  Integrating fluorescent nanoparticles with high-Q, small mode volume cavities
is indispensable for nanophotonics and quantum technologies. To date,
nanoparticles have largely been coupled to evanescent fields of cavity modes,
which limits the strength of the interaction. Here, we developed both a cavity
design and a fabrication method that enable efficient coupling between a
fluorescent nanoparticle and a cavity optical mode. The design consists of a
fishbone-shaped, one-dimensional photonic crystal cavity with a nano-pocket
located at the electric field maximum of the fundamental optical mode.
Furthermore, the presence of a nanoparticle inside the pocket reduces the mode
volume substantially and induces subwavelength light confinement. Our approach
opens exciting pathways to achieve strong light confinement around fluorescent
nanoparticles for applications in energy, sensing, lasing and quantum
technologies.
