The era of Big Data requires nanophotonic chips to have large information processing capacity. Multiple frequency on-chip nanophotonic devices are highly desirable for density integration, but such devices are more susceptible to structural imperfection because of their nano-scale. Topological photonics provides a robust platform for next-generation nanophotonic chips. Here we give an experimental report of an on-chip nanophotonic topological rainbow realized by employing a translational deformation freedom as a synthetic dimension. The topological rainbow can separate, slow, and trap topological photonic states of different frequencies into different positions. A homemade scattering scanning near-field optical microscope with high resolution is introduced to directly measure the topological rainbow effect of the silicon-based photonic chip. The topological rainbow based on synthetic dimension have no restrictions for optical lattice types, symmetries, materials, wavelength band, and is easy for on-chip integration. This work builds a bridge between silicon chip technologies and topological photonics.

Photonic-plasmonic hybrid microcavities, which possess a higher figure of merit Q/V (the ratio of quality factor to mode volume) than that of pure photonic microcavities or pure plasmonic nano-antennas, play key roles in enhancing light–matter interaction. In this review, we summarize the typical photonic-plasmonic hybrid microcavities, such as photonic crystal microcavities combined with plasmonic nano-antenna, whispering gallery mode microcavities combined with plasmonic nano-antenna, and Fabry–Perot microcavities with plasmonic nano-antenna. The physics and applications of each hybrid photonic-plasmonic system are illustrated. The recent developments of topological photonic crystal microcavities and topological hybrid nano-cavities are also introduced, which demonstrates that topological microcavities can provide a robust platform for the realization of nanophotonic devices. This review can bring comprehensive physical insights of the hybrid system, and reveal that the hybrid system is a good platform for realizing strong light–matter interaction.

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The topological state in photonics was first realized based on the magnetic-optic (MO) effect and developed rapidly in recent years. This review summarizes various topological states. First, the conventional topological chiral edge states, which are accomplished in periodic and aperiodic systems based on the MO effect, are introduced. Some typical novel topological states, including valley-dependent edge states, helical edge states, antichiral edge states, and multimode edge states with large Chern numbers in two-dimensional and Weyl points three-dimensional spaces, have been introduced. The manifest point of these topological states is the wide range of applications in wave propagation and manipulation, to name a few, one-way waveguides, isolator, slow light, and nonreciprocal Goos–Hänchen shift. This review can bring comprehensive physical insights into the topological states based on the MO effect and provides reference mechanisms for light one-way transmission and light control.

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