Showing papers by "Sylwester Bargiel published in 2015"

Dense arrays of millimeter-sized glass lenses fabricated at wafer-level.

Abstract: This paper presents the study of a fabrication technique of lenses arrays based on the reflow of glass inside cylindrical silicon cavities. Lenses whose sizes are out of the microfabrication standards are considered. In particular, the case of high fill factor arrays is discussed in detail since the proximity between lenses generates undesired effects. These effects, not experienced when lenses are sufficiently separated so that they can be considered as single items, are corrected by properly designing the silicon cavities. Complete topographic as well as optical characterizations are reported. The compatibility of materials with Micro-Opto-Electromechanical Systems (MOEMS) integration processes makes this technology attractive for the miniaturization of inspection systems, especially those devoted to imaging.

Swept Source Optical Coherence Tomography Endomicroscope Based on Vertically Integrated Mirau Micro Interferometer: Concept and Technology

Abstract: This paper presents a concept of an endomicroscope for an early detection of neoplastic lesions in the human stomach tissue, based on the swept source optical coherence tomography (SS-OCT) and a measurement probe with integrated Mirau micro interferometer. The system consists of pigtailed illumination and detection blocks, connected via a Gradient Index (GRIN) lens collimator to a micro-opto-electro-mechanical systems (MOEMS) measurement probe (4 mm × 4 mm × 20 mm). The technology of Mirau micro interferometer is based on vertical multi-wafer bonding approach. The MOEMS probe is intended to be mounted on a continuum robot arm to perform in vivo microscopy of stomach tissues. First, the optical design of the SS-OCT endomicroscope is described, including an analysis of sensitivity. Then, we focus on the fabrication technologies and optical characterization of a key component of the Mirau micro interferometer, i.e., monolithically integrated focusing glass lens. SS-OCT endomicroscope will provide a fast axial scanning of tissues with A-scan sweep rate of 110 kHz, offering the axial resolution of 5.2 μm and the lateral resolution of 10.2 μm.

Micro-optical design of a three-dimensional microlens scanner for vertically integrated micro-opto-electro-mechanical systems.

Abstract: This paper presents the optical design of a miniature 3D scanning system, which is fully compatible with the vertical integration technology of micro-opto-electro-mechanical systems (MOEMS). The constraints related to this integration strategy are considered, resulting in a simple three-element micro-optical setup based on an afocal scanning microlens doublet and a focusing microlens, which is tolerant to axial position inaccuracy. The 3D scanning is achieved by axial and lateral displacement of microlenses of the scanning doublet, realized by micro-electro-mechanical systems microactuators (the transmission scanning approach). Optical scanning performance of the system is determined analytically by use of the extended ray transfer matrix method, leading to two different optical configurations, relying either on a ball lens or plano–convex microlenses. The presented system is aimed to be a core component of miniature MOEMS-based optical devices, which require a 3D optical scanning function, e.g., miniature imaging systems (confocal or optical coherence microscopes) or optical tweezers.

An electrostatic vertical microscanner for phase modulating array-type Mirau microinterferometry

Abstract: We present a micromachined vertical scanner with a array of suspended 'spider-type' micromirrors which is a key component of a multi-channel 'active' Mirau microinterferometer. The microscanner provides for the vertical displacement of the reference micromirrors for the implementation of the phase shifting technique. Vertical comb-drive structures are employed for actuation of the micromirrors (displacement range of hundreds of nm at 500 Hz) as well as for in situ capacitive displacement sensing. Integration of micro-opto-electro-mechanical microscanners in a handheld interference microscope has the advantage of significantly decreasing instrument size because of the small footprint of the microscanner. Particularly interesting applications of the microscanner are low-cost and portable microsystems for the parallel inspection of biological tissues, e.g. for early diagnosis of specific diseases such as skin cancers.

Impact of mirror spider legs on imaging quality in Mirau micro-interferometry.

Abstract: We report the impact on imaging quality of mirror suspensions, referred to as spider legs, used to support the reference mirror in a Mirau micro-interferometer that requires the vertical alignment of lens, mirror, and beamsplitter. Because the light goes from the microlens to the beamsplitter through the mirror plane, the spider legs are a source of diffraction. This impact is studied as a function of different parameters of the spider legs design. Imaging criteria, such as the resolution as well as the symmetry of the imaging system, are determined using the point spread function and the modulation transfer function of the pupil. These imaging criteria are used to determine the optimum radius of curvature, thickness, and number of legs of the spider structure. We show that 3 curved legs give performances, with specific radius of curvature and thickness, similar to a suspension-free mirror.

Multi-wafer bonding technology for the integration of a micromachined Mirau interferometer

Abstract: The paper presents the multi-wafer bonding technology as well as the integration of electrical connection to the zscanner wafer of the micromachined array-type Mirau interferometer. A Mirau interferometer, which is a key-component of optical coherence tomography (OCT) microsystem, consists of a microlens doublet, a MOEMS Z-scanner, a focusadjustment spacer and a beam splitter plate. For the integration of this MOEMS device heterogeneous bonding of Si, glass and SOI wafers is necessary. Previously, most of the existing methods for multilayer wafer bonding require annealing at high temperature, i.e., 1100°C. To be compatible with MEMS devices, bonding of different material stacks at temperatures lower than 400°C has also been investigated. However, if more components are involved, it becomes less effective due to the alignment accuracy or degradation of surface quality of the not-bonded side after each bonding operation. The proposed technology focuses on 3D integration of heterogeneous building blocks, where the assembly process is compatible with the materials of each wafer stack and with position accuracy which fits optical requirement. A demonstrator with up to 5 wafers bonded lower than 400°C is presented and bond interfaces are evaluated. To avoid the complexity of through wafer vias, a design which creates electrical connections along vertical direction by mounting a wafer stack on a flip chip PCB is proposed. The approach, which adopts vertically-stacked wafers along with electrical connection functionality, provides not only a space-effective integration of MOEMS device but also a design where the Mirau stack can be further integrated with other components of the OCT microsystem easily.

Technological platform for vertical multi-wafer integration of miniature imaging instruments

Abstract: 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.

Mirau micro-interferometer for Swept-Source Optical Coherence Tomography endomicroscopy

Abstract: We focus on the design and technology of Mirau micro-interferometer, which is a key part of MOEMS endomicroscopic probe, operating with Swept-Source Optical Coherence Tomography detection.