TEMPERATURE-DEPENDENCE OF THE BIREFRINGENCE OF OPTICAL-DISK SUBSTRATES

Injection-molded polycarbonate substrates are used predominantly in re ad-only, write-once, phase-change and magneto-optic disks for data sto rage. The in-plane and vertical birefringences of these substrates adv ersely affect the performance of optical data-storage systems. The dis ks are typically expected to operate in the ambient temperature range of 5-50 degrees C. We have investigated the behavior of the in-plane a nd vertical birefringences of a polycarbonate disk substrate in this t emperature range using a custom-built ellipsometer. This study reveals that the in-plane birefringence changes dramatically within the inves tigated range of temperatures, whereas the vertical birefringence rema ins essentially constant. We suspect that the change in birefringence is due primarily to thermally induced stress in the substrate. (C) 199 6 Optical Society of America