Twisted nematic polarizing element with a concentric circle orientation surface and optical head device incorporating the same

摘要

An optical head device has a light source for emitting a light, a polarizing element for converting the linearly polarized emitted light into a concentric-circle polarized light or a radially polarized light, a concentric grating coupler through which the polarized light is introduced into a waveguide layer, and another polarizing element for converting the light radiated from the waveguide layer into a linearly polarized light. The light is applied to and reflected by the surface of an optical disk and introduced into the waveguide layer again as a concentric-circle polarized light or radially polarized light due to reversability of light, whereby the reflected light is detected. Each of the polarizing elements has a twist nematic liquid crystal layer having a linearly oriented liquid crystal orientation surface and a concentric- circle oriented liquid crystal orientation surface.