Successful Fabrication of 2D Photonic Crystals

Masaya Notomi, Akihiko Shinya, and Itaru Yokohama
Materials Science Laboratory

    A photonic crystal is an artificial periodical structure composed of different refractive-index materials and its use is expected to lead to the development of smaller optical devices and larger scales of integration. We have been focusing on the SOI (Silicon On Insulator) structure and have been researching 2D photonic crystals in cooperation with Telecommunications Energy Laboratories.
    We have fabricated vertical holes with a triangular lattice pattern in a 200 nm-thick silicon layer with a period of 400 nm. The structure of this 2D photonic crystal is characterized by silicon regions (high refractive index) and air regions (low refractive index) in the vertical holes that are periodically arranged along the horizontal plane of the silicon layer. The propagated light is vertically confined in the silicon layers because silicon has a higher refractive index than silicon oxide or air. Measurements have revealed that a clear photonic bandgap (a feature of photonic crystals that functions as an optical insulator) is formed in the optical-communications wavelength region [1]. We have also proposed a width-varied line-defect structure that is applicable to the above structure. Figure 1 shows a SEM photograph of the width-varied line-defect structure we fabricated. Measurement results, such as the transmission-spectrum (Fig. 2), show that we have achieved low-loss transmission under single-mode conditions for the first time [2].
    In this research, we have demonstrated the 2D photonic crystal and line-defect structures using SOI structures. These structures are suitable as basic elements for ultra-small optical integrated circuits.

[1] I. Yokohama et al., OECC 2000 (2000) 11B2-4.
[2] M. Notomi et al., Electron. Lett. 37 (2001) 293.

Fig. 1. SEM viewgraph of fabricated line- defect waveguide structure.
Fig. 2. Tranmission spectra.

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