A simple fiber optic vibration sensor is designed and demonstrated using fiber optic fused 2 × 2 coupler that utilized the principle of reflected light intensity modulation. In order to avoid source signal power fluctuations and fiber bending losses, the rational output (RO) technique is adopted. A calibrated 1-mm linear and high sensitivity of 0.36 a:u:∕mm (2.1 mV∕μm) region of the displacement characteristic curve is considered for vibration measurement. The experimental results show that the sensor is capable of measuring the frequency up to 3500 Hz with ∼0.03 − μm resolution of vibration amplitude over a dynamic range of 0 to 1 mm. The signal-to-noise ratio of the RO is also improved with respect to the sensing signal. In comparison with dual-fiber and bifurcated-bundle fiber, the designed sensor consists only of a single slope that makes the sensor alignment simple by eliminating the dark region and front slope. Simplicity in design, noncontact measurement, high degree of sensitivity, and economical, along with advantages of fiber optic sensors, are the attractive attributes of the designed sensor that lend support to real-time monitoring and embedded applications.

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A temperature compensated liquid level sensor using FBGs and a bourdon tube that works on hydrostatic pressure is presented. An FBG (FBG1) is fixed between free end and a fixed end of the bourdon tube. When hydrostatic pressure applied to the bourdon tube FBG1 experience an axial strain due to the movement of free end. Experimental result shows, a good linearity in shift in Bragg wavelength with the applied pressure. The performance of this arrangement is tested for 21metre water column pressure. Another FBG (FBG2) is included for temperature compensation. The design of the sensor head is simple and easy mountable external to any tank for liquid level measurements.

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