An angle-selective photonic crystal for multi-physical sensing applications

Abstract

This study reports a high-transmission photonic crystal (PC) that was optimized for TM waves at a frequency of 43.8 GHz and engineered using photonic band gap (PBG) principles to achieve angle selection. The structure demonstrated a remarkable transmission from −68° to 0°, consistently exceeding 80% efficiency. Assessing the fragility of the medium within the PC using the critical angle, a multi-physical sensor (MS) comprising both refractive index sensing (RIS) and plasma density sensing (PDS) functions was proposed. The PDS could detect concentrations from 0.4 × 10¹⁸ m⁻³ to 0.8 × 10¹⁸ m⁻³ with a sensitivity of 10.925° per m⁻³. For RIS, with the change in magnetic field intensity, it could detect refractive index in the ranges of 2.45–2.33 at 1.25 T, 2.33–2.21 at 1.15 T, 2.21–2.09 at 1.05 T, and 2.09–1.97 at 0.65 T, with respective sensitivities of −28° per RIU, −16° per RIU, −18.33° per RIU, and −9.38° per RIU, showcasing broad detection ranges and high sensitivities. Notably, the MS could maintain high transmission (greater than 0.8) in the RIS range from −60° to 0°, enabling dynamic angle selection for refractive index and plasma density. Therefore, it holds promising prospects in the real-time monitoring of refractive index and plasma density changes in healthcare- and environment-related applications, such as in early disease diagnosis, air quality monitoring and detecting metabolic activity or harmful substances.