Abstract
A fibre Bragg grating sensing configuration is presented for simultaneous measurement of strain and temperature. The proposed concept relies on writing a single Bragg grating on the splice region of two fibres with different levels of germanium doping. Doing so, a grating structure appears with three resonance peaks, which show distinct temperature sensitivities but similar strain responses. The experimental validation of the concept indicated resolutions of +/-1.5 degreesC Hz(-1/2) and +/-5.6 muepsilon Hz(-1/2) over measurement ranges of 80 degreesC and 1000 muepsilon for temperature and strain, respectively.

Abstract
A novel sensing head for simultaneous measurement of strain and temperature is demonstrated, based on two Bragg gratings arranged in a twisted configuration. Choosing an appropriate twisting period, the grating resonance wavelengths show similar temperature sensitivities but different strain responses, permitting simultaneous discrimination of these parameters with rms deviations of +/- 1.5 degrees C and +/- 4.7 mu epsilon respectively.

Abstract
The results of an investigation of the performance of a time-division-multiplexed (TDM) fiber Bragg grating (FBG) sensor array using a tunable laser source are reported. The system performance is found limited by the extinction ratio of the optical pulse modulator used for pulse amplitude modulation. Formulas that relate the crosstalk to the extinction ratio of the optical pulse modulator, the modulation parameters of the tunable laser, and the optical path differences among sensing channels are derived. Computer simulation shows that an array of 20 FBG sensors with 3 µe resolution can be realized with a commercially available single Mach-Zehnder type optical pulse modulator of -35-dB extinction ratio.

Abstract
A scheme to frequency multiplex a group of sensors based on all-fiber Michelson interferometers is presented. Lead insensitivity is obtained by using the two fibre leads of the configuration as an extra Michelson interferometer whose differential phase is kept constant by active compensation. Topics concerning the system design, sensor sensitivity, and crosstalk between sensors are investigated. Experimental and numerical computational results are presented.

Abstract
The overall procedure toward the implementation of a compact tunable athermal filter mounted on a piezoelectric actuator and based on a pi-shift chirped fiber Bragg grating is presented. This package ensures an active tunablility over 2 nm with a cross thermal induced Bragg wavelength shift below 100 pm over a temperature range from -20 degrees C to + 80 degrees C. The proposed filter makes use of the overall response of a p-shift chirped fiber Bragg grating and a bulk broadband microfilter that enables a sharp optical transmission spectrum response having a FWHM below 20 pm within a 2 nm region and 20 dB rejection band to be obtained. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3656751]

Abstract
We present a compact in-line fiber interferometric sensor fabricated in a boron doped two-mode highly birefringent microstructured fiber using a CO2 laser. The intermodal interference arises at the fiber output due to coupling between the fundamental and the first order modes occurring at two fiber tapers distant by a few millimeters. The visibility of intermodal interference fringes is modulated by a polarimetric differential signal and varies in response to measurand changes. The proposed interferometer was tested for measurements of the strain and temperature, respectively, in the range of 20-700 degrees C and 0-17 mstrain. The sensitivity coefficients corresponding to fringe displacement and contrast variations are equal respectively for strain -2.51 nm/mstrain and -0.02561/mstrain and for temperature 16.7 pm/degrees C and 5.74 x 10(-5) 1/degrees C. This allows for simultaneous measurements of the two parameters by interrogation of the visibility and the displacement of interference fringes. (C) 2011 Optical Society of America