An optical fiber sensor for biofilm measurement using intensitymodulation and image analysis

摘要

The development of an online sensor to determine the foulingnproperties of aqueous process fluids is described. A plastic opticalnfiber with its cladding removed over a sensitized length measures thengrowth of biofilms in a closed loop water process system by evanescentnfield attenuation and intensity modulation. The sensor detects materialnbuild-up at the core-cladding interface by means of refractive indexnmodulation. A theoretical model is developed showing that an increase inncladding refractive index reduces the intensity of light propagating innthe fiber and attenuates the high order modes. The modulation mechanismnof the sensor is demonstrated using a CCD camera and frame grabber tonrecord the far field modal distribution of the fiber, when the outernmodes are excited. The intensity distribution changes spatially innresponse to the biofilm deposit on the sensor, indicating evanescentnfield attenuation