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In bulk glass optical current sensing systems with polarization-preserving total reflection layers and wide spectral optical sources, the Verdet constant of the material of the sensing head, the linear birefringence inside the sensing element and the reflection-induced-retardance are all a function of the wavelength. Therefore, there will be error accumulation due to spectral width variation shown in the output of the systems, which has scarcely been discussed before. In this paper, the dispersion formulae of the Verdet constant, reflection-induced-retardance and linear birefringence inside a current sensing cell made of ZF-7 glass are given, then their error accumulation due to spectral width variation upon the output of the system is theoretically analysed and digitally simulated. Finally, the effect of the spectral width of the optical source upon the output of the system is simulated and analysed. The result shows that the effect of the spectral width variation of optical sources on the output of the system is less than 0.025%; the effect of the Verdet constant is dominant in the joint effect, and the system output increases with increasing source spectral width, which is confirmed qualitatively by an experiment. Therefore, the treatment using a monochromatic model to describe systems with a broad-band optical source is adequate.

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