Current sensing by mode coupling in fibre via the Faraday effect

Temperature compensation of a highly birefringent optical fiber current sensor

“…The peak value of the coupling varied linearly with the current through the conductors, and was found to be independent of the frequency of the applied current [11]. By varying the wavelength of the light through the visible range, with the aid of a dye laser [11]. while maintaining a constant fibre angle (with respect to the conductors), a variation similar to that shown in figure 2 was obtained, as can been seen from figure 3.…”

“…(2), which indicates clearly the sharp peak as the resonance condition is satisfied at 3.88mm, and which is thus the accurate value for the beat length of the fibre at 632.8nm. The peak value of the coupling varied linearly with the current through the conductors, and was found to be independent of the frequency of the applied current [11]. By varying the wavelength of the light through the visible range, with the aid of a dye laser [11].…”

“…This is not surprising, as clearly, the fibre beat length will vary with temperature causing the device to drift (penodicity and phase) of resonance. The temperature coefficient of the beat length, b, has been measured as (11) 1.db= 3.38x1O (K') Clearly this temperature dependence of the coupling must be overcome if the device isto have any practical applications.…”