EAGER - Directed Total Internal Reflection Devices

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

Many modern devices such as solar cells, cameras, and optical detectors require a high light transmission and the presence of electrical circuitry within the same structure. This poses a major challenge: metallic electrical wiring is highly absorptive and reflective, and consequently devices often sacrifice optical performance in order to maintain efficient electrical access. If this seemingly unavoidable problem could be bypassed, a large number of devices could achieve greater performance, for example larger optical transmission, larger energy efficiency, or higher device speed. The work proposed here aims to experimentally demonstrate an entirely new device structure to achieve these goals by developing a new type of electrode that turns the detrimental high reflection of metallic wires into an asset. The structure consists of an array of conductive wires on transparent substrate. The wires are embedded in a transparent cover layer that is index matched to the substrate. By defining electrodes with a tilted top surface, light reflected by the wires is not lost but instead directed to large angle inside the cover layer, resulting in a virtually lossless total internal reflection. In this way, light that would otherwise be lost is given another chance to reach the substrate. Surprisingly, a ray analysis of this structure predicts complete optical transparency even when half the surface is covered with metal. The experimental demonstration of this concept could have far reaching implications for a wide range of optical devices. The concept of using directed total internal reflection in order to develop a transparent interdigitated electrode has been theoretically proposed, but has not yet been demonstrated experimentally. The current proposal aims to generate transparent electrode structures in order to explore fabrication strategies and to investigate the achievable performance in a non-idealized real-world system. In addition, two key theoretical aspects will be addressed. The transmission performance of double surface tilt and parabolic electrode surfaces will be investigated theoretically, and the performance of these structures will be studied as a function of incidence angle. In order to fabricate electrodes with a well-defined surface tilt, a combination of photolithography and shadow evaporation will be used. Automated sample motion during thermal evaporation onto a patterned resist layer enables the generation of non-planar metal surfaces. After liftoff the resulting angled metallic wires will be covered embedded in a transparent cover layer using spin-coating, and transmission spectra in the visible and near-infrared regions will be measured as a function of incidence angle. The results will be compared with reference electrode structures that do not have a surface tilt. The flexibility of the shadow evaporation process will enable the experimental investigation of a wide range of electrode surface shapes, including tilted surfaces with subwavelength steps, as well as double-tilt electrodes. The proposed experiments constitute a critical step toward implementing this new concept in practical optical devices.