Refractometer using photonic crystals for fermentation process characterization

A refractometer using nanostructured one-dimensional photonic crystals (1D PCs) for characterization of fermentation processes is presented. The measurement equipment consists of SMD LEDs as light sources, tunable optical 1D PC in a closed measurement chamber, photodetector and handheld unit with signal processing and display. The sensor signal was defined by convolution of the light source and the wavelength-shifted PC reflectance spectra. Pore filling of the nanostructured layer caused red spectral shift. Wine fermentation process as application was investigated. Apodized and index-matched narrow and wideband optical filters with pronounced peak position and without ripples outside the stop band were used as optical elements. Corresponding signal processing was developed to achieve high sensitivity and accuracy in wide spectral range. The mathematical model of the signal processing was supported by calibration measurements using gases and fluids with defined concentration. Temperature dependence of the optical sensor was measured at different application conditions.