Integrated optical multisensors for water quality

Quigley, Geoffrey Richard (2000) Integrated optical multisensors for water quality. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis is concerned with research into the development of integrated optical sensors for simultaneous measurement of the levels of a panel of analytes in water at concentrations of order 0.1 parts per billion.

A numerical model was established to investigate the optimum waveguide geometry for the application. This modelling yielded predictions that low numerical aperture waveguide devices could have their sensitivity increased by more than an order of magnitude by the addition of a thin overlay of high refractive index material.

Mach-Zehnder interferometers were used to measure the refractive index of aqueous solutions of sucrose. The devices were fabricated with different thickness high index over-lays and were used to validate the predictions of the numerical modelling and to provide information about potential shortcomings of the sensor designs and materials. The test devices achieved a limit of detection of 4 x 10^-7 refractive index units, the best reported results for integrated optical refractometers. These devices are also believed to be the first practical demonstration of the use of non-guiding high index films to improve the performance of channel waveguide sensors.

Fluoropolymer films used in the early sensor designs were found to be detrimental to the performance of the sensors. Silica was chosen as a substitute material and a series of experiments was performed to determine the optimum deposition parameters.

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