An all-fiber optical current transformer inspection method based on the analysis of the spectrum of the output light

All fiber optical current transducers (FOCTs) are widely used and it is urgent demand to monitor and check the FOCTs. In this paper, a novel method to examine the state of the FOCT system and its components is proposed and demonstrated theoretically. Taking the reflective FOCT as an example, the transmittance of the FOCT, which is a function of wavelength is deduced using Jones matrix and the relationship between the transmittance and the parameters (phase shift and alignment angle) of the components such as modulator, high birefringent delay fiber, quarter wavelength plate is discussed respectively. By measuring the spectrum of the output light and processing the transmittance data, each of the parameters can be calculated and then the states of the components and whole system can be evaluated in some simple situations.