Thermal performance of a controlled cooling system for low-level optical signals

Low-level light signals that are highly dependent on temperature are very common in measurement applications that employ sensors coupled to optical fibres. In order to amplify and condition the signal, photomultipliers are traditionally used together with climatic chambers in which the ambient temperature of the chamber is controlled. The present paper proposes the use of an avalanche photodiode (due to its lower price and size) to amplify the signal. However, this change implies more careful temperature control. This is why we propose to control the temperature in the photodiode itself and to use a thermoelectric cooler. This system design suggests the convenience of the development of a thermal study that is presented here. The electrical intensity of the thermoelectric cooler, the influence of the surrounding temperature and the use of isolating material or air in the space between the photodiode and the walls of the chamber are analysed. Computational fluid dynamic (CFD) techniques were applied to model the system and the model was satisfactorily validated. The feasibility of carrying out the temperature control in the cold junction of the thermoelectric cooler instead of in the photodiode itself was tested and was found to improve control.