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In this Letter, we theoretically propose and experimentally demonstrate the formation of a super bound state in a continuum (BIC) on a photonic crystal flat band. This unique state simultaneously exhibits an enhanced quality factor and near-zero group velocity across an extended region of the Brillouin zone. It is achieved at the topological transition when a symmetry-protected BIC pinned at k=0 merges with two Friedrich-Wintgen quasi-BICs, which arise from the destructive interference between lossy photonic modes of opposite symmetries. As a proof of concept, we employ the ultraflat super BIC to demonstrate three-dimensional optical trapping of individual particles. Our findings present a novel approach to engineering both the real and imaginary components of photonic states on a subwavelength scale for innovative optoelectronic devices.

We propose a new holographic interferometric technique of phase interrogation for nanophotonic sensors, allowing to reach low phase noise and fluctuation by using a digital micromirror device spatial light modulator. With the spatial light modulator, both beam shaping and phase shifting interferometry can be simultaneously managed, hence enabling the interrogation of nanophotonic devices with a common-path heterodyne Young's interference experiment. The efficiency of the technique is illustrated in the particular case of temperature sensing using Tamm plasmon photonic crystals. The hologram sensor allows to probe resonant structures with deep attenuation at resonance, such as resonant structures at critical coupling or with phase singularities.

Exceptional points (EPs), singularities of non-Hermitian physics where complex spectral resonances degenerate, are one of the most exotic features of nonequilibrium open systems with unique properties. For instance, the emission rate of quantum emitters placed near resonators with EPs is enhanced (compared to the free-space emission rate) by a factor that scales quadratically with the resonance quality factor. Here, we verify the theory of spontaneous emission at EPs by measuring photoluminescence from photonic-crystal slabs that are embedded with a high-quantum-yield active material. While our experimental results verify the theoretically predicted enhancement, they also highlight the practical limitations on the enhancement due to material loss. Our designed structures can be used in applications that require enhanced and controlled emission, such as quantum sensing and imaging.

In this paper, we present a simple approach to study the coupling mechanisms between a plasmonic system consisting of bowtie nanoantennas and a photonic structure based on a Fabry-Perot interferometer. The nanoantenna array is represented by an equivalent homogeneous layer placed at the interferometer surface and yielding the effective dielectric function of the NA resonance. A phase matching model based on thin film interference is developed to describe the multi-layer interferences in the device and to analyze the fringe variations induced by the introduction of the plasmonic layer. The general model is validated by an experimental system consisting of a bowtie nanoantenna array and a porous-silicon-based interferometer. The optical response of this hybrid device exhibits both the enhancement induced by the nanoantenna resonance and the fringe pattern of the interferometer. Using the phase matching model, we demonstrate that strong coupling can occur in such a system, leading to fringe splitting. A study of the splitting strength and of the coupling behavior is given. The model study performed in this work enables to gain deeper understanding of the optical behavior of plasmonic/photonic hybrid devices.