Development of a platform for low intensity light detection used for optical analysis of water purity

Abstract

As is well-known, Singapore is currently making great efforts for building a robust, diversified and sustainable water supply. Desalination is one of the main methods to obtain drinkable water, but the process lacks on-line procedures/tools to assess water purity easily and rapidly. This project, in collaboration with NEWRI, explores the tremendous potential to utilize optical analysis (e.g. UV absorbance and/or fluorescence) to monitor the output of the desalination processes and assess the quality of purified water. However, the setup and signal processing circuits used for this purpose need to detect very low light levels. Hence, other methods need to be applied here, very different from the well-known simple transimpedance amplifier for a photodiode, which is feasible only for normal applications when the light intensity is high enough. For instance, lock-in amplifier, or quadrature modulation and detection, or (sometimes even) time-domain photon counting, are among the main types of circuits and methods for signal processing used for such applications. The dissertation will investigate a few of these methods for processing the signal output from low intensity light detection, assess their advantages and disadvantages, as well as their performance characteristics. In this paper, we will investigate several of these methods for processing the output of low-intensity light detection signals, including which include phase-locked amplification, sampling integration, correlation detection, adaptive noise cancellation, and amplification by differential amplification circuits. Their advantages and disadvantages iii Abstract as well as their performance characteristics are evaluated. In this paper, a new elliptical low-intensity light detection platform is simulated in Zemax by means of mathematical geometry and design of amplification circuits to detect small differences between the reference light source and the actual light source.