Intensity-modulated refractometer with long period fiber grating cascaded by chirped fiber grating

Abstract

An intensity-modulated refractometer is proposed and experimentally demonstrated by using a long period fiber grating (LPG) cascaded with a chirped-fiber Bragg grating (CFBG). The reflection wavelength band of the CFBG was properly selected to contain the most sensitive spectral part of the LPG. As a result, intensity of the reflected signal was modulated linearly by refractive index (RI) of surrounding liquid outside the LPG. RI measurement in a range from 1.33 to ~1.45 was realized with enhanced sensitivity up to 48.93 μW/R.I.U.