Optical Negative Refraction in Bulk Metamaterials of Nanowires
Abstract
Metamaterials are artificially designed subwavelength composites possessing extraordinary optical properties that do not exist in nature. They can alter the propagation of electromagnetic waves, resulting in negative refraction (1), subwavelength imaging (2), and cloaking (3). First reported at microwave frequencies by using metamaterials made of an array of split ring resonators and metallic wires (4), negative refraction has been observed in two-dimensional (2D) photonic crystals into the infrared (IR) region (5 8) and in surface plasmon waveguides at visible frequencies (9). In both cases, negative refraction is constrained in two dimensions and is limited to a narrow band of frequencies. An indirect observation of negative refraction in the mid-IR region was also reported in a semiconductor multilayer structure (10). Creating bulk metamaterials that exhibit negative refraction for visible light remains a major challenge because of substantial resonance losses and fabrication difficulties. Recent theoretical studies suggest that metamaterials consisting of metal wire arrays exhibit an optical response at frequencies far away from resonances (11, 12), in which electromagnetic (EM) waves propagating along the nanowires exhibit negative refraction at a broad frequency band for all angles (13). Moreover, the material loss is much lower than traditional metamaterials with similar functionality. We report observations of negative refraction in bulk metamaterials composed of silver nanowires with separation distance much smaller than the wavelength at optical frequencies (Fig. 1A). A porous alumina template was prepared by electrochemical anodization (14), intowhich silver nanowires were electrochemically deposited. A 1-mm-wide slit, etched through a 250-nm thick silver film coated on the metamaterials, was illuminated by a collimated diode laser beam at different incident angles (see left side of Fig. 1A).
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 15, 2008
- Accession Number
- ADA624604
Entities
People
- Angelica M. Stacy
- Cheng Sun
- Guy Bartal
- Jie Yao
- Xiang Zhang
- Yongmin Liu
- Yuan Wang
- Zhaowei Liu
Organizations
- University of California, Berkeley