Abstract
In optical coherence tomography (OCT), it is often assumed that the signal-to-noise ratio, at higher optical power regimes, is limited by beat noise. Nonetheless it was often noticed that the limiting value could not be experimentally achieved, despite minimizing the stray reflectance and increasing the optical source effective bandwidth. In this work we present a new model for the noise in a balanced OCT configuration, which accounts for the limited spectral response of fiber directional couplers, as well as imperfections in the photo-detectors. As a consequence, and due to different spectrum content between the two balanced-OCT outputs, excess photon noise is larger than previously considered. The model also allows for the determination of SNR optimized parameters for maximum performance of the balanced system, and can be applied to any coupler or broadband source. Results for optimized and non-optimized configurations, for different balanced detection configurations, implemented in an OCT system, are presented and discussed.

Abstract
A simple method for crystallizing amorphous thin films was developed using platinum bottom electrodes as heating elements. A current was applied to tungsten wires in contact with the platinum and the temperature was measured using a type-K thermocouple. A proportional feedback algorithm was used for controlling the process. The performance of different platinum electrodes was studied. Pt films with different thicknesses were alternatively deposited over Ti and Zr at 700degreesC. Applying currents up to 2 A to the Pt films, the resistance dependence of temperature was studied. The maximum temperature, 675degreesC, was obtained when using 200 nm Pt films deposited at 700degreesC over Ti, with a power consumption of 16 W. The method was applied to the crystallization of PbZr0.52Ti0.48O3 thin films using Pt films deposited at 500degreesC over Ti and at 700degreesC over Zr. The results obtained for heat treatments at 650degreesC with 10degreesC/s heating and cooling rates showed a pure perovskite phase; the ferroelectric properties were comparable with those from films crystallized by rapid thermal annealing. (C) 2004 American Institute of Physics.

Abstract
The concepts of time refraction was introduced in recent years, as the temporal analogue of the usual (space) refraction, for waves propagating in non-stationary optical media. We discuss possible experimental configurations for time refraction of low intensity and short laser pulses propagating in optical fibers, and their eventual use in photonics. We generalize our previous work to the case of guided propagation. The expected frequency shifts, amplitudes and shapes of the secondary pulses resulting from time refraction are calculated.

Abstract
We present a fibre optic sensing head for making simultaneous measurements of temperature and strain, which operates over a large temperature range. The configuration is based on the different temperature sensitivities of type I and type IIA gratings written in a fibre with high germanium content. Maximal errors of +/-0.7 degreesC Hz(-1/2) and +/-3.8 muepsilon Hz(-1/2) are reported over 500 degreesC and 1200 muepsilon measurement ranges, respectively.

Abstract
A network for multiplexing fiber Bragg gratings (FBGs) and intensity-modulated fiber-optic sensors with no need to distinguish between the two kinds of sensor is proposed and experimentally demonstrated. Two FBG sensors and two intensity-modulated sensors are wavelength-division multiplexed; the electrical phase of the output signal is measured as a common parameter for both types of sensor. Furthermore, the intensity sensors become power referenced, and the FBG sensors are interrogated by a low-cost technique. Low cross talk is achieved by use of a tunable optical filter at the detector. (C) 2003 Optical Society of America.

Abstract
The demand for a low cost, portable and accurate instrumentation system for structural monitoring is increasing as civil structures appear to be monitored for their lifetime. Face to conventional solutions, the issue can be handled as to develop an interrogation system based on a CCD spectrometer. A method pointing out to improve the instrumentation characteristics of the whole system was developed The initial low wavelength resolution of the spectrometer (0.2 nm) is enhanced through a sub-pixel resolution algorithm. This algorithm, capable of a approximate to 200 times improvement in the resolution, is presented in this work. Final characteristics are validated within the calibration process. It is made a comparison between the results obtained with the designed system and others reported, using similar models. As the measurement quality depends on the interrogation method and associated wavelength resolution, future developments are planned They are described and analyzed in the final part of the paper.