Silicon based near infrared tunable filters based on liquid crystals

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) lambda/4 (lambda = 1.5 mum) Dielectric Bragg Reflectors separated by 950 run 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 (Deltaepsilon = 13.8) and Merck-6608 LC (Deltaepsilon = -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 similar to120 nm and similar to50 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