A modified phase generated carrier (PGC) demodulation algorithm for interferometric sensor is presented in this letter. Compared with the differential-cross-multiplying measure (PGC-DCM algorithm), the effect of light intensity disturbance (LID) is eliminated. Additionally, the harmonic distortion of arctangent measure (PGC-arctan algorithm) is well suppressed. In the experiment, while the simulated LID frequency is settled to 50 Hz, the signal-to-noise of the improved PGC algorithm respectively receives an increase of 10.3 dB and 18.2 dB over PGC-DCM and PGC-Arctan algorithms. The system has a dynamic range of 45.9 dB at 600 Hz by employing the improved PGC demodulation algorithm.
A novel fiber-optic Fabry–Perot accelerometer (FOFPA) based on a spherical air bubble cavity is demonstrated. The cavity is fabricated by corroding a fiber end to form a groove and then arc discharging several times to form a spherical bubble. The bubble diameter and wall thickness are about 130 μm and 5 μm, respectively. Experimental results show that the resonance frequency of the accelerometer is 1520 Hz, the signal to noise ratio (SNR) is 40 dB at 706 Hz under 2 mg acceleration excitation, the voltage sensitivity is 14.16 V/g, and the minimum detectable acceleration of the measuring system is 20 μg/sqrt Hz at 706 Hz. Moreover, the accelerometer has a very low temperature sensitivity of 1.7 pm/°C, which means that FOFPA is basically immune to environmental temperature variation. Thus with advantages of miniaturization and simple structure, the FOFPA can be applied widely in the field of vibration measurements.
The phase-shifted sensitivity of an interferometer can be enhanced by increasing the group index. In this paper, we experimentally demonstrate a slow light sensor by placing an active fiber Bragg grating (FBG) in one arm of the Michelson’s interferometer. A 25 KHz AC voltage was applied to a piezoelectric (PZT) set nearby the active FBG. Once the wavelength is varied to near the FBG band edge, the maximum phase-shifted amplitude appears, which is about 1.8 rad and is 4 times greater than that when wavelength is near the center of the reflection band. The active FBG is pumped by a 980 nm laser diode, which can help us to stabilize the system works in the slow light regime to obtain the maximum phase shift. It provides a very simple approach to increase the phase-shifted sensitivity, which is likely to have important applications for strain and acoustic sensors.
A fiber-optic flexural disk microphone is developed to detect acoustic signals in the air. It consists of a Mach-Zehnder interferometer with an optimized sensing arm of 7.93 m. The disk’s resonance frequencies and their influence on the microphone’s sensitivity are investigated. The microphone’s frequency response is measured in the frequency range from 100 Hz to 5 kHz and the average phase sensitivity is about -120.7 dB re 1rad/μPa.