Phase Bias Independent Fade-free Optical Fiber Interferometric Vibration Sensor

We propose a novel fade-free optical fiber interferometric vibration sensor using a simple setup with a 90 degrees optical hybrid. The interferometer consists of all-optical components without the phase modulators and complex demodulation processes that were previously used to compensate for signal fading induced by phase bias change. Fade-free output was successfully obtained by in-phase and quadrature detection with a pi/2 phase shifting scheme. Theoretical analysis and measurement results showed that the proposed interferometric vibration sensor operates independently of the phase bias state of interfering waves.