Topological Photonic Crystal Sensors: Fundamental Principles, Recent Advances, and Emerging Applications

Topological photonic sensors have emerged as a breakthrough in modern optical sensing by integrating topological protection and light confinement mechanisms such as topological states, quasi-bound states in the continuum (quasi-BICs), and Tamm plasmon polaritons (TPPs). These devices exhibit exceptional sensitivity and high-Q resonances, making them ideal for high-precision environmental monitoring, biomedical diagnostics, and industrial sensing applications. This review explores the foundational physics and diverse sensor architectures, from refractive index sensors and biosensors to gas and thermal sensors, emphasizing their working principles and performance metrics. We further examine the challenges of achieving ultrahigh-Q operation in practical devices, limitations in multiparameter sensing, and design complexity. We propose physics-driven solutions to overcome these barriers, such as integrating Weyl semimetals, graphene-based heterostructures, and non-Hermitian photonic systems. This comparative study highlights the transformative impact of topological photonic sensors in achieving ultra-sensitive detection across multiple fields.