This thesis focusses on two aspects of tunable optics: Fabry-Pérot interferometers with a variable distance between their mirrors and electrowetting liquid lenses. The need for a device to detect child abuse has motivated us to design and build a camera that can detect the chemical composition of the upper skin layers of a bruise using a self-made Fabry-Pérot interferometer. The research described in the first part of this thesis has shown that wide-angle spectral imaging can be achieved with compact and cost-effective cameras using Fabry-Pérot interferometers. Designs with a full field of 90◦ in which the Fabry-Pérot interferometer is mounted either in front of an imaging system or behind a telecentric lens system are presented and analysed. The dependency of the spectral resolution on the numerical aperture of the lens system is derived and its value as a design criterion is shown. It is shown that the telecentric camera design is preferable over the collimated design for bruise imaging with a Fabry-Pérot interferometer. The idea to use a liquid lens for spectral imaging has directed the research towards a new concept of controlling surface waves on the surface of a liquid lens. We investigate and model surface waves because they decrease the imaging quality during fast focal switching. We propose a model that describes the surface modes appearing on a liquid lens and that predicts the resonance frequencies. The effects of those surface modes on a laser beam are simulated using geometrical optics and Fresnel propagation, and the model is verified experimentally. The model of the surface oscillations is used to develop a technique to create aspheric surface shapes on commercially available electrowetting liquid lenses. The surface waves on the liquid lens are described by Bessel functions of which a linear combination can be used to create any circularly symmetrical aspheric lens shape at an instant of time. With these surface profiles, one can realise a large set of circularly symmetrical wavefronts and hence intensity distributions of beams transmitted by the lens. The necessary liquid lens actuation to achieve a desired shape is calculated via a Hankel transform and confirmed experimentally. The voltage signal can be repeated at video rate. Measurements taken with a Mach-Zehnder interferometer confirm the model of the surface waves. The capabilities and limitations of the proposed method are demonstrated using the examples of a Bessel surface, spherical aberration, an axicon, and a top hat structure.@en

A technique to create aspheric surface shapes on commercially available electrowetting liquid lenses is demonstrated. Based on a previously published surface oscillation model a technique using a Hankel transform is proposed and tested experimentally. An alternating actuation voltage is applied to the liquid lens to stimulate surface oscillations, that temporarily add up to the desired surface shape. The voltage signal can be repeated at video rate. The measurements were taken with a Mach-Zehnder interferometer and confirm the previous results. The capabilities and limitations of the proposed method are demonstrated using the examples of a Bessel surface, spherical aberration, an axicon, and a top hat structure.@en

Liquid lenses are a widespread solution for easy adaptive optics problems due to their low price. We present a technique based on surface oscillations, that extends the functionality to create a tunable asphere at the expense of light efficiency without the use of additional hardware.@en

Liquid lenses are an emerging technology, that allows focal switching without any moving parts. While standard liquid lenses focus on tuning the defocus aberration, higher order aberrations shift into the focus of the current research. We propose a method using standing waves on a liquid lens to design more complex phase fronts. Similar to common speaker membranes, it is possible to create a large variety of different surface functions on the liquid’s surface by controlling the AC input voltage. The created phase fronts are circularly symmetric and can for example take the shape of spherical aberrations. Liquid lenses might therefore be used as a cheap tuneable phase manipulator for beam shaping, or image correction.@en

The increased usage of liquid lenses motivates us to investigate surface waves on the liquid's surface. During fast focal switching, the surface waves decrease the imaging quality. We propose a model that describes the surface modes appearing on a liquid lens and predicts the resonance frequencies. The effects of those surface modes on a laser beam are simulated using Fresnel propagation, and the model is verified experimentally.

@en

We extend the tunability of liquid lenses to non-spherical surfaces by inducing oscillations on the liquid lens surface. We investigate their nature and whether we can make use of them in optical systems.@en

We extend the tunability of liquid lenses to non-spherical surfaces by inducing oscillations on the liquid lens surface. We investigate their nature and whether we can make use of them in optical systems.@en

Liquid lenses using the electrowetting effect can be used to manufacture small-sized autofocus and zoom cameras. We extend the tunability to non-spherical surfaces by inducing oscillations of the liquid–liquid interface and will explore its possibilities in a wider range of applications.@en

Wide-angle spectral imaging systems using Fabry-Pérot interferometers face spectral resolution problems, which can only be corrected with high computational effort. A standard lens system is analysed and an alternative telecentric solution is proposed, that solves the issues optically without the use of intensive computation.@en