A high-resolution integrated optical spectrometer with applications to fibre sensor signal processing

An integrated optical device has been developed to realize the instrumentation for the processing of the optical signal such as those from fibre optic Bragg grating sensors (FBG) embedded in composite materials. The optical circuit integrates on X-cut LiNbO3 an acousto-optical TE-TM converter included between two crossed polarizers, in order to realize a tunable high-resolution optical filter. The design and fabrication process parameters and solutions adopted with the aim of obtaining very-high-resolution filters (FWHM < 0.45 nm at 1300 nm) are discussed. The device has been demonstrated to allow the polarization-independent spectrum analysis of in-fibre optical radiation, exploiting the heterodyne detection of the optical signals from the output of the acousto-optical tunable filter. The application as instrumentation for the processing of optical signals from such sensors is described and the experimental results are presented for the monitoring of static and dynamic deformations of composite material structures such as those in which the FBG sensors have been embedded.