Fig. 1. (a) Schematic of the proposed sensor; (b) typical microscopic image of the fabricated sensor and the HCF cross section; (c) transmission spectrum of a sensor with an HCF of 2050 µm in length; (d) reflection spectrum of a sensor with an HCF of 450 µm in length.

Fig. 2. Calculated spectra of the proposed sensor with different temperature and strain. (a), (b) Reflection spectra with increasing temperature and strain, respectively; (c)–(f) AR envelopes and FP fringes under different temperature and strain.

Fig. 3. Experimental setup for temperature measurement.

Fig. 4. (a) Dip of AR envelope with increasing temperature; (b) FP fringes with increasing temperature; (c) wavelength shift of AR envelope and FP fringe versus temperature.

Fig. 5. Experimental setup for strain measurement.

Fig. 6. (a) Typical AR envelope of the sensor under different strains; (b) FP fringe under different strains; (c) FP fringe and AR envelope wavelength shift at different strains.

Fig. 7. (a) Strain response of the proposed sensor at 30°C, 50°C, and 70°C by tracing FP fringe wavelength shift; (b) temperature response of the proposed sensor at specific strain by tracing AR envelope wavelength shift.

Fig. 8. (a) Strain repeatability of the experimental result from the proposed sensor by tracing FP fringe wavelength shift; (b) temperature repeatability of the experimental result from the proposed sensor by tracing the AR envelope wavelength shift; (c) long-time stability of the AR mechanism and the FP interference.