Breaking bandwidth limitation: an ESPRIT-assisted microwave photonic interrogation approach for spatially dense FBG sensors

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Abstract
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.
Funding Information
  • National Natural Science Foundation of China (62571456)
  • National Key R&D Program of China (2024YFC3015200)
  • Sichuan Science and Technology Program (2024ZHCG0190)

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