Abstract: Fibre optic apparatus for accurate and repeatable measurements of light comprising one or more wavelength ranges, and system employing the apparatus. The apparatus according to the invention comprises: a directional coupler adapted to lead the light into an optical fibre, said optical fibre containing at least one analysis filter for each wavelength range, said analysis filters consisting of at least one fibre-optical Bragg-grating (FBG) which reflects incident light with a chosen wavelength back through said directional coupler and onto a detector having an associated signal processing unit, a modulator device for pulsing the incident light with a chosen pulse width, and an optical fibre delay line in front of each analysis filter, with a length adapted to provide for a sufficient time delay larger than the pulse width, so that the pulses reflected from each analysis filter at different wavelengths can be separated in time and thereby be demodulated in the signal processing unit.

Abstract: Method and system for obtaining scale factor calibration of a fiber optic sensor head (3, 6) comprising a conversion unit (3) with a conversion element (14) made from a material being subject to changes in its shape or physical dimensions under the influence of magnetic or electric fields, e.g. a magnetostrictive, electrostrictive, or piezoelectric material, and an optical fiber (4) being attached to the conversion element (14), the conversion element (14) thus straining the optical fiber causing a phase and/or intensity modulation of the optical signal in the fiber when subject to the fields. The method is characterized in that a chosen electrical energy is applied to the sensor head (3, 6) resulting in a change in the optical signal being received by the optical interrogation device, and calculating a calibration signal, e.g. a calibration scale factor, based on the applied electrical energy and the measured change in the optical signal.