This paper presents a single-probe Michelson interferometer that uses mode coupling in a long-period grating to establish the two optical paths in a single optical fibre. The interferometer phase shift depends on the refractive index of the material that surrounds the fibre probe, with the phase sensitivity directly proportional to the probe length. A simple phenomenological model explains the experimental results obtained with a liquid level sensor and a refractive index sensor. Its temperature sensitivity depends on the type of fibre that constitutes the probe. With a 45 mm long fibre probe, it is -2.5 and 12.8 degrees • C −1 for normal single mode fibre (SMF28) and germanium-boron co-doped fibre (PS1500), respectively.

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Non-contact measurement of torsion on a rotating shaft was done with fibre Bragg gratings and involved the use of graded index lenses for transmitting optical information between the light source and the gratings, and back to a spectrum analyser. Special Böhler steel with high yield strength was used for the shaft. For the experimental measurements, one end of the shaft was clamped in a lathe chuck, and the other end was fixed to a brake system, allowing the application of torque on the rotating shaft. Up to 97 N m of torque was applied to the shaft rotating at 190 rpm, and the results were very close to the expected values. Whereas torsion changes the differential-mode wavelength of the gratings in the proposed configuration, this wavelength difference is insensitive to temperature. For the particular system investigated experimentally, the differential wavelength change was 7.4 pm N −1 m −1 , and the corresponding temperature sensitivity was −0.547 pm • C −1 .

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We report a chirped fiber Bragg grating transducer for the measurement of acceleration, in which a cantilever beam and fiber Bragg grating are used. The cantilever induces strain on the grating resulting in a Bragg grating wavelength modification that is subsequently detected. The output signal is insensitive to temperature variations and for a temperature change from -20 degrees C to 40 degrees C, the output signal fluctuated less than 5 % without any temperature compensation schemes. Because the accelerometer does not utilize the complex demodulation techniques it is potentially inexpensive. For the experimental system a linear output range of 8 g could be detected.