ANALYSIS OF DISPERSION EFFECTS FOR WHITE-LIGHT INTERFEROMETRIC FIBEROPTIC SENSORS

We derived the transfer function for a white-light interferometric sen sor based on highly birefringent (HB) fiber, assuming that both sensin g 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 o r the interference fringes is detected. In the first case the sensitiv ity of the sensor is determined by the influence of the measurand on m odal polarization dispersion while in the second case it depends on th e influence of the measurand on modal birefringence of the HB fiber. T his sensitivity difference limits the operation range of recently prop osed zero-order fringe-tracking methods within which the unambiguous m easurement is possible. The dispersion effects for a white-light inter ferometric strain sensor composed of York HB or Andrew E-type fiber as a sensing element and a quartz Wollaston prism as a receiving interfe rometer were studied experimentally. Sensitivities of modal polarizati on 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 interferom eters we also determined the unambiguous measurement range for zero-or der fringe-tracking techniques.