We report on the physical observation of mixtures of volume contractional monohydric alcohol solutions interrogated by a planar Bragg grating sensor. Via evanescent field interaction, the sensor detects any changes of the composition of a liquid compound on the sensor surface that are associated with a change of the refractive index. Studying various aqueous solutions of monohydric alcohols, we found a nonlinear relationship of the analytes refractive index on its mixing ratio, indicating the different nature of the mixed phases in the solution and the effect of volume contraction. Analyzing aqueous solutions of methanol, ethanol, and 2-propanol reveals a local maximum of the refractive index for the application of smaller monohydric alcohol molecules, which is displaced in the direction of a higher alcohol content with an increasing number of carbon atoms in the chain of the alcohols. In turn, this sensor can be used for the online monitoring and observation of the water content in aqueous alcohol solutions, including volume contractional solutions.
We report on a refractive index sensor based on a planar Bragg grating (PBG) capable to online monitor the water
content in Biodiesel and the amount of ethanol admixture to conventional fuels, respectively. Our results demonstrate the
capability of the sensor to distinguish the transition between about 190 and 500 ppm water in Biodiesel, enabling to
monitor the production process of Biodiesel in the relevant range according to industrial standards. The ethanol content
in petrol has been investigated in the range of 0-100%, covering the entire standardized range of E-5 to E-85 fuel mixing
ratios. These experiments reveal a sensitivity of 112 nm/riu allowing the measurement of the ethanol content with a
resolution of 8.9·10<sup>-6</sup>.
An evanescent field refractive index sensor consisting of a Bragg grating that is written into a silica-on-silicon planar
optical waveguide structure by UV laser radiation is utilized to monitor the composition of liquid binary chemical
systems. We have investigated various selected liquid compounds that are commonly used in the pharmaceutical and
chemical industry, finding sensitivities on the order of 100nm/RIU and minimum detectable index resolution on the
order of 5•10<sup>-6</sup> fulfilling industrial demands on detection limits and partly being superior to other electrical transducer
systems. The planar structure of the sensor chip allows on chip integration of fluidic structures that we have generated by
laser ablation using a pulsed fiber laser, enabling connection to the adjacencies.