Abstract
In structural health monitoring, the propagation of ultrasonic waves along a structure can reveal interesting data relevant to the integrity of the whole structure. The availability of a system for distributed sensing of ultrasonic waves could, in some cases (e.g. pipelines) provide extremely valuable information to civil engineers. Phase-sensitive optical time domain reflectometry (phi OTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, phi OTDRs have been used mostly for the measurement of sub-kHz vibrations. In this work, the authors present an experimental characterization of a high-visibility phi OTDR and its performance when used for ultrasonic vibration measurements. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a phi OTDR is demonstrated for distributed measurement of ultrasonic waves.

Abstract
An interrogation sensor system combining the "figure-of-eight" fiber loop mirror using a single directional 3×3 fiber optic coupler was proposed. One fiber loop mirror was formed by inserting a length of high birefringent optical fiber at the input ports of the 3×3 coupler. Splicing the output ports of the 3×3 coupler between them created the other fiber loop mirror. The introduction of this second loop gave rise to two polarization states of light with the same frequency but different optical phase. The mechanical torsion sensing head was located at the second loop and was exhibited an average modulus torsion sensitivity of 7.9×10-4 degree/dB. The performance of the sensor was not affected by environmental temperature variations. © 2012 The Author(s).

Abstract
Phase-sensitive optical time domain reflectometry (phi OTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, phi OTDRs have been used mostly for the measurement of sub-kHz vibrations, normally in the context of intrusion sensing. In this paper, the authors present an experimental and theoretical description of a high-visibility phi OTDR and its performance when used for ultrasonic vibration measurements. The use of a semiconductor optical amplifier in the setup allows to suppress coherent noise and also to improve the spectral response of the pump pulses. These two advantages greatly decrease the detected intra-band noise thus allowing frequency measurements in the limits set by the time of flight of the light pulses while maintaining the simplicity of the scheme, as no post-processing, extremely high coherence lasers or coherent detection methods are required. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a fully distributed measurement of ultrasonic waves was achieved. The statistical behavior of the system was also described theoretically and characterized experimentally.

Abstract
Optical fibre Bragg grating (FBG) sensors are now quite established and widely used in strain measurements in composites. However, insufficient understanding of the limitations of the embedment and measuring techniques often leads to inaccurate results. This work is a continuation of a novel method to improve the reliability and accuracy of the strain measurements on unidirectional composites using embedded FBG sensors [1]. A new combination of the pair host material/sensor was studied and characterized. Test specimens were manufactured with longitudinally embedded FBG sensors, using a glass/epoxy prepreg system, in order to compare with a carbon/epoxy prepreg system. The combined behaviour of the sensors and the host material was characterized and a procedure to obtain a more accurate strain was defined for this new chosen material.

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.