Bias-free optical current sensors based on quadrature interferometric integrated optics

A reflective quadrature interferometer was constructed by integrating polymeric optical waveguide components, to demonstrate an optical current sensor that could operate without bias feedback control. In order to obtain two interference signals with a phase difference of 90°, half-wave and quarter-wave plates were inserted in the polymeric optical waveguide chip, and a polarization-dependent birefringence modulator was used for the initialization of the optical sensor, including detector gain adjustment. During the bias-free operation of the sensor, the measurement error was less than ± 0.2%, and it was confirmed that the sensor output was stable for 15 h even if the operating point was not maintained.