Surface Plasmon and Nano-metallic layout simulation with OptiFDTD
1. Lorentz_Drude Model and Surface Plasma wave
Metallic photonic materials demonstrate unique properties due to the existence on metals ofelectromagnetic surface waves known as surface plasmons. Surface plasmons are set to become
part of the photonics revolution in which the interaction between light and matter is controlled byproducing patterned structures that are periodic on the scale of the wavelength of light. Surface
plasmons open up a wealth of new possibilities for photonics because they allow theconcentration and propagation of light below the usual resolution limit, thus opening up suchpossibilities as sub-wavelength optical components. OptiFDTD was the first software that
employed the Lorentz_Drude model for the surface Plasmon and metallic layout simulation. The
Frequency domain Lorentz_Drude model is discussed in reference [1]. Figure 1 is thepermittivity [1] for the noble metal gold and silver, as we can see they are very dispersive.
OptiFDTD used the time domain Lorentz_Drude model [2] (Please provide the link for ourpaper). Figure 2 shows the OptiFDTD simulated surface wave propagate along a Silver surface.

Figure 1

Permittivity of Gold and Silver [1]Figure 2 OptiFDTD simulated Surface Plasmon wave propagates along the silver surface[1] A. D. Rakic, et al. “Optical Properties of metallic films for vertical-cavity optoelectronicdevices”, Applied Optics, Vol. 22, No.22, Aug.1998, pp.5271[2] Richard Zhang, et al. “Finite-difference time-Domain method guides optical design ofmetallic nanostrcutures”, LaserFocusWorld,2004,

2. Example 1: Beaming light from metallic aperture
Original reference:
OptiFDTD simulation results can be compared with the following reference:[3] H.J. lezec, et al. “Beaming light from a subwavelength Aperture”, Science, Vol. 297, August
2002, pp.820.

Figure 3 Bull’s eye structure of Ag film [3]Layout in OptiFDTD

Figure 4 Side view of the layout.
Simulation results
Wave propagation effect can be observed in the simulator as shown in figure 5

Figure 5 Beam propagation through the holesPower transmission spectrum can be detected (See figure 6). Figure 7 is the optical image fromthe OptiFDTD for this bull’s eyes Ag film.

Figure 6 Power transmission for normal incident wave

Figure 7 Optical images of the layout.

3. Example 2: Nano-scale image
Introduction
In this example, a subwavelength image system layout using the metallic nano-rods is simulated.
The point sources under the nano rods compose a letter λ shape. The OptiFDTD simulationshows the silver nano-rods works as a mirror read successfully the shape λ. The original concept
can be found in the following reference[4] Atsuchi Ono, et al. “Subwavelength optical imaging through a metallic nanorod array”,
Physical review letters, 31December, 2005.

Figure 8 Nano-rod image system [4]OptiFDTD Results
After the OptiFDTD simulation, the field patterns are recorded at the different transverse slice ofthe nano-silver-rod array. Figure 9 shows these images, as we can see that the image shape λ canbe successfully repeated in the other end of the nano-rods.

Figure 9 Read the image of shape λ by the OptiFDTD

4. Example 3: Field enhancement for Nano-bow-tie antennaIn the past several years, nano-antenna was being studied actively. As rewarded software,OptiFDTD did some contributions in this study. The following examples show the fieldenhancement effect for the nano-bow-tie antenna. The project took David P. Fromm, et al two
published papers as reference[5-6]. The OptiFDTD project Layout is shown in Figure 10,[5] David P. Fromm, et al. “Gap-Dependent Optical coupling of single “bowtie” nanoantennas
resonant in Visible”, Nano Letters, Vol. 4, No.5, 2004, pp. 957-961[6] P. J. Schuck, David P. Fromm, et al. “Improving the mismatch between light and nanoscale
objects with gold bowtie antennas”, Physical review letters. 14 Jan. 2005,Figure 10, Gold Bowtie antenna in OptiFDTD

Simulation Notes


Input wave is the plane wave in xy plane, propagate to direction

X-direction polarization (parallel to the axis of bowtie)

Input plane wave amplitude is 1.0 (Ex,inc=1.0)

Use the VB to sweep the CW input wavelength or used pulse to cover a relative broadband

Simulation resolution is 2nm

Simulation used the periodic symmetric boundary condition for x-y boundary and PML
for z direction boundary (negative x edge is mapped to positive x edge boundary---cansave the memory

Simulation results
The Field enhancement effect (as shown in figure 11) in the bow tie surface can be observed.
Field enhancement factor can also be extracted in from the field response (Figure 12)

Figure 11 Field enhancements in the edge of the bow-tie antenna

Figure 12 Field enhancement factor as a function of input wavelength