Principal Investigator Vladimir Bulovic
Exciton-polariton-based photonic devices are a novel platform for realizing low-threshold lasing and optical switching in a scalable integrated architecture. Use of organic materials such as the excitonic component facilitates room-temperature operation of such devices. Here we report room-temperature exciton-polariton devices consisting of layer-by-layer (LBL) assembled thin films of polyelectrolyte and the J-aggregates of the cyanine dye TDBC inserted in a resonantly-tuned planar lambda/2n optical microcavity with metal mirror and dielectric Bragg reflector (DBR). The device exhibits Rabi-splitting of OMEGA-R = 125 ± 7 meV with a polyelectrolyte/J-aggregate layer that is only 5.1 ± 0.5 nm thick. Furthermore, the linewidth of the lower energy polariton state, measured on resonance, is GAMMA = 12.1 meV. The ratio OMEGA-R/2_ = 5.1 indicates that the device operates in a limit where the light-matter coupling (OMEGA-R) significantly exceeds competing dephasing processes (GAMMA). These figures of merit are achieved by virtue of the nanostructured film's large absorption coefficient of alpha ~ 1.0x106 cm-1 and by location of the 5.1 ± 0.5-nm-thick layer at the microcavity anti-node. Rabi-splitting and polaritonic dispersion are observed in the reflectance, transmittance, and photoluminescence measurements of the device. Because strong coupling is achieved with such thin films, the majority of the microcavity modal volume is available for integrating a variety of optically active materials, such as colloidal quantum dots and fluorescent polymers, into devices that could leverage the coherent properties of the strongly coupled states. Moreover, the LBL process provides nanometer-scale thickness control of ~1.7 nm per polymer/dye bi-layer, suggesting that this device can be used to investigate fundamental physical phenomena such as non-radiative energy transfer and laser action in the strong coupling limit.