Optical fiber sensor is a device, which is used for measuring various physical parameters by the changes of physical characteristics such as interference, diffraction, polarization, reflection and loss of light caused by light propagation in the optical fiber [1,2,3,4,5,6,7,8]. The optical fiber offer many excellent characteristics such as low loss, wide frequency band, large amount of information, small size, light weight, and good winding property. However, the traditional sensor can not be used in the harsh environment of high temperature and electromagnetic field. The optical fiber sensors with the diversity structure have rapidly developed and used in different disciplines application. Nowadays, the optical fiber sensor is widely applied in the optical communication, computer, automatic control, biomedicine, measurement, transportation, national defense and civil appliances.
There are several existing methods to measure physical parameters. The main types of optical sensors include Mach-Zehnder interferometer sensors [9, 10], surface plasmon resonance (SPR) sensors [11, 12], Fabry-Perot (FB)interferometer sensors , whispering gallery mode (WGM) resonator sensors [14, 15] and Sagnac interferometer sensors [16, 17]. Presently, Sagnac interferometer sensors have evolved into a powerful contender of sensing applications for multiple physical parameters because of their high reliability and sensitivity, small volume, rapid response and easy integration . The sensing principle of the Sagnac interferometer sensor can be traced back to 1982 and was first studied on a nonreciprocal configuration of fiber optic gyroscope in theory and experiment by J Pavlath and Shaw . The FBG can be used for stress, refractive index (RI), hydrogen and temperature sensor. Actually, The FBG sensor is more suitable for the distributed measurement due to its wavelength multipliable capability, and can be used for temperature compensation [20,21,22]. For PCF, the photonic band-gap fiber with air core was successfully fabricated in 1999. With the development of technology, PCF has been rapidly applied and used for the strain [23, 24], temperature , curvature and refractive index sensing [26, 27]. However, the single device multiple parameters sensor is limited by the two limitation factor of cross-sensitivity and demodulation complex, which greatly hinders the development of multi-parameter sensors.
In this paper, a new experimental device is proposed which can measure the dual parameters of temperature and stress simultaneously. The PCF and FBG were composed in the hybrid structure to be used for stress and temperature sensing respectively. The corresponding characteristic peaks move to opposite direction when the stress and temperature are changing with the environment. Therefore, the mutual interference of parameters is avoided in the sensing system successfully. The designed concept has a guiding significance in the field of multi-parameter sensing.