Y.N. Ning

Recent progress in optical current sensing techniques

This paper reviews recent developments in the field of current measurement which employ a wide range of optical and fiber optic techniques. Depending on the current sensing mechanisms involved and the sensing materials used, optical current sensors (OCSs) may be categorized into four main groups: (i) OCSs employing optical fiber as their sensing elements, (ii) OCSs using bulk glass to sense the current, (iii) OCSs using electro‐optic hybrid sensing devices, and (iv) OCSs using magnetic field sensing devices. The operational modes of a variety of OCSs have been grouped and discussed, and several examples given. It can be seen that as a result of an intensive and wide ranging research effort using various approaches, substantial progress in the differing aspects of the optical current sensing techniques considered, such as the sensing material used, the configurations of sensing elements introduced, and the detection schemes adapted, has been achieved during the past years. An overall view of the field shows it to be as an active and exciting research area, highlighting several recently introduced and novel sensing materials and configurations which provide impressive results in this field of instrumentation. Examples of applications for the electric power industry are discussed more extensively.

Characteristics of laser diodes for interferometric use

Low-coherence-length light from laser diode sources has applications in extending the useful range of interferometric fiber optic sensors. The characteristics of two commercial low-coherence laser diodes were investigated and compared with theoretical models to determine the operational characteristics of the devices. Reasonable trends in the comparison were seen.

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.

The optimized wavelength combinations of two broadband sources for white light interferometry

Two broadband sources can be used in combination in white light interferometry to simplify the problem of central fringe identification. In this paper, a method for selecting the optimum wavelength combinations of such sources is presented. The results are obtained from a theoretical analysis and computer simulations, verified by experiment. It has been shown that the minimum signal-to-noise ratio required by the system to identify the central fringe position can be greatly reduced by using the optimum wavelength combination. >

Three-wavelength combination source for white-light interferometry

A three-wavelength combination source in white-light interferometry (WLI) is used to simplify the central fringe identification. It is found that, by using this technique, the minimum signal-to-noise ratio required by the system to identify the central fringe position can be reduced when compared with the use of two-wavelength combination sources. This technique is simple and effective and has potential uses in coherence-multiplexed interferometric sensor systems.<<ETX>>

A systematic classification and identification of optical fibre sensors

Abstract In this work, a new kind of classification for optical fibre sensors is introduced. Optical fibre sensors are classified according to the type of fibre, the light source and the modulation scheme on which they are based. Each of these categories is further subdivided and illustrations from systems developed and reported in the literature are given, with various sensor designs represented according to these criteria.

Optimized multiwavelength combination sources for interferometric use

We present the use of multiwavelength combination sources in a direct method for improved central fringe identification in a white-light interferometric system. The optimum wavelength combinations of such sources can be obtained by the use of the results of a simple analysis. We find that this multiwavelength technique can greatly reduce the minimum signal-to-noise ratio required by the systemwhen used to identify the central fringe, and thus it offers an increased signal resolution. As a result, it is suitable for high-precision measurement purposes as well as for applications in coherence multiplexed interferometric sensor systems.

Fibre-optic interferometric systems using low-coherence light sources

Abstract With the increasing interest in the use of optical-fibre interferometer measurement systems, the importance of the incorporation of low-coherence light sources is becoming of particular significance. In this work, the optical characteristics of different types of such sources in several interferometers are reviewed and examples are given. Their advantages in terms of increased unambiguous range, immunity to perturbation, high resolution and dynamic range, are 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. >

Central fringe identification in a white light interferometer using a multi-stage-squaring signal processing scheme

Abstract A new signal processing scheme for central fringe identification in a white light interferometer is described. With the use of a simple, fast and low-cost multi-stage-squaring processing unit, the central fringe in the output fringe pattern can be considerably enhanced and the SNR min required to identify the central fringe can be reduced from about 30 dB to 17 dB in a practical application.