Modelling of the optical detector system in a compact disc player servo system

The cross-couplings between focus and radial tracking servos in compact disc players are important, but the optical cross couplings are not well described in the literature. In this paper and optical model of a compact disc player based on the three beam single foucault detector principle is found. The general principle of the three beam focus and radial detector system is first described, followed by a non-linear static model of the relationship between the detector signals as outputs and focus and radial errors as inputs. The parameters in these models are found by using actual data from a compact disc player, and the model is validated by comparing the simulated model response to the measured system response to a given set of inputs. This validation shows that the derived model gives a good and usable description of the optical three beam single foucault detector system in a compact disc player, which includes the cross couplings between focus and radial loops.