Reflected light intensity-modulated continuous liquid level sensor based on oblique end face coupling optical fibers

A light intensity-modulated optical fiber sensor for continuous level measurement is proposed and demonstrated. The sensor is constructed by vertically arranging groups of fibers on the oblique surface which reflects all the incident light when the fibers are in the air but a small proportion of light when the fibers are immersed in the liquid. In order to implement easy modulation and detection, the angle of oblique surface is specially designed to get the maximum intensity modulation according to Fresnel reflection. The fiber groups consist of emitting and receiving fibers, which are tightly fixed to make it easy to detect reflected light based on side coupling effect. The calculation model of the oblique structure and the light path simulation by finite element analysis are used to optimize the oblique angle and prove the feasibility of the sensor. Gradient level experiments and stability tests in the laboratory indicate that the sensor has high sensitivity of 0.21mW/cm, superior resolution and good stability.