Xingnan Chen | Searcharxiv

arXiv2026

A Dual-Dip Heterogeneous LPFG Sensing System via Annealing under Bending with Temperature and Humidity Compensation

Optical fiber multi parameter sensing is fundamentally constrained by cross-sensitivity and the complexity of multi sensor integration. Here, we present a dual-dip heterogeneous long-period fiber grating (LPFG) sensing platform enabled by bending assisted annealing, which introduces anisotropic refractive index redistribution and mode dependent coupling enhancement. This process yields enhanced sensitivity, improved dip contrast, and opposite spectral responses between dual resonance dips, providing intrinsic spectral heterogeneity. To overcome temperature cross sensitivity, a polymer-encapsulated cascaded LPFG-FBG architecture is developed, where the LPFG serves as the microbending sensitive element and the FBG acts as a reference channel. PDMS encapsulation enhances stress transfer and suppresses interfacial slippage, improving linearity and repeatability. As a result, the bending sensitivity increases from -3.44 to -8.97 nm per cm, and the detection limit improves from 0.017 to 0.006 cm. Building on this, a multi parameter sensing paradigm is established by integrating dual dip heterogeneity with LPFGFBG spectral orthogonality. With PAAm functionalization, the platform enables simultaneous and decoupled sensing of temperature, bending, and humidity, demonstrating scalable and versatile multi parameter capability. Overall, this work establishes a minimalistic yet robust paradigm for multi-parameter fiber-optic sensing, offering a scalable strategy for high-performance sensing in structural health monitoring and harsh environments.

physics.optics↗

arXiv2026

Multi parameter discrimination using multiple spectral troughs in a cascaded fiber sensor

Accurate monitoring of temperature, axial strain, and refractive index is critical for structural health monitoring, industrial process control, and environmental sensing. However, conventional optical fiber sensors are often limited by strong parameter cross sensitivity, poor discrimination capability, and increased system complexity when multiple sensing units are required. In this work, a compact multi-parameter optical fiber sensing platform is proposed based on a cascaded single-mode fiber, multimode fiber, and long-period fiber grating structure, combined with a wavelength-based spectral demodulation strategy. Within the cascaded configuration, multiple characteristic spectral troughs arising from distinct physical mechanisms coexist in a single transmission spectrum. Interference-induced troughs are generated by the multimode fiber section, while a resonance-induced trough is introduced by the long-period fiber grating. Although none of these troughs responds exclusively to a single parameter, each exhibits simultaneous and linearly independent responses to temperature, axial strain, and refractive index with distinct sensitivity magnitudes and trends. Consequently, each trough can be described by a unique sensitivity vector, enabling robust multi-parameter discrimination through multi-wavelength spectral demodulation.

physics.optics↗