Fig. 1. Frequency relationship between the CFBG and FRM and corresponding beat frequencies. Inset: differential frequency offset δf(λA) of the CFBG under strain. SG, grating section.

Fig. 2. Schematic of the experimental setup. Inset: beat frequency relationship between the time and position. The blue dotted line is the linear fit, which reflects the distance-induced beat frequency, while the black spots show the DFO. SS, swept laser source; PD, photodiode; PA, power amplifier; DAQ, data acquisition; DSP, digital signal processor.

Fig. 3. Optical setup for chirped grating inscription.

Fig. 4. Microwave spectrogram calculated by STFT without strain. (a) Silica fiber. (b) PMMA fiber. Insets: (i) measured reflection spectrum and (ii) measured initial temporal interference waveform.

Fig. 5. Microwave spectrogram calculated by STFT under strain. (a) Silica fiber. (b) PMMA fiber. Insets: reflection spectra of the (i) silica and (ii) PMMA fibers under stress.

Fig. 6. DFO at various strains. The insets show spectrograms of the temporal interference patterns at uniform strains of 4060 and 5540 με.

Fig. 7. Characterization of the system by applying various uniform strains at distances of (a) 4 mm, (b) 3 mm, (c) 2 mm, and (d) 1 mm.

Fig. 8. Comparison of theoretical and experimental values of spatial resolution.