Adjustable Optical Slit Based on Electrowetting

In this letter, we report an adjustable optical slit using two immiscible liquids, including an opaque liquid and a clear liquid. The opaque liquid is conductive, whereas the clear liquid is insulating. The opaque liquid is divided into two droplets, which are surrounded by the clear liquid. In the voltage- off state, the two droplets keep away from each other. When a voltage is applied to the device, the two droplets move in opposite directions and form a slit-like opening due to force balance between electrostatic force and charge repelling force. Our results show that the width of the slit can be tuned from ~ 160 to ~ 570 μm as the applied voltage is changed from ~ 40 to ~ 80 V. The shape deforming response time of the droplets and the transmittance in the opening area were measured to be ~ 390 ms and ~ 86%, respectively. Our optical slit has potential applications in spectrophotometers, line spread functions, and masking.