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

TL;DR

This paper presents a compact fiber optic sensor capable of simultaneously measuring temperature, strain, and refractive index with high discrimination accuracy by analyzing multiple spectral troughs arising from different physical mechanisms.

Contribution

It introduces a novel cascaded fiber sensor structure with spectral demodulation that achieves independent multi-parameter sensing using multiple spectral troughs.

Findings

Multiple spectral troughs exhibit distinct responses to each parameter.

The sensor can discriminate between temperature, strain, and refractive index simultaneously.

High sensitivity and linear response for each parameter were demonstrated.

Abstract

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.