Picosecond ultrasonics is a technique that offers the possibility to generate and detect acoustic waves remotely with an unequalled frequency bandwidth and with a sub-micron resolution. Its temporal and spatial resolutions allow us to characterize the mechanics of micrometric structures. In order to improve the measurement rates and sensibility the opto- acoustic transducer has to be upgraded. To achieve this goal, a theoretical model for the generation and detection is developed to design an innovative transducer. The photon and phonon coupling in a structure composed of transparent and/or absorbent materials is first analyzed from a general multi-layered model based on a transfer matrix formalism. It has been implemented numerically and calculations have been performed for different multi-layers. The interplay of optics and mechanics is then investigated to understand how the Fabry Perot effect can be used efficiently to optimize and increase the sensitivity of the transducer reflectivity to the acoustic signal.