration of the membrane surface was also detected in the rapid excursion and recursion phases of the pump cycle while pumping air. Analysis of the vibration transients allowed the resonant frequency and damping ratio of the system to be calculated. In addition, the amplitude of the membrane displacement was demonstrated to be dependent on the pumping frequency when pumping air. Analysis of the driving voltage and displacement profiles indicated that this frequency dependent relationship was primarily due to two effects: insufficient settling time between pump cycles and capacitive loading of the driving voltage at high pumping frequencies.
In the paper the problems connected with analysis of mechanical properties of silicon microelements being basic part of MEMS are discussed. The quality of these microproducts is strongly depended on the material properties, mechanical design and on technology process. The best-suited methods for their testing are optical full-field measuring methods. In this paper two types of interferometers specially suited for microelements testing are presented: The first type, based on the concept of waveguide grating interferometer for in-plane displacement measurement, is designed for small size field of view (0.18 x 0.12 mm2). It is integrated with a standard optical microscope and it seems to be an excellent tool for local material studies and strain analysis of microcomponents. It includes also miniature Twyman-Green interferometer, which allows measuring out-of- plane displacements. The waveguide interferometer presented requires the specimen grating integrated with element under test. The second type, digital holographic interferometer for shape deformation measurement, is used for testing of elements with rough surface. It overcomes several drawbacks of conventional holography by storing the hologram directly in the computer using a CCD matrix as optical sensor. The applications of these instruments are shown on examples of Young's modulus determination in microbeams, 3-D displacements determination in laser diode array during its technological process and shape deformation analysis of pressure sensor micromembrane.
High precision and passive alignment of opto devices is of great important in order to reduce assembling costs in hybrid micro systems. Silicon micromachining is suitable in this aspect since it enables the fabrication of high precision structures. This paper will present both generic results conserning high precision silicon micromachining as well as applications in form of fibre alignment structures and chip mounting with interconnects on a silicon substrate. Firstly, ways of producing 45 degree(s) slanted walls in silicon for light reflection are presented. Secondly, flexible clamping structures for holding opto fibres into v- grooves are discussed, both bulk and surface micromachined. These holding structures facilitate the mounting of optical fibres. Finally, a technique for chip mounting and interconnects on a silicon substrate is presented where chips are placed in etched pits and photo patterned BCB is used as dielectrica.
Ferroelectric materials such as LiNbO3 and LiTaO3 offer many potential advantages over silicon for MEMS structures and self-actuating miniature devices. These materials possess numerous useful intrinsic properties such as piezoelectricity, pyroelectric and electro-optic coefficients, enabling the construction of micro-scale cantilevers, membranes, tips and switches. So far however, reliable and accurate methods for machining and microstructuring LiNbO3 single crystals have been lacking. We have recently been exploring several such methods, which are sensitive to ferroelectric domain orientation. A sample that has been domain-engineered shows a large difference in etch characteristics: the +z face does not etch at all, whereas the -z face etches normally. Microstructured devices can be fabricated therefore, via spatially selective domain poling followed by etching. The extreme sensitivity of the etch process to domain orientation has enabled us to fabricate ridge waveguides for electro-optic modulator applications, alignment grooves for efficient fibre pig-tailing to LiNbO3 modulators, and micro-cantilevers using a novel technique of contact bonding of dissimilar ferroelectric hosts.
Realisation of low-cost and reliable packaging techniques to couple the optical fibre with the photodetector has become a critical area of research today. In the present work we have developed a simple technique to automatically align the fibre with the detector by micromachining the InP substrate (used for fabricating the p-i-n detector) and using the resulting V-groove for accurate positioning of the fibre. A masking material has been depositied on the back surface of the wafer and patterned by photolithography to open an window exactly aligned to the p-i-n detector realised on the top surface. InP has been etched anisotropically through this window. This has resulted in a V-groove through which the fibre can be inserted and held in position. Three different etch maskmaterials viz Ti, Cr, and SiN have been tried and their effects on the shape of the v-groove have been compared. Two different etch solutions have bene sued to etch InP. It has been found that while the choice of the etching solution determines the angle of the v-groove as well as the surface finish, the mask material dictates the amount of undercut. Ti as the mask material has been found to give the best results.
The paper reports on methods to fabricate novel materials and associated processing for optoelectronics and optical structures compatible with manufacturing of microsystems. Furthermore, the paper presents results on designing, fabrication and packaging of different modules and microsystems for sensor, instrumentation and optical communication applications. New materials are developed and liquid phase deposition methods are applied for the fabrication of lithography compatible glasses, conducive transparent glasses and protective materials. The developed lithographic glasses are used for example to fabricate micro-opto-mechanical structures. By using these materials and structures, a miniaturized micro-optical table is constructed. Furthermore, organic and hybrid semiconductors and light emitting materials are manufactured and their integration as micro-optical components and systems are described. From the view-point of module integration, a wavelength tunable laser diode, i.e., a MOEMS consisting of laser diode and a silicon micromachined Fabry-Perot interferometer, is demonstrated and modeled. A ~4nm wavelength tuning range with ~0.3nm FWHM spectral width is experimentally obtained at 980 nm. Moreover, the use of a passive alignment structure for the fiber pigtailing of a multimode laser diode is demonstrated. The ceramic alignment structure is hot embossed with a LIGA machined tool and results in a ~56% coupling efficiency, corresponding to the theoretical maximum.
Micro Optics frequently require the fabrication of complex 3D structures with surface qualities and metrological tolerances that challenge many manufacturing techniques. In this paper we describe two excimer laser abalation techniques for creating spiral phase modulation structures and a technique for fabricating a diffractive optical structure. The spiral phase structures are intended to be used to convert a 780nm TEM00 laser beam into the doughnut mose TEM*01 field and the diffractive structure is used to create the double-D TEM01 mode in the transmitted first order diffraction. Each of the techniques involve the use of mask projection excimer laser abalation. One of the techniques used to create the smoothly varying ramp of the spiral phase structure involes the use of a single mask that rotates about one of its vertices while the matching laser is pulsed. The second process uses a set of 15 separate patterns that are prepared on a chrome-on-quartz mask. The fabrication of the diffractive optical element is performed in a similar way. We have used 248nm radiation from a KrF laser source to demonstrate the fabrication in polycarbonate of the spiral phase modulation structure and have been able to produce the diffractive optical element in both polycarbonate and glass microscope slides.
F2 lasers emitting radiation with a wavelength (lambda) equals 157 nm allow the direct laser based micro-structuring of materials like PTFE (e.g. Teflon) or quartz glass for MST-applications. This paper reports about the fundamental basis of controlling and modelling the structuring process and about existing tools for the 3-D micron structuring with F2 excimer lasers. The concept of three-dimensional micro-structuring is based on gradual ablation, using single laser pulses. A CNC-controlled precision machining centre with a vacuum encapsulated beam guiding system has been developed. For the material processing with F2 lasers a model of the single ablation size was qualified, which provides an exact description of the laser pulse taking the material properties, the energy density and the lateral dimensions of the single ablation into account. The non- linear characteristics between pulse geometry and process parameters were experimentally determined and implemented into software for automated NC-data generation. A special software tool makes the simulation of manufacturing micro-components possible. It is based on the complex NC-code and on the exact model of the single ablation. Using this simulation, the process parameters can be optimised before processing with a laser micro-machining centre. The described technology was verified by manufacturing 3-D micro-structures in several materials, such as quartz glass and PTFE.
We discuss here the capability of direct manufacture of various high- resolution diffractive optics, in particular regarding micromachining of DOEs in 3D. Preliminary demonstrations were made in 2-D using an automated FIB system operated at 30 KeV with a Gallium liquid metal ion source and equipped with a gas injection system (GIS). Gratings with a 20 nm line width and zone plates with 32 nm outer ring were milled in a reactive atmosphere (iodine) directly through 3.5 (mu) m and 800 nm of gold respectively. Plans for combining FIB and X-ray lithography to make diffractive optical elements (DOEs) for JPL are also mentioned.
Surface tension self-assembly of MEMS has been shown to be an excellent approach for assembling three-dimensional MEMS structures by allowing more precise alignments and vastly increased complexity. This paper investigates and addresses some of the factors that limit the precision of surface tension self-assembly. Each factor can be analyzed and addressed for a simple structure, but for more complex structures, these effects need to be addressed additively and in unison. This paper also discusses, the additive tolerance effects of these structures and present several methods of tolerance analysis. The toleranceing, in conjunction with the precision analysis, will in the future allow for the creation of extremely precise surface tension self-assembled structures, allowing for the creation of MEMS applications that were previously unobtainable using any existing fabrication or packaging process.
We will present an overview of the different polymer/liquid crystal micro-composites and their uses for the control of the optical flux. The preparation method is the key element of this generic family of materials. There is a great number of pertinent parameters (relative concentration of constituents, irradiation conditions, ...) Acting on the morphology and therefore on the final properties. Materials with very different electro-optical properties can be obtained. We will discuss the case where the spatial repartition of heterogeneity is uniform in the sample: light occlusion films (with direct or reverse mode, selective reflection films, films with optical bistability). The cholesteric films will be particularly emphasized. We will focus on the relation between the preparation, the electro-optical properties and the colorimetric properties of the films. Next, the effect of introducing a gradient in some parameters (as irradiation, ...) influencing the material will be discussed. The use of these electrically controllable materials in adaptive optical materials for some applications such as optical components, smart windows, laser protection... will be reviewed.
The spectacular growth in MOEMS interest is highlighted by the involvement of R&D centres and industrial companies. A lot of application fields offer large opportunities for Micro-Opto-Electro- Mechanical Systems (MOEMS): optical communications (switches, cross- connect matrix, DWDM systems ...), digital image processing, adaptive optics... but also industrial maintenance, environment, medicine,... After general ideas on MEMS and MOEMS, this paper presents the main application fields for MOEMS and a few outstanding devices are presented to illustrate the recent developments. Then the work of LETI in MOEMS is presented. Some devices are fabrication with MEMS technologies such as tunable Fabry-Perot interferometers for DWDM telecommunications or 2D micro-scanners for obstacle detection. But a more specific technology has also been developed by LETI, resulting in devices made of silica such as 1D micro-scanners for obstacle detection. Moreover some devices are constituted of micro-mechanical structures combined with Integrated Optics: micro-switches for protection applications and network reconfiguration in optical communications, micro-vibration sensor for surveillance of rotating machines in electrical generators.