B. T. Meggitt

Optical fiber sensor technology

List of contributors. Preface. 1. Overview of fiber sensor developments D.A. Jackson. 2. Foundations of optical fiber technology V. Handerek. 3. Sources for optical fiber sensors K.T.V. Grattan. 4. Optical detectors and receivers J.D.C. Jones. 5. Multimode optical fiber sensors G.R. Jones, R.E. Jones, R. Jones. 6. Multimode optical fiber chemical sensors J.O.W. Norris. 7. Single mode optical fiber sensors V. Handerek. 8. Optical fiber modulation techniques for single mode fiber sensors R.P. Tatam. 9. Fiber optic white-light interferometric sensors B.T. Meggitt. 10. Nonlinear effects in optical fibers A.J. Rogers. 11. Distributed fiber optic sensors A.H. Hartog. 12. Schemes for referencing of intensity-modulated optical sensor systems G. Murtaza, J.M. Senior. 13A. Hybrid optical fiber sensors R.C. Spooncer, G.S. Philp. 13B. Optical fiber current measurement A.J. Rogers. 13C. Fiber optic techniques for temperature measurement K.T.V. Grattan. 14. Advanced external fiber optic sensors D.A. Jackson. Index.

A field deployable, multiplexed Bragg grating sensor system used in an extensive highway bridge monitoring evaluation tests

A multiplexed optical fiber Bragg grating sensor system with a measurement bandwidth of up to 200 Hz enabling dynamic loading events, e.g., road traffic, to be observed has been designed, installed, and tested over an 18-month period on a 346-m road bridge in Norway, for design verification and structural integrity monitoring purposes. A network of 32 fiber Bragg sensors was surface bonded along with a corresponding set of resistive strain gauges for comparative tests to be made. The wavelength data were calibrated against two thermally stabilized (/spl sim/0.15 pm) reference gratings, which rejected common mode noise and provided absolute wavelength scaling. These data provides independent strain and temperature information. Long-term test results showed good linearity and repeatability of <10 /spl mu//spl epsiv/ over the test period with a precision of /spl plusmn/5 /spl mu//spl epsiv/ and a resolution of /spl plusmn/1 /spl mu//spl epsiv/. The readings from the FBG sensors were comparable to those from the foil gauge sensors to within /spl plusmn/4 /spl mu//spl epsiv/.

Prony’s method for exponential lifetime estimations in fluorescence‐based thermometers

Noniterative algorithms using Prony’s method are proposed for the estimation of the exponential lifetime in fluorescence‐based fiber‐optic sensor systems. The uses of a variety of Prony’s algorithms are evaluated using Monte Carlo simulations. It is shown that the performance of Prony’s algorithms is quite close to that of Marquardt algorithms and they are the better alternatives to their Marquardt counterparts, when illustrated for real‐time applications in temperature sensors with a 98% decrease in running time.

Bragg grating sensing instrument using a tunable Fabry-Pérot filter to detect wavelength variations

A two-Bragg-grating sensing system, demodulated with the use of a tunable Fabry-P?rot filter to detect the associated wavelength variation has been developed. To show the practicality of the system, a low cost ELED (with an output of at ) was used as the light source, incorporating readily available Bragg gratings centred around this wavelength. The relevant parameters considered in designing such a system have been analysed and are discussed in detail. With the use of a digital Gaussian filter to limit the noise, under the same conditions, the repeatability obtained was close to the optimum level achievable (with the 12-bit A/D card used), and the repeatability of the Bragg wavelength, determined with individual data points being averaged over ten measurements was 7 pm, when the signal to noise ratio was as low as 30:1. Temperature and strain sensitivities of and have been demonstrated with such an instrument. The potential for achieving a higher repeatability of the measurement is discussed.

Characteristics of a multimode laser diode in a dual-interferometer configuration

The results of an experimental investigation of an interferometric sensor scheme using a Michelson interferometer in conjunction with a Fabry-Perot reference cavity, illuminated by light from a multimode compact disk (CD)-type laser diode, are reported. The results are compared with the results of calculations using a simple theoretical model and good agreement is seen. Potential applications to interferometric-based sensors are discussed. >

Interferometric detection scheme for measuring wavelength shift using a stabilized interferometer with an additional reference wavelength

Abstract A novel interferometric detection scheme for measuring wavelength shift, with applications to optical sensing systems is described. In this scheme, in addition to the source wavelength to be measured, a further reference wavelength is employed to stabilize the optical path difference of the interferometer. This is designed to make the wavelength detection system insensitive to environmental disturbances such as temperature fluctuations and mechanical vibration, and using this scheme a signal-to-noise ratio improvement of ∼ 25 dB has been shown in a demonstration system.

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>>

Bragg-grating-based multisensor system for structural integrity monitoring of a large civil engineering structure: a road bridge in Norway

A spatially multiplexed high bandwidth WDM based fibre Bragg grating sensor system has been developed for structural condition monitoring and health maintenance of large civil engineering structures under both static and dynamic loading conditions. The system has been field deployed for real-time strain monitoring on a new 346m long steel road bridge in Norway. The bridge was instrumented with both fibre Bragg grating sensors and conventional resistive strain gauges at various points optimally identified. In this paper laboratory results from small-scale structures as well as field results on the real bridge structure are reported.

A novel digital phase tracking algorithm for a high resolution fibre Bragg grating based sensor system

The development of a high-resolution, optical fibre Bragg grating sensor system is described that incorporates a novel digital, condition-based, phase-tracking algorithm for unwrapping the 2π phase ambiguity and permits the continuous up/down phase-tracking of multiple fringe changes. An all-fibre, Michelson interferometric phase-measurement approach is utilised for the determination of strain and temperature induced Bragg wavelength shifts. The system incorporates orthoconjugate mirrors and a stabilised reference channel to compensate for polarisation and random thermal induced drifts and has the potential for resolving sub-μstrain and mK temperature changes with a resolutions of <100n/√Hz (at 1Hz) and <10mK respectively.

Finite Element Simulation of an In—Fiber Interferometric System for Hydraulic Pressure Measurement Applications

A computer simulation of an in-fiber interferometric hydraulic pressure sensor is carried out by use of a finite element method. Both the interference between the same modes from the two arms of the interferometer and the beat length of the two orthogonal modes in the polarization- maintaining fiber which is used as the working arm of the interferometric hydraulic pressure sensor are examined, for various types of polarization-maintaining fibers under different values of hydraulic pressure. As a result, the design of the in-fiber interferometric hydraulic pressure sensors may be optimized.