Silicon-based near-infrared tunable filters filled with positive or negative dielectric anisotropic liquid crystals

Complementary metal-oxide-semiconductor-compatible tunable Fabry–Pérot microcavities filled with liquid crystals (LCs) were realized and studied in the near-infrared region. The microcavities were produced by chip bonding technique, which allows one to infill LC between two [SiO2/Si]3λ/4 (λ=1.5 μm) dielectric Bragg reflectors separated by 950-nm-thick SiO2 posts. Liquid crystals with positive and negative dielectric anisotropy were used, i.e. MerckE7 (Δε=13.8) and Merck-6608 LC (Δε=−4.2). Mirror-integrated electrodes allow an external bias to induce an electric field and to tune the LC properties and, hence, the microcavity resonance. Electric-field-induced shifts of the second-order cavity modes of 127 and 49 nm were obtained for Merck-E7 and Merck-6608 LC, with driving potentials of 5 and 10 V, respectively.