Embedded coupler based on selectively infiltrated photonic crystal fiber for strain measurement.

A photonic crystal fiber (PCF) with embedded coupler is demonstrated for strain measurement. The embedded coupler is constructed by the selective filling of one of the air holes in the PCF. Light propagated in the fiber core can be efficiently coupled to the liquid-filled rod waveguide under phase-matching conditions, resulting in sharp decreasing of resonant wavelength intensity. The highest strain sensitivity is calculated to be ~23.8 pm/με due to the coupling between core mode and fundamental mode of the liquid rod, when the refractive index (RI) of the liquid is 1.46. With the increase of the RI, the resonance can also be observed between the core mode and the higher-order modes of the liquid rod, whereas the strain sensitivity drops to ~6.4 pm/με. The experimentally obtained static strain sensitivity values are ~22 and ~3.8 pm/με for the coupling between the core mode and the fundamental mode or linearly polarized LP(11) modes of the liquid rod, respectively, which are in good agreement with the simulations. The dynamic strain measurement resolution obtained is ~1.2 nε/(Hz)(1/2).