POLARIZATION DIFFRACTION ELEMENT AND POLARIZATION DETECTOR EMPLOYING THE SAME

摘要

A polarization diffraction element comprising two diffraction gratings formed on both faces of a substrate respectively. Both the diffraction gratings have grating lines which are arranged at the same grating pitch, and whose directions mutually form a predetermined minute angle. The grating lines may also be arranged parallel to each other. In this case, the relationship between grating pitches D1, D2 of the respective diffraction gratings and the wavelength .lambda. of an incident light is expressed as: 0 < ¦ .lambda.(1/D1 - 1/D2)(1 - (.lambda./2D1)2) - (1/2) ¦ ~ 0.35; or 0 < ¦ .lambda.(1/D1 - 1/D2)(1 - (.lambda./D1 - .lambda./2D2)2) - (1/2) ¦ ~ 0.35 In a polarization detector employing this polarization diffraction element, a single converging lens of a small effective diameter separates one polarization from another polarization and converges them separately on different photodetectors. Consequently, a still more compact and lightweight optical pickup can be manufactured.