  We proposed a refractive index (RI) sensing method with temperature
compensation by using an optical frequency comb (OFC) sensing cavity employing
a multimode-interference (MMI) fiber, namely, the MMI-OFC sensing cavity. The
MMI-OFC sensing cavity enables simultaneous measurement of material-dependent
RI and sample temperature by decoding from the comb spacing frequency shift and
the wavelength shift of the OFC. We realized the simultaneous and continuous
measurement of RI-related concentration of a liquid sample and its temperature
with precisions of 1.6*10^-4 RIU and 0.08 degree. The proposed method would be
a useful means for the various applications based on RI sensing.
