Coupled π-shifted fibre Bragg grating ring resonant strain sensors
Resonant optical strain sensors, obtained by closing in loop coupled π-shifted Bragg gratings (π-FBGs), are reported. Despite of a conventional π-FBG, showing a transmission Lorentzian resonance in the reflection band, the coupled π-shifted Bragg grating structure is characterised by a spectral response formed by a split doublet of the primary transmission Lorentzian mode of π-FBG. By closing in loop this structure, the coupled π-shifted Bragg grating ring resonators show better performance than π-shifted Bragg grating ring resonators in terms of strain sensitivity (i.e. 2.86 pm/με) is demonstrated. Thus, the coupled π-FBGRR is suitable for enhanced sensitivity strain sensing applications.