A new type of remote query sensor for monitoring pressure, relative humidity, and phase-transitions is presented. The sensor consists of a planar inductor-capacitor resonant circuit, the resonant frequency of which changes in response to different environmental parameters. The sensor does not require an internal power source, rather it responds to the interrogation field. A loop antenna is used to monitor the sensor.

https://iopscience.iop.org/article/10.1088/0964-1726/9/4/305/pdf

A resonant printed-circuit sensor for remote query monitoring of environmental parameters

A Sagnac interferometer with a section of a polarization maintaining side-hole fiber for multiparameter measurement is proposed The sensor was experimentally demonstrated to be sensitive to torsion, temperature, and longitudinal strain, simultaneously The birefringence in the investigated side-hole fiber is induced simultaneously by the elliptical shape of a germanium-doped core and by field overlap with the air holes surrounding the core The latter effect is purely geometrical and causes high chromatic dispersion of the group birefringence in the long wavelength range, which results in a different period of spectral interference fringes A different wavelength response is obtained for each interference fringe peak when the fiber is subjected to torsion, temperature, or longitudinal strain A matrix equation for simultaneous measurement of the three parameters--torsion, temperature, and longitudinal strain--is also proposed

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Simultaneous measurement of multiparameters using a Sagnac interferometer with polarization maintaining side-hole fiber.

Modal birefringence and its sensitivity to temperature and hydrostatic pressure were measured versus wavelength in three elliptical-core fibers and one fiber with stress-induced birefringence. We carried out the measurements in the spectral range from 633 to 843 nm by using interferometric methods. In fibers with elliptical cores all the measured parameters showed high chromatic dependence, whereas in fibers with stress-induced birefringence this dependence was weak. We modeled the dispersion characteristics of two elliptical-core fibers by using the modified perturbation approach first proposed by Kumar. The modification consists of introducing into the expression for the normalized propagation constants an additional perturbation term that contains information about stress-induced birefringence. The results of modeling show that the temperature and pressure sensitivity of elliptical-core fiber are associated primarily with variations in stress induced by these parameters. The agreement between measured and calculated values of sensitivity in the worst case was equal to 20% for modal birefringence and temperature sensitivity and 50% for pressure sensitivity. Lower agreement between measured and calculated values of pressure sensitivity is most probably associated with uncertainties in the material constants used in modeling.

Dispersion effects in elliptical-core highly birefringent fibers

New experimental studies on the effects of high hydrostatic pressure on highly birefringent optical fibers are presented. Using Rayleigh scattering, the effect of beat length modification in highly birefringent singlemode bow tie fibers under high pressure up to 100 MPa was investigated. The results indicate that the beat length decreases with pressure, with the mean coefficient of 1/L(B0)|dL(B)/dp| = 0.15%/MPa. A similar decrease of beat length was observed when uniaxial longitudinal stress was applied to the bow tie fiber. A more developed semiphenomenological interpretation of these experimental results is also presented in the paper.

Influence of high hydrostatic pressure on beat length in highly birefringent single-mode bow tie fibers.

We calculated the sensitivity of phase (dB/dp) and group (dG/dp) modal birefringence to hydrostatic pressure versus wavelength in two birefringent holey fibers of different construction, where B is the phase modal birefringence, G is the group modal birefringence, and p is the pressure applied to the fiber. The contributions of the geometrical effects that were related only to deformation of the holey structure and the stress-related contribution to the overall pressure sensitivities were analyzed separately. Our results show that these two factors decrease the phase modal birefringence in both structures, which results in negative signs of dB/dp and dG/dp. Furthermore, we demonstrate that the geometrical effects are much weaker than the stress-related effects and contribute only a few percent to the overall pressure sensitivity.

Effects of Hydrostatic Pressure on Phase and Group Modal Birefringence in Microstructured Holey Fibers

The effect of high hydrostatic pressure on polarization properties in highly birefringent (HB) optical fibers is experimentally evaluated up to 200 MPa. The results are discussed in terms of beat-length changes under high pressure. It is found that oscillatory behavior of the output signal exiting from the HB bow-tie fiber and monitored in the plane parallel to one of its own two principal axes can be attributed to a pressure-induced increase of beat-length parameter. This effect can be applied to sense high hydrostatic pressure using appropriately configured HB fiber, but it could be a disadvantage in underwater communication systems using HB fibers if these are not adequately protected. >

High hydrostatic pressure effects in highly birefringent optical fibers

A theoretical and experimental analysis of thermal stress effects on the modal polarization properties of highly elliptical-core fibers is presented. The theoretical analysis is based on solving the vectorial Maxwell's equations, using a finite-element scheme, when form-induced and stress-induced effects are introduced simultaneously through appropriate calculation of the refractive indexes of the anisotropic media. The experimental analysis is done by studying the temperature response of a white-light interferometric sensor employing highly elliptical-core fibers. The calculated temperature sensitivities of the modal birefringence and the polarization mode dispersion in highly elliptical-core fiber are in close agreement with the experimental results. Interpretation of the results useful for designing white-light interferometric sensors composed of highly elliptical-core fibers is also given.

Theoretical and experimental analysis of thermal stress effects on modal polarization properties of highly birefringent optical fibers

A new type of fiber-optic pressure sensor based on a specially developed side-hole fiber is presented. It allows for unambiguous and fast phase-shift measurements in the range from -/spl pi//2 to +/spl pi//2 with a sampling rate of 5 kHz and resolution of about 1% of full scale (2 /spl middot/ 10/sup -3/ atm).

Highly sensitive fiber-optic sensor for dynamic pressure measurements

A new method of sensing high hydrostatic pressure utilizing cholesteric liquid crystals (ChLCs) as a sensing element and optical fibers for communication with the high-pressure region is proposed and demonstrated the concept exploits the effect of pressure-induced changes in the peak light-reflection wavelength observed in ChLCs. Measurements were performed on an encapsulated ChLC sample obtained by dispersion of a mixture consisting of nematic-host phase with cholesteryl oleyl carbonate and cholesteryl nanoate in a polymer matrix. We used multimode optical fibers for guiding the light to the ChLC sensing element and for transmitting the selectively reflected signal from the cholesteric layers to a detector. The ChLC sample with the optical fibers was placed inside a high-pressure chamber equipped with a fiber-optic leadthrough system, designed to sustain pressure up to 200 MPa. As a result we obtained a set of pressure and temperature characteristics of the device clearly demonstrating its press...

Cholesteric Liquid Crystal Sensing of High Hydrostatic Pressure Utilizing Optical Fibers

The authors present the results of birefringence measurements in highly birefringent optical bow-tie fibers under hydrostatic pressure up to 100 MPa. The birefringence measurement method is based on twist-induced effects and has never before been applied in a high-pressure environment. The experiments were conducted using a specially designed pressure facility, which made it possible to simultaneously generate several mechanical perturbations, including twist and hydrostatic stress, and to investigate their effects on mode transmission in optical fibers. A comparison with theoretical results as well as with previous experimental data on pressure influence on the beat length parameter in highly birefringent fibers is provided. >

W.J. Bock

Papers

High hydrostatic pressure effects in highly birefringent optical fibers

Theoretical and experimental analysis of thermal stress effects on modal polarization properties of highly birefringent optical fibers

Highly sensitive fiber-optic sensor for dynamic pressure measurements

Cholesteric Liquid Crystal Sensing of High Hydrostatic Pressure Utilizing Optical Fibers

Simultaneous twist and pressure effects in highly birefringent single-mode bow-tie fibers