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A thermal convection-based fiber lever sensor is proposed and experimentally demonstrated. Instead of the solid or liquid mass found in a conventional lever sensor, a Co 2+ -doped microfiber is self-heated with a pump laser as the heat source, generating a symmetrical temperature profile inside a hermetic chamber due to thermal convection. The convection current generated by the temperature gradient remains in the opposite direction to gravity with different tilt angles, due to a natural convection effect acting as a "gas pendulum". However, the locations of two micro-single mode fibers are asymmetric, corresponding to the central axis of the temperature gradient. Therefore, the tilt angle can be detected by interrogating the wavelength shift of the Michelson interferometer induced by the temperature difference. The experimental results show that a tilt-angle sensitivity of 95 pm/deg can be achieved. The proposed fiber-optic lever sensor possesses large dynamic range, low cost, and high sensitivity.

A parallel microfiber array for the measurement of directional acoustic signals is proposed and experimentally demonstrated. Two microfiber Bragg gratings (micro-FBGs) in single-mode fibers were placed on two sides of a Co 2+ -doped microfiber, forming an array of three parallel microfibers. The micro-FBGs can measure the temperature difference between the two sides of the Co 2+ -doped microfiber through interrogation of the matched FBGs. Due to the asymmetrical temperature distribution of the Co 2+ -doped microfiber under the applied acoustic signal, sound source localization can be realized through the acoustic particle velocity. The experimental results show that an acoustic particle velocity sensitivity of 44.2 V/(m/s) and a direction sensitivity of 0.83mV/deg can be achieved at a frequency of 1000 Hz, and the sound source localization has been realized through the orthogonal direction responses of two crossed Co 2+ -doped microfibers. The results demonstrate that the parallel microfiber array has the ability to recognize orientation, offering potential for directional acoustic signal detection with miniature size.