Micro Branch Filter Fabricated by Alignment of Microspheres

Optical Wiring of Integrated Circuits using Self-Assembly Process

2008.05.30

National Institute for Materials Science

A team headed by Senior Researcher Tadashi Mitsui of the Quantum Dot Research Center, National Institute for Materials Science, in joint work with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, succeed in the development of micron-scale optical wiring and a branch filter which enables 90° bending by alignment of microspherical resonators using a self-assembly technique.

Abstract

  1. A team headed by Senior Researcher Tadashi Mitsui of the Quantum Dot Research Center, National Institute for Materials Science (President: Prof. Teruo Kishi), in joint work with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, succeed in the development of micron-scale optical wiring and a branch filter which enables 90° bending by alignment of microspherical resonators using a self-assembly technique.
  2. In recent years, methods of converting part of the information transmission in integrated circuits to optical communications have attracted attention as an approach to further increasing computer speed. In order to realize this, it is necessary to propagate light with a width of several μm across a maximum distance of several mm, and also to perform wiring freely using bending radii of several μm. However, such small bending radii could not be achieved with the conventional optical waveguide technology that was unable to realize a large refractive index difference in waveguide. On the other hand, methods using air-trench type cladding and photonic crystals have been reported, but because a structure for confining the light is necessary on the outer side, it was also difficult to produce optical waveguides "freely with micron-scale width" using these novel methods.
  3. The coupled-resonator optical waveguide (CROW), which is fabricated by coupling optical resonators with high refractive indexes, enables free optical wiring by arrangement of the resonators themselves and does not require cladding. In particular, with a method that utilizes microspheres as the resonator, arrangement of resonators is possible using a self-assembly technique. In this research, when microspheres were arranged using a patterned substrate as a template, and the light propagating in these spheres was observed by polarized guide-collection-mode near-field scanning optical microscopy, it was found that the spheres split the light into different resonant wavelengths, and thus function as a branch filter.
  4. The optical wiring developed in this research can be applied as an optical waveguide for high speed information communications between central processing units (CPU) when multiple CPUs are arranged in an integrated circuit. Furthermore, by enabling differentiated use of multiple wavelengths, realization of information transmission to designated destinations can be expected. In the future, research will focus on optical waveguides with more advanced functions.
  5. These research results were obtained as part of a collaborative laboratory project of Tohoku University's Institute of Multidisciplinary Research for Advanced Materials and the National Institute for Materials Science. The results are scheduled to be announced at the 17th Nano Optics Workshop of the Optical Society of Japan to be held at the International Congress Center Epochal Tsukuba June 26-27, and will also be published in the American science journal "Optics Letters" in the near future.