Fiber laser refractometer operating in the 2 μm spectral region based on the MMI effect

We experimentally demonstrate a fiber laser refractometer based on the use of a multimode interference (MMI) fiber structure. The MMI filter is constructed with an uncladded fiber segment which acts as sensing element to determine the refractive index (RI) of liquid solutions. The laser emission, generated at the 2 μm waveband, is wavelength shifted in linear proportion to the RI of the liquid. The proposed fiber laser refractometer exhibits high sensibility of 937.81 nm/RIU.