<title>1D photonic crystals based on periodically grooved Si</title>

Abstract

Periodic structures of grooved Si with lattice constants A = 2 - 4 µm, having the horizontal modulation of the refractive index, <i>n</i>, and acting as the 1D Photonic Crystal (PC) in the middle and far IR range (5-50 µm), have been fabricated by means of wet anisotropic etching of (110) oriented single crystalline silicon. The “gap maps” for both the empty matrices of periodically grooved Si and the composites infiltrated with liquid crystal (LC) of the average refractive index <i>n</i>=1.6 have been calculated. These maps display the frequency regions of photonic band gaps (PBGs) as a function of the filling factor D_si/A and simplify the design of 1D PC structures for user-specified wavelength range. FTIR measurement revealed wide stop bands in the reflection and transmission spectra. Infiltration of the periodically grooved Si with the nematic liquid crystal E7 results in a shift of the main band gap to the higher wavelengths and in the consequent changes in the secondary stop bands. It is shown that polarized spectra of grooved Si infiltrated with LC allows determination the refractive index of the LC and the orientation of its molecules.