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High sensitivity micro-vibration sensor with cascaded optical fiber gratings

We propose an optical micro-vibration sensor cascaded a long period fiber grating (LPFG) and a fiber Bragg grating (FBG). The sensor is constructed as a cantilever beam, and the top of it discharged to make a microsphere to increase the sensitivity. The length of the sensor sample was 8 cm, and the diameter of the microsphere was 280 μm. Its first-order resonant frequency is 15.7 Hz, the sensitivity at 15.7 Hz (first-order resonant frequency) and 38.0 Hz (flat region) are 42.25 mV/g and 1.62 mV/g, the noise equivalent resolution can reach 0.7 mg (at 15.7 Hz). It can obtain the better signal-to-noise ratios at low frequencies than the electrical sensors used as reference.