Abstract

Interferometric fiber sensing techniques are typically used for applications requiring very high sensitivity to weak perturbing fields, such as acoustic, magnetic and electric fields. There has also been interest, however, in the use of interferometric configurations for the measurement of quasi-static parameters, e.g. temperature and strain. In general, the ambiguous form of the cosine squared transfer function of an interferometric sensor negates the determination of the measurand value on initialization of the sensor. This can be overcome using various forms of signal processing which typically involve multi-wavelength operation, or source spectral modulation. In this paper we describe a fiber Fabry–Perot sensor for the measurement of strain which utilizes a mode of operation based on matching the spectral characteristics of a strongly frequency-modulated source to the frequency dependence of the Fabry–Perot resonator (or other form of resonant cavity, e.g., ring resonator). This matching allows the precise determination of the free-spectral range of the cavity, and thus the optical length of the cavity. Strain induced changes in cavity length are then reflected in a shift in the laser modulation frequency required to achieve matching of the laser and sensor resonance spectral characteristics. The principle of operation of the technique, and results obtained using a 20 m fiber Fabry Perot cavity will be reported.

© 1993 Optical Society of America