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Fibre Optic Magnetic Field Sensors Utilizing Iron Garnet Materials
KTH, Superseded Departments, Signals, Sensors and Systems. (Mikrosystemteknik)ORCID iD: 0000-0002-2650-0121
1993 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the subject of fibre optic magnetic field sensors utilizing iron garnet materials. Such materials exhibit a large Faraday rotation which make them advantageous for application in compact mag­netic field sensors.

After an introduction, in which fibre optic sensors and optical methods to measure electric current are reviewed, the original research work is summarized.

A system for the measurement of the magneto-optic properties of trans­parent materials is described. Measurement results, showing the influence of temperature, magnetic field direction and sample treatment on the magneto-optical proper­ties of YIG-crystals, are presented. The proper­ties of thin magneto-optical waveguiding films have also been studied using different light coupling methods. Measurement results obtained for holo­graphic grating, prism and edge (end-fire) light coupling to different substituted YIG films are presented. It is shown that the launching method may affect the properties to be measured.

The design and performance of several versions of extrinsic guided wave fibre optic magnetic field sensors are then reported. The sensors employ substi­tuted YIG (Yttrium Iron Garnet, Y3Fe5O12) thin film waveguides as sensing elements. Polari­zation maintaining fibres were used as feed and return to provide two signal channels. The signals were combined in a balanced measure­ment system, providing insensitivity to both fluctuations in optical power and loss. Sensors have been made both with separate fibres to guide the light to and from the sensing element and with a single fibre for both functions. The two fibre version, although less ”elegant”, is found to have a better performance. This version also makes it possible to determine both the magnitude and sign of the magnetic field. Measurement results indicate a usable measurement range of at least several mT with a noise equivalent magnetic field level of less than 8 nT/root(Hz).

The design and performance of multimode fibre optic magnetic field sensors utilizing the Faraday effect in an epitaxially grown thick (YbTbBi)IG film is also described. This type of sensor is found to be linear over a range from 27 mT to less than 270 nT. Sensor prototypes suitable for current monitoring in high voltage transmission lines have also been developed. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 1993. , x, 59 p.
Trita-ILA, ISSN 0281-2878 ; 93.01
Keyword [en]
yig, iron garnets, rare earth garnets, magneto-opics, optical waveguide, fibre optical sensors, magnetic field measurement, current measurement
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-48332OAI: diva2:457370
Public defence
Kollegiesalen, Administrationsbyggnaden, KTH, Valhallavägen 79, Stockholm (Swedish)
QC 20111209Available from: 2011-12-09 Created: 2011-11-17 Last updated: 2011-12-09Bibliographically approved

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