4.2 - Novel Optical Titration Sensor Based on Integrated Planar Polymer Waveguides

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings OPTO 2011
O4 - Applications
F. Betschon, M. Halter - vario-optics AG, M. Michler, J. Kremmel - University of Applied Sciences Buchs (NTB), B. Christensen, P. Schraner - Metrohm AG, Herisau (Switzerland)
89 - 94


The presented paper describes a novel optical titration sensor based on planar polymer waveguides integrated on a printed circuit board. The advantage of titration as an analytical method is that small quantities of a substance can be determined with inexpensive equipment (100 to 3000 EUR) in a short time (within a few minutes) with good accuracy and repeatability (1% to 0.05%).

The first section gives an overview over the compact opto-electronic sensor. It is integrated into a glass cuvette in order to be chemically inert and mechanically compatible to conventional glass electrodes. The optical system consists of 8 light sources (LEDs) of different wavelengths and a coupling system based on planar polymer waveguides, which collects and couples the light into a free-space measuring section. Thereafter, the light is collected and converted to a electrical signal by a photodiode.

Second, the design of the optical system is presented. Zemax ray-tracing software was used to layout the collection of the light emitted by the LEDs, the combiner system and the out-coupling to the freespace measuring section. The simulation results were confirmed by the subsequent characterization of the individual components.

Third, the panel-format manufacturing of the planar polymer waveguides is explained. The system contains several polymer layers which were structured using photolithography, which is very cost- and time efficient especially for complex optical structures like couplers, tapers or lenses. A process optimized for large core light guides was developed. The results, presented in the last section, prove the ability of the sensor module to determine a 4-acid mixture with only one indicator mixture in only one titration run. The speed can be set much faster than in a classical titration. Various tests showed the homogenous mixture of the liquids to be the limiting factor in titration speed. The selection of an appropriate indicator is also no longer of great importance. This is due to the fact that the sensor covers the whole visual range in which the color changes can occur.