Klaus Dietrich

Mass production of planar polymer waveguides and their applications

The increasing demand for planar polymer optical waveguides integrated into electrical printed circuit boards (PCB) calls for mass production capabilities: Hence, appropriate materials, systems, assembly concepts and production technologies become vital, in order to guarantee a high reproducibility and quality of the waveguides. The manufacturing and assembly costs have to be kept on a low level, while the integration of the highly sensible waveguides into the rough environment of PCBs with their cheap and non-ideal substrates is a particular challenge. The present paper describes an assembly and manufacturing technology for electro-optical circuit boards which meets these requirements. First, the manufacturing and characterization of multimode polymer waveguides is presented and the process for layer deposition and structuring is described. Specific attention is given to the reproducibility of these processes ensuring the high optical quality of the waveguides. Additionally, some problems arising from the integration of the waveguides into the PCBs are discussed. Second, various light coupling concepts are presented. In particular, a novel mirror element based on parabolic reflectors is described. The optical design was calculated analytically and optimized using computer simulations. The mirror element was fabricated using injection molding in a reproducible manner at high quantities and lowest cost. To allow for a wider tolerance in the subsequent assembly steps our novel electro-optical transceivers concept facilitates the use of conventional SMD- placement machines for mounting which makes the process very cost effective. This concept was demonstrated successfully and is also described within the third section. In the last part the practical use of this building set is illustrated with different successfully realized applications in the field of ICT and optical sensor technology.

Homogeneous fluorescent thin films as long-term stable microscopy reference layers

Calibration and validation of fluorescence microscopy devices and components require a high level of stability and repeatability in their fluorescent properties, both spatially and temporally. In order to establish a dependable reference point, from which all variations within the microscope and peripheral devices can be tested, an exceedingly homogeneous fluorescence response must be provided through a calibration tool. We present material system optimization and microfabrication process development, as well as long-term stability considerations for such a calibration tool. Stringent specifications for film thickness (< 1μm ± 0.1% over 1.5x1.5 mm) and for fluorescence response distribution (within 1%) apply, and should hold for up to 100 hours under continuous white irradiation. Low conversion efficiency demands high pick up efficiency and therefor reduces focal depth by high NA of applied fluorescence microscope lens. High spatial resolutions demands use of high quality lenses that typically show low field curvatures and good chromatic corrections. Therefore, the focal plane is flat and well defined in the z-plane. Fluorescent, ligand capped core-shell quantum dots (SMQDs) were embedded in diluted PMMA at low concentrations. The formulations were spin-coated on silicon and glass wafers to obtain films with thicknesses under 1 μm and low variations on a 100 mm wafer. Fluorescence properties of the SMQD were preserved in the matrix material, and agglomerations were not detectable in the fluorescence response nor in SEM images. Gradual degradation of the fluorescence response due to film aging was managed through robust packaging solutions.

In-focal-plane characterization of excitation distribution for quantitative fluorescence microscopy applications

The applications of fluorescence microscopy span medical diagnostics, bioengineering and biomaterial analytics. Full exploitation of fluorescent microscopy is hampered by imperfections in illumination, detection and filtering. Mainly, errors stem from deviations induced by real-world components inducing spatial or angular variations of propagation properties along the optical path, and they can be addressed through consistent and accurate calibration. For many applications, uniform signal to noise ratio (SNR) over the imaging area is required. Homogeneous SNR can be achieved by quantifying and compensating for the signal bias. We present a method to quantitatively characterize novel reference materials as a calibration reference for biomaterials analytics. The reference materials under investigation comprise thin layers of fluorophores embedded in polymer matrices. These layers are highly homogeneous in their fluorescence response, where cumulative variations do not exceed 1% over the field of view (1.5 x 1.1 mm). An automated and reproducible measurement methodology, enabling sufficient correction for measurement artefacts, is reported. The measurement setup is equipped with an autofocus system, ensuring that the measured film quality is not artificially increased by out-of-focus reduction of the system modulation transfer function. The quantitative characterization method is suitable for analysis of modified bio-materials, especially through patterned protein decoration. The imaging method presented here can be used to statistically analyze protein patterns, thereby increasing both precision and throughput. Further, the method can be developed to include a reference emitter and detector pair on the image surface of the reference object, in order to provide traceable measurements.