Abstract
In the last decade refractometric sensors have attracted an increasing interest by the scientific community due to their ability to perform ambient monitoring, to assess food quality and safety, and also to the fact that they enable the development of label free sensors in the biomedical area. These advances result, namely, from the use of long period fibre gratings in the turning points and/ or with thin films in the transition region that allows resolutions of 10(-6) to changes in the refractive index of the surrounding medium. Resolutions exceeding 10(-8) can also be achieved when long period fibre gratings are combined with evanescent field based devices. This paper reviews the recent path towards the development of ultrahigh sensitive optical fibre refractometric sensors.

Abstract
The principle of all-optical logical operations utilizing the unique nonlinear optical properties of a protein was demonstrated by a logic gate constructed from an integrated optical Mach-Zehnder interferometer as a passive structure, covered by a bacteriorhodopsin (bR) adlayer as the active element. Logical operations were based on a reversible change of the refractive index of the bR adlayer over one or both arms of the interferometer. Depending on the operating point of the interferometer, we demonstrated binary and ternary logical modes of operation. Using an ultrafast transition of the bR photocycle (BR-K), we achieved high-speed (nanosecond) logical switching. This is the fastest operation of a protein-based integrated optical logic gate that has been demonstrated so far. The results are expected to have important implications for finding novel, alternative solutions in all-optical data processing research.

Abstract
This work reports a variable attenuator/waveplate based on thermo-optic (TO) effect induced on a waveguide patterned by direct UV-laser writing on films of organic-inorganic di-ureasil hybrids. The waveguide temperature was tuned inducing phase retardation between the transverse electric (TE) and transverse magnetic (TM) modes, resulting in a controllable waveplate. Furthermore, the waveguide TO actuation allows obtaining a variable optical attenuator. The relevant properties, such as attenuation, polarization dependence of the thermal actuation and power consumption will be presented in the NIR (1550 nm). The required electrical power and temperature variation to attain the optical signal extinction and the retardation phase of pi/2 were estimated.

Abstract
Using low cost portable devices that enable a single analytical step for screening environmental contaminants is today a demanding issue. This concept is here tried out by recycling screen-printed electrodes that were to be disposed of and by choosing as sensory element a low cost material offering specific response for an environmental contaminant. Microcystins (MCs) were used as target analyte, for being dangerous toxins produced by cyanobacteria released into water bodies. The sensory element was a plastic antibody designed by surface imprinting with carefully selected monomers to ensure a specific response. These were designed on the wall of carbon nanotubes, taking advantage of their exceptional electrical properties. The stereochemical ability of the sensory material to detect MCs was checked by preparing blank materials where the imprinting stage was made without the template molecule. The novel sensory material for MCs was introduced in a polymeric matrix and evaluated against potentiometric measurements. Nernstian response was observed from 7.24 x 10(-10) to 1.28 x 10(-9) M in buffer solution (10 mM HEPES, 150 mM NaCl, pH 6.6), with average slopes of -62 mV decade(-1) and detection capabilities below 1 nM. The blank materials were unable to provide a linear response against log(concentration), showing only a slight potential change towards more positive potentials with increasing concentrations (while that of the plastic antibodies moved to more negative values), with a maximum rate of +33 mV decade(-1). The sensors presented good selectivity towards sulphate, iron and ammonium ions, and also chloroform and tetrachloroethylene (TCE) and fast response (<20 s). This concept was successfully tested on the analysis of spiked environmental water samples. The sensors were further applied onto recycled chips, comprehending one site for the reference electrode and two sites for different selective membranes, in a biparametric approach for "in situ" analysis.

Abstract
Birefringence tunability is demonstrated in waveguides formed in bulk fused silica and in the core of single mode fibers, by femtosecond laser writing of stress inducing tracks that are placed with different geometries around the core of the waveguides. The femtosecond laser generated stress effect was probed by the birefringence induced spectral splitting of either Bragg grating waveguides in bulk fused silica or weakly modulated, femtosecond laser induced Bragg gratings in optical fibers. Birefringence values as low as 4 x 10(-6) and up to 2 x 10(-3) were obtained by controlling the fabrication conditions such as the laser pulse energy, the writing femtosecond laser polarization, the number of overwriting exposures, and the geometry of the induced stress tracks. Wave retarders are developed and characterized by a cross polarization technique to provide the spectral response of the stress induced birefringence, offering the convenient fabrication of short length and broadband in-line polarization devices. With this approach, millimeter length tracks provided 10 nm bandwidth polarization retarders in a single mode fiber and a 65 nm bandwidth retarders in bulk fused silica.

Abstract
The most relevant aspects related to the phase mask dithering/moving method for the fabrication of complex Bragg grating designs are reviewed. Details for experimental implementation of this technique is presented, including theoretical analysis of the calibration functions for the correct dither/displacement. Results from tailored Bragg grating structures fabricated by this method are shown. Apodized Bragg gratings with modeled spatial profiles were implemented, resulting in side mode suppression levels of more than 20 dB in gratings showing transmission filtering level higher than 30 dB. Chirped gratings with the spectral bandwidth up to 4 nm, p-shift and sampled Bragg gratings with equalized peaks equally spaced by 0.8 nm (100 GHz) were also fabricated. © 2012 The Author(s).