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. 2015 Oct 15;15(10):26128-42.
doi: 10.3390/s151026128.

Analytical modelling of a refractive index sensor based on an intrinsic micro Fabry-Perot interferometer

Everardo Vargas-Rodriguez  1 , Ana D Guzman-Chavez  2 , Martin Cano-Contreras  3   4 , Eloisa Gallegos-Arellano  5   6 , Daniel Jauregui-Vazquez  7 , Juan C Hernández-García  8 , Julian M Estudillo-Ayala  9 , Roberto Rojas-Laguna  10
Affiliations

Analytical modelling of a refractive index sensor based on an intrinsic micro Fabry-Perot interferometer

Everardo Vargas-Rodriguez et al. Sensors (Basel). .

Abstract

In this work a refractive index sensor based on a combination of the non-dispersive sensing (NDS) and the Tunable Laser Spectroscopy (TLS) principles is presented. Here, in order to have one reference and one measurement channel a single-beam dual-path configuration is used for implementing the NDS principle. These channels are monitored with a couple of identical optical detectors which are correlated to calculate the overall sensor response, called here the depth of modulation. It is shown that this is useful to minimize drifting errors due to source power variations. Furthermore, a comprehensive analysis of a refractive index sensing setup, based on an intrinsic micro Fabry-Perot Interferometer (FPI) is described. Here, the changes over the FPI pattern as the exit refractive index is varied are analytically modelled by using the characteristic matrix method. Additionally, our simulated results are supported by experimental measurements which are also provided. Finally it is shown that by using this principle a simple refractive index sensor with a resolution in the order of 2.15 × 10(-4) RIU can be implemented by using a couple of standard and low cost photodetectors.

Keywords: Fabry-Perot interferometer; fiber optics sensors; interferometry; non dispersive sensing; tunable laser spectroscopy.

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Figures

Figure 1
Figure 1
Refractive index sensing setup.
Figure 2
Figure 2
(a) Setup used to characterize the micro FPI spectral response as a function of the exit medium refractive index; (b) Picture of the fabricated FPI.
Figure 3
Figure 3
FPI structure.
Figure 4
Figure 4
(a) Simulated FPI reflectivity spectra considering an exit medium with different refractive indexes; (b) Detail of the FPI reflectivity spectra showing a single fringe peak and valley.
Figure 5
Figure 5
Measured source spectral profile S(λ); IM(λ,ne) and IS(λ,ne) are the measured and the simulated FPI reflection spectrum respectively. For this case ne=1 was considered.
Figure 6
Figure 6
(a) Measured reflected power spectra IM(λ,ne) for different values of exit medium refractive index; (b) detail of the IM(λ,ne) spectra showing only a single spectral FPI fringe.
Figure 7
Figure 7
Measured reflected energy at λ=1528.3 nm as a function of the exit medium refractive index and its linear fitting.
Figure 8
Figure 8
Detector outputs as a function of the exit refractive index, (a) simulated results; (b) experimental measurements.
Figure 9
Figure 9
Calculated depth of modulation from simulated and measured signals.
See this image and copyright information in PMC

References

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