Liquid Level Sensor Utilising a Long Period Fiber Grating

摘要

We propose here a liquid level sensor using a long period fiber grating (LPFG) in which direct liquid level measurementis carried out by utilising an LPFG, 100mm in length and a periodicity of Imm. The LPFG was exposed to liquids withvarying levels and the wavelength shift of a selected loss band of the transmission spectra was monitored using abroadband light source and an optical spectrum analyzer. The mechanism of this LPFG sensor is based on the fact thatthe effective Refractive Index (RI) of a cladding mode is directly dependant on the RI of the surrounding medium, be itair, or in this case water and petrol. As the surrounding RI changes, so does the phase matching condition of the LPFG.The result for the level change of the liquid with a specific RI is both a shift in wavelength and a change in theattenuation level of the selected loss band. For the selected loss band, continuous wavelength shifts of 9.5 nm and 25 nmfor 100 mm of water and petrol level change have been observed respectively, with sub-millimetre accuracy.