White-light Interferometric Sensor Research Articles

Precision and sensitivity optimization for white-light interferometric fiber-optic sensors

A detailed analysis for accuracy and sensitivity of fiber-optic sensor based on white-light interferometric technique with wavelength scanning is presented. Analytical equations for optimal optical path difference were obtained, which allow to reach the minimum measurement uncertainty. The results of the analysis can be applied for optimization of any sensor based on low coherence spectrum domain technique, though our experimental validation of analysis has been carried out with the temperature sensor based on the Sagnac interferometer having a twisted high-birefringent fiber as a sensing element.

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.

Influence of dispersion on sensitivity of highly birefringent fibers to temperature and hydrostatic pressure

The influence of dispersion on the sensitivity of highly birefringent fibers to temperature and hydrostatic pressure was experimentally investigated. In fibers with geometric birefringence that shows high dispersion, great differences were observed between group and phase sensitivities to temperature and hydrostatic pressure. This difference may reach 400% in the case of temperature response. In contrast, in weakly dispersive fibers with stress-induced birefringence these differences were of the order of 8% and 14%, respectively, for temperature and pressure. The influence of the dispersion effect on the temperature compensation of white-light interferometric sensors based on highly birefringent fibers was also discussed.

Evaluation of different adaptive filtering techniques applied to white-light interferometric sensor systems

The performance of several digital processing schemes is compared in this paper, including a number which have been proposed to a.d the identic Sn of the antral fringe in white-light interferometric sensor systems. The paper aims to illustrate those technques which enable the best performance to be achieved and conclusions are drawnonthecomparative selection, resource implications and operating ranges and speeds.

Contrast analysis for a fiber-optic white-light interferometric system

The behavior of a system of fiber-optic white-light interferometric sensors is analyzed. Analytical expressions for contrasts of all the interference patterns that may occur at the setup's output are derived as a function of coupling coefficients between successive sensors. Two cases of exemplary systems consisting of highly birefringent optical fibers, one with nondichroic the other with some polarizing fibers, are analyzed.

Dispersion effect analysis with multiwavelength combination sources in optical sensor applications

Using a multiwavelength combination source, the central fringe in the interference fringe pattern in a white light interferometric sensor system can often be more easily identified, which is important for high precision and absolute measurement. However, owing to the possible optical path imbalance inside the optical dispersive elements which are usually involved in such systems, the zero optical path difference (OPD) position corresponding to one of the individual sources may not coincide with that of the others and consequently the central fringe intensity may decrease. This may be associated with a substantial degree of fringe pattern asymmetry, which causes a significant problem with central fringe identification. In this work, the effect of zero OPD position variation with the wavelength on fringe patterns of multiwavelength combination sources are analyzed and a method to alleviate such an effect is proposed, supported by a simple theoretical analysis and experimental results.

Theoretical and experimental analysis of thermal stress effects on modal polarization properties of highly birefringent optical fibers

A theoretical and experimental analysis of thermal stress effects on the modal polarization properties of highly elliptical-core fibers is presented. The theoretical analysis is based on solving the vectorial Maxwell's equations, using a finite-element scheme, when form-induced and stress-induced effects are introduced simultaneously through appropriate calculation of the refractive indexes of the anisotropic media. The experimental analysis is done by studying the temperature response of a white-light interferometric sensor employing highly elliptical-core fibers. The calculated temperature sensitivities of the modal birefringence and the polarization mode dispersion in highly elliptical-core fiber are in close agreement with the experimental results. Interpretation of the results useful for designing white-light interferometric sensors composed of highly elliptical-core fibers is also given.

Use of a Sm/sup 3+/-doped fiber as a low-coherence light source

A Sm/sup 3+/-doped fiber pumped by an Ar-ion laser can produce a low coherence, visible light source for white light interferometric use. By the use of two spectral filters, a two wavelength combination source can also be generated flexibly and efficiently. This fiber light source is compatible with other fiber components in the optical sensor system, has good coupling efficiency into single mode fibers and high spatial coherence thus showing significant potential for this family of doped fibers, for use in white light interferometric sensor applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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 xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Polarization insensitive fibre-optic white-light interferometry

Interferometric systems consisting of two tandem interferometers with white-light illumination have been used as optical-fibre remote-sensing systems. Recently, it has been shown that both phase and amplitude of the output signal are significantly affected by externally induced birefringence in the fibre linking the interferometers; in some cases, this may cause total fading of the interference signal. In this letter, a new scheme is proposed to overcome this problem in white-light fibre-optic interferometric sensors. The approach is based on birefringence compensation using Faraday rotator mirror elements. The principle is experimentally verified, and the results confirm the theoretical expectation.

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.

Detection scheme for white-light interferometric sensors

Static interferometers whose optical path difference is not constant over the field of interferences are well adapted to demodulate sensing interferometers in the coherence multiplexing method. In this configuration the correlation peak can be spatially recorded on a linear detector array. However, the determination of the position of the peak maximum amplitude is often difficult because of the spatial sine amplitude modulation. This drawback can be eliminated by using a grating interferometer as a demodulator. In this case it is possible to record, on the detector, only the envelope of the correlation peak.

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.

White-light interferometric multimode fiber-optic strain sensor

A white-light interferometric extrinsic Fabry-Perot strain sensor that uses a multimode fiber is demonstrated. The Fabry-Perot cavity length is measured with the help of a Fizeau interferometer. The sensor is described, and some results obtained at this time are given. The strain measurements are absolute and perfectly linear, with a sensitivity of 0.25 micrometers per meter (micro). the design of a thermally autocompensated strain sensor is also presented.

Study of electronically-scanned optical-fibre white-light Fizeau interferometer

A theoretical analysis and experimental evaluation of a Fizeau interferometer with a broadband optical-fibre source and a linear CCD detector is presented. Using such an interferometer as the scanner in an optical-fibre white-light interferometric sensor system has the advantages of a simple, compact structure and high stability. A further study on the configuration to improve fringe visibility is also presented.