Serge J. Huard

Dual-wavelenth passive homodyne detection unit for fiber-coupled white-light interferometers

This paper is devoted to the description of a prototype Emission/Detection Unit, the ACCORD® Module, developed for the accurate demodulation of fiber optic sensors using spectral modulation encoding techniques. This prototype contains a static polarimetric interferometer with 4 ports to provide the four phase signals needed by the passive homodyne scheme, and uses a dual-wavelength arrangement to extend the measurement range by removing the 2ic ambiguity in the phase determination. Resolution as high as A/40000 has been achieved with 1 Hz bandwith and Optical Path Difference mismatch in a 20 microns range.

USE OF A GRATING INTERFEROMETER AS A PARALLEL RECEIVER FOR FIBRE OPTICS WHITE LIGHT QUASI DISTRIBUTED SENSORS

We show that a grating interferometer can be used as a receiver for quasi-distributed fiber optic sensors using white light interferometry. We report the results obtained when the sensor is based on an embedded fiber optic polarimetric interferometer for strain measurement of carbon/epoxy composites.

Fiber optic Sagnac interferometer as polarimetric sensor using a nonpolarized and a broadband source

The principle of an interferometric single-mode fiber optic sensor using birefringent components and a broadband source is described. This device is sensitive to the magnetic field variation or to the mechanical rotations of its components. In this paper, we show that only one additional birefringent element is needed to make this fiber optic sensor. Besides, this device can be used for characterizing optical fibers or any birefringent element inside the Sagnac.

White-light interferometry: new developments applied to high-accuracy optical measurements

The main results obtained with optical devices using coherence multiplexing are described. The demodulation methods for interferometers illuminated by low coherence sources are studied. The applications of coherence multiplexing in the field of fiber-optics sensors and telecommunications together with the future developments are also presented.

Tunable wavelength filter using the Faraday effect

This paper reports how to realize a new type of tunable filter using the Faraday effect. The properties of a Fabry-Perot etalon whose cavity is made with a Faraday rotator are recalled. The analysis of the polarization state of the emergent light permits us to find the configuration of the device to realize such a tunable filter. This latter finds application in wavelength demultiplexing.

Use of a grating interferometer for the demodulation of white-light interferometric sensors

In order to demodulate optical fiber interferometric sensors in the coherence multiplexing scheme it is worthwhile using static interferomers. Measurement of a physical parameter is obtained by matching the optical path difference (OPD) of each interferometric sensor with a receiver. An attractive solution consists in using grating interferometer as a demodulator. Indeed, it permits one to record correlation peaks (each one corresponding to a sensor) on a photodiode array, thus making demultiplexing easier. On the other hand, it is possible to record only the peak envelope if the grating interferometer is adjusted in a well defined configuration. In this paper we concern ourselves with the theoretical determination of the conditions needed to simplify calculations and interpretation of the experimental results.