Ulf Holm

Magneto-optical garnet materials in fiber optic sensor systems for magnetic field sensing

Magneto-optical garnet materials such as YIG, undoped as well as substituted, exhibit a large Faraday rotation. This fact makes them potentially suitable as sensing elements in fibre optic magnetic field sensor systems. We describe both an intensity based multimode system using bulk materials and a singlemode polarization based system using waveguiding films. A number of different material compositions, such as undoped YIG, (GdGa)- and different Bisubstituted YIG have been used for the sensor elements. Measurement results are presented and discussed. A detection limit in the xT range and a measurement range exceeding 10 have been achieved.

Yig-Sensor Design For Fibre Optical Magnetic Field Measurements

Aiming at the design of a magnetic field sensor utilizing the Faraday effect, we give in this paper a description of measurements of magneto-optical properties of YIG. We also give sensor design rules based upon these measurements.

Transmission loss compensation for Faraday effect fibre optic sensors

We present a novel scheme for compensation of transmission loss variations in Faraday effect-based fibre optic magnetic field sensors. Light is sent through the sensing element in opposite directions to form the two signal channels needed for the compensation. Experiments have been made with a time-multiplexed multimode system in which IR emitting diodes are alternately used as emitters and detectors. With transmission loss variations of less than 25%, which is reasonable in a real system, the resulting error is well below 1%.

Characterization Of Magnetooptical Thin Films For Sensor Use

As a part of a fibre optical sensor development project we have made an evaluation of different optical waveguiding techniques to study the properties of thin magnetooptical films. Because of the application the methods are focused on the determination of the Faraday rotation, the linear birefringence and the dynamics and anisotropy of the magnetic properties of the samples. Measurements using holographic grating, prism and edge (end-fire) light coupling to different substituted YIG films are presented. The advantages of the different methods are discussed and it is shown that the launching technique may affect the properties to be measured. Film stress caused by the prism coupling method is found to influence the magnetic anisotropy.