Fig. 1. Optimal simulated transmittance (red line) of the Reuleaux-triangle-shaped hole array on Ge for T1=1.1μm, R=1μm, and r=0.8μm. Inset (a) is a single Reuleaux-triangle-shaped hole, and (b) shows Reuleaux-triangle-shaped holes forming a closely packed hexagonal array (top view). The polarization direction of the incident light is 0° with the x axis.

Fig. 2. Electric field distributions for a single period of the Reuleaux-triangle-shaped hole array: (a) incident 3–12 μm electromagnetic wave with uniform distribution of field intensity, and (b)–(h) different mid-IR wavelengths passing through the Reuleaux-triangle-shaped holes. The incident light is TE polarized.

Fig. 3. (a) Photograph and (b) SEM micrograph of the fabricated Ge wafer with a Reuleaux-triangle hole array. (c) SEM side view of two Reuleaux-triangle holes.

Fig. 4. (a) Transmission spectra of the fabricated element (yellow line), Ge substrate (2 mm thickness, blue line), updated simulated element with nonuniform hole depths (green dot-dashed line), and the maximum theoretical antireflection on one side (red line). (b) The measured transmittance versus incident angle.