Demodulation of CFBG With a Microwave Photonic Filter for Temperature-Insensitive Strain Measurement

An interrogation method of chirped fiber Bragg grating (FBG) based on a microwave photonic filter (MPF) is proposed to realize temperature-insensitive strain measurement. In the proposed MPF, two identical chirped FBGs are embedded to form a Michelson interferometer. When strain is applied to one of the chirped FBGs, its wavelength shift will produce a change in signal transmission latency due to the chromatic dispersion of chirped FBG, resulting in a path difference for the Michelson interferometer. Consequently, a variation on the central frequency of MPF is introduced. Therefore, the wavelength shift of chirped FBG induced by strain can be interrogated by monitoring the frequency response of MPF. Moreover, the effect of ambient temperature can be compensated with the other chirped FBG. The experimental results show that frequency shift of MPF in response to strain with a sensitivity of 1.9 MHz/ $\mu \varepsilon $ is achieved for a measurement range of 0 $\sim 1167~\mu \varepsilon $ . Besides, the system keeps unchanged within a temperature range from 30 °C to 100 °C.