Waclaw Urbanczyk

Measurement of polarization mode dispersion and modal birefringence in highly birefringent fibers by means of electronically scanned shearing-type interferometry

A method for measuring modal birefringence and polarization mode dispersion in highly birefringent fibers is presented. It employs a white-light interference phenomenon arising between polarization modes as a result of mode coupling induced by a pointlike lateral force applied in approximately one half the length of the tested fiber. This permits the use of a Wollaston prism without a delay line as an analyzing interferometer. Results of measurements of modal birefringence and polarization mode dispersion at λ(0)= 826 nm are reported for four commercially available fibers: the York Bow-Tie, the Fujikura Panda, the Andrew E-type, and the Andrew D-type.

Cross-sensitivity effect in temperature-compensated sensors based on highly birefringent fibers

We analyzed the influence of the measurand-temperature cross-sensitivity effect on temperature stability in fiber-optic cross-spliced sensors that employ highly birefringent fibers. We show that the ratio of the measurand-temperature cross-sensitivity coefficient to the measurand first-order sensitivity determines the physical limit for temperature stability in cross-spliced sensors. Employing polarimetric as well as white-light interferometric methods, we experimentally determine a hydrostatic pressure-temperature cross-sensitivity coefficient in York bow-tie 800 fiber. From this we estimate the achievable limit for temperature stability of cross-spliced pressure sensors under environmental temperature changes.

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

Abstract 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.

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.

White-light interferometric fiber-optic pressure sensor

A novel configuration for a fiber-optic white-light interferometric sensor is presented which allows for absolute measurements of hydrostatic pressure with an improved operation range. The performance of two fibers (York bow-tie 800 and especially designed elliptical-core side-hole fiber) used as sensing elements was experimentally studied. The sensor itself was composed of two equal lengths of the fiber spliced at 90/spl deg/. This structure assures temperature compensation and enables application of a Wollaston prism as a receiving interferometer. A step delay line made of crystalline quartz was used to increase the operation range of the sensor.<<ETX>>

Multiplexing of electronically scanned white-light interferometric strain sensors based on HB fibers

Application of electronic scanning to a sequence of coherence-multiplexed strain sensors is proposed in this paper. The sensors consist of a cascade of HB fibers spliced with their polarization axes rotated by certain angles. We theoretically analyzed the behavior of such chains as a function of their alignment and found the optimal alignment ensuring readout of every sensor with the maximum S/N ratio. The performance of parallel and serial multiplexing configurations was experimentally studied. As a receiving interferometer we used a Wollaston prism followed by a CCD camera and an image processing system while a stepped delay line made of calcite and crystalline quartz was used to match the group delays between sensing and receiving interferometers.

Measurements of temperature and strain sensitivity for two-mode Bragg gratings imprinted in bow-tie fiber

A method for measuring sensitivity of Bragg gratings to external parameters for different spatial and polarization modes is presented, along with the results of sensitivity measurements to temperature and elongation for LP01x, LP01y, LP11x, LP11y modes. The difference in responses according to the type of mode shows the possibility of simultaneous temperature and elongation measurement using two-mode Bragg gratings.