Liquid level measurement sensor using a long-period fiber grating

A liquid level sensor based on a long-period fiber grating is proposed. The principle of this type of sensor is based on the refractive index sensitivity of long-period fiber grating. As the cladding mode's effective refractive index depends on the refractive index of the surrounding material, the resonant wavelengths of the long period fiber grating will shift when the surrounding refractive index changes. By monitoring a given attenuation band's resonant wavelength shifts, one can measure the immersed lengths of long period fiber gratings and then the liquid level. A direct liquid level measurement is demonstrated by using a long-period fiber grating which was fabricated in a photosensitive B-Ge co-doped optical fiber from Fibercore Inc. (Fibercore PS 1250/1500). The long-period fiber grating was immersed in two solutions which have different refractive indexes. A maximum shift of 7.69 nm for 50 mm of solution which has the highest refractive index has been observed.