A kind of liquid-level sensor is presented using the long-period fiber grating(LPFG).It is based on the coupling between the LPFG′s fundamental mode and cladding mode,which is affected by the refractive index of the medium around the LPFG.The liquid-level changes of distilled water and ethanol are measured using this sensor.When the liquid-level are changes between 0 mmand 17.5 mm,the transmission power of LPFG changes accordingly.The changes are up to 6.871 9 dB and 13.4360 dB,and the sensitivi...