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. 2019 Sep 21;19(19):4080.
doi: 10.3390/s19194080.

Design and Implementation of a Novel Measuring Scheme for Fiber Interferometer Based Sensors

Chao-Tsung Ma  1 , Cheng-Ling Lee  2 , Yan-Wun You  3
Affiliations

Design and Implementation of a Novel Measuring Scheme for Fiber Interferometer Based Sensors

Chao-Tsung Ma et al. Sensors (Basel). .

Abstract

This paper presents a novel measuring scheme for fiber interferometer (FI) based sensors. With the advantages of being small sizes, having high sensitivity, a simple structure, good durability, being easy to integrate fiber optic communication and having immunity to electromagnetic interference (EMI), FI based sensing devices are suitable for monitoring remote system states or variations in physical parameters. However, the sensing mechanism for the interference spectrum shift of FI based sensors requires expensive equipment, such as a broadband light source (BLS) and an optical spectrum analyzer (OSA). This has strongly handicapped their wide application in practice. To solve this problem, we have, for the first time, proposed a smart measuring scheme, in which a commercial laser diode (LD) and a photodetector (PD) are used to detect the equivalent changes of optical power corresponding to the variation in measuring parameters, and a signal processing system is used to analyze the optical power changes and to determine the spectrum shifts. To demonstrate the proposed scheme, a sensing device on polymer microcavity fiber Fizeau interferometer (PMCFFI) is taken as an example for constructing a measuring system capable of long-distance monitoring of the temperature and relative humidity. In this paper, theoretical analysis and fundamental tests have been carried out. Typical results are presented to verify the feasibility and effectiveness of the proposed measuring scheme, smartly converting the interference spectrum shifts of an FI sensing device into the corresponding variations of voltage signals. With many attractive features, e.g., simplicity, low cost, and reliable remote-monitoring, the proposed scheme is very suitable for practical applications.

Keywords: fast measurement scheme; fiber interferometer; optical fiber sensor.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Polymer microcavity fiber Fizeau interferometer (PMCFFI): (a) schematic diagram; (b) actual photo.
Figure 2
Figure 2
(a) Schematic diagram of light propagation characteristics in the resonant cavity of a PMCFFI; (b) The transmission of the designed sensing device with the PMCFFI (27 µm).
Figure 3
Figure 3
Schematic diagram of the PMCFFI experimental measurement configuration.
Figure 4
Figure 4
(a) Interference spectra of the PMCFFI (L = 10 μm) with only relative humidity (RH) variations; (b) Sensitivity comparison of different L based on wavelength shift due to RH changes; (c) the FFT result of the PMCFFI (L = 10 μm) with only RH variations (from 20% to 90%).
Figure 5
Figure 5
System configuration of the proposed fast measurement system with a PMCFFI sensor.
Figure 6
Figure 6
Schematic diagrams of spectrum shift monitoring on two wavelengths: (a) initial state; (b) right shift within feasible detecting range; (c) when the spectrum shift has reached its extremum.
Figure 7
Figure 7
The developed prototype: (a) front view; (b) back view; (c) lower layer; (d) upper layer.
Figure 7
Figure 7
The developed prototype: (a) front view; (b) back view; (c) lower layer; (d) upper layer.
Figure 8
Figure 8
Using 2 laser diodes (LDs) to monitor the reflective power spectrum at 20 °C.
Figure 9
Figure 9
Relationship between voltage and RH at different temperatures.
Figure 10
Figure 10
Comparison of calculated and experiment results of voltages vs. RHs at (a) 20 °C, 25 °C, and 30 °C, with λB; (b) voltages vs. RHs at 35 °C, 40 °C, and 45 °C, with λA.
Figure 11
Figure 11
The detailed results of the measured voltages vs. RHs: (a) 20 °C to 30 °C, with λB; (b) 35 °C to 45 °C, with λA.
See this image and copyright information in PMC

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