Florian Krogmann

Electrowetting for Tunable Microoptics

The design, fabrication, and optical properties of tunable liquid microoptical components based on electrowetting are presented. Two optical microsystems are discussed: a single liquid microlens with tunable focal length, centered and stabilized in a micromachined positioning structure, and laterally repositionable tunable liquid microlens arrays. The latter employs electrowetting for lateral movement as well as focal length tuning of the optical elements. Through the use of novel microstructuring techniques, a high positioning accuracy may be achieved with low electrode count.

Tunable liquid micro-lens system

Electro-wetting technology has become a promising approach for the fabrication of liquid micro-lenses with tunable focal length. By applying a voltage between a liquid droplet and an electrode covered by an insulating layer, the surface free energy, and thereby the contact angle of the droplet, is modified. By embedding the droplet in a fluid of the same density, the influence of gravity can be removed and a maximum of mechanical stability can be reached. A novel, tunable liquid micro-lens system fabricated in MEMS technology is presented and characterization results using three kinds of liquids, including an equal-density fluid system, are presented. The back focal length of this latter system can be tuned between 2.3 mm and infinity with applied voltages of 0 V to 45 V.

AC characterisation of thermal flow sensor with fluid characterisation feature

We have investigated the determination of flow speed and simultaneously gas concentration in a binary gas mixture. The fabrication process and characterization of a sensor element, based on the thermal principle, is presented in this paper. The sensor is equipped with an unsymmetrical 1D-array of temperature sensors and a heater. Time modulated heating is used to extract flow speed from thermal gas properties. Phase shift determines the thermal conductivity of the gas mixture. The accurate flow velocity can be calculated from amplitude measurement afterwards. Thermal conductivity can be already determined with an accuracy of 90%.

Fabrication and Characterization of a Repositionable Liquid Micro Lens System

A novel method to improve both the lateral positioning and focal length tuning accuracy of a liquid lens in a micro lens system, based on the electrowetting on dielectrics (EWOD) principle, is described. This system consists of a device, encapsulated with a packaging technique, fabricated on a transparent substrate featured with an array of electrodes and a structured surface whose periodicity is smaller than the electrodes dimension. With variable applied voltage signals, the liquid lens is actuated precisely in the lateral position and also tuned dynamically irrespective of the lens position on the substrate. The accuracy of lateral positioning is mainly dependent on the structure of the dielectric surface. Measurements of the focal length tuning range and the positioning accuracy are presented. A first design of reconfigurable micro lens system, which has diverse application as adaptive wave-front sensing, optical tweezers and etc, is demonstrated.

Repositionable liquid micro-lenses with variable focal length

A reconfigurable micro-lens system whose lateral position and focal length may be dynamically tuned is presented. Based on the electro-wetting effect, the system uses a patterned electrode array under the dielectric layers to allow separate control of a liquid droplet which acts as a spherical lens. By application of a custom voltage pulse sequence, the micro-lenses may be positioned and tuned along a two-dimensional surface.

Silicon-based tunable liquid lens system

We present a novel silicon-based micro-lens system actuated by electro-wetting including a lens centering mechanism and taking advantage of silicon dioxide dielectric layers and low surface roughness of standard MEMS-processes

Design and characterization of a thermal sensor achieving simultaneous measurement of thermal conductivity and flow speed

In this contribution, we present a novel design and excitation procedure for a thermal flow sensor to simultaneously determine thermal conductivity and flow rate of gas in a channel. For the first time, these two parameters can be detected by using a time-independent (DC) excitation mode. Theoretical and experimental results are discussed in order to specify possible application fields.

New technologies for tunable micro-optics

Microsystems technology may be employed for the conceptualization and fabrication of new types of tunable micro-optical components. Tunable polymer membrane-based micro-lenses, tunable liquid lenses and lens arrays as well as deformable membrane mirrors are presented here.

Optical Characterization of Repositionable Liquid Micro-Lenses

A reconfigurable micro-lens array based on a transparent substrate and liquid micro-lenses actuated by electro-wetting on dielectrics (EWOD) is presented. The substrate features an array of electrodes and a surface structure with a periodicity smaller than that of the electrode array. The device is shown to be capable of individually adjusting the position and the focal length of liquid micro-lenses. Measurements of the focal length as a function of applied voltage are presented. The tunable micro-lens array may have applications for adaptive wavefront sensing, for parallelized confocal microscopy, and for parallel optical tweezers.

Light-Actuated Push/Pull Manipulation of Liquid Droplets

An opto-electrowetting system allowing both pushing and pulling a droplet is presented for the first time. Experimentally demonstrated and described theoretically, the technique allows new flexibility in the design of freely-reconfigurable two-dimensional liquid micro-lens arrays