Substrate birefringence in coated optical storage disks

Abstract

The in-plane and vertical birefringences of polycarbonate optical disk substrates are important parameters that can adversely affect the system performance. However, these parameters are difficult to measure in coated disks with current techniques. An approach based on a variable-angle spectroscopic ellipsometer allows measurement of the birefringence for coated disks. In particular, it is possible to obtain the vertical birefringence, which is of increasing importance, in a relatively simple manner. Comparison between coated and uncoated substrates shows that the birefringence can decrease after coating with magneto-optical layers.