Analysis of D-Shaped Optical Fiber based Corrosion Sensor Using LMR and SPR Effects

Silva Júnior, Valdemir M. da; Nascimento, Jehan F.; Martins Filho, Joaquim F.

doi:10.1590/2179-10742021v20i3254063

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Journal of Microwaves, Optoelectronics and Electromagnetic Applications

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Article • J. Microw. Optoelectron. Electromagn. Appl. 20 (3) • Sept 2021 • https://doi.org/10.1590/2179-10742021v20i3254063 copy

Analysis of D-Shaped Optical Fiber based Corrosion Sensor Using LMR and SPR Effects

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

This article presents the proposed structure and the simulation results from analytical and numerical modeling of two corrosion sensor elements in D-shaped optical fiber: one based on the lossy mode resonance (LMR) effect and the other based on the effect of surface plasmon resonance (SPR). In the first sensor element, a bilayer of titanium dioxide – aluminum (TiO₂-Al) is deposited on the D-shaped region, operating in LMR conditions, while, in the second sensor element, an aluminum (Al) monolayer is deposited under D-shaped region, operating in SPR condition. The sensor elements can operate separately, enabling simultaneous two-parameter measurements at two different points, or they can operate in cascade configuration, increasing the operating range and sensitivity of the sensor set. The D-shaped region of the optical fiber is modeled with an analytical model based on the Fresnel formulation, and also with a numerical model, which uses the finite element method with the COMSOL Multiphysics 5.2 software. The transmission of light through the D-shaped region causes peculiar variations in each light polarization in each sensor element, depending on the metal thickness. Both regions are subject to a corrosive environment. The sensor elements are evaluated separately and in cascade configuration, using polarized and nonpolarized light. Finally, the obtained results show two resonance valleys for the same operating wavelength, resulting in a higher operating range with high sensitivity, compared to other corrosion sensor structures found in the literature.

Index Terms
Cascaded Structure; Corrosion Sensor; D-shaped Optical Fiber Sensor; Lossy Mode Resonance; Surface Plasmon Resonance

Parameters	SPR	LMR
Polarization of light	TM polarized	TM and TE polarized light
Material Permitivity (ε=ε_r+iε_i)	ε_r negative and higher in magnitude than both the ε_i and the surrounding medium.	ε_r positive and higher in magnitude than both the ε_i and the surrounding medium. Metal oxides and polymers (wide range of materials).
Thin film materials	Metals, Ag (silver) and Au (gold).	Metal oxides and polymers (wide range of materials).
Thin film thickness	No multiple SPRs with increase in thickness.	Multiple LMRs can be generated with increase in thickness
Sensitivity	Maximum for a particular thickness of coating layer.	Can be tuned just changing thickness of the coating layer.

Parameter	Symbol	Value	Ref.
Operating wavelength	λ	1550nm	-
Core refractive index	n₁	1.4503	[ ²⁰[20] D. F. d. N. d. Santos, “Investigação Numérica do Desempenho de um Sensor de Fibra Óptica de Índice de Refração, Baseado em SPR e Utilizando COMSOL Multiphysics”, Master’s Dissertation (Master’s Dissertation in Telecommunications Engineering and Power Networks) - UMA, Funchal, 2013. ]
Cladding refractive index	n₂	1.4422	[ ²⁰[20] D. F. d. N. d. Santos, “Investigação Numérica do Desempenho de um Sensor de Fibra Óptica de Índice de Refração, Baseado em SPR e Utilizando COMSOL Multiphysics”, Master’s Dissertation (Master’s Dissertation in Telecommunications Engineering and Power Networks) - UMA, Funchal, 2013. ]
Oxide refractive index (TiO₂)	n₃	2.4532	[ ²⁰[20] D. F. d. N. d. Santos, “Investigação Numérica do Desempenho de um Sensor de Fibra Óptica de Índice de Refração, Baseado em SPR e Utilizando COMSOL Multiphysics”, Master’s Dissertation (Master’s Dissertation in Telecommunications Engineering and Power Networks) - UMA, Funchal, 2013. ]
Metal refractive index (Al)	n₄	0.4598+j14.882	[ ²⁰[20] D. F. d. N. d. Santos, “Investigação Numérica do Desempenho de um Sensor de Fibra Óptica de Índice de Refração, Baseado em SPR e Utilizando COMSOL Multiphysics”, Master’s Dissertation (Master’s Dissertation in Telecommunications Engineering and Power Networks) - UMA, Funchal, 2013. ]
Refractive index of corrosive medium (Al-Etcher)	n₅	1.38	[ ²³[23] E. A. Silva-Jr, A. P. C. da Cruz, J. F. Martins-Filho and J. N. Nascimento, “Sensor de Corrosão Utilizando Dupla Camada Metálica em Fibra Óptica”, in 16aSBMO - Simpósio Brasileiro de Micro-ondas e Optoeletrônica e 11aCBMag - Congresso Brasileiro de Eletromagnetismo , Curitiba, Brazil, 2014. ]
Core radius	r_core	4 μm	-
Cladding radius	r_clad	62.5 μm	-
Length of the D-shaped region	L	1 mm	-
Residual cladding thickness in the D-shaped region	d_c	2 μm	-
Oxide thickness on the D-shaped region of the sensor element 1	d_o	255 nm	-
Initial metal thickness on the D-shaped region of the sensor elements 1 and 2	d_m	40 nm	-

Model	Polarization	Operating range	Sensitivity Module
Analytical	TM	3 nm - 4.5 nm	0.53/nm
Numerical	TM	3 nm - 4.5 nm	0.43/nm
Analytical	TM	4.5 nm - 6 nm	0.46/nm
Numerical	TM	4.5 nm- 6 nm	0.37/nm
Analytical	TE	5 nm - 12 nm	0.13/nm
Numerical	TE	5 nm - 12 nm	0.13/nm
Analytical	TE	15 nm - 22 nm	0.09/nm
Numerical	TE	15 nm - 22 nm	0.07/nm

Model	Polarization	Operating range	Sensitivity Module
Analytical	TM	5 nm - 35 nm	0.023/nm
Numerical	TM	5 nm - 35 nm	0.018/nm
Analytical	TE	-	-
Numerical	TE	-	-

Model	Ratio	Operating range	Sensitivity Module
Analytical	TE/TM	2.5 nm -4.5 nm and 4.5 nm -6 nm	2/nm
Numerical	TE/TM	2.5 nm - 4.5 nm and 4.5 nm - 6 nm	1/nm
Analytical	TE/TM	6 nm -11 nm	0.2/nm
Numerical	TE/TM	6 nm - 11 nm	0.2/nm
Analytical	TE/TM	15 nm - 35 nm	0.15/nm
Numerical	TE/TM	15 nm - 35 nm	0.13/nm

Model	Operating range	Sensitivity Module
Analytical	3 nm - 4.5 nm	0.26/nm
Numerical	3 nm - 4.5 nm	0.22/nm
Analytical	4.5 nm - 6 nm	0.16/nm
Numerical	4.5 nm - 6 nm	0.14/nm
Analytical	6 nm - 12 nm	0.06/nm
Numerical	6 nm - 12 nm	0.07/nm
Analytical	15 nm - 22 nm	0.016/nm
Numerical	15 nm - 22 nm	0.02/nm

Sociedade Brasileira de Microondas e Optoeletrônica e Sociedade Brasileira de Eletromagnetismo Praça Mauá, n°1, 09580-900 São Caetano do Sul - S. Paulo/Brasil, Tel./Fax: (55 11) 4238 8988 - São Caetano do Sul - SP - Brazil
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