Silica optical fibres were used to measure colour (mg anthocyanin/g fresh berry weight) in samples of red wine grape
homogenates via optical Fibre Evanescent Field Absorbance (FEFA). Colour measurements from 126 samples of grape
homogenate were compared against the standard industry spectrophotometric reference method that involves chemical
extraction and subsequent optical absorption measurements of clarified samples at 520 nm. FEFA absorbance on
homogenates at 520 nm (FEFA520h) was correlated with the industry reference method measurements of colour (R2 =
0.46, n = 126). Using a simple regression equation colour could be predicted with a standard error of cross-validation
(SECV) of 0.21 mg/g, with a range of 0.6 to 2.2 mg anthocyanin/g and a standard deviation of 0.33 mg/g. With a Ratio
of Performance Deviation (RPD) of 1.6, the technique when utilizing only a single detection wavelength, is not robust
enough to apply in a diagnostic sense, however the results do demonstrate the potential of the FEFA method as a fast and
low-cost assay of colour in homogenized samples.
Intrinsic Exposed Core Optical Fibre Sensors (IECOFS) based on step-index, silica fibres have been used to monitor surface
crystallization processes. When applied to scale (CaCO3) detection, the sensor is fully recoverable; requiring only immersion
in a solution of dilute HCl. Unlike conventional scale sensors, the IECOFS responds only to heterogenous (surface) crystal
growth and the optical response correlates to several crystal growth processes, offering a tool for monitoring surface crystal
growth kinetics. Kinetic parameters extracted from the IECOFS response profiles are similar to those obtained from surface
crystal growth on stainless steel surfaces indicating the potential for IECOFS as a sensor of scale formation in industrial
processes.
An unclad section of silica optical fiber has been used to detect, and measure heterogeneous (surface) crystal growth in a
solution of calcium carbonate. Surface crystal growth is found to attenuate radiation transmitted along the fiber core via
the refraction of guided modes out of the core. Optical power output was found to be linearly correlated with crystal size
(R2 = 0.97, n = 9) and the optical signal was found to be restored following chemical removal of deposited crystals
(without physical intervention). Sensitivity to crystal growth was found to be proportional to the length of the unclad
(exposed) core and inversely-proportional to fiber diameter. These results suggest a simple skip-length ray model,
coupled with refraction of guided modes out of the fiber core can be invoked to explain the mechanism of optical power
attenuation.
Polymethylmethacrylate (PMMA) optical fibers are evaluated for their potential as intrinsic sensors of
surface crystal growth. Superior mechanical flexibility means they can be configured to maximize sensitivity, primarily
via coiling to promote higher-order modes of radiation propagation in their core. The effects of coiling and exposing the
fiber to elevated temperatures (greater than the glass transition temperature) are found to increase sensitivity of the
PMMA fibers to surface crystallization while pre-bending is found to reduce sensitivity.
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