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We demonstrate a method for self-sensing of a magnetically actuated prism that can be used, e.g., in a feedback-loop without the need of additional sensors. In order to use the impedance of the actuation coils as a measurement parameter, we first obtained the optimal measurement frequency that is well separated from the actuation frequencies and at the same time provides the best compromise between sensitivity to the position and robustness. We then developed a combined actuation and measurement driver, and correlated its output signal to the mechanical state of the prism using a defined calibration sequence. We demonstrate that we can reliably measure the state of each actuator and determine the tilt angle of the prism with an accuracy of ±0.1∘ in the polar angle over a range of ±4∘ and ±20 mrad in the azimuthal angle.

We present two versions of tunable achromatic doublets based on each two piezoelectrically actuated glass membranes that create the surface of fluid volumes with different dispersions: a straightforward back-to-back and a more intricate stack of the fluid volumes. In both cases, we can control the chromatic focal shift and focal power independently by a suitable combination of actuation voltages on both active membranes. The doublets have a large aperture of 12 mm at an outer diameter of the actuator of 18 mm, an overall thickness of 3 mm and a short response time of around 0.5 ms and, in addition, provide spherical aberration correction. The two designs have an achromatic focal power range of ±2.2 m−1 and ±3.2 m−1 or, for the purpose of actively correcting chromatic errors, a chromatic focal shift at vanishing combined focal power of up to ±0.08 m−1 and ±0.12 m−1.

We present the prototype and analytical model of a miniaturized impact actuation mechanism, providing a fast out-of-plane displacement to accelerate objects against gravity, allowing for freely moving objects and hence for large displacements without the need of cantilevers. To achieve the necessary high speed, we chose a piezo electric stack actuator driven by a high-current pulse generator, connected to a rigid support and a rigid three-point contact with the object. We describe this mechanism with a spring-mass model and compare various inertial masses, all of them spheres, from different diameters and materials. As expected, we found that larger flight heights are achieved by harder projectiles, achieving, e.g., approx. 3 mm displacement for a 3 mm steel sphere using a 3x3x2 mm³ piezo stack.

We compare different aspects of the robustness to environmental conditions of two different types of piezo-actuated fluid-membrane lenses: a silicone membrane lens, where the piezo actuator indirectly deforms the flexible membrane through fluid displacement, and a glass membrane lens, where the piezo actuator directly deforms the stiff membrane. While both lenses operated reliably over the temperature range of 0°–75°C, there was a significant effect on their actuation characteristics, which can be well described through a simple model. The silicone lens in particular showed a variation in focal power of up to 0.1m−1∘C−1. We demonstrated that integrated pressure and temperature sensors can provide feedback for focal power, however, limited by the response time of the elastomers in the lenses, with polyurethane in the support structures of the glass membrane lens being more critical than the silicone. Studying the mechanical effects, the silicone membrane lens showed a gravity-induced coma and tilt, and a reduced imaging quality with the Strehl ratio decreasing from 0.89 to 0.31 at a vibration frequency of 100 Hz and an acceleration of 3g. The glass membrane lens was unaffected by gravity, and the Strehl ratio decreased from 0.92 to 0.73 at a vibration of 100 Hz, 3g. Overall, the stiffer glass membrane lens is more robust against environmental influences.

Plenoptic cameras capture the spatial and angular information of a scene. The use of plenoptic cameras in areas such as research, microscopy, industry and consumer markets has steadily increased over the past two decades. When designing a plenoptic camera a decision must always be made between spatial and angular resolution. Many factors such as the size and number of microlenses in a microlens array or the relative position of the microlens array and sensor to the main lens play a role. Here we examine the two most common designs of plenoptic cameras. The plenoptic cameras 1.0, also called the unfocused plenoptic camera, and the plenoptic cameras 2.0, the focused plenoptic camera. We derive the mathematical equations that describe the connection between spatial and angular resolution. Supported by experimental results we show the relationship between the equations and a real object with different object distances taken from the plenoptic camera 1.0 and 2.0. These analyzes make it easier for researchers and engineers to choose the right camera design for a particular application. The user only has to determine beforehand which depth-of-field or which spatial resolution is needed.

We present a novel approach to integrate the piezoelectric actuators in a tunable fluid-membrane lens. We achieved a large aperture of 2.5 cm and a small footprint of $3\times 3\times 0.6 \text{cm}^{3}$ , The actuators are fixed on the fluid chamber's sidewalls to displace the fluid towards the center and deform the flexible membrane. COMSOL Multiphysics® was used to simulate and optimize the lens design. The simulation resulted in a refractive power range of ± 2 dpt for a glass membrane lens and ± 5 dpt for a silicone membrane lens. The refractive power of the fabricated lenses was ± 0.9 dpt and ± 2.3 dpt, respectively.

In this paper we show the proof of concept for a magnetically actuated bi-axial tunable prism. Our modular design gives a high robustness and efficient fabrication. Even without optimizations, we achieved physical tilt angles of ±8° to ±9,6° and a response time of 14.4 ms for an aperture of 8 mm.

In this paper, we present a wireless power transfer (WPT) system with a two-dimensional (2-D) magnetoinductive wave (MIW) device composed by two orthogonal sets of 1-D MIW devices woven together. The device is made by 112 double-spiral coils, a geometry that we have optimized to render a low attenuation propagation. This approach enables a charging area of 22 × 22 cm2 from which a receiver device can be supplied with energy with optimum efficiency from 32 different locations with the use of a single excitation port. We present a detailed optimization of the design and fabrication of the device. To describe the behavior of the device, we use a modeling method based on the impedance matrix that allows us to include all coupling interactions among the increased number of cells. With this method, we are able to find the optimal operating conditions like the location of the excitation and the coupling conditions of the receiver device. With the proposed 2-D MIW device, we can provide up to 5 W to a load of 5 $\Omega$ located at the optimal axial separation. We corroborate our calculations with vector network analysis and dc output power measurements. Furthermore, we demonstrate the device supplying to distinct types of loads simultaneously. This paper is accompanied by a supplementary file showing the required MATLAB script and input files to calculate the mutual inductance between a receiver and the cells of the pad.

We present a new and accurate method to determine the Poisson's ratio of PDMS, using thermal expansion and an optical surface profilometer. The Poisson's ratio of Sylgard 184 was found to be ν = 0.4950 ± 0.0010 and for Sylgard 182, ν = 0.4974 ± 0.0006. Furthermore, we found that for both PDMS types, the coefficient of thermal expansion depends approximately linearly on the curing temperature. This method can be used for almost any kind of soft polymer that can be cured from a liquid at elevated temperatures.

Point-scanning-based microscopy systems require combination of axial and lateral scanning to obtain three-dimensional (3D) data. Axial scanning was commonly achieved by mechanical displacement of the objective or the sample. To improve, various adaptive lens-based solutions have been reported to circumvent the need for mechanically moving parts. The lateral scanning is predominantly implemented using galvanometric mirrors. Although the performance of such devices is flawless, they require bulky, folded beam-paths that make their incorporation in compact hand-held devices challenging. Recently, we introduced an adaptive prism as a transmissive device that enables lateral scanning. We demonstrate the first all-adaptive 3D scanning in laser scanning microscopes employing a compact in-line transmission geometry without mechanically moving parts and beam folding, combining an adaptive lens and a novel adaptive prism. Characterization of the all-adaptive microscope performance shows a lateral tuning range of approximately X = Y = 130 μm and an axial tuning range of about Z = 500 μm. We successfully demonstrate 3D raster scanning of the fluorescence of a thyroid of a zebrafish embryo.

Previously we studied the spectral Gouy rotation as a specific rotational phenomenon of conical polychromatic light fields shaped by spiral gratings. The rotation of spectral anomalies around singularities results from accumulated spectrally dependent Gouy phase shift. We proposed to apply radially chirped spiral structures to obtain an axial modulation of the rotational characteristics. Here we present related experimental results with non-uniform spiral gratings which were programmed into a 10-Megapixel, phase-only, liquid-crystal-on-silicon (LCoS) spatial light modulator (SLM). A propagation-dependent variation of the Gouy rotation was indicated. More complex non-uniform geometries are considered.

We present a smart and stand-alone surface thought to wirelessly charge consumer electronic products without precise alignment between the transmitter and receiver coils. The system has two stages, an inductive sensing stage, working at 688 kHz, and a power stage based on the propagation of magnetoinductive waves throughout metamaterials. The power stage is identified as a two-dimensional (2D) magnetoinductive wave (MIW) device whose coupled, inductive-capacitive resonating cells have been optimized in previous work to provide efficient power transmission to a load of 5 Ω. The work presented here addresses standing waves inside the device that cause zones completely deprived of energy, the power nulls. We present in detail the inexpensive and simple circuitry used to detect the location of a receiver in real-time and consequently adjust the number of active cells of the 2D MIW device, avoiding in this way a receiver standing above a po wer null. The proposed system enables a charging surface of 22x22 cm2 without power nulls along the X-direction.

Recently, the spatio-spectral propagation dynamic of ultrashort-pulsed vortex beams was demonstrated by 2D mapping of spectral moments. The rotation of characteristic anomalies, so-called &ldquo, spectral eyes&rdquo, was explained by wavelength-dependent Gouy phase shift. Controlling of this spectral rotation is essential for specific applications, e.g., communication and processing. Here, we report on advanced concepts for spectral rotational control and related first-proof-of-principle experiments. The speed of rotation of spectral eyes during propagation is shown to be essentially determined by angular and spectral parameters. The performance of fixed diffractive optical elements (DOE) and programmable liquid-crystal-on silicon spatial light modulators (LCoS-SLMs) that act as spiral phase gratings (SPG) or spiral phase plates (SPP) is compared. The approach is extended to radially chirped SPGs inducing axially variable angular velocity. The generation of time-dependent orbital angular momentum (self-torque) by superimposing multiple vortex pulses is proposed.

The large bandwidth and high intensity of ultrafast vortex pulses, i.e. pulses with orbital angular momentum (OAM), open new prospects for applications in communication, imaging or nonlinear photonics. In previous experiments, we demonstrated the peculiar spatio-spectral behavior of pulsed polychromatic vortex beams in the vicinity of phase singularities. It was shown that the rotation of characteristic, so-called “spectral eyes” and the spectral dependent Gouy phase are closely connected. For practical applications, a controlled variation of spatio-spectral distributions is required. Here we report on our most recent studies concerning the dependence of time-integrated spectral maps on key optical parameters. It is shown that the speed of rotation of spectral eyes during the propagation is essentially determined by the angular and spectral profiles. This enables to modify the spectral rotation characteristics by applying low-dispersion, adaptive optical components. The performance of reflective liquid-crystal-on silicon spatial light modulators (LCoSSLMs) is compared to diffractive spiral gratings with variable illumination. Moreover, the generation of wavepackets with a time-dependent orbital angular momentum (self-torque) by superimposing multiple tailored vortex pulses is proposed. This allows for extending the capabilities vortex pulses by defined non-stationary spatio-spectral and topological characteristics.

This paper reports a novel telemetric smart bracket (TSB) for in vivo force/moment measurements during clinical orthodontic applications. The prototype implements a novel microcoil design resulting in a significant increase of the transmission distance compared to the previous state-of-the-art TSB. Using an automatic wirebonder, the microcoil is wound around an SU-8 post attached to the CMOS sensor wafer. For the first time, thus, 3D wirebonder-fabricated microcoils were integrated on a CMOS substrate, without compromising CMOS functionality. The augmented CMOS system serves here as a force/moment measurement device with six-degree-of-freedom ( $f_{x}, f_{y}, f_{z}, m_{x},\ m_{y},\ m_{z}$ ) functionality. The achieved transmission distance, i.e. coil-to-coil distance, was thereby increased by 80% compared to the best previous design to 5 mm, without the need for the system to exceed the severe size constraints of $2\times 2.8\times 1\ \mathrm{mm}^{3}$ defined by the bracket dimensions. The increased transmission distance allows uncritical contactless system powering and readout.

A current goal in microsystem research is to overcome small working ranges, typically resulting from mechanical connections and restoring forces such as for cantilevers. In the case of predefined resting positions and unidirectional motion, pseudo-levitation as in magnetic bearings is a promising solution. In order to investigate concepts for energy efficient, cooperative microactuators, which allow free motion of small objects, we present a bistable levitation setup. The system consists of a magnetic proof mass within a glass tube, a piezoelectric staple actuator, two permanent magnets and a solenoid used as an electromagnet. The movable mass is mechanically unconstrained in its upper vertical motion and is intended to switch between two predefined equilibrium positions, namely on the staple actuator and levitating at a defined upper position. The transition is accomplished by an impulse-like kick force by the staple actuator, and subsequent feedback controlled following of a trajectory via electromagnetic actuation. The goal of this work consists of both adapting the system parameters, guaranteeing stable and preferably robust equilibrium positions for the unactuated system, and finding optimal trajectories with a short settling time and minimum input effort for the controlled transition. These design and control objectives are combined within a co-design. In this approach, the system and controller optimizations are not performed consecutively, but within a single optimization, taking into account the coupling between the design and control. Here, we apply flatness-based control combined with feedback linearization, allowing for trajectories to be tracked without error in case of the undisturbed system. Thus, the controller is solely used for disturbance compensation and the problem can be simplified by optimizing only the trajectory without the controller parameters. We show that the combined optimization process is of advantage in comparison to the sequential approach and proficiently exploits the design parameters to improve the generated trajectories.

In this work, a novel environmentally friendly method for the microstructuring of metal thin films, which is an essential fabrication step within the production of microchips, is presented. Through employing digital lithography by inkjet printing of inks based on the natural biomaterial shellac, solely comparably safe chemicals (e.g. shellac, ethanol and isopropanol) are employed while hazardous developer solutions needed for conventional masking methods using photoresists are avoided. Within the newly developed process, shellac inks are printed on reusable transfer layers, which highly increase the masking resolution in contrast to directly printing on metal thin films to linewidths of approximately 60 μm and renders the process virtually independent on the surface properties of the material to be structured. The printed shellac mask patterns are thermally transferred onto the metal thin films and stripped after wet etching using ethanol or isopropanol. Using the method presented, rigid and flexible circuits made of copper or aluminum were successfully fabricated and tested. Inkjet printing of different shellac inks was evaluated through contact angle and viscosity measurements and morphology assessments of inkjet printed line patterns, indicating that a shellac/isopropanol ink with a concentration of 0.05 g/mL showed the optimum printing performance. Sorption experiments in common aluminum and copper wet etchants revealed that for low to medium etchant concentrations shellac shows a decrease in swelling for increasing etchant concentrations.

Due to its extraordinary properties diamond can be used as mold in a hot embossing process which allows the replication of micro-optical structures. For this application a low surface roughness is indispensable. We investigated the ability of ion beam etching (IBE) to smooth defined rough areas after reactive ion etching (RIE). Simulations based on the influence of the angle dependence of the ion beam etch rate showed the suitability of this approach. Different surface qualities were achieved for nanocrystalline diamond films by RIE with three different oxygen-argon gas mixtures and etch depth, respectively. SEM images displayed the expected increase of surface roughness with the oxygen share of the gas mixture and the achieved etch depth. No masking layers were employed during ion beam post-processing. The comparison of different AFM images confirm that this process enlarged the etch depths corresponding to the initial surface roughness until the rough areas are smoothed completely. With increasing surface roughness the expenditure of time necessary to reach saturation rose. Etch rates measured for reactive ion etching were 5 to 6 times higher than the etch rate measured for IBE. Simply comparing the etch time the combination of RIE and IBE is up to four times faster than only employing IBE for the fabrication of structures despite using low RIE plasma powers.

Diffraction-limited deep focusing into biological tissue is challenging due to aberrations that lead to a broadening of the focal spot. The diffraction limit can be restored by employing aberration correction for example with a deformable mirror. However, this results in a bulky setup due to the required beam folding. We propose a bi-actuator adaptive lens that simultaneously enables axial scanning and the correction of specimen-induced spherical aberrations with a compact setup. Using the bi-actuator lens in a confocal microscope, we show diffraction-limited axial scanning up to 340 μm deep inside a phantom specimen. The application of this technique to in vivo measurements of zebrafish embryos with reporter-gene-driven fluorescence in a thyroid gland reveals substructures of the thyroid follicles, indicating that the bi-actuator adaptive lens is a meaningful supplement to the existing adaptive optics toolset.

Quasi-non-diffracting beams are used in a wide range of applications because of their ability to localize the radiation energy in narrow spatial and angular distributions. We present the development of free-form tunable MEMS mirrors to generate non-diffracting beams with unique spatial profiles. The mirror surface defined by a polynomial function is produced by shape optimization of a mold for subsequent molding profiting explicitly from a well-defined volume shrinkage. The actuation is achieved by thermal expansion of a polymer layer, which defines the final tuned shape of the mirror. The deflection of the mirror surface and the resulting iry beam is characterized.

We present a biaxial adaptive prism that allows for a simplified light path compared to scanning mirrors. Using three piezo bimorph actuators with stepless control, we actively tilt a fluid-glass interface, achieving scan angles up to 8.5° with response times down to 5.5 ms. The compact and optimized design has an outer diameter of 33 mm for a 7 mm aperture.

We present an integrated, compact micro-optical system capable to generate depth-controlled Bessel beams by integrating a miniaturized adaptive liquid crystal ring aperture array with a micro-lens array, a lensacon, which is a combination of a lens and an axicon. We were able to successfully demonstrate a functional system that is able to generate and control Bessel beams.

We present in this paper the design and fabrication of a miniaturized array of piezoelectrically tunable Fresnel mirrors, which can be used to generate propagation invariant and self-healing interference pattern. The mirrors are actuated using a circular piezoelectric actuator, and the resulting change in the tilting angles of the mirrors changes the widths of the interference patterns generated. The array consists of four Fresnel mirrors arranged in 2 × 2 configuration with each mirror having an area of 2 × 2 mm2. The achievable mirror angle ranges from −10 to +10 mrad.

We present the design and fabrication of a miniaturized array of piezoelectrically actuated high speed Fresnel mirrors with individual mirror control. These Fresnel mirrors can be used to generate propagation invariant and self-healing interference patterns. The mirrors are actuated using piezobimorph actuators, and the consequent change of the tilting angle of the mirrors changes the fringe spacing of the interference pattern generated. The array consists of four Fresnel mirrors each having an area of 2x2 mm2 arranged in a 2x2 configuration. The device, optimized using FEM simulations, is able to achieve maximum mirror deflections of 15 mrad, and has a resonance frequency of 28 kHz., Comment: 8 pages, 9 figures, submitted to IOP SMS

We present the, to our knowledge, so far fastest deformable lens, with a response time of 100 to $200\ \mu \mathrm{s}$ and a clear aperture of 7.6 mm at 9 mm outer diameter (84%). This is achieved using transparent compliant elastomer structures with an index-matched optical fluid and an actuator covering just 11% of the diameter that we bond in a two-stage gluing process using a gas phase curing agent.

We present two different piezo-actuated adaptive prisms with apertures ≥8 mm based on a tiltable glass window on top of an optical fluid. In the first prism, we realized a simple monoaxial scanner based on a lever principle. In our second design, we extended the scanning to two axes using three individually controllable piezo cantilevers. We were able to prove the concept for continuously adjustable variable prisms and achieved a tilt angle up to ±3.7° with a response time of 36 ms.

This paper presents a dual-mode spectral imaging system, which allows switching between pure lateral imaging and the spectrally resolved recording of spatial information. The optical system was equipped with tunable functionalities in order to achieve high flexibility, cover a wide range of object distances, and address extended field angles. A fluidic membrane lens was used for the variable focus, and the recording of the laterally extended scene was made possible by successively adjusting the different tilting angles to the different object positions. The capability and performance of the spectral imaging system were assessed using various test scenes, with different aimed field positions and changing object distances.