Abstract
Wavelength or light intensity demodulation method for a polarization maintaining fiber loop mirror (PM-FLM) sensor is not only expensive but also unsuitable for vibration monitoring. This paper studies the voltage demodulation principle and explores theoretically the influence of light source on the sensitivity. Then a PM-FLM sensor is applied to vibration monitoring. A low-power narrow-band light source reflected from FBG and a high-power laser light source are used respectively as input. The time domain voltage signals of vibration from a photo-detector are collected by a data acquisition card and converted via a fast Fourier transform algorithm. The experimental result shows that a PM-FLM sensor using a high-power narrow-band light source as input has a higher sensitivity to vibration than the one using a low-power narrow-band light source. In practical application, we can choose a high-power narrow-band light source as input to improve the sensitivity to vibration.
Highlights
The narrow-band light source reflected from FBG is shown in Figure 2, which was marked with “FBG”, and it is used as the input of a PM-FLM at port 5
According to the voltage demodulation principle, the sensitivity of the PM-FLM using the laser light source as input is larger than the one using the narrow-band light source reflected from FBG as input
We demonstrated the sensitivity of a PM-FLM vibration sensor using two types of different input light source on the condition of the same experimental systems and methods
Summary
Polarization maintaining fiber (PMF) loop mirror (PM-FLM) sensors have many advantages, such as lightweight, corrosion resistance, anti-electromagnetic interference, easy fabrication, low cost, polarization independence to input light and great flexibility.[1,2] They have been widely used in measuring strain,[3,4] temperature,[5] torsion,[6] curvature,[7,8] twist,[9] pressure[10] and liquid level.[11]A PM-FLM sensor is usually demodulated by a wavelength[12,13,14,15,16,17] or light intensity[18] monitored by an optical spectrum analyzer (OSA) or optical power meter. The curves marked with “0 le” and “202 le” represent the output interference spectra of a PM-FLM when the applied strain on the PMF was 0 le and 202 le using a broadband light source as input. When a photo-detector was used to convert light intensity signals into voltage signals, a narrow-band light source is usually used as the input of a PMFLM instead of a broadband light source.
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