Lukasz Nieradko

Fabrication of spherical microlenses by a combination of isotropic wet etching of silicon and molding techniques

We report a novel process technology of hemispherical shaped microlenses, using isotropic wet etching of silicon in an acid solution to produce the microlenses molds. Governed by process parameters such as temperature and etchant concentration, the isotropic wet etching is controlled to minimize various defects that appear during the molding creation. From the molds, microlenses are fabricated in polymer by conventional replication techniques such as hot embossing and UV-molding. The characterization of molds and measurements of replicated microlenses demonstrate high smoothness of the surfaces, excellent repeatability of mold fabrication and good optical properties. Using the proposed method, a wide range of lens geometries and lens arrays can be achieved.

On-Chip Scanning Confocal Microscope with 3D MEMS Scanner and VCSEL Feedback Detection

We propose an original approach of a miniature scanning confocal microscope that uses two electrostatic scanners with microoptical lenses. For this chip-scale microscope, we demonstrated the use of optical feedback of VCSELs laser as an active detection. The z-axis scanner will provide a vertical motion of the first microlens in the range of 100 mum, controlling the focal length of the objective. Raster scanning (30 mum in both directions) of a specimen by the focused illumination spot will be implemented by actuating of second microlens by x-y-axis scanner.

Silicon components for gas chromatograph

A gas analyzer based on chromatography method using silicon- glass components has been built. Its main components were made by using MAMS-like technology, and its conception is concurrent to the idea of an integrated silicon chromatography proposed by SC Terry.

New generation of fully integrated optical microscopes on-chip: application to confocal microscope

In the paper the new concept of fully integrated scanning confocal optical microscope on-chip is proposed. The operation of this microscope combines the 3-D transmissive scanning of VCSEL laser beam by use of two MOEMS scanners, and active signal detection, based on the optical feedback in the VCSEL laser cavity. The silicon-based electrostatically driven scanners provide controlled movement of two convex microlenses, working as an objective lens of microscope. Glass microlenses are monolithically integrated on movable silicon tables of scanners. The first results of technological investigation on the microscope components are presented.

Characterization of MEMS cantilevers using lensless digital holographic microscope

In this paper vibration characterization of MEMS cantilevers are presented using lens-less in-line digital holographic microscope (LDHM). In-line digital holography provides larger information capability with higher phase sensitivity, and full CCD sensor area is utilized for real image reconstruction. In lensless in-line digital holographic microscope, a highly diverging beam replaces the conventional microscope objectives to provide the required magnification. The diverging wave geometry also reduces the effect of twin-image wave caused by the in-line holographic geometry. For vibration analysis, the time averaged holograms were recorded corresponding to different vibration states of the cantilevers. Direct numerical evaluation of the amplitude and phase information from single time averaged hologram provides the full-field real time quantitative analysis. The experimental study of vibration measurements of Aluminum nitride (AlN) driven cantilevers is performed. The full field study shows the simultaneous vibration behavior of many cantilevers corresponding to same input conditions. Our study shows the shift in the resonant condition of cantilevers both for first and second resonant frequencies. This kind of analysis is most suitable to optimize and monitoring the fabrication process of cantilevers.

Fabrication and optical packaging of an integrated Mach-Zehnder interferometer on top of a moveable micromirror

While testing electrical properties in microsystems is a well-developed art, the testing of mechanical properties of MEMS devices is not. There is a great need for techniques that will permit the evaluation of MEMS devices, in all stages of manufacturing, with respect to material and micromechanical properties. In this contribution we propose a new approach, based on the integrated optical read-out using a Mach-Zehnder interferometer (MZI). MZI is monolithically integrated on top of a electrostatically rotatable micromirror loaded with the sensing arm of MZI. A single mode buried channel waveguide based on silica/silicon oxinitride/silica structure is used. It performs a low optical attenuation and a coupling efficiency of 55% from waveguide to a standard fiber, connecting MZI to outside world (light source and detector). The working principle of MZI read out is based on the change of effective refractive index of guided waves of MZI induced by displacement of the deformable structure, obtained via the elastooptic effect. The technology process steps with special emphasis to the fiber-to-waveguide coupling based on V-grooves is detailed here. Our goal is aiming to obtain an angular alignment of ± 0.2 deg. of V-groove walls with <110> directions and the vertical misalignment not, exceeding ± 0.6 μm.

Optical microlenses for MOEMS

A new concept of the fabrication process for glass microlenses (external diameter ED<1 mm, focal length a few millimeters), based on the silicon master mask-less anisotropic wet etching in KOH, vacuum anodic bonding and re-flow of borosilicate glass, followed by the precise wafer-scale polishing and DRIE has been presented. A single spherical microlens as well as an array of spherical microlenses with focal length between 44.8 and 8.6 mm and external diameter 0.35 to 0.985 mm have been repeatable manufactured.

Optical characterization of a polymer micro-optical light coupler for silicon channels

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Level set method for microfabrication simulations

The article describes application of Level Set method for two different microfabrication processes. First is shape evolution of during reflow of the glass structure. Investigated problem were approximated by viscous flow of material thus kinetics of the process were known from physical model. Second problem is isotropic wet etching of silicon. Which is much more complicated because dynamics of the shape evolution is strongly coupled with time and geometry shapes history. In etching simulations Level Set method is coupled with Finite Element Method (FEM) that is used for calculation of etching acid concentration that determine geometry evolution of the structure. The problem arising from working with FEM with time varying boundaries was solved with the use of the dynamic mesh technique employing the Level Set formalism of higher dimensional function for geometry description. Isotropic etching was investigated in context of mico-lenses fabrication. Model was compared with experimental data obtained in etching of the silicon moulds used for micro-lenses fabrication.

Twymann Green interferometry in study of AlN material as an actuation layer in MEMS

In this study we focus on the aluminium nitride (AlN). This material shows a large number of advantages associated with good piezoelectric properties. Therefore, AlN is an excellent candidate for MEMS actuation where low dielectric loss, low thermal drift and high signal-to-noise ratios are required. In this paper, the case of AlN driven cantilevers composed of three thin layers deposited on the silicon substrate will be considered. Precise knowledge of physical and material parameters of AlN applied in these simple elements are necessary for their further applications. However, up to now, AlN still represents a technological challenge and many of its micromechanical and piezoelectric properties are not precisely described. That is why, our study has been concentrated on determination of such parameters like the residual thin film stresses, thermal expansion coefficient α and piezoelectric coefficient d31. In this paper the interactions between the theoretical solution, the numerical FEM simulations and experimental results were performed. This hybrid methodology allows to identify the main source of behaviors discrepancy between the physical and numerical model of tested cantilevers. Obtained knowledge leads to optimization of the technological process and required parameters of actuator functionality achievement by better understanding of the tested microdevices properties. In experimental procedure, it was used nanoindentation tests for obtaining an elastic properties of AlN, interferometric techniques for performing the static and dynamic measurements of cantilevers and scanning electron microscope for measuring topography.