Peter Liebetraut

A fully integrated optofluidic attenuator

A fast and reliable, fully integrated optofluidic optical attenuator is demonstrated. The concept employs only liquid and thus has no mechanically moving parts. Transparent and opaque aqueous liquid droplets are displaced using an on-chip electrowetting actuator and, due to the flexibility in the choice of liquids, various transmission spectra can be defined. The microfluidic attenuator system is fabricated using wafer-level bonding and dry film resists resulting in an ultra-compact (11×23×1.6 mm3) device requiring no external components for operation. The measured dynamic range of optical transmission is up to 47 dB, while the response times are below 100 ms for a 2 mm input beam. Using a novel double-actuator configuration, actuation speeds of the liquids of up to 39 mm s−1 were measured.

Chromatic aberration control for tunable all-silicone membrane microlenses

Tunable multi-chamber microfluidic membrane microlenses with achromaticity over a given focal length range are demonstrated. In analogy to a fixed-focus achromatic doublet lens, the multi-lens system is based on a stack of microfluidic cavities filled with optically optimized liquids with precisely defined refractive index and Abbe number, and these are independently pneumatically actuated. The membranes separating the cavities form the refractive optical surfaces, and the curvatures as a function of pressure are calculated using a mechanical model for deformation of flexible plates. The results are combined with optical ray tracing simulations of the multi-lens system to yield chromatic aberration behavior, which is verified experimentally. A focal length tuning range of 5-40 mm and reduction in chromatic aberration of over 30% is demonstrated, limited by the availability of optical fluids.

Tunable solid-body elastomer lenses with electromagnetic actuation

We present novel biconvex solid-body elastomer (polydimethylsiloxane) lenses, which can be tuned in focal length by using magnetic or mechanical actuation. The focal length change is induced by applying radial elastic strain and is investigated for different initial radii of curvature of the lenses and different actuation designs. In all cases, a linear correlation between induced strain and focal length tuning, in the range of about 10% (approximately 3 mm), is found. These results compare favorably with finite element simulations.

Real-time monitoring of ethene/1-hexene copolymerizations: determination of catalyst activity, copolymer composition and copolymerization parameters

High-throughput development of catalysts, initiators, and polymeric materials combines automated parallel catalyst synthesis and automated polymerization reactors. The reactors can be additionally equipped with on-line monitoring (ReactIR from Mettler) based on ATR-FT-IR technique. This powerful tool has proven to be a very valuable probe for high-throughput experiments. During copolymerizations of ethene and 1-hexene monomers, the ReactIR was used to monitor the 1-hexene conversion as well as polymer formation, polymer concentration, and polymer composition. This gives access to information on catalyst activity, activation and deactivation times of the catalyst, polymerization kinetics, copolymerization parameters, and the degree of homogeneity of the resulting copolymers. The technology is especially useful for solution copolymerization. The spectrometer can be applied in the lab as well as in pilot plants and production facilities where rapid on-line analyses are useful for product quality control.

Optical properties of liquids for fluidic optics

We present the dispersion characteristics of 18 liquids and one resin, which are widely used as media for liquid lenses in adaptive and tunable optics and for index matching in spectrochemical analysis. These are measured by using a refractometer operating at six different wavelengths. We provide a short description of the measurement setup and present a detailed uncertainty analysis of the measurement system to provide a measure of the reliability of the data. We conclude with a catalog of refractive indices and Sellmeier coefficients of the measured liquids and show the location of the analyzed materials in an Abbe diagram.

Miniaturized tunable imaging system inspired by the human eye

We demonstrate the combination of a tunable lens and tunable aperture in a compact imaging system whose structure is inspired by the human eye. The concept is based on innovative optical materials and tuning mechanisms including an optofluidic iris for a tunable aperture and an elastomer lens for focal length tuning. Wavefront and modulation transfer function analysis reveals a high imaging performance of both the individual elements and the complete system. Most significantly, the wavefront is not degraded (ΔPV

Tunable all-silicone multi-chamber achromatic microlens

We present an all-silicone, multi-chamber fluidic microlens system designed for achromatic focal length tunability in a given wavelength range. This micro-optical system is composed of an integrated stack of multiple microlenses, all fabricated by a simple silicone molding technique. Focal-length tuning of the multi-chamber lenses is realized by external pressure actuation, although the design allows integration of the micropump developed separately for this family of tunable fluidic lenses. A focal length tuning range of −40 mm to −5 mm and 5 mm to 40 mm was determined, and measurements of chromatic aberrationwere shown at two discrete focal lengths, 12 mm and 15 mm.

A versatile fabrication process for reaction injection molded elastomeric micro-lenses

We propose a lens fabrication process for reaction injection molding of elastomeric micro-lenses. The versatile and flexible process allows manufacturing a broad spectrum of lens shapes, including compound achromatic lenses, entirely consisting of PDMS.

Tunable solid-body elastomeric diffractive lens

We present a mechanically tunable diffractive lens. The lens is fabricated by using standard photolithography in combination with a molding technique, and is made of the highly transparent silicone elastomer polydimethyl-siloxane (PDMS). The focal length is tuned by radial mechanical expansion. By using a precisely machined mechanical actuator for tuning the lens, we achieved a tunability in focal length of 20 %, while the optical quality is maintained for the full tuning range.