Fiber-optic sensors based on fluctuation oscillations of waveguide micro-optomechanical resonance structures

The characteristics of fiber-optic oscillation frequency sensors of deformation and temperature that employ the thermal fluctuation resonant oscillations in the SMS(M) fiber structures (sensitive elements that represent oscillation systems with distributed parameters based on series-connected single- and multimode step-index fibers) are developed and studied. The measurements of the fluctuation oscillations are based on the amplitude-phase modulation of the optical wave in the multimode oscillating section due to variations in the path-length difference and tunneling of interfering beams. Accuracies of temperature and relative deformation measurements of $\pm$ 2$^\circ$C and $\pm$ 10$^{-5}$, respectively, are demonstrated. The estimation of the ultimate measurement sensitivity of the resonance frequency is based on the approximate calculation of the Allan variance that shows a possibility of the above sensors with temperature and deformation threshold sensitivities of 0.001$^\circ$C and 10$^{-8}$, respectively.