Dual-passband microwave photonic filter for fiber axial strain measurement

A dual-passband microwave photonics filter (MPF) for fiber axial measurement is proposed and experimentally demonstrated. The MPF is mainly implemented using a phase modulator (PM) and two cascaded fiber Bragg grating Fabry-Perot (FBG-FP) filters with different central wavelengths. According to the phase-modulation to intensity-modulation (PM-IM) conversion in the MPF, dual-passband can be generated. The fiber axial strain will change the wavelength of the FBG-FP filter, and resulting in the frequency difference variation between the notch of the FBG-FP and the laser source. Thus, the passband frequency can be easily affected by the fiber axial strain applied onto the FBG-FP filter. Strain measurement is executed by recording the change of frequency difference between the sensing passband and reference passband so as to overcome the environmental influence. Finally, a high strain sensitivity of 137.046 MHz/με is achieved.