Abstract
Optically coupled microcavities have emerged as photonic structures with promising properties for investigation of fundamental science as well as for applications. We report on the fabrication and spatially resolved spectroscopy of on-chip photonic molecule (PM) lasers consisting of two coupled, dye-doped polymeric microdisks on a silicon substrate. We investigate the fundamental lasing properties with focus on the spatial distribution of modes, the coupling dependent suppression of lasing modes, and in particular the application-oriented operation of these devices in aqueous environments. By depositing an additional polymer layer onto the lithographically structured cavities made of dye-doped poly(methyl methacrylate), coupling-gap widths below 150 nm with aspect ratios of the micro-/nanostructure exceeding 9∶1 are achieved. This enables strong optical coupling at visible wavelengths despite relatively small resonator radii of 25 µm. The lasing properties of dye-doped PMs are investigated using spatially resolved micro-photoluminescence (μ-PL) spectroscopy. This technique allows for the direct imaging of whispering-gallery modes (WGMs) in the photonics molecules. For subwavelength coupling gaps, we observe lasing from delocalized eigenstates of the PMs (termed in the following as super-modes). Using size-mismatched cavities, the lasing mode suppression for different coupling-gap widths is investigated. We further demonstrate single-mode lasing operation in aqueous environments with PMs, which are realized on a low-cost, polymer-on-silicon platform.
Highlights
Coupled microcavities are attractive devices for the investigation of fundamental physics, e.g., quantum optics,1–4 as well as for applications, such as sensing5–9 or telecommunications.10,11 Two or more coupled microresonators are often referred to as photonic molecule (PM), due to the formation of optical bonding and antibonding modes in analogy to the electronic states in molecules formed by atoms.12 In comparison to single microcavities PMs provide additional degrees of freedom to tailor the optical density of states and the spatial distribution of modes
We report on the fabrication and spatially resolved spectroscopy of on-chip photonic molecule (PM) lasers consisting of two coupled, dye-doped polymeric microdisks on a silicon substrate
The coupling between two resonators is known to play a major role for the suppression of laser modes,13 so far no detailed experimental studies have been performed to investigate the localization of lasing whispering-gallery modes in PMs and the effect of coupling on the localization as well as on the suppression of lasing modes
Summary
Coupled microcavities are attractive devices for the investigation of fundamental physics, e.g., quantum optics,1–4 as well as for applications, such as sensing5–9 or telecommunications.10,11 Two or more coupled microresonators are often referred to as photonic molecule (PM), due to the formation of optical bonding and antibonding modes in analogy to the electronic states in molecules formed by atoms.12 In comparison to single microcavities PMs provide additional degrees of freedom to tailor the optical density of states and the spatial distribution of modes. We report on the fabrication and spatially resolved spectroscopy of on-chip photonic molecule (PM) lasers consisting of two coupled, dye-doped polymeric microdisks on a silicon substrate. Using size-mismatched cavities, the lasing mode suppression for different coupling-gap widths is investigated.
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