We describe a technological platform developed for miniaturization of optical imaging instruments, such as laser scanning
confocal microscopes or Optical Coherence Tomography devices. The platform employs multi-wafer vertical integration
approach, combined with integrated glass-based micro-optics and heterogeneous bonding and interconnecting technologies.
In this paper we focus on the unconventional fabrication methods of monolithic micro-optical structures and components in
borosilicate glass (e.g. micro beamsplitters, refractive microlenses) for optical beam shaping and routing. In addition, we
present hybrid laser-assisted integration of glass ball microlenses on the silicon MEMS actuators for transmissive beam
scanning as well as methods of electrical signals distribution through thick glass substrates, based on HF etched via holes.
Scientific articles focusing on fabrication of micro-components often evaluate their optical performances by techniques such as scanning electron microscopy or surface topography only. However, deriving the optical characteristics from the shape of the optical element requires using propagation algorithms. In this paper, we present a simple and intuitive method, based on the measurement of the intensity point spread function generated by the micro-component. The setup is less expensive than common systems and does not require heavy equipments, since it requires only a microscope objective, a CMOS camera and a displacement stage. This direct characterization method consists in scanning axially and recording sequentially the focal volume. Our system, in transmissive configuration, consists in the investigation of the focus generated by the microlens, allowing measuring the axial and lateral resolutions, estimating the Strehl ratio and calculating the numerical aperture of the microlens. The optical system can also be used in reflective configuration in order to characterize micro-reflective components such as molds. The fixed imaging configuration allows rapid estimation of quality and repeatability of fabricated micro-optical elements.
In this paper, we adapt a technique employed for glass microlenses fabrication in order to obtain matrices of millimeter size lenses for inspection applications. The use of microfabrication processes and Micro-Electro-Mechanical Systems (MEMS) compatible materials allow the integration of lenses larger than usual in microsystems. Since the presented lenses can have 2 mm in diameter or more, some aspects apparently irrelevant when diameters are lower than 500 μm must be reviewed and taken into account. Indeed, when the lenses are in the millimeter range, problems such as size nonuniformities within a matrix and asymmetric shapes of each lens are dependent on parameters as mask design, depth of the silicon cavities and enclosed vacuum control after anodic bonding, glass reflow temperature and even the position of the lenses on the substrate. Issues related to the fabrication flow-chart are addressed in this paper and solutions are proposed. First results are shown to prove the pertinence of this technique to fabricate MEMS-compatible millimetersized lenses to be integrated in miniature inspection systems. We also discuss some of the paths to follow that could help improving the performances.
High-resolution miniature imaging systems require high quality micro-optical elements. Therefore, it is essential to characterize their optical performances in order to optimize their fabrication. Usually, basic evaluation of micro-optical elements quality is based on the measurement of their topography since their optical properties are largely defined by their shape. However, optical characteristics have to be derived from the measured geometry. An alternative method is the direct measurement of their optical properties. Unlike topography measurement, it allows characterization of high numerical aperture components. Moreover, it can be applied to single elements but also to optical systems composed of several micro-optical components. In this work, we propose a simple method based on the measurement of the 3D intensity point spread function (IPSF). IPSF is defined by the 3D shape of the focal spot generated by the micro-element. The direct characterization of focusing response through the measurement of IPSF allows very precise estimation of micro-structures quality. The considered method consists in imaging different slices of the focal volume generated by the focusing component. It allows, depending on the configuration, characterizing both transmissive and reflective micro-optical components.