Variable optofluidic slit aperture

The shape of liquid interfaces can be precisely controlled using electrowetting, an actuation mechanism which has been widely used for tunable optofluidic micro-optical components such as lenses or irises. We have expanded the considerable flexibility inherent in electrowetting actuation to realize a variable optofluidic slit, a tunable and reconfigurable two-dimensional aperture with no mechanically moving parts. This optofluidic slit is formed by precisely controlled movement of the liquid interfaces of two highly opaque ink droplets. The 1.5 mm long slit aperture, with controllably variable discrete widths down to 45 µm, may be scanned across a length of 1.5 mm with switching times between adjacent slit positions of less than 120 ms. In addition, for a fixed slit aperture position, the width may be tuned to a minimum of 3 µm with high uniformity and linearity over the entire slit length. This compact, purely fluidic device offers an electrically controlled aperture tuning range not achievable with extant mechanical alternatives of a similar size. A variable optofluidic slit aperture that is based on electrowetting has been fabricated by researchers in Germany. Compact variable slit apertures are desired for use in miniaturized optical systems, but mechanical slits tend to be too bulky to be used in such systems. Now, Stefan Schuhladen and coworkers at the University of Freiburg have realized a tunable and reconfigurable two-dimensional optofluidic aperture that has no mechanically moving parts. It is formed by the precisely controlled movement of the liquid interfaces of two highly opaque ink droplets. The slit is 1.5 mm long and its width can be controlled down to 45 µm. It can be scanned across its length with a switching time of less than 120 ms between adjacent slit positions. This performance surpasses that of mechanical slits of the same size.