Niklas Weber

Highly compact imaging using Bessel beams generated by ultraminiaturized multi-micro-axicon systems

Employing Bessel beams in imaging takes advantage of their self-reconstructing properties to achieve small focal points while maintaining a large depth of focus. Bessel beams are efficiently generated using axicons, and their utility in scanning imaging systems, such as optical coherence tomography (OCT), has been demonstrated. As these systems are miniaturized to allow, for example, endoscopic implementations, micro-axicons are required to assure the maintenance of a large depth of focus. We demonstrate here the design, fabrication, and application of molded micro-axicons for use in silicon-based micro-optical benches. It is shown that arrangements of multiple convex and concave axicons may be implemented to optimize the depth of focus in a miniaturized OCT system, using a telescopic optical arrangement of considerably shorter optical system length than that achievable with classical micro-optics.

Polymer/Silicon Hard Magnetic Micromirrors

Extremely compact hard magnetic micromirrors are realized using a combination of silicon and polymer microelectromechanical systems technologies. Due to their hard magnetic properties, the mirrors may achieve high deflection angles with the application of very low magnetic fields, a few microteslas, which may be generated by means of miniaturized microcoils. Since no electrical wiring is required for the mirrors, they may be mounted on rotating platforms and thus used for complete circumferential scanning, as required, for example, in optical endoscopic diagnostics.

A Tunable Optofluidic Silicon Optical Bench

A miniaturized optical bench, based on silicon micromachining and with high modularity and flexibility, is presented. This optical microsystem integrates optics, fluidics, high-precision mechanics, and focal length tunable lenses and allows the realization of numerous optical arrangements, such as telephoto and retrofocus systems. Due to its dimensions, the technology may be used for designing a variety of endoscopic imaging probes, including those for optical coherence tomography. As the measuring beam can be dynamically adapted to the surroundings and application, this microbench yields an optical system with greatly enhanced functionality and performance when compared to existing concepts.

Varifocal MOEMS fiber scanner for confocal endomicroscopy

Based on an advanced silicon optical bench technology with integrated MOEMS (Micro-Opto-Electro-Mechanical-System) components, a piezo-driven fiber scanner for confocal microscopy has been developed. This highly-miniaturized technology allows integration into an endoscope with a total outer probe diameter of 2.5 mm. The system features a hydraulically-driven varifocal lens providing axial confocal scanning without any translational movement of components. The demonstrated resolutions are 1.7 μm laterally and 19 μm axially.

Endoscopic optical probes for linear and rotational scanning

Two fully integrated optical microprobes, based on an advanced silicon optical bench (SiOB) technology, are developed for endoscopic OCT (optical coherence tomography). The probes incorporate diverse optical components and scan mechanics, such as magnetostatic micromirrors and rotating prisms, to realize linear side-looking and rotational scanning. The outer diameter of the assembled systems is below 2.75 mm allowing integration into the 3mm working channels of commercial endoscopes.

Implantable optical sensor for continuous monitoring of various hemoglobin derivatives and tissue perfusion

A novel implantable optical sensor for continuous long-term monitoring of arterial oxygen saturation and monitoring of tissue perfusion is introduced. The photoplethysmo-graphic multi-wavelength sensor with optoelectronic components mounted onto a flexible substrate and encapsulated in biocompatible silicone is attached to well-perfused intrathoracic tissue or directly onto organ surfaces. A proof-of-principle could be shown by first measurements carried out on custom-developed artificial tissue and by in vivo finger-tip measurements as well as in a domestic pig.

Ultra-compact micromirror with polymeric hard magnet for use in endoscopic imaging

An ultra-compact magnetically actuated micromirror with a polymeric hard magnetic layer on its back-side is developed for use in an endoscopic probe. This novel construction yields high deflection angles at extremely low magnetic fields which can be generated by a separate actuation coil. As no direct electrical connection is required for operating the micromirror, it can be mounted on a rotating platform and used for tubular scanning of the interior of body passageways or blood vessels.

In vivo monitoring of blood oxygenation using an implantable MEMS-based sensor

We present a novel implantable, but extravascular, optical sensor for continuous long-term monitoring of vital medical parameters such as arterial blood oxygen saturation, pulse and respiratory frequencies. The biocompatible sensor uses a silicone-based manufacturing technique. It consists of two elastic silicone stripes that house the optoelectronic devices. These flexible stripes can be wrapped around an arterial blood vessel without constricting the vessel or influencing the blood flow - even at large dilatations of 10 %. In vivo experiments on domestic pigs have shown that real-time measurements with this sensor deliver excellent data.

Optical micro-system with highly flexible tunability for endoscopic micro-probes

A highly flexible tunable optical micro-system has been developed and characterized for its use in endoscopic optics, such as optical coherence tomography (OCT). By using two individually tunable lenses, various optical arrangements can easily be realized, allowing great variability in beam shaping. This innovative approach surpasses common endoscopic optics in terms of flexibility, as the measuring beam can be adapted to the surrounding tissue at any time.

High-precision optical & fluidic micro-bench for endoscopic imaging

An optical and fluidic micro-bench with integrated liquid-filled tunable micro-lenses is developed for an endoscopic probe. This novel approach offers not only dynamic focussing, but also a greatly increased working range for biomedical optical imaging. The fabrication and assembly method is highly precise and flexible and can be used for designing optical probes with high functionality.