The paper proposes a version of realization for a fiber optic vibration sensor. The sensor possesses a wide range of operation frequencies with such interrogation devices as optical power meters. In comparison to spectral measuring complexes, the sensor imposes lower requirements on operating conditions. The authors investigated a sensing head based on a fiber SMF-MMF-SMF structure and a fiber Bragg grating inscribed in this structure. The external vibration frequency applied to the tested sensor structure is obtained using the Fourier transform of the signal received from the photodetector. The structure designed in this study with a fiber Bragg grating inscribed in it can be used as a sensing head of a fiber optic vibration sensor. It is demonstrated that the sensor based on the developed sensitive structure is able to obtain the external vibration frequency in the range of 20-9000 Hz with accuracy up to 1%. The research results are essential for monitoring systems for the state of structural elements of buildings and structures. The implementation of the vibration sensor in the format of a fiber optic device allows overcoming the limitations of piezoelectric sensors, providing high noise immunity and resistance to harsh environmental effects.

Subject of Research.The paper presents the study of effect that occurs when pressure is applied to the phase-shifted fiber Bragg gratings perpendicular to the fiber axis. Method. Fiber Bragg gratings inscription was performed using Talbot interferometer, and the introduction of a phase shift – by means of the electrical discharge of an arc fusion splicer. The excimer laser system was used as a radiation source. The change in the reflection spectra at different pressures on the optical fiber is measured. Main Results. Fiber Bragg gratings with a phase shift are obtained by the procedure that excludes the use of high-precision instruments during the phase-shift introduction step. Experiment results are given showing up the distance dependence between the local minima in the reflection spectrum of fiber Bragg grating with a phase shift on the applied mass arising as a result of the induced birefringence. It is shown that the change in spectral characteristics is related to the birefringence effect owing to stresses inside the fiber. As a result, the second local minimum appears in reflectance band. Practical Relevance. Research results can be used in creation of a sensing element of a fiber optic pressure sensor. This study demonstrates the application possibilities of Bragg gratings with a phase shift as sensing elements in fiber-optic pressure sensors