Polarimetric Sensitivity to Torsion in Spun Highly Birefringent Fibers

We report on experimental studies of polarimetric sensitivity to torsion in spun highly birefringent fibers. Two classes of spun fibers were examined, namely spun side-hole fibers and birefringent microstructured fibers with different birefringence dispersion, spin pitches, and spin directions. The polarimetric sensitivity to torsion was determined by monitoring a displacement of the spectral interference fringes arising in the output signal because of interference of polarization modes and induced by an additional fiber twist. Both the experimental results and the analytical predictions showed that the sensitivity to torsion normalized to the fringe width in the spun highly birefringent fibers increased asymptotically with the twist rate to the value of 1/ π rad−1. We have also studied the polarimetric response to temperature in the spun side-hole fibers. We have found that, in contrast to the torsional sensitivity, the temperature sensitivity decays asymptotically to zero with increasing fiber twist rate. Therefore, the spun fibers with short spin pitches are especially well suited for torsion measurements because the torsional sensitivity and the range of linear response are both enhanced in such fibers, while at the same time, the cross-sensitivity to temperature is reduced.

The land–sea coastal border: a quantitative definition by considering the wind and wave conditions in a wave-dominated, micro-tidal environment

A quantitative definition for the land–sea (coastal) transitional area is proposed here for wave-driven areas, based on the variability and isotropy of met-ocean processes. Wind velocity and significant wave height fields are examined for geostatistical anisotropy along four cross-shore transects on the Catalan coast (north-western Mediterranean), illustrating a case of significant changes along the shelf. The variation in the geostatistical anisotropy as a function of distance from the coast and water depth has been analysed through heat maps and scatter plots. The results show how the anisotropy of wind velocity and significant wave height decrease towards the offshore region, suggesting an objective definition for the coastal fringe width. The more viable estimator turns out to be the distance at which the significant wave height anisotropy is equal to the 90th percentile of variance in the anisotropies within a 100 km distance from the coast. Such a definition, when applied to the Spanish Mediterranean coast, determines a fringe width of 2–4 km. Regarding the probabilistic characterization, the inverse of wind velocity anisotropy can be fitted to a log-normal distribution function, while the significant wave height anisotropy can be fitted to a log-logistic distribution function. The joint probability structure of the two anisotropies can be best described by a Gaussian copula, where the dependence parameter denotes a mild to moderate dependence between both anisotropies, reflecting a certain decoupling between wind velocity and significant wave height near the coast. This wind–wave dependence remains stronger in the central bay-like part of the study area, where the wave field is being more actively generated by the overlaying wind. Such a pattern controls the spatial variation in the coastal fringe width.

The land-sea coastal border: A quantitative definition

A quantitative definition for the land-sea (coastal) transitional area is here proposed, based on variability and isotropy of met-ocean processes.Wind velocity and significant wave height fields are examined for anisotropy along four perpendicular transects on the Catalan coast (northwestern Mediterranean) illustrating a case of significant changes along shelf. The variation of anisotropy as a function of distance from the coast and water depth has been analyzed through heatmaps and scatter plots. The results show how the anisotropy of wind velocity and significant wave height decrease towards the offshore, suggesting an objective definition for the coastal fringe width. The more robust estimator turns out to be the distance at which the significant wave height anisotropy is equal to the 90th quantile of variance within a 100 km distance from the coast. Such a definition, when applied to the Spanish Mediterranean coast, determines a fringe of width of 2–4 km. Regarding the probabilistic characterization, the inverse of wind velocity anisotropy can be fitted to a lognormal distribution function, while the significant wave height anisotropy can be fitted to a log-logistic distribution function. The joint probability structure of the two anisotropies can be best described by a Gaussian copula, where the dependence parameter denotes mild to moderate dependence between both anisotropies, reflecting a certain decoupling between wind velocity and significant wave height near the coast. This wind-wave dependence remains stronger in the central, bay-like part of the study area, where the wave field is being more actively generated by the overlaying wind. Such a pattern controls the spatial variation of the coastal fringe width.

Understanding ghost interference

The ghost interference observed for entangled photons is theoretically analyzed using wave-packet dynamics. It is shown that ghost interference is a combined effect of virtual double-slit creation due to entanglement, and quantum erasure of which-path information for the interfering photon. For the case where the two photons are of different color, it is shown that fringe width of the interfering photon depends not only on its own wavelength, but also on the wavelength of the other photon which it is entangled with.

Investigation of Thermal Expansion Coefficient of Metals from Light Diffraction Pattern

In this work, an experimental set for determining the linear thermal expansion coefficient (α) of a metal was designed and constructed. It was divided into three parts: metal rod holder, light source, and heating system. A cylindrical plastic pipe with an inner diameter of 16 cm was used as a metal rod holder. The sample metal rod with unknown linear thermal expansion coefficient was inserted vertically into a holder and covered by the first razor blade at one end, while the other end was fixed. The second razor blade was attached with posts. Two razor blades were aligned and separated with a distance of 0.05 cm; therefore, two razor blades were acted as a thin single slit. The steam generated from heating system was transferred into metal rod holder; subsequently, the length of metal rod increased with increasing temperature. The design of the apparatus for this proposed method based on decreasing the width of single slit with the same amount of increasing the metal rod length due to linear thermal expansion. A He-Ne laser with a wavelength of 632.8 nm used as a light source was passed through a single slit and produced a diffraction pattern on a screen. The decrease in slit width was determined by measuring the fringe width. The value of linear thermal expansion coefficient of a metal can be calculated from alteration of fringe width. In our case, stainless steel (314), copper (UNS C11000), and aluminium (6063) rods with the original length of 45.3 cm were used as samples. The experimental values of α for stainless steel, copper, and aluminium are 15.25 × 10-6, 17.74 × 10-6, and 23.13 × 10-6 (°C)-1, respectively. These values are in good agreement with the standard values as reported by the National Metal and Materials Technology Center (MTEC), Thailand. The error of this proposed method is found to be less than 1.2%.

Simultaneous Flatness and Surface Roughness Measurement of a Plastic Sheet Using a Fan-Shaped Laser Beam Scanning System

A fan-shaped laser beam scanning measuring system based on the triangulation principle, was newly developed in this study to measure simultaneously the flatness and the surface roughness of a surface plate with good reflectivity after a suitable calibration. The developed system mainly consists of a micro-focus fan-shaped line laser, an image processing system, a PC-based 3-axis machine, and a PC. The height value of the object can be calculated, based on the offset between the position projected onto the object and the position projected onto the platform, after carrying out the height calibration with gauge blocks. According to the scattering theorem, a correlation between the surface roughness of the test object measured with a precision stylus instrument and the average fringe width projected onto the test object surface, has been constructed.