Abstract
The properties of a Brillouin-Raman comb fiber laser are compared for two different configurations: co-propagating and counter-propagating Raman pump. The optical spectrum is compared for changing the Raman pump power and the power or the wavelength of seed laser. A Brillouin-Raman comb with 400 linewidth lasers in a flat-amplitude bandwidth of 32 nm between 1538 and 1570 nm, with an average optical power 20 dB above the nearby frequencies was generated. The lasers in the comb had an OSNR of 20 dB and a wavelength spacing of 0.08 nm. The results for the counter-propagating configuration were observed to have better quality.

Abstract
A temperature-insensitive strain sensor based on Four-Wave Mixing (FWM) using two Raman fiber Bragg grating (FBG) lasers with cooperative Rayleigh scattering is proposed. Two FBG were used to form two linear cavities laser sensors based on Raman amplification combined with cooperative Rayleigh scattering. Due to the very low dispersion coefficient of the fiber, it is possible to obtain the FWM using the two lasers. This configuration allows the operation as a temperature-insensitive strain sensor where both sensors have the same sensitivity to temperature but only one of the FBG laser is sensitive to strain. The difference between the wavelengths of the signal sensor and the converted signal presents a strain coefficient sensitivity of 2 pm/mu epsilon with insensitivity to temperature. The FWM efficiency is also dependent on the applied strain, but it is temperature independent, presenting a maximum sensibility of 0.01 dB/mu epsilon.

Abstract
The purpose of this study is to design a composite strain rosette using embedded fiber Bragg grating (FBG) sensors. Those strain rosettes are meant to be used as alternative to the conventional electric rosettes in structural health monitoring applications being glued at the structure surface. A thin (400 mu m) and flexible weaved carbon fiber reinforced plastic (CFRP) composite rosette is proposed. The three FBG sensors were written in a single optical fiber. Special care was devoted to the embedding process of the optical fiber sensors in the weaved composite plate in order to avoid significant alteration of the light reflected back by the FBG. The strain response of the composite rosette was compared to electrical strain gage's when applied at the surface of an aluminium sample submitted to tension, flexion and to dynamic strain. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53: 1853-1857, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26098

Abstract
In this work, a simple real-static nanostrain sensor based on a Bragg grating structure is presented. The setup is constituted by a narrow linewidth laser as light source, an optical circulator and a photodetector. The sensing head is formed by a chirped Bragg grating inscribed in a standard single mode fiber (SMF-28) by the phase technique. The fiber face end is cleaved and coated with a silver mirror, obtaining a Fabry-Perot interferometer. It is observable that the fringes period increases along the grating, due to the chirp spectrum (0.4 nm/cm) characteristics. The laser is fixed in one slope region of the fringe pattern. When strain is applied, the optical power changes linearly. A sensitivity of 5.72 mu W/mu epsilon in a range of 2 mu epsilon. The sensing head resolution is 70 n epsilon for a measurement step of 875 n epsilon.

Abstract
A Brillouin Stokes comb laser with increased flatness is reported. The feedback for the laser is provided by a distributed mirror combined with a narrowband seed laser. The Brillouin seed power and wavelength optimization is crucial in order to obtain a uniform power level between Stokes lines. The Brillouin seed must have a relatively large power and its wavelength must be located close to the Raman peak gain region. The flat-amplitude bandwidth is also determined by the choice of Raman pump wavelength. A flat-amplitude bandwidth of 34 nm from 1538 nm to 1572 nm is measured when Raman pump wavelength is set to 1455 nm. 425 uniform Brillouin Stokes lines with 0.08 nm spacing are generated across the wavelength range. The average signal-to-noise ratio of 15 dB is obtained for all the Brillouin Stokes lines. This type of laser can be used in optical communications as a multiwavelength source and also in metrology as a frequency ruler.

Abstract
In this work, a high-birefringent Sagnac loop interferometer torsion sensor is presented. The sensing head is inserted between the output ports of a high-birefringent coupler and it is formed by a section of standard single mode fiber. The sensing head characterization is done for torsion, temperature and strain measurements. The spectral response of this sensing head presents two interferometers, which are dependent on the light polarization states. Interference occurs due to the different lengths of the coupler output arms. This configuration allows the exclusion of a polarization controller, since it is possible to manipulate directly the polarization of light that travels inside the coupler. When the sensing head is subjected to torsion, it is possible to observe a beat between the two interferometers. In this case, there is a simultaneous pi/4 excitation of the two polarization states in the splices region. The torsion sensitivity is related to the sensing head length. The sensor response is periodic and the twist range can be from -2 pi to 2 pi. The sensor is unaffected by temperature and strain variations. This configuration is simple and when compared to the conventional configuration, the polarization controller is suppressed. The setup can be used in specific applications, such as in mechanical engineering.