Erbium-doped fiber ring cavity for the measurement of refractive index variations

In this work, an erbium-doped fiber ring cavity based on a 3dB optical coupler for refractive index measurements is presented and experimentally verified. This interrogation system, based on a 1 x 2 optical coupler, uses one of these output ports to increase the reflected optical power by means of a fiber Bragg Grating (FBG), used as a reflector. Moreover, the other output port is used as a refractive index sensing head. A spectral analysis of this interrogator system as well as a fiber cavity ring refractive index sensor characterization are carried out. Finally, an experimental comparison of the refractive index sensor range when the 3dB coupler is replace by a 1x3 one is also presented.