Temperature-insensitive polarimetric vibration sensor based on HiBi microstructured optical fiber

A new type of highly birefringent microstructured optical fiber has been tested for vibration measurements using a polarimetric technique. This technique takes advantage of the stress-induced phase shift between the two orthogonally polarized fiber eigenmodes. Comparison of three different fiber types shows that standard single-mode fibers do not provide stable measurements and that conventional polarization-maintaining fibers lead to a significant cross-sensitivity to temperature. However, for highly birefringent microstructured fibers specifically designed to provide a temperature-independent birefringence, our experiments show repeatable vibration measurements over a frequency range extending from 50?Hz to 1?kHz that are unaffected by temperature variations (up to 120?°C).     

Transverse Strain Measurements Using the Birefringence Effect in Fiber Bragg Gratings

Birefringence in fiber Bragg gratings (FBGs) leads to polarization-dependent properties such as polarization-dependent loss (PDL). Although this property is not desired for telecommunications applications, we demonstrate that the PDL generated by uniform FBGs written into standard single-mode fiber can be advantageously used for transverse strain measurements, which is not directly possible through amplitude spectral measurements.     

Relationship Between Chromatic Dispersion and Differential Group Delay in Weakly Birefringent Fiber Gratings

The presence of weak birefringence in fiber gratings slightly affects their amplitude response. In this case, we report that the wavelength dependencies of chromatic dispersion and differential group delay (DGD) are linked by the birefringence value. This relationship is used to analyze the grating DGD and exploited to get the grating birefringence. Experimental results are finally reported in good agreement with the theory.     

Interrogation technique for TFBG-SPR refractometers based on differential orthogonal light states

The generation of near-IR surface plasmon resonance in gold-coated tilted fiber Bragg gratings is strongly dependent on both the polarization state of the transmission light and the property of confining materials (including the coating materials and surrounding media). These dependencies can be advantageously used to demodulate the amplitude spectrum and retrieve the surrounding refractive index. In this paper, we present an automated demodulation technique that measures the surrounding refractive index by comparing the differential amplitude of resonance peaks near the plasmon attenuation for two orthogonal amplitude spectra recorded in the same operating conditions. A mean sensitivity of more than 500?nm per refractive index unit is reported. This new refractive index measurement method is shown to be accurate to 5×10(-5) over a full range of 0.01 in water solutions.     

Catalytic Fiber Bragg Grating Sensor for Hydrogen Leak Detection in Air

The explosion risk linked to the use of hydrogen as fuel requires low-cost and efficient sensors. We present here a multipoint in-fiber sensor capable of hydrogen leak detection in air as low as 1% concentration with a response time smaller than a few seconds. Our solution makes use of fiber Bragg gratings (FBGs) covered by a catalytic sensitive layer made of a ceramic doped with noble metal which, in turn, induces a temperature elevation around the FBGs in the presence of hydrogen in air.     

Polarisation properties of long-period grating inscribed in pure-fused-silica photonic crystal fibre

The first measurements of polarisation properties of a long-period grating inscribed in an endlessly singlemode photonic crystal fibre are reported. Strong modulation in the spectra of polarisation-dependent loss and differential group delay with periods of 2.6 and 1.3 nm, respectively, were found. As such an effect has not been observed in standard optical fibres, it is believed that this is due to the specific mode structure of the holey fibre used for grating fabrication     

Synthesis of fiber Bragg grating parameters from experimental reflectivity: a simplex approach and its application to the determination of temperature-dependent properties

A simple, accurate, and fast method to synthesize the physical parameters of a fiber Bragg grating numerically from its reflectivity is proposed and demonstrated. Our program uses the transfer matrix method and is based on a Nelder-Mead simplex optimization algorithm. It can be applied to both uniform and nonuniform (apodized and chirped) fiber Bragg gratings. The method is then used to synthesize a uniform Bragg grating from its reflectivity taken at different temperatures. It gives a good estimate of the thermal expansion coefficient and the thermo-optic coefficient of the fiber.