Hydrostatic Pressure and Temperature Measurements Using an In-Line Mach-Zehnder Interferometer Based on a Two-Mode Highly Birefringent Microstructured Fiber.

Gabriela Statkiewicz-Barabach,Waclaw Urbanczyk,Jacek Olszewski,Pawel Mergo

doi:10.3390/s17071648

Abstract

We present a comprehensive study of an in-line Mach-Zehnder intermodal interferometer fabricated in a boron-doped two-mode highly birefringent microstructured fiber. We observed different interference signals at the output of the interferometer, related to the intermodal interference of the fundamental and the first order modes of the orthogonal polarizations and a beating of the polarimetric signal related to the difference in the group modal birefringence between the fundamental and the first order modes, respectively. The proposed interferometer was tested for measurements of hydrostatic pressure and temperature for different alignments of the input polarizer with no analyzer at the output. The sensitivities to hydrostatic pressure of the intermodal interference signals for x- and y-polarizations had an opposite sign and were equal to 0.229 nm/MPa and −0.179 nm/MPa, respectively, while the temperature sensitivities for both polarizations were similar and equal 0.020 nm/°C and 0.019 nm/°C. In the case of pressure, for the simultaneous excitation of both polarization modes, we observed a displacement of intermodal fringes with a sensitivity depending on the azimuth of the input polarization state, as well as on the displacement of their envelope with a sensitivity of 2.14 nm/MPa, accompanied by a change in the fringes visibility. Such properties of the proposed interferometer allow for convenient adjustments to the pressure sensitivity of the intermodal fringes and possible applications for the simultaneous interrogation of temperature and pressure.

Highlights

In recent years, traditional fiber-optic Mach-Zehnder interferometers (MZIs) with two separated reference and sensing arms have been replaced in many applications by simpler in-line fiber interferometers
Simultaneous measurements of temperature and strain were reported by using an in-line MZI with a pair of long period gratings (LPGs) made in double cladding fiber [4], an interferometer fabricated in a boron-doped highly birefringent microstructured fiber with two tapered regions [8], and an MZI with a core-offset and taper in a single mode fiber [14]
We studied the sensitivity to hydrostatic pressure and to temperature of the in-line Mach-Zehnder interferometer fabricated in a two-mode highly birefringent boron-doped microstructured fiber

Summary

Introduction

Traditional fiber-optic Mach-Zehnder interferometers (MZIs) with two separated reference and sensing arms have been replaced in many applications by simpler in-line fiber interferometers. Sensors 2017, 17, 1648 a relatively simple and fast method of making coupling points [5,6,7,8] In such an approach, the interference fringes are not limited to the spectral range of the LPGs. in such an approach, the interference fringes are not limited to the spectral range of the LPGs Some drawbacks to these methods are weaker fiber strength at the tapered regions and high insertion loss at the collapsing points [7]. Simultaneous measurements of temperature and strain were reported by using an in-line MZI with a pair of LPGs made in double cladding fiber [4], an interferometer fabricated in a boron-doped highly birefringent microstructured fiber with two tapered regions [8], and an MZI with a core-offset and taper in a single mode fiber [14]. Such properties of the proposed sensor allowed for simultaneous measurements of temperature and hydrostatic pressure, or other parameters by interrogating the visibility and displacement of the intermodal interference fringes and their envelope

The Principle of the Sensor Operation

Scanning Electron

Spectral

Calculated

Sensing

Conclusions