Current sensing using Faraday rotation and a common path optical fiber heterodyne interferometer

Abstract

An optical configuration for a current sensor utilizing the Faraday effect is described. A common path optical fiber heterodyne interferometer is used to greatly reduce noise produced by environmental effects. A miniature sensing element at the distal end of the fiber allows remote magnetic field or current measurements to be made. Solenoid generated magnetic fields over the range 0.7 to 10 μT, corresponding to solenoid currents from 10 to 150 mA, have been detected over a frequency range from 25 to 125 Hz with a linear response.

Fiber Optic Sensors Based on the Faraday Effect

“…If the feedback electronics that control the phase modulator keep the sensor in the point of maximum sensitivity, the response is linear and the measurement range is limited by modulator properties rather than transfer function. A high-frequency carrier signal can be generated in several ways [ 100 , 110 , 111 , 112 , 113 , 114 , 115 ]. Temkina et al [ 116 , 117 ] recognized the problem of economic competitiveness and proposed a solution for the temperature dependence of quarter wave plates based on signal processing.…”

Recent progress in monomode fibre-optic sensors

“…If the highly birefringent link is subject to environmental noise, the effects of this noise may be eliminated, to first order, by comparing the modulated signal with the reference signal using a phase meter. Using Hoya Fr-5 glass, sensitivities of 7 x 10' nT have been achieved (Bartlett et al 1990). This heterodyne technique is particularly effective for measuring small-amplitude highfrequency magnetic fields and could be used for probes based upon Ga: YIG films, which have demonstrated 100 pT Hz"' sensitivities at 500 Hz with bandwidths up to 1 GHz (Day er al 1991).…”

Route to OCT from OFS at University of Kent

“…More examples are from the field of tandem interferometers [9] and signal processing for such sensing configurations [10], common path heterodyne LCI [11], polarization insensitive tandem [12] and Fizeau interferometer with a broadband source, such as a super-fluorescent source [13].…”