Abstract
The rainbow trapping effect has attracted gathering attention due to its potential application in data processing, energy storage, and light-matter interaction enhancement. The interest has increased recently with the advent of topological photonic crystals (PCs), as the topological PC affords a robust platform for nanophotonic devices. We proposed a chirped one-dimensional (1D) PC as a sandwiched trapped between two1D topological PCs to realize two topological edge states (TESs) for topological protection and trap the formed rainbow. Through graded the thickness of dielectric layers of the chirped 1D PC, light of different wavelengths components localizes and stores at different spatial positions leading to rainbow trapping formation. Unidirectional rainbow trapping can be observed by progressively increasing the thicknesses of the chirped PC. Nonetheless, changing increasingly one of its thicknesses and solidifying the other leads to bidirectional rainbow trapping. Achieving bidirectional rainbow trapping will reduce the footprint of nanophotonic devices in the future. This work brings inspiration to the realization of the rainbow trapping effect and provides a way to design topological nanophotonic devices.
Highlights
Photonics is principally concerned with the wave properties of frequency, wavevector, and polarization, representing the degrees of freedom of essential information for any optical system
The topological edge states (TESs) can exist in TPCL(PC1 + PC2) and TPCR(PC2 + PC1) at the heterostructure interface because the two photonic crystals (PCs) possess bandgaps in the same wavelength range with different topological properties [14]
We find that the formed rainbow is trapped between the two TESs, which act as a strong cavity and enhance the field localization and Q-factor
Summary
Photonics is principally concerned with the wave properties of frequency, wavevector, and polarization, representing the degrees of freedom of essential information for any optical system. It has been shown that in a tapered metamaterial structure, light can be trapped and slowed down in exact positions depending on its frequency [1]. This phenomenon is named a trapped rainbow, just as sunlight is scattered in a continuous color spectrum through a prism ( the name is rainbow). Achieving bidirectional rainbow trapping will reduce the footprint of the nanophotonic device in the future It is possible for this type of rainbow trapping to have numerous applications, for example, a bidirectional optical filter, a bidirectional laser, etc
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