Bandpass notch filter based on valley photonic crystals

As one of the core components of quantum photonics, optical filtering devices play a pivotal role in the manipulation of photonic signals. Conventional filters are generally limited to single-function operations, such as bandpass or bandstop filtering, which fall short of addressing the demand for coordinated control of broadband transmission and narrowband suppression in complex optical systems. To overcome this challenge, we propose a valley photonic crystal (VPC)-based bandpass notch filter that integrates the dual functionalities of bandpass filtering and notch filtering. The core structure of this device is constructed by coupling a topological straight waveguide with a triangular resonant cavity, enabling highly efficient optical signal transmission across a broad frequency spectrum while achieving precise suppression of targeted narrowband noise. By breaking the symmetry of a hexagonal lattice, we designed an all-dielectric silicon-based VPC structure supporting topological edge states, achieving a wide TE-polarized bandgap spanning 171.97–194.06 THz and a high-Q resonant mode (Q≈3.5226×10 8 ) at 185.77 THz via the spin-valley locking effect. Through single- and dual-cavity coupling configurations, we demonstrate flexible filtering characteristics in the frequency ranges of 178.0–178.8 THz and 185.4–186.0 THz, with a notch bandwidth as narrow as 0.01 THz. Simulation results validate the flexibility of this design principle and provide an innovative approach for realizing frequency-selective notch filters with high precision. This design can be readily integrated with quantum photonic chips, offering promising potential for applications in on-chip optical communications and integrated photonic devices.