Birefringence distribution in magneto-optical disk substrate fabricated byinjection compression molding

It is necessary to improve optical and mechanical properties in optical dis k substrates as information storage devices with high storage density using short-wavelength lasers are being developed. Injection compression molding is regarded as the most suitable process to manufacture optical disk subst rates with high dimensional accuracy, low residual stress, and superb optic al properties. Polycarbonate magnetooptical disk substrates are fabricated by injection compression molding, and the birefringence, regarded as one of the most important optical properties for optical disk, is measured. The e ffects of various processing conditions on the development of birefringence distribution are examined experimentally. It is found that the values of t he birefringence distribution are very sensitive to the mold wall temperatu re history. By controlling the compression process, the overall birefringen ce value can be reduced. (C) 2000 society of Photo-Optical instrumentation Engineers. [S0091-3286(00)00703-0].