Han Li

In conventional microwave photonic (MWP) interrogation based on frequency-domain response analysis, the spatial resolution of fiber Bragg grating (FBG) arrays is inherently limited by the measurement bandwidth. Interrogating spatially dense FBG arrays under narrow bandwidth conditions remains a severe bottleneck. To address this issue, this Letter introduces the estimation of signal parameters via rotational invariance techniques (ESPRIT) into the MWP interrogation scheme. By utilizing the rotational invariance property of the signal subspace to achieve super-resolution extraction of time delays, high spatial resolution FBG interrogation is realized under a narrow measurement bandwidth. In a proof-of-concept experiment, an MWP system comprising three FBG tilt sensors was constructed, with each sensor consisting of two FBGs spaced by merely ~10 cm. Experimental results demonstrate that under a highly restricted measurement bandwidth of only 600 MHz, the proposed method effectively resolves each spatially adjacent grating pair. Within a tilt measurement range of ±12°, the interrogation linearity reaches 0.9992, with a measurement root-mean-square error (RMSE) of ≤0.096°. Under identical parameters, the conventional inverse discrete Fourier transform (IDFT) method completely fails to distinguish the closely spaced FBG pairs. Ultimately, the proposed method breaks the inherent Fourier spatial resolution limit of IDFT schemes, effectively interrogating dense FBG arrays under narrow measurement bandwidths.

This study proposes a high-performance fiber Bragg grating (FBG)-based inclinometer with the capability to self-compensate for initial installation deviation. On one hand, the proposed inclinometer, featuring an improved pendulum design and equipped with a pair of FBGs, can accurately identify both the magnitude and direction of inclination, and it exhibits temperature-insensitive characteristics. On the other hand, with the help of a self-developed compact universal joint structure, the issue of the inclinometer's initial tilt angle caused by installation deviation has been effectively resolved. The experimental results demonstrate that a high degree of linearity with a sensitivity of 89.464 pm/° is achieved over a wide range from -20° to 20°. The self-developed universal joint structure is compact and can effectively compensate for initial installation deviation of up to ±5° in any tilt orientation. The developed inclinometer exhibits a high degree of repeatability and long-term stability, demonstrating great potential for practical engineering applications.