Simultaneous force and temperature measurement using long-period grating written on the joint of a microstructured optical fiber and a single mode fiber.

A novel approach to simultaneous force and temperature measurement is proposed and demonstrated in this paper. The sensing element is based on a single long-period grating (LPG) formed by irradiating the joint of a microstructured optical fiber (MOF) and standard single mode fiber (SMF) with CO(2) laser pulses. The grating exhibits two groups of attenuation bands with distinctly different responses to temperature and force: the resonant notches in the MOF involving couplings between fundamental mode and core LP(11) modes are almost temperature insensitive but highly sensitive to force, while resonant notches in the SMF coming out of couplings between fundamental mode and cladding modes show high sensitivity to temperature but marginal sensitivity to force. Based on the LPG, a simple and efficient dual-parameter sensor simultaneously measuring temperature and force with a sensitivity of approximately 0.086 nm/degrees C and approximately -2.18 nm/N, respectively, is achieved. Furthermore, we propose a simple sensing configuration for simultaneous strain and temperature measurement.