Critical couplings in topological-insulator waveguide-resonator systems observed in elastic waves

Abstract

Waveguides and resonators are core components in the large-scale integration of electronics, photonics, and phononics, both in existing and future scenarios. In certain situations, there is critical coupling of the two components; i.e. no energy passes through the waveguide after the incoming wave couples into the resonator. The transmission spectral characteristics resulting from this phenomenon are highly advantageous for signal filtering, switching, multiplexing, and sensing. In the present study, adopting an elastic-wave platform, we introduce topological insulator (TI), a remarkable achievement in condensed matter physics over the past decade, into a classical waveguide-ring-resonator configuration. Along with basic similarities with classical systems, a TI system has important differences and advantages, mostly owing to the spin-momentum locked transmission states at the TI boundaries. As an example, a two-port TI waveguide resonator can fundamentally eliminate upstream reflections while completely retaining useful transmission spectral characteristics, and maximize the energy in the resonator, with possible applications being novel signal processing, gyro/sensing, lasering, energy harvesting, and intense wave–matter interactions, using phonons, photons, or even electrons. The present work further enhances the confidence of using topological protection for practical device performance and functionalities, especially considering the crucial advantage of introducing (pseudo)spins to existing conventional configurations. More in-depth research on advancing phononics/photonics, especially on-chip, is foreseen.

THz wave Mux/DeMux operation using bearded-type topological photonic crystal waveguide structure

“…[30][31][32] The oblique rectangular waveguide was arranged under the VPC waveguide, which was designed to demultiplex a specific frequency signal from its resonance state. A schematic of the THz demultiplexing 02SP27-5 © 2024 The Japan Society of Applied Physics IC based on the VPC-based resonator, which was electromagnetically coupled with the VPC waveguide [32][33][34] and the simulated intensity distribution of the magnetic field at the resonant frequency is shown in Fig. 6.…”

Topological phononic metamaterials

“…The input wave efficiently couples to the whisper-gallery resonator and then turns back to the straight waveguide with total transmission. Recently, the coupling behaviors between a topological insulator waveguide and a ring resonator have been systematically studied [574].…”

Phototunable chip-scale topological photonics: 160 Gbps waveguide and demultiplexer for THz 6G communication

“…Further, the intensity dip (peak) in S21 (S31) can be actively tuned by bringing the topological waveguide-cavity chip into the critical coupling regime. Critical coupling [39][40][41] is the condition when the total loss of the cavity becomes equal to the waveguide-cavity coupling loss that manifests as enhanced dip/peak in the transmission spectrum. Here, we attain the critical coupling condition by photoexciting the domain wall of the topological cavity.…”