Pressure-induced Birefringence Research Articles

Pressure sensor with large sensing dynamic range based on pressure-induced birefringence in LN crystal

In this paper, an optical pressure sensor based on pressure-induced birefringence in Lithium Niobate (LN) crystal is designed to achieve large sensing dynamic range. By using the photo-elastic effect of LN crystal, the optical phase change caused by the external pressure can be converted into the change of the output light intensity. Considerable sensor range can be obtained without special processing of the LN crystal, which makes it have high pressure tolerance. The sensing range of 24.85 MPa is demonstrated to be achievable on x-cut LN crystal with a length of 10 mm in the z-axis direction. The sensing sensitivity can reach 0.281 mW/MPa. By customizing the sensing range, it is expected to use the LN crystal based pressure sensor with the ease of fabrication to monitor high pressure scenarios, such as marine and large buildings monitoring.

High Sensitivity Polarimetric Optical Fiber Pressure Sensor Based on Tapered Polarization-Maintaining and Fiber Bragg Grating.

In this paper, we propose a high sensitivity polarimetric optical fiber pressure sensor (OFPS) using a polarization-diversity loop composed of a polarization beam splitter, polarization controllers, and a sensor head. The sensor head consists of 8-cm-long tapered panda-type polarization-maintaining fiber (PMF) and a fiber Bragg grating (FBG) directly spliced with PMF, and the sensor head is located inside a pressure chamber. A pressure-induced birefringence change due to the photoelastic effect can be greatly enhanced at the tapered section of PMF, thereby increasing the pressure sensitivity of the sensor head. The tapered PMF was fabricated using a fusion splicer, and the tapered length and center waist diameter of the tapered PMF segment were ~350 and ~56.82 μm, respectively. At the polarization-diversity loop, PMF is used as a birefringent element to create an interference spectrum due to polarization interference. A pressure-induced birefringence change of PMF results in a wavelength shift of the interference spectrum. Because the PMF birefringence also has a cross sensitivity to temperature, the FBG is utilized for the compensation of the temperature effect on it. The resonance wavelength of the FBG is sensitive to ambient temperature changes but insensitive to changes in pressure. This spectral response of the FBG can be used to compensate additional ambient temperature changes occurred at the sensor head. The pressure sensitivity of our sensor was measured as approximately -27.70 nm/MPa, and an adjusted R² value representing the sensor linearity was measured as ~0.9903 in a measurement range of 0-0.5 MPa. Our fabricated sensor exhibits the highest pressure sensitivity among previously reported polarimetric OFPS.

Pressure-Induced Birefringence Analysis of Side-Hole Optic Fiber

Pressure-Induced Birefringence Analysis of Side-Hole Optic Fiber

Curvature sensor based on a pressure-induced birefringence single mode fiber loop mirror

An optical fiber curvature sensor based on a pressure-induced birefringence singlemode fiber loop mirror is presented. The birefringer SMF is made by applying a transverse force against a short length of singlemode fiber. The length of the sensing element for the curvature sensing is about 150mm. The sensitivity of the curvature measurement experimentally is 0.0263m−1/pm. And the temperature effect of the proposed sensor is also analyzed. Comparing with the sensor of photonic crystal fiber, it is more convenient and simply.

Distributed high-temperature pressure sensing using air-hole microstructural fibers

We present spatially resolved Rayleigh scattering measurements in different polarization-maintaining (PM) fibers for high-temperature pressure sensing. The pressure-induced birefringence in the fiber cores is interrogated using polarization-resolved frequency-swept interferometry. The pressure responses of a PM photonic crystal fiber and a twin-air-hole PM fiber are investigated for a pressure range of 0 to 13.8 MPa (0-2000 psi) at room temperature and at temperatures as high as 800 °C. The proposed sensing system provides, for the first time to our knowledge, a truly distributed pressure-sensing solution for high-temperature applications.

High pressure ellipsometry: A novel method for measuring the optical properties and electronic structure of materials in diamond anvil cells

High pressure ellipsometry (HPE) method was developed for determining the index of refraction of opaque materials in a diamond anvil cell (DAC). A main difficulty in DAC-based HPE, namely, the pressure-induced birefringence developed in the diamond, was overcome enabling the extraction of the ellipsometric parameters of the sample. The method used was based on the fact that an unpolarized light is unaffected by a retarding optical element and thus reduces the number of unknown parameters in the problem. Because of technical difficulties in using unpolarized light, a linear combination of orthogonal polarizations was applied. In the experimental procedure, multiangle measurements of the ellipsometric parameter ψ are collected at each pressure and the data is fitted together with a measurement of the near normal reflectivity, in order to extract the complex index of refraction. As a test case, this procedure was used to measure the high pressure index of refraction of iron up to 30 GPa for light with wavelengths of 532 and 633 nm. From the index of refraction as a function of pressure the diamond-iron interface emissivity for different pressures was derived and from which the phase transition α → ε could be identified and characterized. The emissivity increases with pressure both at the α (0-9 GPa) and the ε phase (21-30 GPa) however decreases at the mixed α - ε (9-21 GPa) range. From the imaginary part of the index of refraction the pressure dependence of the energy skin depth of iron was extracted. It was found that the energy skin depth increases by an order of magnitude at 30 GPa relative to ambient conditions.

The Resonant Bandwidth Enhancement in a Mechanically Induced Long Period Fiber Grating Formed over a Twisted Fiber

A mechanically induced grating formed over a twisted fiber can increase the resonant bandwidth. The tunability and control of the resonant bandwidth is found to be dependent on the induced twist. The effective group indices of cladding modes increase with the twist-induced birefringence. The difference in group indices between the LP 01 and the cladding modes LP 11 , LP 12 , and LP 13 decreases as the fiber twist rate increases above 0.5 turns/cm. This results in bandwidth enhancement of the grating. This broadband mode converter, which has a wide tunability, is cost effective and insensitive to pressure-induced birefringence. The resonant bandwidth can be increased and tuned further by forming two gratings in series with a twist-free and twisted fiber portions. A coupling bandwidth of around 100 nm (< 3 db) is achieved in this dual grating technique.

Pressure sensitivity of side-hole optical fiber sensors

The dependency of the pressure-induced birefringence of a side-hole fiber on its geometry has been numerically investigated using the finite element method. We demonstrate that the pressure sensitivity of such a fiber shows a linear dependence on /spl phi//sup 2/, where /spl phi/ is the angle between the side hole center and core center axis and the core center to side-hole tangent. Experimental data obtained with two different side-hole fiber sensors are shown to agree extremely well (to within 10%) with theoretical predictions.

Design of highly birefringent fibers to optimize or minimize pressure-induced birefringence

A simple formula is derived to describe the effect of radial pressure on the birefringence in a coated birefringent optical fiber. Both plastic and metal coating materials are studied. Theoretical analysis shows that the pressure-induced birefringence in the fiber is determined mainly by the elastic properties of the fiber glasses and is rather insensitive to the coating material and thickness. The condition for zero pressure sensitivity is found to be strictly independent of the coating parameters. The use of boron-doped stress-applying sections to optimize the pressure sensitivity of a silica fiber is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pressure-induced birefringence in a coated highly birefringent optical fiber

An attempt is made to explain the pressure-induced birefringence in a birefringent fiber based on a consideration of the effect due to the difference between the elastic properties of the stress-applying regions and the cladding of the fiber. The elastic properties and the thickness of a single fiber coating are also incorporated into the analysis. Numerical results for some typical coating materials are presented and compared with existing experimental data. The implications of the results with regard to sensor applications are also discussed. A polarimetric sensor using a suitably coated highly birefringent fiber should be useful for the detection of static and low-frequency acoustic pressures. >