Multichannel Chromatic Dispersion Measurement Using Long-Period Fibre Gratings : tests of Wine Fermentation Monitoring

Optical fibre sensors (OFS) offer potentials to the challenging continuous control of manufacture processes, because they are reliable, cheap, versatile and, quite critically, fast. For example in the food and drink industry, monitoring is usually performed randomly and off-line. In contrary, OFS are sturdy, are easy to implement online for continuous monitoring, have a small footprint and typical response times of less than minutes or even seconds, depending on the required sensitivity and limit of detection. In particular, measuring of the chromatic dispersion (CD) of liquids may provide very interesting insight in the progress of the manufacture. For instance, in the wine industry, fermentation of must extracted from grapes is complex and dynamical. Its monitoring is done on experimental model production lines, using performant techniques such as HPLC. OFS have proven interesting performances, mostly for temperature, and refractive index [1]. Recently, we have proven the concept of an original multi-channels CD sensor using a dual long-period fibre grating (Bi-LPG). We demonstrated that some chemical compounds in liquids could be discriminated from others through their CD signature [2]. Indeed, each LPG attenuation band being associated with the matching of the core mode to one cladding mode (that interacts with the external medium via its evanescent field), all « channels » are independent refractive index sensors, and can be used to estimate the CD of the surrounding medium.