Abstract
A new fiber Bragg grating sensor configuration is presented for simultaneous measurement of strain and temperature. The sensor utilizes the effect of boron codoping on the temperature dependence of the refractive index in germanosilicate fibers. By writing gratings with close wavelengths in undoped and boron doped fibers, different temperature sensitivities are obtained while strain sensitivities remain the same. These gratings are then spliced to obtain a simple sensor head suitable for applications in smart structures and composite materials.

Abstract
A signal processing scheme for fiber Bragg grating sensors based on the utilization of adjacent modes of a multimode laser diode light source is demonstrated which allows high sensitivity to be obtained over a large measurement range, For strain measurements, a range of 4800 mu epsilon is achieved with a resolution of 0.08 mu epsilon/root Hz, yielding a dynamic range of 95 dB.

Abstract
A pseudoheterodyne, open-loop demodulation technique? for detecting wavelength shifts in wavelength encoded fiber Bragg grating sensors is presented, The scheme uses a processing Bragg grating that is identical to one used as a sensor, When the processing fiber grating is stretched periodically, the system of two gratings produces a carrier at this frequency with its phase modulated by the measurand signal applied to the sensing grating, The demodulation technique is intrinsically immune to fluctuation of optical power in the system and is independent of the source spectral profile characteristics. A resolution of approximate to 1 mu epsilon/root Hz for static axial strain was achieved.

Abstract
An optical sensor capable of simultaneously measuring displacement and temperature is presented. It incorporates a fiber Bragg grating temperature sensor and a low-finesse extrinsic Fabry-Perot cavity. A white light tandem interferometric technique is used to recover signal from the low finesse cavity. Signals obtained from the interferometer and the Bragg grating provide required information to simultaneously determine temperature and displacement. Experimental results are presented which demonstrate the feasibility of this sensor topology in practical applications.

Abstract
A theoretical and experimental investigation is reported on a novel all-fiber technique for interrogation of interferometric low-finesse Fabry-Perot cavities, It is based on the modulation of the spectral transfer function of a wavelength-division multiplexer, Results are given when both serrodyne and sinusoidal modulation formats are considered.

Abstract
A demodulation scheme for fiber Bragg grating (FBG) sensors is presented. It is based on the generation of an electrical carrier by using a modulated multimode laser diode to illuminate the fiber grating. The change in Bragg wavelength is measured by tracking the phase of the carrier at the detector output in either an open- or a closed-loop scheme. A theoretical analysis of the interrogation technique in terms of linearity and dynamic range is presented. Experimental data were obtained for both strain and temperature measurements. Sensitivities of 0.7 mu epsilon/root Hz and 0.05 degrees C/root Hz were obtained over a dynamic range of approximate to 60 dB, The application of this demodulation scheme to a multiplexed sensing system is also demonstrated.