Thermal fiber optic electric current sensors with predifferentiation technique

A previous electric current sensing scheme employing two metal-coated single-mode optical fibers is modified for the purpose of much wider band measurement. As the same optical setup is used, the proposed sensing scheme incorporates the use of a differentiator that differentiates the measured before it splits into two parts and flows on the two metallic coatings, respectively. Two kinds of optical fibers (which have different cladding sizes) are tested. With regular polarization-maintaining fibers (which have a 125 micrometers cladding diameter), a measurement bandwidth of approximately 500 Hz can be obtained. With thinner fibers (with 80 micrometers claddings), the measurement bandwidth can reach approximately 1.1 kHz. The measurement scheme proposed compares much more favorably to the previously reported sensing scheme, in which the measurement bandwidth is only 0.06 Hz.