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Broadband Mirrors in the Near-Infrared Based on Subwavelength Gratings in SOI

Figure 1

Figure 1
Diagram of a 1-D (a) and a 2-D (b) SWG on an SOI wafer.

Figure 2

Figure 2
Simulated reflectivity (blue continuous lines) and transmission in logarithmic scale (dashed green lines) for 1-D (a) and 2-D (b) SWG. The lattice constants and fill factors were chosen for maximum reflectivity and bandwidth in the near-IR, i.e., Formula$a = 340\ \hbox{nm}$ and Formula$F = 0.68$ in (a) and Formula$a = 500\ \hbox{nm}$ and Formula$F = 0.39$ in (b). Contour plots of reflectivity versus the duty cycle (c)/fill factor (d). The operating points chosen in (a) and (b) are indicated by a dashed line.

Figure 3

Figure 3
SEM images of the fabricated 1-D (a) and 2-D (b) devices. The air lines width in the inset of (a) is about 90 nm, corresponding to a value of Formula$F = 0.74$. The inset of (b) shows the ellipticity of the patterned holes. The difference between the hole radii along the two perpendicular directions is of about 15 nm (Formula$r_{x} \approx 220\ \hbox{nm}$ and Formula$r_{y} \approx 205\ \hbox{nm}$).

Figure 4

Figure 4
Experimental (continuous lines) and numerical (dashed black lines) reflection spectra for the 1-D SWG (a) and (c) and the 2-D SWG (b) and (d). The blue (electric field directed along Formula$x$—see Fig. 3) and red lines (electric field directed along Formula$y$) indicate the two different polarization of the incident wave. The parameters used to calculate the numerical spectra for 1-D SWG are Formula$a = 340$ and Formula$F = 0.74$. For the 2-D case, we have simulated the lattice with Formula$a = 500\ \hbox{nm}$ and with an elliptical hole of radii Formula$r_{x} = 222\ \hbox{nm}$ and Formula$r_{y} = 208\ \hbox{nm}$ corresponding to a ratio of 93.7%.

Figure 5

Figure 5
Numerical (a) and experimental (b) 1-D SWG spectra contour plot. The experimental data refer to SWGs with a period of 300 nm–380 nm in 20 nm steps, the intermediate points having been interpolated. The color scheme divides the 80%–100% reflectivity range into 10 steps of 2% each.

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