Sebastian Petsch

Iris‐Like Tunable Aperture Employing Liquid‐Crystal Elastomers

A liquid-crystal elastomer (LCE) iris inspired by the human eye is demonstrated. With integrated polyimide-based platinum heaters, the LCE material is thermally actuated. The radial contraction direction, similar to a mammalian iris, is imprinted to the LCE by a custom-designed magnetic field. Actuation of the device is reproducible over multiple cycles and controllable at intermediate contraction states.

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.

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

Ultrathin Alvarez lens system actuated by artificial muscles

A key feature of Alvarez lenses is that they may be tuned in focal length using lateral rather than axial translation, thus reducing the overall length of a focus-tunable optical system. Nevertheless the bulk of classical microsystems actuators limits further miniaturization. We present here a new, ultrathin focus-tunable Alvarez lens fabricated using molding techniques and actuated using liquid crystal elastomer (LCE) artificial muscle actuators. The large deformation generated by the LCE actuators permits the integration of the actuators in-plane with the mechanical and optical system and thus reduces the device thickness to only 1.6 mm. Movement of the Alvarez lens pair of 178 μm results in a focal length change of 3.3 mm, based on an initial focal length of 28.4 mm. This design is of considerable interest for realization of ultraflat focus-tunable and zoom systems.

The engineered eyeball, a tunable imaging system using soft-matter micro-optics

We demonstrate a tunable imaging system based on the functionality of the mammalian eye using soft-matter micro-optical components. Inspired by the structure of the eye, as well as by the means through which nature tunes its optical behavior, we show that the technologies of microsystems engineering and micro-optics may be used to realize a technical imaging system whose biomimetic functionality is entirely distinct from that of conventional optics. The engineered eyeball integrates a deformable elastomeric refractive structure whose shape is mechanically controlled through application of strain using liquid crystal elastomer (LCE) actuators; two forms of tunable iris, one based on optofluidics and the other on LCEs with embedded heaters; a fixed lens arrangement; and a commercial imaging sensor chip. The complete microsystem, optimized to yield optical characteristics close to those of the human eye, represents the first fully functional, soft-matter-based tunable single-aperture eye-like imager.

A thermotropic liquid crystal elastomer micro-actuator with integrated deformable micro-heater

We present a liquid crystal elastomer (LCE) actuator with large stroke and fast reaction time. LCEs show a large macroscopic shape change when heated above the phase transition (≈120°C). Buried wafer-level fabricated micro-heaters offer optimal thermal reaction times and compact design of the actuators. A relative length change of λ = 1.28 was obtained with 320 mW power consumption. Heating the device from room temperature takes τrise = 19.7 s, cooling below the phase transition temperature from the fully contracted state needs τfall - 5.6s. We verify that the displacement may be accurately controlled by varying electrical input power.

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.

Phase shifting in the spatial frequency domain

Abstract. We present a simple mathematical method for phase shifting that overcomes some phase shift errors and limitations of commonly used methods. The method is used to generate a sequence of phase-shifted interferograms from a single interferogram. The generated interferograms are employed to reconstruct the wavefront aberrations, as an application. The approach yields results with only very small deviations compared to both simulated wavefront aberrations, including the first 25 Zernike polynomials (0.05%) and those measured with a Shack-Hartmann sensor (0.5%).