Advanced characterization of electrowetting retroreflectors

Abstract

Electrowetting retroreflectors use a simple and scalable construction, and incorporate an electrically tunable liquid lenslet. By electrically modulating the lenslet geometry, the reflection is switched between retroreflection and scattering. In this paper, we report new capability and characterization, including higher index liquids and contrast ratio as a function of contact angle (theta(V)). The reflected intensity is also spatially profiled and reported as a function of view angle. A high contrast ratio of >16X is demonstrated, and methods for further improving performance are discussed. Because the electrowetting retroreflector platform is broad spectrum (VIS-IR), the electrowetting retroreflector may be useful for a large variety of naked eye applications such as safety markings, road-signage, or friend-foe-identification.

Investigation of five types of switchable retroreflector films for enhanced visible and infrared conspicuity applications

“…The maximum input angle at 30% of maximum reflection (θ 30% ) is at 30°-35°, and can be increased by use of higher refractive index oils with little to no loss to the electrical operation of the device. Uncharacteristic (for a basic retroreflector) dips and peaks in reflection can be seen for ∼ 10°and ∼ 20°, which is speculated to be due to thin film interference from the hydrophobic dielectric stack [23].…”

“…2. Detailed information on the fabrication and operation of this device is provided elsewhere [22,23].…”

Recent Developments in Optofluidic Lens Technology

“…Figure 10 illustrates a few examples of such devices that can be integrated into various optical devices for a wide range of applications, from photonics [ 74 ], display technologies [ 75 ], and the biomedical industry to integral imaging for 3D vision [ 76 ]. These examples include elements such as shutters [ 77 ], beam steering prisms [ 78 ], and controllable reflectors [ 79 ]. All examples shown make use of the enormous flexibility of electrowetting to manipulate the shape and orientation of fluid interfaces.…”

Electrically tunable optofluidic lenses : fabrication and characterization

“…Figure 2.10 illustrates a few examples of such devices that can be integrated into various optical devices for a wide range of applications, from photonics [74], display technologies [75], and the biomedical industry to integral imaging for 3D vision [76]. These examples include elements such as shutters [77], beam steering prisms [78], and controllable reflectors [79]. All examples shown make use of the enormous flexibility of electrowetting to manipulate the shape and orientation of fluid interfaces.…”

“…10B shows an EW-actuated microprism with a flat (uncurved) liquid-liquid interface of variable tilt[78] that enables steering of beams in two independent directions on a time scale of ms. Similarly, wedge-shaped geometric structures can be exploited to create efficient switchable retroreflectors[79] by alternating between a flat and a curved liquid-liquid interface,Figure 2.10C. Recently, Schuhladen et al[80] constructed a tunable optofluidic slit aperture actuated by AC electrowetting.…”