Incorporating news from O plus E magazine, Tokyo
TOKYOMasaya Notomi and colleagues at the materials science division of NTT Basic Research Laboratories have developed a photonic-crystal optical waveguide that operates on principles fundamentally different from the principles used in conventional optical waveguides such as optical fibers. This waveguide is created using semiconductor nanofabrication technologies on a silicon-on-insulator (SOI) substrate.
Photonic-crystal waveguide fabricated on a silicon-on-insulator substrate has single-mode optical transmission. (Photo courtesy of NTT)
Conventional technologies have made it difficult to create large-scale optoelectronic integrated circuits (OEICs) while miniaturizing the optical circuitry. This is because losses in waveguides become very high as the radii of bends reach microscopic dimensions. It is for this reason that optical circuits with photonic crystals have been in the spotlight. The NTT research group has succeeded in creating an optical waveguide with high-quality modes using photonic crystals on an SOI substrate. The SOI substrate is widely used by semiconductor companies to create next-generation computer chips and consists of a thin layer of glass sandwiched between two silicon layers.
This new photonic crystal uses semiconductor nanofabrication technology so that a silica cladding is not required. The photonic crystal has a large band gap in the 1.3- to 1.6-µm wavelength region. By forming stringlike defects, line-defect waveguides are created. It is the first time that clear single-mode optical transmission has been observed.
The waveguide consists of a silicon film of thickness 200 nm with holes in a 390-nm-period triangular lattice configuration. The line defects are created by removing a line of holes (see figure). The light is trapped within defect regions with widths of approximately 400 nm. The research group proposes that OEICs three or four orders of magnitude smaller than current OEICs can be created with SOI technology.
Courtesy O plus E magazine, Tokyo