Most optical systems benefit from tunability. The ability to controllably change the focal length, magnification, or orientation of a single component or optical assembly is essential for many applications, and is typically accomplished macroscopically using mechanical movement of parts of the system with respect to each other. If we think of focusing a microscope, zooming a camera lens, or rotating a mirror for beam alignment, tunability is usually accomplished by twisting a dial, pushing a knob, or shifting a fixture.

In the micro-world a host of effects provides a number of novel means to tune micro-optical components, such that tunable micro-optics has developed into a dynamic research area (Friese et al., 2007; Krogmann et al., 2007). On the one hand, new materials, such as liquids, distensible membranes, liquid crystals, and deformable structures, may be used for the fabrication of micro-optical components, and on the other, phenomena such as surface tension, pressure, mechanical deformation, and the application of electric or magnetic fields may be employed to tune the optical characteristics. Most of these do not apply to macroscopic systems, so that we have a uniquely micro-optical topic at hand.

We consider in this chapter some of the techniques and devices that have been used to realize tunable micro-optical components and systems. A sizable fraction of the concepts employ liquids, either as droplet lenses or in microfluidic systems, and other softmatter elements, such that we study a number of these in detail.