Fig. 5: High-resolution RI sensing enabled by FBGs with different hole diameters.
From: Laser nano-filament explosion for enabling open-grating sensing in optical fibre
Reflection spectra recorded from uniform FBGs (Epulse = 4.5 µJ, Ʌ = 1072 nm, 600 holes) filled with low (a nH= 1), medium (b nH = 1.44), and high (c nH = 1.661) refractive index materials, revealing the influence of increasing nanohole diameter due to varying chemical etching time (0–6 min). Peak reflection strength (d) and 3-dB linewidth (e) of the Bragg resonances plotted as a function of refractive index for different chemical etching times (following legend a). Bragg resonance wavelength (shifts on right axis) plotted versus refractive index f for different chemical etching times. A global fit of the data by EME simulation is presented (dashed lines) for hole diameters of 220–700 nm (see legend). The slopes of data provide a strongly increasing refractive index sensitivity (inset) for increasing RI and increasing hole diameter (colour-coded lines). Shaded zones mark axis scale changes.
