White-light Interferometric Strain Research Articles

An all fibre white light interferometric strain measurement system

We report on an all fibre implementation of a white light interferometric fibre strain sensor. Utilising white light tandem interferometry, two all fibre Michelson interferometers are used, one to form the sensor element and the other the optical path scanning interferometer. Results are presented which demonstrate the performance of the system and the measurement of applied strain up to 10 000 με.

Analysis of dispersion effects for white-light interferometric fiber-optic sensors

We derived the transfer function for a white-light interferometric sensor based on highly birefringent (HB) fiber, assuming that both sensing and receiving interferometers are dispersive. This transfer function indicates that different responses to changes in the measurand may be observed depending on whether displacement of the contrast function or the interference fringes is detected. In the first case the sensitivity of the sensor is determined by the influence of the measurand on modal polarization dispersion while in the second case it depends on the influence of the measurand on modal birefringence of the HB fiber. This sensitivity difference limits the operation range of recently proposed zero-order fringe-tracking methods within which the unambiguous measurement is possible. The dispersion effects for a white-light interferometric strain sensor composed of York HB or Andrew E-type fiber as a sensing element and a quartz Wollaston prism as a receiving interferometer were studied experimentally. Sensites of modal polarization dispersion, modal birefringence, and chromatic dispersion of modal birefringence to the strain were determined for both types of sensing fiber. For these specific combinations of sensing/receiving interferometers we also determined the unambiguous measurement range for zero-order fringe-tracking techniques.

Electronically scanned white-light interferometric strain sensor employing highly birefringent fibers

An electronically scanned strain sensor employing highly birefringent fiber as a sensing element and using a low-coherent light source is described. The sensor is composed of two sections of exactly equal length of HB fiber spliced at 90°. This structure compensates the spatial coherence mismatch which enables application of a Wollaston prism alone without expensive bulk delay line as a receiving interferometer, and assures good temperature stability of the sensor. Absolute measurements of strain within the range up to 4000 μstrain with apparent temperature cross-sensitivity less than 1.3 μstrain/°C are possible with this sensor.