A long-period grating refractometer: measurements of refractive index sensitivity

We report the development and demonstration of a long-period grating refractometer. The principle of operation is based on in the use of a long-period grating that is structurally induced by a CO₂ laser, and where the resonance wavelengths are shifted by the refractive index of the medium surrounding the cladding of the long-period grating. The different concentrations for three types of solutions (ethylene glycol, salt, and sugar) were experimentally measured, and results show that, as a refractometer, this fiber-based device can not only differentiate chemicals based on their refractive index, but it can also become a concentration indicator of a particular chemical solution, and applied in the oil and petroleum industry.