Optical fiber °Brix sensor based on Lossy Mode Resonances (LMRs)

The fabrication and characterization of an optical fiber °Brix sensor based on Lossy Mode Resonances (LMRs) is presented. ITO coatings deposited on side-polished D-shaped optical fibers are used as LMR supporting coatings. LMRs are highly sensitive to external medium refractive index variations and enable an accurate determination of sugar concentration in the surroundings of the device by means of a LMR wavelength shift when the device is immersed in sugar based solution. The fabricated sensors have been used to measure sugar concentrations from 5% to 50%, which is within the requirements of most common applications. The response of the devices is linear with a linearity factor R
²
0.9961 and a sensitivity of 11.8 nm/°Brix, which means a resolution of ∼0.005 °Brix by using a conventional communications Optical Spectrum Analyzer (OSA). Presented device shows a twenty-fold improvement in sensitivity compared with comercial Brix refractometers.