A novel approach to simultaneous force and temperature measurement is proposed and demonstrated inthis paper. The sensing element is based on a single long-period grating (LPG) formed by irradiating thejoint of a microstructured optical fiber (MOF) and standard single mode fiber (SMF) with CO2 laserpulses. The grating exhibits two groups of attenuation bands with distinctly different responses to temperatureand force: the resonant notches in the MOF involving couplings between fundamental mode andcore LP11 modes are almost temperature insensitive but highly sensitive to force, while resonant notchesin the SMF coming out of couplings between fundamental mode and cladding modes show high sensitivityto temperature but marginal sensitivity to force. Based on the LPG, a simple and efficient dualparametersensor simultaneously measuring temperature and force with a sensitivity of ∼0:086nm=℃and∼−2:18nm=N, respectively, is achieved. Furthermore, we propose a simple sensing configuration forsimultaneous strain and temperature measurement.

We propose and demonstrate an ultrasensitive photonic crystal fiber refractive index sensor by introducing theavoided-crossing effect in a bent-controlled fluid-filled photonic-bandgap fiber (FF-PBGF). By controlling the bendradius of the FF-PBGF, resonant couplings between the fundamental core mode and the cladding modes are realizedand transmission notches are observed in the transmission band of the FF-PBGF. By changing the refractive index ortemperature of the bent FF-PBGF, a sensitivity of 32,400 nm per refractive index unit (or 13:1 nm=℃) is achieved,which is the highest for a fiber device to date, to our best knowledge.