Triple detection fiber differentiating interferometer based on low-coherence interferometer and its passive demodulation scheme

• The differentiating interferometer is composed of ASE source and hybrid configuration.
• This interferometer adopts triple detection passive demodulation scheme.
• It can realize the real-time measurement of absolute phase amplitude.
• The signal absolute measurement range is from 6×10−5 rad to up to 90 rad.
• Low frequency environmental disturbance is avoided naturally.

This paper presents a triple detection fiber differential interferometer and its passive demodulation scheme. The interferometer is based on an all fiber Mach–Zehnder and Sagnac hybrid configuration, which is composed of a fiber ASE source, a section of delay fiber, a 3×3 fiber coupler and several other fiber components. In the interferometer, the signal beam and reference beam travel along the same path but in opposite directions. The received signal is demodulated by a triple detection passive demodulation scheme. The interferometer can measure the absolute amplitudes and frequencies of phase sensitive signals with large dynamic range, and the low frequency environmental disturbance is removed simultaneously due to the phase compression mechanism. The experimental results demonstrate that the phase demodulation resolution is 6×10−5 rad and the maximum measuring amplitude is up to 90 rad. This method can be used to measure many kinds of parameters such as vibration and refractive index.