Fig. 1. Schematic diagram of TOF structure

Fig. 2. Photoelastic effect simulation of PDMS. (a) PDMS refractive index variation varies with applied pressure; (b) first derivative of PDMS refractive index variation with respect to pressure

Fig. 3. Simulated spectrum of the single tapered optical fiber sensor. (a) Initial output spectrum; (b) output spectrum under 1 N pressure

Fig. 4. Simulated spectra of cascaded sensors. (a) Output spectrum and envelope of cascaded sensor; (b) drift of vernier spectrum after applying 1 N pressure

Fig. 5. Physical photos and experimental setup of tapered fiber optic sensor. (a) TOF sensor guiding 650 nm light; (b) microscopic image of tapered fiber; (c) schematic diagram of force response test setup

Fig. 6. Experimental spectra of single TOF sensor. (a) Wavelength drift under applied force; (b) linear fitting of wavelength drift at 1550 nm

Fig. 7. Experimental spectra of the reference TOF and cascaded sensors. (a) Initial spectrum of the reference TOF; (b) initial spectrum and envelope of the cascaded sensor; (c) wavelength drift under applied force; (d) linear fitting of wavelength drift at 1550 nm

Fig. 8. Cascaded sensor repeatability and stability test. (a) Repeatability test; (b) stability test