Abstract
Various metal-insulator-metal- (MIM-) type plasmonic waveguides and gratings are investigated numerically. Three gratings are treated: one is formed by alternately stacking two kinds of MIM waveguides, another by periodic changes in the dielectric insulator materials of an MIM waveguide, and the other by a periodic variation of the air core width in an MIM waveguide. The dispersion property of each MIM waveguide of which the grating consists is analyzed using the implicit Yee-mesh-based beam-propagation method. It is shown that the third one has a relatively large effective index modulation of the guided mode with a simple grating structure, while maintaining a low propagation loss. Further examination is given to modifications of this grating structure. The transmission characteristics are examined using the frequency-dependent implicit locally one-dimensional FDTD method. We discuss how the modified grating structure affects the bandgap of the transmission characteristics.
Highlights
Metal-insulator-metal- (MIM-) type plasmonic waveguides have received considerable attention, since compact optical circuits may be realized [1, 2]
The alternative effective index modulation of an MIM waveguide leads to a plasmonic waveguide Bragg grating that is one of the basic building blocks for small size plasmonic circuits
It is shown that the grating with a periodic variation of the air core width (Figure 1(c)) yields a relatively large effective index modulation of the guided mode in the grating section, while maintaining a low propagation loss
Summary
Metal-insulator-metal- (MIM-) type plasmonic waveguides have received considerable attention, since compact optical circuits may be realized [1, 2]. The alternative effective index modulation of an MIM waveguide leads to a plasmonic waveguide Bragg grating that is one of the basic building blocks for small size plasmonic circuits. We compare the basic characteristics of several MIM waveguides of which gratings are composed. The effective index versus core width of each MIM waveguide is calculated using the imaginary-distance Yee-mesh-based beam-propagation method (YM-BPM) [8]. It is shown that the grating with a periodic variation of the air core width (Figure 1(c)) yields a relatively large effective index modulation of the guided mode, while maintaining a low propagation loss. It is found that the convex grating gives a wide bandgap in the transmission coefficient because of a large index modulation.
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