Fig. 1. Schematic diagram of the proposed optoelectronic hybrid oscillating fiber-optic sensor. PM, phase modulator; OC, optical coupler; PC, polarization controller; AOM, acousto-optic modulator; WS, waveshaper; PD, photodetector; EA, electrical amplifier; BPF, bandpass filter; PS, phase shifter.

Fig. 2. (a), (b) Optical spectra at the output of the WS when the frequency interval is 20 GHz and 150 GHz. (c) Bandwidths and group delays of two custom-made narrowband filters. The horizontal axis is calculated as the offset from the central frequency. (d), (e) Electrical spectra of the generated signal for the filter with a bandwidth of 400 kHz and 2 MHz under static measurement. The resolution bandwidth (RBW) is 1 kHz.

Fig. 3. Experimental results of dynamic characteristics of the proposed sensor. (a) Comparison between different frequency intervals when using the 400 kHz filter. (b) Comparison between different frequency intervals when using the 2 MHz filter. (c) Comparison between measured and estimated results in detail.

Fig. 4. Comparison of instrument resolution requirement with or without an oscillating cavity.

Fig. 5. Comparison of sensing precision between the proposed sensor and existing advanced distance measurement techniques [38,39]. The relevant data are read from the Allan deviation in the unit of distance given in the reference and converted into the unit of delay.