A novel concept for an intrinsic relative humidity (RH) sensor that uses polyimide-recoated fiber Bragg gratings is presented. Tests in a controlled environment indicate that the sensor has a linear, reversible, and accurate response behavior at 10-90% RH and at 13-60 degrees C. The RH and temperature sensitivities were measured as a function of coating thickness, and the thermal and hygroscopic expansion coefficients of the polyimide coating were determined.

No abstract

A goal of this paper is to efficiently adapt the best ingredients of the graph colouring techniques to an NPhard satellite range scheduling problem, called MuRRSP. We propose two new heuristics for the MuRRSP, where as many jobs as possible have to be scheduled on several resources, while respecting time and capacity constraints. In the permutation solution space, which is widely used by other researchers, a solution is represented by a permutation of the jobs, and a schedule builder is needed to generate and evaluate a feasible schedule from the permutation. On the contrary, our heuristics are based on the solution space which contains all the feasible schedules. Based on the similarities between the graph colouring problem and the MuRRSP, we show that the latter solution space has significant advantages. A tabu search and an adaptive memory algorithms are designed to tackle the MuRRSP. These heuristics are derived from efficient graph colouring methods. Numerical experiments, performed on large, realistic, and challenging instances, showed that our heuristics are very competitive, robust, and outperform algorithms based on the permutation solution space

A new approach is described to compensate the variations induced by laser frequency instabilities in the recently demonstrated Fourier transform spectroscopy that is based on the RF beating spectra of two frequency combs generated by mode-locked lasers. The proposed method extracts the mutual fluctuations of the lasers by monitoring the beating signal for two known optical frequencies. From this information, a phase correction and a new time grid are determined that allow the full correction of the measured interferograms. A complete mathematical description of the new active spectroscopy method is provided. An implementation with fiberbased mode-locked lasers is also demonstrated and combined with the correction method a resolution of 0.067 cm(-1) (2 GHz) is reported. The ability to use slightly varying and inexpensive frequency comb sources is a significant improvement compared to previous systems that were limited to controlled environment and showed reduced spectral resolution. The fast measurement rate inherent to the RF beating principle and the ease of use brought by the correction method opens the venue to many applications.

In this paper, the behaviour of fibre Bragg grating sensors subjected to transversal as well as axial strains is characterized, both in the case of low-birefringent and polarization-maintaining single-mode optical fibres. Two configurations are considered. Firstly, diametrical compression is studied and the results compared to those previously obtained in the literature. Secondly, the sensors are embedded in an epoxy specimen and their response monitored when the latter is subjected to biaxial loading. In both cases, the experimental results are compared to those obtained by means of finite-element simulations and an appropriate analytical description of the opto-mechanical response of polarization-maintaining fibres.