Optical Properties and Optoelectronic Applications of Nano-size Metallic Films and Metamaterials.

Abstract

Future optical and optoelectronic devices are desired to have compact sizes, high efficiencies, robust performance, and low manufacturing costs. All these advances demand developments both in their constituent materials and design concepts. Silver (Ag) is one of the most widely used materials for optoelectronic devices and metamaterials. However, Ag is well known to have several issues, including difficulty to form high-quality thin films, poor stability in an ambient environment and under elevated temperatures, and inferior adhesion with substrates. In light of this, a new kind of silver: doped silver is developed. With the aid of a small amount of doping elements during the Ag deposition, ultra-thin, smooth, and low-loss Ag films are obtained. Compared to pure Ag films, doped Ag films have a significantly improved long-term and thermal stability, as well as good adhesion to various substrates. Doped Ag films have facilitated diverse high-performance optical and optoelectronic devices, such as organic solar cells, organic light emitting diodes, optical metamaterials, and plasmonic devices.

Metamaterials are artificially designed materials with extraordinary optical properties. Nano-size metamaterials (metasurfaces) are demonstrated for controlling various properties of light. An asymmetric light transmitting metasurface consisting of coupled metallic sheets is demonstrated. It has a measured transmission efficiency of 80%, extinction ratio of 13.8 dB around 1.5 µm, and a full width half maximum bandwidth of 1.7 µm. It is as thin as 290 nm, has good performance tolerance against the angle of incidence and constituent nano-structure geometry variations. In addition, a large-area, printed metasurface is designed and fabricated. It is made of lossless dielectric (silicon) materials and offers the functionality of converting a linearly polarized incident light into a radially polarized transmitted light.

These optical and optoelectronic devices also provide valuable solutions to problems in other fields, such as acoustic wave detection. It is shown that optical resonant structures provide a unique approach for acoustic wave detection. Nanoimprinted polymer microring resonators are investigated as high-performance ultrasound detectors. To further reduce the detector size, polymer filled silicon metasurfaces on fiber tips are also designed and fabricated.