Low coherence fiber differentiating interferometer and its passive demodulation schemes

• The fiber interferometer adopts ASE source and passive demodulation scheme.
• The phase measurement resolution of the interferometer can reach 6 × 10−5 rad.
• The interferometer adopts balanced detection to reduce the intensity noise.
• The DCM method is suitable to acquire signals and has a wide dynamic range.

In this paper, a low coherence fiber differentiating interferometer and its passive demodulation schemes are presented and experimentally demonstrated. The interferometer which adopts a broadband light resource and balanced detection is a hybrid configuration of Mach–Zehnder and Sagnac interferometer. The two passive demodulation schemes employ an approximate method and a differential-and-cross-multiply (DCM) method to obtain the vibration signal. The phase measurement resolution (PMR) of both methods can reach 6 × 10−5 rad. Comparing with the approximate method which is usually adopted to restore weak signal, the experiment results demonstrated the dynamic range of the DCM demodulation method has increased 30 dB, which extends the measurement range and can be used widely in various physical fields.