Predictions of spectral properties in the mid-IR wavelength range can be obtained from the available literature and/or database of Lumerical (E. Palik's data sets). Figure ) shows the complex refractive indices of SiO 2 -glass and CaF 2 extracted from the Lumerical database. The complex refractive index ñ ≡ n + ik and the complex dielectric constant (permittivity) ε 1 =n 2k 2 and ε 2 = 2nk (ε ≡ ε 1 + iε 2 ). The complex refractive index ñ and complex dielectric constant ε were determined based these relations from experimental database (Lumerical). Furthermore, the reflection and transmission spectra were calculated by the FDTD method as described below. The refractive indices and dielectric constants of CaF 2 show that the values of n and k are 1.43 and 0, respectively, from the visible to the near-IR region, while for SiO 2 , a significant modulation of refractive index in the range below 2000 cm -1 (λ > 5 µm). This absorption is due to the oscillations occurring in SiO 2 bonds in the mid-IR. When the refractive index is rewritten as a dielectric constant, the dielectric constant shows the Lorenz type resonance, which indicates that the absorption follows spectral line-shape of a harmonic oscillator. For the CaF 2 however, an almost flat refractive index and dielectric constant in the wavenumber range up to 1000 cm -1 is evident. The absorption losses are slight and the influence of the refractive index and dielectric constant is revealed in the spectrum by FDTD calculations in Fig. ). From the FDTD calculation of the reflection and transmission of the film with 400 nm thickness: SiO 2 shows a significant absorption in the range of 1000-2000 cm -1 while CaF 2 has almost zero absorption characteristics. How these mid-IR optical properties affect the overall optical characteristics of the MIM metasurface is examined next.