ABSTRACT Topological corner states with wavelength‐selective excitation and directional routing enable on‐chip wavelength‐dependent beam splitters (WDBSs) for multiplexing technology. In this work, we employ two types of topological corner states to implement WDBS in kagome lattice photonic crystals. A tight‐binding model incorporating both nearest‐neighbor and next‐nearest‐neighbor couplings is applied to describe the bulk and corner states in the second‐order topological photonic crystal. A 120‐degree‐turning interface is constructed that supports two types of corner states, where the type‐I corner state is even mode originating from nearest‐neighbor coupling and the type‐II state is odd mode originating from next‐nearest‐neighbor coupling. The spatial Fourier transformation of eigenstates indicates that the type‐I mode supports propagating waves along 30‐degree channel and is inhibited along the 90‐degree channel, and vice versa for type II. With different resonant wavelengths, the two types of corner states have direction‐wavelength locking mechanisms, enabling us to propose a 1 × 2 channel WDBS. Such WDBS design has achieved a low‐crosstalk multiplexing based on the directionality of corner states. This finding provides guidance for multiplexing different types of topological photonic states, which is conducive to promoting the design of on‐chip wavelength/mode‐division multiplexers with topological protection.
Luo et al. (Wed,) studied this question.