Recent progress in optical current sensing techniques

Abstract

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.

Micromachined optical fiber current sensor

“…Several reviews give an idea of the magneto-optical and non-magneto-optical OCS. 9,10 Among the non-magneto-optical devices, several magnetomechanical solutions have been suggested. Their working principle is based on the movement of an element due to the action of the magnetic field.…”

Sensitivity improvement of an optical current sensor with enhanced Faraday rotation

“…Suppose after a single reflection of an optical beam, its power retains a fraction of of that before reflection ( ). Then, if we assume that at the reference glass thickness the total reflection number is , the transmission coefficient of the optical beam through the bulk glass is (8) Similarly if there are reflections for a glass thickness , the transmission coefficient becomes (9) After the polarization state of an optical beam is Faraday rotated, the light intensity measured with an analyzer at 45 with respect to the polarizer is reduced to [19] (10) where are the light intensity measured after the optical beam's passage through the polarizer and the analyzer, respectively, and is the Faraday rotation angle. The above equation does not take into account the optical power losses both within the bulk glass material and at the reflection films.…”

“…OCS's using optical fibers are of straightforward configuration but often suffer from a large amount of linear birefringence induced in the fiber when it is deployed. For OCS's using bulk optical glass, on the other hand, the problems associated with bend-induced birefringence do not occur [7]- [8], [23]. These devices also benefit from the higher Verdet constants of many suitable glasses than that of silica and this can usually lead to a greater sensitivity of the eventual device.…”

“…T HE measurement of electric current by means of optical methods is attractive especially for power system applications due to many desirable features such as the large inherent bandwidth and relative immunity to electromagnetic interference [1]- [8]. Among optical current sensors (OCS's) developed, one class is based on the principle of Faraday rotation [5]- [8].…”

“…Among optical current sensors (OCS's) developed, one class is based on the principle of Faraday rotation [5]- [8]. The sensing element can be implemented from either a continuous length of optical fiber [9]- [15] or a bulk optical glass [16]- [22].…”