Optofluidic switch ducts light for solar illumination

Solar interior lighting can be very low-tech, as in a window, or high-tech, as in light collected by roof-based optics and ducted into and around rooms. One way of doing the latter is to focus light via a concentrator into an optical fiber, which can be a very adaptable way to route light within buildings. However, one thing this type of system needs is a device to configurably switch the light stream from a fiber into a room. Mechanical switches with flipping mirrors and additional optics are possible, but are large, costly, and ultimately unreliable.

A simple optofluidic alternative has been created by Wuzhou Song and Demetri Psaltis of the Swiss Federal Institute of Technology Lausanne (Lausanne, Switzerland), which is based on a waveguide that has a thin oil film and closely spaced interdigitated electrodes on one side. When there is no voltage drop across the electrodes, the oil film has a uniform thickness and the light passes through the waveguide. When a voltage is applied, the oil bunches up between the electrodes due to electrophoretic effects and creates a leaking (not a diffraction) grating, ducting light that is zigzagging in the waveguide out the side. With a film of 18 to 24 μm of silicone oil and an electrode period of 200 μm, a 50-mm-long waveguide with a cross-section of 535 μm × 4 mm (with light coupled in and out via fiber bundles), the light is switched one way or the other by switching on and off a voltage of 800 V. On and off response times were 0.15 and 5 s, respectively; the latter time was shortened to 0.3 s if the electrodes were short-circuited to eliminate capacitance effects. Contact Wuzhou Song at [email protected].