Silicon based near infrared tunable filters based on liquid crystals

摘要

Complementary metal-oxide-semiconductor-compatible tunable Fabry-Perot 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 [SiO_2/Si]_n λ/4 (λ = 1.5 μm) Dielectric Bragg Reflectors separated by 950 nm thick SiO_2 posts. The Dielectric Bragg reflectors were realized on Si or SiO_2 substrates 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 electrical field and to tune the LC properties and, hence, the microcavity resonance. Electric-field-induced shifts of the second-order cavity modes of ～120 nm and ～50 nm were obtained for Merck-E7 and Merck-6608 LC, with driving potentials of 5 V and 10 V, respectively. The transmittance at the cavity resonance is typically in the order of 10%. Simulation of cavities allows to identify surface roughness of the Dielectric-Bragg-Reflectors as the major origin of the transmission losses. The switching behavior of microcavities filled with E7 were studied as function of applied fields. Both switch-on t_(on) and switch-off t_(off) times were measured and were found to be lower than 5 ms.