A tunable Fabry-Perot optical filter for application in biochemical analysis of human’s fluids

This paper reports a Fabry-Perot tunable optical filter for application in clinical analysis, especially to measure the concentration of biochemical substances in biological fluids. Its tunable characteristics enable the measurement of different biochemical substances with the same device. It is composed of two parallel thin silver mirrors with a β-PVDF (Poly(Vinylidene Fluoride) in its β phase) film in-between as the resonance cavity. The filter is tuned by adjusting the space between the mirrors through an electric voltage inducing dipolar orientation in the β-PVDF film. Once the thickness changes of the β-PVDF film is due to variations at a molecular level, the changes are rather homogeneous within the samples. As a result, this approach achieves parallelism between the two mirrors, which is a complex problem to solve in conventional Fabry-Perot optical filters. Moreover, compared with an array of non-tunable optical filters with different cavity lengths, usually used to solve the parallelism problem, this device has a reduced area, its fabrication process is easier and it covers a wider spectral range. In addition, when used as a part of a biological fluids analysis system, it avoids the need for expensive optics and enables low-cost and portable devices, which would improve the use of spectrophotometric analysis in clinical diagnostics.R&D Centro Algoritmi da Universidade do Minho.Escola de Engenharia da Universidade do Minho - program IN2TEC.Fundação para a Ciência e a Tecnologia (FCT) - Grant POCI/CTM/59425/2004