Integrated topological photonic circuit for on-chip second-harmonic generation and frequency demultiplexing

We propose a monolithic topological photonic circuit that integrates second-harmonic generation (SHG) and wavelength demultiplexing in a single platform. Leveraging the finite element method (FEM) for electromagnetic simulations, a sandwich waveguide heterostructure with air-gap-tuned edge states simultaneously generates SHG at 280.6 THz and routes fundamental (FW) and second-harmonic waves (SHW) through topologically distinct paths: FW propagates via a nontrivial edge state (near-zero backscattering), while SHW transmits through a trivial boundary mode (optimized dispersion). Simulated results demonstrate greater than 99.88% separation efficiency—matching the state-of-the-art in topological isolation systems. The dual-functionality design eliminates hybrid-component losses, yielding a normalized SHG efficiency of η =139.4 % W −1 cm −2 . Field profiles confirm that the spatial isolation of FW/SHW outputs a minimum crosstalk suppression of −29.2 dB . This work establishes a scalable paradigm for topology-enabled nonlinear light management in quantum frequency conversion and photonic signal processing.