Theoretical And Experimental Investigation Of Novel Photonic Topological Insulators

Electromagnetic devices have wide applications in electronic information,quantum computation,aerospace and other fields.With the rapid development of science and technology,the performance of electromagnetic devices needs to meet higher requirements,such as low transmission loss and robustness to perturbations and so on.However,in conventional electromagnetic devices,electromagnetic waves will occur scattering or refraction when they encounter obstacles such as bends,disorder and impurities,leading to a sharp decrease in transmission efficiency.The development of photonic topological insulators essentially solves this problem.The interior of the photonic topological insulator cannot transmit electromagnetic waves,while surface waves can propagate through its surface that are robust to the obstacles.In this thesis,we propose and experimentally demonstrate topological wireless power transfer systems,valley kink states in substrate-integrated photonic circuitry and higher-order topological states in surface-wave photonics crystals.In addition,we propose and experimentally realize non-Hermitian skin effect based on non-Hermitian topological theory.This thesis provides theoretical and experimental support for the application and interdiscipline of photonic topological insulators.The contents of the thesis can be cataloged as follows:1.We realize the first work based on one-dimensional photonic topological insulators.In conventional wireless power transfer systems with long transfer distances,the transmission efficiency is relatively low and sensitive to perturbations.To solve this problem,the concept of topological wireless power transfer is proposed,which combines electromagnetic topological insulators with the non-radiative magnetically coupled wireless power transfer system based on magnetic resonance and near-field coupling.Near the exceptional point,the transmission efficiency of the proposed topological wireless power system can reach 60.2%.This system can maintain high transmission efficiency and less than 0.5% frequency shift even in the presence of disorder.2.We realize the second work based on two-dimensional photonic topological insulators.Photonic topological insulators have difficulties in integration due to their bulky sizes.To solve this problem,valley kink states in subwavelength substrate-integrated photonic circuitry are experimentally demonstrated and manipulated.The topological valley kink state in the proposed photonic topological insulator can propagate along generic interfaces.The valley kink states are experimentally verified to be robust against obstacles such as sharp bendings and disorders.In addition,geometry-dependent topological channel intersections are designed by utilizing valley lock chirality.3.We realize the third work based on two-dimensional high-order photonic topological insulators.High-order topological insulators suffer from either limited operational frequencies or bulky structures.To solve this problem,a two-dimensional high-order photonic topological insulator based on surfacewave photonic crystals is proposed,which has a subwavelength structure.Due to the multiple Bragg scattering,this system has a relatively large topological bandgap.by tuning the parameters in the system,one-dimensional edge states and zero-dimensional corner state are experimentally observed.In addition,the robustness of corner state is verified by introducing various perturbations.The design principle can be applied to terahertz,infrared and other higher frequency regimes.4.We realize the last work based on non-Hermitian topology.Demonstrations of non-Hermitian skin effect are all based on a single winding topology.To solve this problem,a tunable non-Hermitian non-reciprocal system is proposed based on amplifiers.By adjusting the nearest-neighbor coupling,non-Hermitian skin effect based on single-winding topology is demonstrated.By adjusting the nextnearest-neighbor coupling,non-Hermitian skin effect based on twisted-winding topology and a Bloch-wave-like extended mode are demonstrated for the first time.