Insights and Perspectives on Modal Characteristics in Tilted Fiber Bragg Gratings: A Review

This article reviews the characteristics and properties of various modes in tilted fiber Bragg gratings (TFBGs). It explores the fundamental theory and optical characteristics of radiation modes, cutoff modes, guided cladding modes, ghost modes, and leaky mode in TFBGs. The unique behaviors of these modes are associated with distinctive fabrication techniques, surface modifications, and characterization methods for optimal performance in diverse applications. In addition, the excitation of surface plasmon resonance (SPR) in TFBGs is reviewed. The excitation involves the coupling between incident light and collective electron oscillations on a metallic surface, within the context of TFBGs. Recent advancements in high refractive index (RI) coatings, femtosecond laser inscription, and graphene integration are further explored for their impact on mode excitation and sensing capabilities. This review offers insights into preserving and enhancing leaky mode resonances (LMRs) and exploring ultrahigh-order cladding modes. The discussion provides valuable perspectives on future research directions and practical applications in optical fiber sensing and photonics.