A Measurement of Ellipticity of Reflected Light for Magnetooptical Disk

It is possible to estimate the ellipticity of light reflected from a magnetooptical disk by determining the pickup phase difference which gives maximal readout signal amplitude. An optical pickup was fabricated with a phase compensator and half-wave plate; this pickup had a variable phase difference and enabled rotation of the plane of polarization of light incident on the disk. The two contributions to the ellipticity, substrate retardation and the Kerr ellipticity, were separated by measuring the ellipticity when the plane of polarization of the incident light was both parallel to and perpendicular to disk grooves. The result indicates that a polycarbonate disk contributes more to the ellipticity than does a glass disk. Also, it was verified that the temperature dependence of the ellipticity originates in variation of the substrate retardation.