Abstract
We describe the effects of the electron trapping due to the background ions in a Rydberg plasma. In the early stages, the ions are not thermalized and obey a Gaussian spatial profile, trapping the coldest electrons. In the present work, we provide expressions for both the electrostatic potential and the electron spatial profiles in two different regimes. We show that in the strong confinement regime F » T/e, a Rydberg plasma can be described by a Thomas-Fermi potential, similar to that obtained for heavy atomic species.

Abstract
In this work, we analyze a remote optical sensor system composed of two Fiber Bragg Gratings (FBGs) and one Long Period Grading (LPG) capable of simultaneously sensing the temperature and the refractive index, separated by 50 km from the optical source and the interrogation unit. Since the active components of the system and the sensor head are separated over such a large distance, it is necessary to consider Raman amplification o strengthen the optical signal. We present both experimental measurements and the results of numerical simulations, which describe the signal evolution and predict the measurement results for a remote sensor based on a LPG. The simulation codes are also used to study a hybrid sensor composed of two FBGs with a LPG. We show that the power ratio between the two central wavelengths of the FBG has a linear relation with the change of refractive index of the sensored medium.

Abstract
We propose and theoretically study a novel surface-plasmon-resonance sensor based on an H-shaped, elliptical-core optical fibre. The two grooves of the H-fibre are coated with a thin, uniform metal layer that in turn is covered with a high-index dielectric layer to allow broad spectral tunability. The sensor maintains linear polarization and facilitates effortless splicing. Electromagnetic mode analysis indicates a sensitivity of 1800 nm/RIU (refractive-index unit) for aqueous analytes.

Abstract
In this work, we analyze a remote optical sensor system based on Raman amplification, composed by one Long Period Grating (LPG) as a sensor head, separated by 50 km from the optical source, and the interrogation unit composed by two Fiber Bragg Gratings (FBGs) modulated by two Piezoelectrics Transductors (PZTs). Optical fiber sensor systems are typically limited to operate at distances of only few kilometers due to the attenuation effects and noise present in the optical fiber that adversely affects the performance of the sensor interrogation process. We present experimental and simulated results obtained in the context of the analysis of remote optical fiber sensors. The simulation models compute the Raman interaction between the pumps and the sensor signals and allow speeding up the analyses regarding the setup to be experimentally implemented in order to measure/monitor environmental temperature. Experimental results obtained in the implemented setup show that under Raman amplification the power ratio between the two central wavelengths of the FBGs has a linear relation with the change of the LPG resonance induced by environmental temperature.

Abstract
Birefringence monitoring of a Hi-Bi fibre under chemical etching is conducted. The Hi-Bi fibre (a bow-tie type) was inserted in a fibre loop mirror and the optical spectral response was measured while chemical etching of the Hi-Bi fibre was taking place. The birefringence of the bow-tie fibre has decreased due to the etching and the wavelength spacing of the fringe minima of the fibre loop mirror has increased.

Abstract
We report on the analysis and experimental validation of the strain sensitivity dependences of a fiber Bragg grating written in standard optical fiber when combined with fused tapers. By controlling the difference between the cross sections of the fused taper and the Bragg grating, the strain sensitivity of the Bragg wavelength can be changed by acting on the gauge length. The strain sensing characteristics of an interferometric structure formed by fabricating a fused taper in the middle of a fiber Bragg grating are also reported. (C) 2007 Optical Society of America.