Research progress of slow-light modulators

Electro-optic modulators are core components of high-speed optical interconnections and information processing systems. However, conventional structures have long been constrained by the difficult balance among modulation efficiency, optical bandwidth and propagation loss. By reducing the optical group velocity, the slow-light effect can effectively enhance light-matter interaction within the modulation region, improving modulation efficiency and lowering half-wave voltage while maintaining a compact device footprint. The physical mechanisms and development of slow-light modulators are systematically reviewed, with particular emphasis on representative devices based on photonic crystal waveguides, silicon-organic hybrid structures, cascaded gratings and coupled resonator optical waveguides. Their respective advantages and limitations are analyzed in detail. Furthermore, this paper introduces topological photonics and elaborates on the recent advances of topological slow-light modulators realized via the one-dimensional Su-Schrieffer-Heeger model and two-dimensional valley photonic crystals. Particular attention is given to the significant potential of topological boundary states to enhance modulator robustness, suppress backscattering, enable the ultra-low power consumption and achieve electro-optic bandwidths exceeding 100 GHz. Finally, future research directions including quasicrystal structures, higher-order topological states and artificial intelligence-assisted design are discussed. Topological slow-light modulators are expected to fundamentally overcome the conventional performance trade-offs and advance next-generation optical interconnection technologies for supercomputing, artificial intelligence and quantum information networks.