| 研究実績の概要 |
The analytic model for double nanoridge is simple. We model that the SPP wave launched from double nanoridge is just interference result of SPP wave launched by each single ridge, which is already discussed. This phase delay occurs because plasmon wave travel along graphene-air interface. When the plasmon wave propagate over ridge, it must follow the ridge curve, resulting in an extra travelling length compared to that of flat graphene. This delay can be calculated analytic from the difference between right curve length and the straight line under the ridge. We also did the simulation (not shown here) to confirm this phase delay, and the numerical result match the analytic result.
For the right side, the SPP wave launched from 100-nm experienced phase delay from 150-nm ridge before interferes with another SPP wave launched from 150-nm ridge. For the left side, the SPP wave launched from 150-nm ridge also got phase delay from 100-nm ridge. However, the two phase delays are not equal. Therefore, the interference on each side is different, resulting in asymmetric directional plasmon launching.
The ratio of right/left launched amplitude from the analytic model was shown. From this graph, one can choose the condition which provide strong directionality of the plasmon launching. We then use the condition (275 nm ridge separation) to perform simulation. Directional plasmon launching is achieved. Wavelength-sorted launching (same structure, SPP wave goes to left or right side depending on wavelength), is also achieved.
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