Optical microcavities (MC) offer a versatile platform to manipulate light-matter interactions at the nanoscale. In these systems, the strong confinement of the electromagnetic field enables the possibility to modify the properties of the emission, interesting for applications in photonics and optoelectronics. These structures consist of a periodical stacking of dielectric materials’ bilayers with different refractive indices, known as Distributed Bragg Reflectors (DBRs), that give rise to constructive or destructive interference due to refraction and reflection at the layer interfaces at distinct wavelengths. This results in controllable reflectance maxima for wavelengths where light cannot propagate into the structure, named Photonic Bandgaps (PBGs).1 Introducing an engineered layer disrupts this periodicity, allowing some wavelengths within the PBG spectral region to propagate, forming microcavity modes.2 In our work, we focus on the design and characterization of entirely polymer-based microcavities in which the defect layer comprises J-aggregates formed from cyanine dyes (e.g., 1,1’-disulfobutyl-3,3’-diethyl-5,5’,6,6’-tetrachloro-benzimidazolylcarbocyanine sodium salt, TDBC). J-aggregates are renowned for their narrow and intense absorption and emission bands, a consequence of the cooperative “head-to-tail” organization of the transitional dipoles. This cooperative behavior not only enhances the overall oscillator strength but also ensures an absorption spectrum bandwidth similar to the width of the cavity mode, both critical factors for achieving a robust strong coupling regime.3 Our fabrication approach utilizes spin coating to cast uniform thin films, combined with the construction of polymeric DBR made from high dielectric contrast materials (e.g., PVK as the high-index layer and Aquivion® as the low-index layer). The cavity is engineered such that the resonant wavelength of the confined mode matches the absorption peak of the J-aggregates, a prerequisite for reaching resonance. Angle-resolved reflection and transmission measurements reveal an anticrossing behavior. This phenomenon is the fingerprint of a strong-coupling regime between the exciton in J-aggregate and the confined photons at the cavity mode, creating a new hybrid state known as polariton. These results demonstrate polymer microcavities do achieve the strong-coupling regime so far possible for inorganic photonic structures only. This opens new perspectives for the integration of light and flexible polymer photonic structures into devices paving the way for new photonic applications. For example, further optimization of the cavity design and the active medium could lead to the development of ultra-low threshold bendable and stretchable lasers.
Strong-Coupling in all-Polymer Microcavities doped with J-Aggregates
Di Fonzo Daniela;Lanfranchi Andrea;Lova Paola;Comoretto Davide
2025-01-01
Abstract
Optical microcavities (MC) offer a versatile platform to manipulate light-matter interactions at the nanoscale. In these systems, the strong confinement of the electromagnetic field enables the possibility to modify the properties of the emission, interesting for applications in photonics and optoelectronics. These structures consist of a periodical stacking of dielectric materials’ bilayers with different refractive indices, known as Distributed Bragg Reflectors (DBRs), that give rise to constructive or destructive interference due to refraction and reflection at the layer interfaces at distinct wavelengths. This results in controllable reflectance maxima for wavelengths where light cannot propagate into the structure, named Photonic Bandgaps (PBGs).1 Introducing an engineered layer disrupts this periodicity, allowing some wavelengths within the PBG spectral region to propagate, forming microcavity modes.2 In our work, we focus on the design and characterization of entirely polymer-based microcavities in which the defect layer comprises J-aggregates formed from cyanine dyes (e.g., 1,1’-disulfobutyl-3,3’-diethyl-5,5’,6,6’-tetrachloro-benzimidazolylcarbocyanine sodium salt, TDBC). J-aggregates are renowned for their narrow and intense absorption and emission bands, a consequence of the cooperative “head-to-tail” organization of the transitional dipoles. This cooperative behavior not only enhances the overall oscillator strength but also ensures an absorption spectrum bandwidth similar to the width of the cavity mode, both critical factors for achieving a robust strong coupling regime.3 Our fabrication approach utilizes spin coating to cast uniform thin films, combined with the construction of polymeric DBR made from high dielectric contrast materials (e.g., PVK as the high-index layer and Aquivion® as the low-index layer). The cavity is engineered such that the resonant wavelength of the confined mode matches the absorption peak of the J-aggregates, a prerequisite for reaching resonance. Angle-resolved reflection and transmission measurements reveal an anticrossing behavior. This phenomenon is the fingerprint of a strong-coupling regime between the exciton in J-aggregate and the confined photons at the cavity mode, creating a new hybrid state known as polariton. These results demonstrate polymer microcavities do achieve the strong-coupling regime so far possible for inorganic photonic structures only. This opens new perspectives for the integration of light and flexible polymer photonic structures into devices paving the way for new photonic applications. For example, further optimization of the cavity design and the active medium could lead to the development of ultra-low threshold bendable and stretchable lasers.
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