# Sensitive Detection of Multi-Point Temperature Based on FMCW Interferometry and DSP Algorithm

## TL;DR

This paper introduces a high-sensitivity system for detecting seawater temperature at multiple points using advanced optical techniques and signal processing.

## Contribution

A novel software-based virtual Vernier effect method is proposed to enhance temperature sensitivity without physical reference arrays.

## Key findings

- An 82.3 m optical fiber link achieved 23.9 μm spatial resolution.
- Temperature sensitivities reached up to −280.67 pm/∘C with amplification factors up to 6.13.
- The system enables quasi-distributed sensing for high-precision oceanographic monitoring.

## Abstract

This paper presents a high-sensitivity multi-point seawater temperature detection system based on the virtual Vernier effect, achieved through multiplexed Fabry–Perot (FP) cavities combined with optical frequency-modulated continuous wave (FMCW) interferometry. To address the nonlinear frequency scanning issue inherent in FMCW systems, this paper implemented a software compensation method. This approach enables accurate positioning of multiple FP sub-sensors and effective demodulation of the sensing interference spectrum (SIS) for each FP interferometer (FPI). Through digital signal processing (DSP) algorithms and spectral demodulation, each sub-FP sensor generates an artificial reference spectrum (ARS). The virtual Vernier effect is then achieved by means of a computational process that combines the SIS intensity with the corresponding ARS intensity. This eliminates the need for physical reference arrays with carefully detuned spatial frequencies, as is required in traditional Vernier effect implementations. The sensitivity amplification can be dynamically adjusted with the modulation function parameters. Experimental results demonstrate that an optical fiber link of 82.3 m was achieved with a high spatial resolution of 23.9 μm. Within the temperature range of 30 ∘C to 70 ∘C, the temperature sensitivities of the three enhanced EIS reached −275.56 pm/∘C, −269.78 pm/∘C, and −280.67 pm/∘C, respectively, representing amplification factors of 3.32, 4.93, and 6.13 compared to a single SIS. The presented approach not only enables effective multiplexing and spatial localization of multiple fiber sensors but also successfully amplifies weak signal detection. This breakthrough provides crucial technical support for implementing quasi-distributed optical sensitization sensing in marine environments, opening new possibilities for high-precision oceanographic monitoring.