Abstract
A theoretical and experimental characterisation of a self-referenced fibre optic intensity sensor based on a multiple beam Sagnac configuration is conducted. Via the definition of the measurement parameter (R parameter) sensor linearity and sensitivity are analysed. Theoretical and experimental results are compared, being considered the problem of sensor design and optimisation.

Abstract
An analysis is performed of the degradation of the signal readout of fiber optic Bragg grating sensors demodulated using the serrodyne interferometric technique. Experimental results are presented that validate the analysis. It is also shown that synchronous detection of the interferometric signal referenced to the serrodyne waveform that modulates the phase of the readout interferometer allows the elimination of the system do offset introduced by the serrodyne flyback, (C) 2000 Society of Photo-Optical Instrumentation Engineers.

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
The potential of different fiber Bragg grating pairs for simultaneous sensing of strain and temperature is analyzed. We demonstrate that interferometric interrogation of a fiber grating written in bow-tie fiber enables strain and temperature to be simultaneously determined. This is achieved by independent measurement of the shift in the wavelengths of the reflected light from the grating components along the fast and the slow axes of the hi-bi fiber. A detailed theoretical analysis is presented that includes the basic sensing principle, sensor design and demodulation scheme. The performance of the proposed technique in simultaneous measurement of temperature and strain is experimentally demonstrated and resolutions of +/-2.5 degrees C/root Hz and +/-26 mu epsilon/root Hz are obtained for a fiber with birefringence of B = 5.5 x 10(-4). (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)00808-4].

Abstract
A compact all-fiber interrogation technique for Bragg sensors is presented. It is based on the generation of an electric carrier by modulating the coupling length of a wavelength-division multiplexer (WDM). Theoretical and experimental results are presented when both serrodyne and sinusoidal modulations are considered. It is shown that this technique provides static microstrain resolution in measurement intervals larger than some millistrain.

Abstract
The interrogation of fiber Bragg grating sensors with multimode laser diodes is theoretically and experimentally analyzed using two different approaches: serrodyne and dithering techniques. It is also demonstrated that by using several laser modes it is possible to enhance the measurement range without compromising sensitivity, (C) 2000 Academic Press.