High-Resolution and Extended-Range Fiber Bragg Grating Sensing System Based on a Microwave Photonic Filter with Period-breaking Interrogation Method

In this paper, a high-resolution and measurement range expanded fiber Bragg grating (FBG) sensing system based on a microwave photonic filter (MPF) with period-breaking interrogation method is illustrated and experimentally demonstrated. With the dispersion of the dispersion compensating fiber (DCF) in the system, the wavelength shift of the FBG in the optical domain can be converted into the notch frequency shift of MPF in the microwave domain, thus realizing high-resolution FBG sensing. Still, the measurement range is limited due to the periodicity of MPF. An optical filter (OF) is inserted into the link that translates the wavelength shift of FBG into the relative amplitude change (RAC) of the MPF. Combined with the frequency shift and RAC of the MPF, this approach can break the periodicity of traditional interrogation methods, overcoming the limitation of measurement range while ensuring high precision. Taking strain sensing as an example, the experimental results show that the sensitivities of the FBG sensing system obtained at the frequencies of 0.9 GHz, 1.9 GHz, and 2.9 GHz are -8.19 kHz/μϵ, -26.57 kHz/μϵ, and -41.52 kHz/μϵ, respectively, and extended measurement ranges are by 1.51 times, 2.96 times, and 4.49 times, respectively. Furthermore, our proposed method, with its simple structure and unique advantages, can achieve adjustable sensitivity and an unrestricted measurement range.