Resonant and non-resonant coupling of one-dimensional microcavity mode and optical Tamm state

Abstract

Coupling between the optical Tamm states (OTS) and microcavity mode in one-dimensional photonic crystal (1DPhC) structures is investigated experimentally and numerically with the help of transfer matrix method in resonant and non-resonant conditions, as a function of the distance between the 1DPhC-metal interface and the cavity layer (in terms of number of bilayers, Ntop, between the Tamm cavity and the microcavity). The system under study comprised of twelve bi-layers of alternating SiO2/TiO2 thin films, a half-wave thick TiO2 microcavity region and a layer of silver metal on top of the structure. It is observed that the microcavity mode and the OTS repel each other when Ntop is reduced indicating strong coupling between the two modes. In the resonant condition, wherein the individual structure consisting of either microcavity alone or Tamm cavity alone are tuned for the configuration Ntop = 2, the coupled modes in the hybrid structures are simultaneously localized at metal-1DPhC interface and at the microcavity. In the non-resonant condition when the microcavity mode and the OTS in the individual structure are not tuned, the coupling between the modes for the hybrid structure with Ntop = 2 leads to an enhanced electric field intensity of the microcavity mode compared to that from the uncoupled microcavity mode. Consequently, four different configurations corresponding to the non-resonant condition, having different Ntop are studied experimentally. The last four TiO2 layers and the microcavity layer of all the fabricated samples were incorporated with carbon quantum dots (CQDs). Comparison of photoluminescence enhancement as a function of Ntop in coupled and uncoupled conditions is discussed.