Abstract
We present and demonstrate a high-resolution absolute-distance measurement system based on multiple-wavelength interferometry. The information on a cavity length is obtained by sampling a fringe of its spectral response at different wavelengths. This is achieved by simultaneously tuning multiple fiber Bragg gratings. For a two wavelength system, an unambiguous measurement range of 262 µm was obtained with a resolution of 14.3 nm.

Abstract
An all fiber interrogation technique for Bragg sensors is presented. It is based on generation of an electric carrier by modulating the coupling length of a wavelength division multiplexer. Results are given when both serrodyne and sinusoidal modulation formats are considered.

Abstract
An all fiber technique for interrogation of interferometric low-finesse Fabry-Perot cavities is presented. 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 sensor based on a Sagnac topology in reflection is described. The sensor uses the properties of its frequency response in order to obtain a self-referenced signal proportional to the measured signal. The sensor is a versatile structure for the monitoring of static and dynamic physical parameters, which require a small number of optical components and simple signal processing.

Abstract
We describe a scheme in which a multimode laser diode, with effective coherence length less than 250 µm, is used to illuminate sensors multiplexed in time and with their status read by coherence sensing. Data is presented which shows that the spectral characteristics of the laser light remain essentially unchanged upon direct modulation of the laser injection current or whilst subject to laser feedback. This has allowed the multiplexing scheme network to be implemented without recourse to either a Bragg cell modular or an optical isolator. The technique was applied to measure displacement, strain and temperature. © 1991.

Abstract
A time division multiplexing technique is described in which the frequency of a laser source is modulated with a sampled ramp. The concept is demonstrated with two Mach-Zehnder interferometers in a parallel configuration, separated by a fibre delay line whose length is determined by the characteristics of the sampling waveform. Pseudo-heterodyne processing was used to recover the phase information from each interferometer. The expansion of the technique to a combined frequency and time division multiplexed fibre-optic sensing system is considered.